Showing papers in "Journal of Electronic Materials in 1991"
TL;DR: In this article, visible light emission from metal-polymer diodes made from semiconducting polymers, with indium-tin oxide as the "ohmic" contact, and a variety of metals as the barrier metal, was reported.
Abstract: We report visible light emission from metal-polymer diodes made from semiconducting polymers, with indium-tin oxide as the “ohmic” contact, and a variety of metals as the barrier metal. Our results, which confirm the discovery by the Cambridge group [Nature347, 539 (1990)], demonstrate that light-emitting diodes can be fabricated by casting the polymer film on indium-tin oxide from solution with no subsequent polymer processing or heat treatment required. Electrical characterization reveals diode behavior with rectification ratios greater than 105 at sufficiently high voltages. Use of an electrode material with low work function leads to more than an order of magnitude improvement in the room-temperature efficiency of the devices. For example, the most efficient devices made with calcium as the rectifying contact display efficiencies of 0.01 photons per electron.
150 citations
TL;DR: In this article, a new class of organic dielectrics, benzocyclobutenes, are described and their application to the fabrication of thin-film multichip modules is detailed.
Abstract: A new class of organic dielectrics, benzocyclobutenes, 1, are described and their application to the fabrication of thin film multichip modules is detailed. Key properties for3, a siloxy containing BCB derivative include low dielectric constant (2.7), low loss (0.008 at 1 MHz), low water absorption (0.25% after 24 h water boil) and high degree of planarization (>90% from one layer coverage). All other properties meet the requirements necessary for fabrication of thin film MCM structures.
142 citations
TL;DR: In this article, the growth and properties of high performance surface light emitting diodes which utilize a GaP window layer are presented, which consist of an AlGaInP double heterostructure lattice matched to a GaAs substrate.
Abstract: The growth and properties of high performance surface light emitting diodes which utilize a GaP window layer are presented. The devices consist of an AlGaInP double heterostructure lattice matched to a GaAs substrate. A lattice mismatched GaP layer is then grown on top of the heterostructure. The resulting upper confining and window layers have high electrical conductivity and optical transmissivity allowing for the fabrication of red-orange and yellow emitters with performance superior to existing commercial technologies. The effect of different confining and window layer structures on device performance is described, including characteristics of the shortest wavelength AlGaInP green emitters yet reported.
93 citations
TL;DR: In this article, a method for the natural reduction of threading dislocations in GaAs on Si by growing on patterned Si substrates was reported. But the GaAs were grown on the 40μ-wide Si mesas and showed a 1.6 increase in luminescence intensity over the luminecence intensity from the unpatterned control area.
Abstract: We report a new method for the natural reduction of threading dislocations in GaAs on Si by growing on patterned Si substrates. We also explore other effects of patterning on dislocation formation during growth: stress relief near the mesa edges at high aspect ratios, and limited dislocation nucleation and propagation. Prior to growth, the Si substrates were processed to produce a plurality of mesas varying in width (5-170 μm) and geometry (circular, rectangular, and square mesas). After growth of the GaAs, the material was characterized with cathodoluminescence (CL) and secondary electron microscopy. For a GaAs growth temperature of 570° C and a thickness of 10 μm, the GaAs grown on the 40μ-wide Si mesas show a factor of 1.6 increase in luminescence intensity over the luminescence intensity from the unpatterned control area. Also, the emission wavelength from the smaller mesas is shifted to shorter wavelengths as compared to GaAs/GaAs and the unpatterned control area. The emission wavelength and CL intensity varies across the mesas; for 40 μm wide mesas, the emission wavelength is fairly constant across the mesa and the CL intensity decreases near the edges, whereas for larger mesas the emission wavelength decreases and the CL intensity increases at the mesa edges. For the 40 μm wide mesas, the integrated CL intensity is equal to that of a control GaAs/GaAs grown with the same doping level. No cracks were observed in the GaAs grown on the Si mesas, even though the thickness of the GaAs was 10 μ,m.
83 citations
TL;DR: In this paper, the effect of cooling rate during solidification on the shear creep and low cycle shear fatigue behavior of 60 Sn/40 Pb solder joints, and on bulk solder tensile properties was investigated.
Abstract: This paper reports the results of a study on the effect of the cooling rate during solidification on the shear creep and low cycle shear fatigue behavior of 60 Sn/40 Pb solder joints, and on bulk solder tensile properties. Solder joints were made with three different initial microstructures by quenching, air-cooling and furnace-cooling. They have similar steady-state strain rates under creep at relatively high shear stresses (i.e. in the matrix creep region) but creep at quite different strain rates at lower shear stresses (i.e. in the grain boundary creep region). These results are ascribed to the refined grain size and less lamellar phase morphology that results on increasing the cooling rate. Tensile tests on bulk solders that were cold-worked, quenched and furnace-cooled show that a faster cooling rate decreases the ultimate strength and increases the ductility at low strain rates. The fatigue life of quenched solder joints is shown to be longer than that of the furnace-cooled joints.
72 citations
TL;DR: In this paper, the results of measurements carried out to determine the thermal conductivity along and normal to the plane of fiber glass laminates used in the manufacture of printed circuit boards are presented.
Abstract: Accurate values of thermal conductivity are required for the simulation of temperature phenomena in electronic circuits. This paper presents the results of measurements carried out to determine the thermal conductivity along and normal to the plane of fibre glass laminates used in the manufacture of printed circuit boards. It has been found that the reinforced fibre-glass substrates used in PCBs are strongly anisotropic with the conductivity normal to the boards being much smaller than tangential to it. The test samples were type FR4 epoxy/glass laminates. An experiment has been designed which determines the thermal conductivity in-the-plane of the laminates by matching the measured temperature distribution along a heated specimen with a finite difference solution. An electrically heated Lees’ disc apparatus is also used to measure the thermal conductivity of these boards in a direction normal to their plane. The samples tested yielded values of 0.343 W/mK and 1.059 W/mK for thermal conductivity through and along the plane of the boards, respectively.
71 citations
TL;DR: In this article, a detailed description of the thermal bonding technique and the ensuing wafer thinning processes for making SOI of various film thicknesses is given. And a comparison of selective etch-back chemistry with different etchstop fabrication techniques is presented.
Abstract: Thermal bonding of oxidized silicon wafers is used to obtain high-quality silicon on insulator (SOI) starting material for electronics and sensor applications. An overview of the technology is followed by a detailed description of the bonding technique and the ensuing wafer thinning processes for making SOI of various film thicknesses. Bonded pairs of wafers can be reproducibly produced free of contact voids. Thick-film SOI is produced using a simple bond and grind/polish technique. Thin-film SOI, suitable for CMOS applications, is produced using the bond and etch back (BE-SOI) process. A comparison of selective etch-back chemistry with different etchstop fabrication techniques is presented. These methods produce inexpensive, low-defect SOI, for integrated circuit applications, using materials and equipment common to silicon integrated circuit process lines.
66 citations
TL;DR: In this paper, the authors investigate the means by which complete stress relaxation can occur through dislocation reactions during annealing of very thick as-deposited lattice mismatch systems.
Abstract: Defect characterization by high-resolution electron microscopy is presented for (001) epitaxy of the CdTe/GaAs and ZnTe/GaAs heterojunctions, before and after a long vacuum anneal. The annealed interface structure consists of a periodic array of perfect edge Lomer misfit dislocations, with spacing corresponding to a strain-free thin film. Since this is the most efficient manner to obtain complete relaxation, it represents the equilibrium microstructure. The as-deposited films are very thick, three to four orders of magnitude greater than the critical thicknesses, which are both less than a monolayer for these large lattice mismatch systems. Their microstructure corresponds to a metastable distribution of defects in that the thin film residual strain is nearly zero and neighboring defects can react to form Lomer misfits. A variety of defects exist both in the form of perfect misfit dislocations at the interface and extended defects into the thin film. The extended defects result from formation of stacking faults bounded by either Shockley or Frank partials, and more complicated defect structures due to interacting perfect and partial dislocations on intersecting slip planes. The purpose of this paper is to investigate the means by which complete stress relaxation can occur through dislocation reactions during annealing of very thick as-deposited films.
52 citations
TL;DR: In this paper, the authors present a modification of the conventional critical thickness calculation which includes balancing forces acting on defects in a strain gradient to define an interface above which strain relief occurs and integration of the strain energy in the portion of the compositionally graded film above this interface.
Abstract: Strain relief mechanisms have been investigated in alloys of Si and Ge formed by high dose ion implantation followed by solid phase epitaxy. Both compressive and tensile strain states were studied by implanting: (i) 200 keV Ge into (001) Si to form Si-rich alloys and (ii) 150 keV29Si into (001) Ge to form Ge-rich alloys. We report that Si-rich compressively strained alloys above a critical implant dose relax via the introduction of a/6(112) partials (bounding stacking faults) when regrown by solid phase epitaxy below ≈600° C. Alloys formed by implanting Si into (001) Ge and regrown at 450° C also undergo strain relaxation above a critical dose but, in this case, relaxation proceeds via the introduction of planar defects + partials, Lomers, and 60° dislocations. The high dose ion implantation technique produces alloys in which the concentration, and hence lattice mismatch, is a Gaussian function of depth from the surface. In this work we present a modification of the conventional critical thickness calculation which includes: (i) balancing forces acting on defects in a strain gradient to define an interface above which strain relief occurs and (ii) integration of the strain energy in the portion of the compositionally graded film above this interface. Critical dose implant plots based on these calculations are presented. The model provides a good fit to cross-sectional and TEM observations of regrown alloys with implant doses above and below the predicted critical dose. A TEM characterization of the strain relieving defects for both compressive and tensile films is presented.
51 citations
TL;DR: In this article, the optical emission characteristics of biaxially compressed InAs x P1− x /InP strained single quantum well (QW) structures, with nominal compositionx=0.67, have been investigated using photoluminescence (PL) and photoline excitation (PLE) spectroscopies.
Abstract: The optical emission characteristics of biaxially compressed InAs x P1− x /InP strained single quantum well (QW) structures, with nominal compositionx=0.67, have been investigated using photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. The highly strained QWs exhibit intense and narrow PL in the 0.9–1.5 μm wavelength range, similar to the lattice-matched InGaAs(P)/InP system. The 20 K PLE spectra exhibit well-resolved features attributed ton=1 heavy hole (E1H1) and light hole (E1L1) transitions in the 1.0–1.5 μm wavelength range. In addition, features attributed to transitions betweenn=2 electrons and heavy holes (E2H2), and betweenn=1 electrons and unconfined holes (E1Hf), were observed. The energy splitting between the heavy-hole and light-hole bands was found to be a sensitive measure of the band offsets in the system. The best prediction of this splitting was obtained for a valence band offset of δE V ∼0.25δE G . This value of band offset was in agreement with the energy position of the E1Hf transition. The observed transition energies were also compared with the results of a finite square well model, taking into account the effects of strain, and the results offer further support for the band offset assignment. This study indicates that the InAsP system may be advantageous for application in strained-layer optoelectronic devices operating in the 1.3–1.6 μm wavelength range.
50 citations
TL;DR: In this article, a study of the hydrogen-passivated Si(100) surface prepared by a remote hydrogen plasma treatment was performed, which serves the dual purpose of cleaning and passivating the Si surface prior to low temperature Si epitaxy by Remote Plasmaenhanced Chemical Vapor Deposition (RPCVD).
Abstract: This paper presents the results of a study of the hydrogen-passivated Si(100) surface prepared by a remote hydrogen plasma treatment which serves the dual purpose of cleaning and passivating the Si(100) surface prior to low temperature Si epitaxy by Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD). The remote hydrogen plasma treatment was optimized for the purposes of cleaning and passivation, respectively. To achieve a clean, defect-free substrate surface, the remote hydrogen plasma process was first optimized using Transmission Electron Microscopy (TEM) and Auger Electron Spectroscopy (AES). For hydrogen passivation, the substrate temperature was varied from room temperature to 250° C in order to investigate the degree of passivation as a function of substrate temperature by examining the amount of oxygen readsorbed on the substrate surface after air exposure. Low temperature Si expitaxy was subsequently performed on the air-exposed substrates without further cleaning to evaluate the effectiveness of the hydrogen passivation. It was found that better Si surface passivation is achieved at lower substrate temperatures as evidenced by the fact that less oxygen is observed on the surface using AES and Secondary Ion Mass Spectroscopy (SIMS) analyses. The amount of readsorbed oxygen on the H-passivated Si surface after a two hour air exposure was found to be as low as 0.1 monolayer from SIMS analysis. Using Reflection High Energy Electron Diffraction (RHEED) analysis, different surface reconstructions ((3 × 1) and (1 × 1)) were observed for H-passivated Si surfaces passivated at various temperatures, which was correlated to the results of AES and SIMS analyses. Epitaxial growth of Si films at 305° C was achieved on the air-exposed Si substrates, indicating a chemically inert Si surface as a result of hydrogen passivation. A novel electron-beam-induced-oxygen-adsorptiom phenomena was observed on the Hpassivated Si surface. Scanning Auger Microscopy (SAM) analysis was performed to study the reaction kinetics as well as the nature of Si—H bonds on the H-passivated Si surface. Preliminary results show that there is a two-step mechanism involved, and oxygen adsorption on the H-passivated Si surface due to electron beam irradiation may be due to the formation of O-H groups rather than the creation of Si—O bonds.
TL;DR: In this article, the alignment marks were etched into the surface of silicon wafers with hot potassium hydroxide, and these V-grooves were then precisely aligned and the wafer was brought into contact for initial bonding.
Abstract: Successful fabrication of critically aligned three dimensional structures has been achieved by combining precision alignment procedures and techniques for direct silicon bonding. This produces three dimensional bonded layers that might include combinations of mechanical, electronic and/or optical elements formed in separate prefabricated layers. We call this techniquealigned wafer bonding. The precise aligned bonding of the features was done with an Optical AssociatesHyperline 400 Infrared Aligner. This machine can hold two imprinted wafers face to face while projecting an infrared image of the surfaces to a viewing screen. An array of alignment marks were etched into the surface of silicon wafers with hot potassium hydroxide. These V-grooves were then precisely aligned and the wafers were brought into contact for initial bonding. Subsequent high temperature annealing was used to strengthen and complete the chemical bonding. The instrumentation used in this work required alignment features with a vertical dimension of 30 micrometers to produce a suitable infrared image. We found that the apparent size of the images produced by the optical system limited the accuracy in precision alignment. However, with reduced wafer separation, we achieved wafer alignment with an accuracy of better than 5 micrometers. This technique would generally be used for the precision alignment and bonding of complementary micromechanical, electrical, or optical structures during the formation of three dimensional devices. The details of the aligned wafer bonding and its applications are presented.
IBM1
TL;DR: In this paper, a large body of experimental and theoretical work, especially in Si-doped GaAs and Al x Ga1-x As, regarding the bistability of theDX center is summarized.
Abstract: We summarize a large body of experimental and theoretical work, especially in Si-doped GaAs and Al x Ga1-x As, regarding the bistability of theDX center. There is good evidence that theDX center is just the simple donor, and that each donor can exist in either of two distinct lattice configurations, each with its own spectrum of bound electronic states. Generally, the substitutional configuration binds electrons in shallow hydrogenic states, but many observations also indicate a deep (highly localized) state ofA 1 symmetry. These states are to be distinguished from bound states of a lattice-distorted configuration, the lowest-lying of which is the deepDX level. The occupation of theDX level in thermal equilibrium with the states of the conduction band can be reasonably well modeled by assuming thatDX is either a one-electron or a two-electron state, and we discuss the reasons for this ambiguity. However, we then show that such thermal equilibrium results are consistent with thermal capture and emission kineticsonly if we assume thatDX is a two-electron state. Our results thus support the model of Chadi and Chang in which the distorted configuration is stabilized by capture of two electrons. In other words, the defect exhibits negative effective correlation energy (negativeU).
TL;DR: The origin of the abrupt decrease in electron concentration and mobility of AlxGa1−xN in the range of 0.4 and 0.6 was investigated by photoluminescence from epitaxial layers covering the entire range of alloy composition.
Abstract: The origin of the abrupt decrease withx both in electron concentration and in mobility of AlxGa1−xN in the range ofx between 0.4 and 0.6 was investigated by photoluminescence from epitaxial layers covering the entire range of alloy composition. Band edge luminescence from undoped layers was observed out to anx value of 0.75. Whenx was larger than 0.2, a peak 0.2–0.5 eV below the band edge peak was also observed both from undoped and from Zn doped samples. This is tentatively ascribed to an unidentified acceptor (or acceptors) related to the presence of Al. No luminescence which could be attributed to a deep native donor defect was observed in semi-insulating AlxGa1−xN layers. When Zn was added in the lowx range of the alloys, a broad band 0.5–0.8 eV below the band edge peak was observed as well as a relatively narrow peak.
TL;DR: In this paper, the stability of GexSn1-x alloys was investigated on (001) InSb substrates, as well as inSb coated GaAs substrates.
Abstract: We have investigated the stabilization of GexSn1-x on (001) InSb substrates, as well as InSb coated GaAs substrates. We find that alloys up to ≈1500A can be stabilized when 0 0.10, we observe partial phase separation into coherent α-Sn and α-GeSn. The films are stable in the temperature range of 125-130° C, depending on Ge concentration. We present a thermodynamic model which exhibits the trends observed in the growth and stability of epitaxially stabilized GexSn1-x alloys. Electrical and optical measurements show consistently high carrier concentrations (1021 cm-3) and low carrier mobility (<1000 cm2/ Vsec) for the alloys.
TL;DR: In this paper, the authors investigated the electrical properties of ZnO varistors through admittance spectroscopy and found that the observed ac admittance dispersion is caused by the existence of two deep bulk trap levels, which are 0.31 eV and 0.245 eV, respectively, below the conduction band.
Abstract: Electrical properties of ZnO varistors are investigated through admittance spectroscopy. The observed ac admittance dispersion is caused by the existence of two deep bulk trap levels, which are 0.31 eV and 0.245 eV, respectively, below the conduction band. The 0.31 eV level is associated with the oxygen vacancy while the origin of the 0.245 eV level is not yet clear. An equivalent circuit model for ZnO varistors is proposed that is based on the existence of deep bulk traps.
TL;DR: In this article, GaAs/Ga1−xInxAs strained layer superlattices with well-widths of 7 nm, barrier widths of 14 nm and periods of 10 to 30 have been examined by transmission electron microscopy in plan view and in cross-section for (001), (111) and (112) substrates.
Abstract: GaAs/Ga1−xInxAs strained layer superlattices with well-widths of 7 nm, barrier widths of 14 nm and periods of 10 to 30 have been examined by transmission electron microscopy in plan view and in cross-section for (001), (111) and (112) substrates. Individual layers are below the critical thickness while the overall SLS's are above the critical thickness for dislocation generation. (001) substrates give rise to square grids of 60° dislocations lying parallel to 〈110〉 directions with inclined 1/2 〈101〉 Burgers vectors, resulting from dislocation motion on 8 slip systems. (111) substrates give triangular networks of 60° dislocations lying parallel to 〈110〉 directions resulting from motion on 6 slip systems. (112) substrates have two sets of primary dislocations lying along (132) directions, along with secondary 60° dislocations lying along [110]. Long Lomer-Cottrell dislocations with Burgers vectors lying parallel to the substrate/SLS interface are occasionally observed for (001) substrates, while short segments are observed for (112) substrates; these are formed by reaction between conjugate dislocations. These dislocations arrangements are discussed in terms of the resolved shear stresses resulting from epitaxy for the various substrates orientations. Dislocation densities are much less than those required for complete strain relief. This is analyzed in terms of the reduction in the stress acting on dislocations from partial strain relief, along with a friction stress due to a combination of the Peierls stress and solution hardening from the In substitution. A friction stress ∼10-3μ is required to explain the observed dislocation densities (μ, is the shear modulus).
TL;DR: In this paper, the electrical properties of a large series of undoped semi-insulating InP samples before and after annealing were investigated. But the results were compared to those obtained from InP crystals grown under stoichiometry control by the horizontal gradient freeze technique.
Abstract: Nominally undoped semi-insulating InP can be prepared reproducibly by annealing under controlled phosphorus pressure. We present the electrical properties of a large series of undoped InP samples before and after annealing. Spectroscopic investigations show that the specimens are contaminated by iron during annealing, but native defects have to be taken into consideration in order to explain the electrical data. Annealed InP specimens are characterized by electrical and optical measurements and the results are compared to those obtained from InP crystals grown under stoichiometry control by the horizontal gradient freeze technique.
TL;DR: An experimental study of the calcination of limestone has been carried out in a highly instrumented pilot-scale rotary kiln as mentioned in this paper, where local gas, solids, and wall temperatures and pct calcination have been measured under a range of operating conditions to determine the influence of limestone type, feed rate, rotational speed, inclination angle, and particle size on calcination and heat flow in the kiln.
Abstract: An experimental study of the calcination of limestone has been carried out in a highly instrumented pilot-scale rotary kiln. Local gas, solids, and wall temperatures and pct calcination have been measured under a range of operating conditions to determine the influence of limestone type, feed rate, rotational speed, inclination angle, and particle size on calcination and heat flow in the kiln. Thus, it has been found that the local calcination is dependent primarily on the solids temperature and hence on heat transfer. Of the variables studied, the limestone feed rate has the strongest effect on the temperature and calcination fields, whereas inclination angle and rotational speed are relatively less important. The different limestones studied exhibited significant differences in heat-absorption capacity and calcination temperature which may be related to their radiative properties. Increasing particle size over a range of 0.75 to 3.5 mm resulted in an increase in both heat transfer to the bed and calcination.
TL;DR: In this article, the average size and growth rate of diamond particles were found to increase with the CH4 to H2 ratio and decrease with the ambient pressure, and the secondary nucleation was substantially reduced, resulting in relatively smooth morphology.
Abstract: Diamond films were grown on Si(100) and boron nitride deposited Si(100) substrates using hot filament chemical vapor deposition (HFCVD) technique. Microstructure and morphology of diamond films have been investigated systematically as a function of CH4 and H2 ratio and the ambient pressure. The deposited films were characterized by employing techniques such as scanning electron microscopy (SEM) and laser Raman spectroscopy. The average size and growth rate of diamond particles were found to increase with the CH4 to H2 ratio and decrease with the ambient pressure. Maximum growth rate of synthetic diamond deposited on Si(100) was found to be ∼3.5 µm/hr for the film deposited at 20 Torr with CH4:H2 ∼ 1.5:100 (substrate temperature ∼850°C). In most of these depositions, the morphology of the diamond crystals was cubic with significant secondary nucleation at higher methane concentrations and ambient pressure. The diamond film deposited on Si(100) with BN buffer layer shows an improvement in growth rate and the coverage, and the secondary nucleation was found to be substantially reduced, resulting in relatively smooth morphology. MicroRaman investigations show less amorphous graphite formation and better structural quality of diamond film than the one deposited without the BN buffer layer.
TL;DR: In this paper, low resistance ohmic contacts were fabricated to Zn-doped p-type InP using an annealed Pd/Zn/Pd/Au metallization.
Abstract: Low resistance ohmic contacts (ρc = 7 x 10-5 Ω-cm2) have been fabricated to Zn-doped p-type InP using an annealed Pd/Zn/Pd/Au metallization. Palladium reacts with InP at low temperatures to form a Pd2InP ternary phase, which is initially amorphous but crystallizes and grows epitaxially on InP. Zinc reacts with some of the overlying Pd to form PdZn (≅250° C), which decomposes at 400-425° C to form PdP2, freeing up Zn to diffuse into Au as well as InP. The contact resistance reaches a minimum as the decomposition reaction takes place. The resultant ohmic contact is laterally uniform and consists of epitaxial Pd2InP adjacent to InP, followed by a thin layer of PdP2 and then the outer Au layer. Further annealing leads to a breakdown of the contact structure,i.e. decomposition of Pd2InP, and an increase in contact resistance.
TL;DR: In this paper, the authors review theoretical work aimed at understanding MS relief in a growing epilayer by the introduction of misfit dislocations, with the view of resolving the discrepancies between predicted and observed critical thickness and residual MS after onset of MS relief.
Abstract: The misfit between an epilayer and a substrate may be accommodated by misfit dislocations (MDs) or misfit strain (MS) or both. In a small misfit system the misfit is accommodated by MS alone up to a critical thickness whereafter the residual MS decreases as the thickness increases. The main objective of this paper is to review theoretical work aimed at understanding MS relief in a growing epilayer by the introduction of MDs, with the view of resolving the discrepancies between predicted and observed critical thickness and residual MS after onset of MS relief. Since the predictions are based on equilibrium principles, equilibrium theories for monolayers (MLs) in the Frenkel-Kontorowa model, and for thickening epilayers (growing ML-by-ML) in the Volterra model, are briefly summarized, including some consideration of the conditions for ML-by-ML growth. Since equilibration can be drastically retarded by barriers to nucleation and motion of dislocations the observed quantities are most often non-equilibrium values. Calculations show (i) that MD sources are normally needed to the onset of MS relief, (ii) that threading dislocations are the “softest” sources, (iii) that even with threading dislocation sources MS relief may lag behind equilibrium predictions and (iv) that Peierls friction may lead to an infinitely large critical thickness.
TL;DR: In this article, the impurities induced disordering of GaInAs quantum well structures with barriers of AlGaInAs and of GaAsP was investigated using boron and fluorine.
Abstract: Impurity induced disordering of GaInAs quantum well structures with barriers of AlGaInAs and of GaInAsP has been investigated using boron and fluorine. The impurities were introduced by ion implantation followed by thermal annealing. Annealing unimplanted P-based quaternary material at temperatures greater than 500° C caused a blue shift of the exciton peak. At annealing temperatures greater than 650° C red shifts in the exciton peak of unimplanted Al-based quaternary material were observed. Boron implantation caused small blue shifts of the exciton peak in both material systems at low annealing temperatures. Much larger blue shifts were observed in the fluorine implanted samples.
TL;DR: In this paper, photo-induced current transient spectroscopy (PICTS) and thermally stimulated current (TSC) were used to characterize the deep levels in the GaAs materials grown at low temperature by molecular beam epitaxy, at least five hole traps and five electron traps have been identified by the TEES measurement employing a simplified sample arrangement.
Abstract: The photo-induced current transient spectroscopy (PICTS), thermoelectric effect spectroscopy (TEES) and thermally stimulated current (TSC) spectroscopy have been used to characterize the deep levels in the GaAs materials grown at low temperature by molecular beam epitaxy. At least five hole traps and five electron traps have been identified by the TEES measurement employing a simplified sample arrangement. We have studied the behavior of various traps as a function of the growth temperature and the post-growth annealing temperature. Some of the shallower hole traps were annealed out above 650‡ C. Electron traps atE
c- 0.29 eV andE
c- 0.49 eV were present in the material, and have been identified as M3 and M4, respectively. The dominant electron trap, atE
c- 0.57 eV, is believed to be associated with the stoichiometric defect caused by the excess As in the material, and our data show evidence of forming a defect band by this trap. A possible model involving As precipitates is proposed for this trap atE
c-0.57 eV.
TL;DR: In this article, a combined magnetic liquid encapsulated Kyropoulos/Czochralski (MLEK/MLEC) technique was used to produce twin-free indium phosphide (InP) crystals.
Abstract: We have used a combined magnetic liquid encapsulated Kyropoulos/Czochralski (MLEK/ MLEC) technique to produce twin-free indium phosphide (InP) crystals. This technique has advantages over the standard LEC method used for commercial production of InP. By stabilizing convective flows with a magnetic field and controlling the angle between solid and liquid, one can grow large diameter twin-free (100) InP crystals; they are shaped with a flat top as is typical for Kyropoulos growth, and then pulled from the magnetically stabilized melt as in Czochralski growth. This shaping method has the benefit of maximizing the number of single crystal wafers which can be sliced from the boule. MLEK InP growth is distinguished from other methods such as LEC and MLEC with respect to solid-liquid interface shape, dislocation density, and impurity distribution. This process has demonstrated that twin-free InP (100) crystals can be consistently grown.
TL;DR: In this article, high sensitivity rocking curve measurements were used to determine differential strains for films as thin as 2.5 nm; while Bragg angle contour mapping had similar sensitivity and was also able to assess coating uniformity and stress distribution over areas covering a whole wafer.
Abstract: Quantitative x-ray diffraction topography techniques have been used to measure the residual strain magnitude and uniformity of deposition for Mo and W sputtered films on Si(100) substrates. High sensitivity rocking curve measurements were able to determine differential strains for films as thin as 2.5 nm; while Bragg angle contour mapping had similar sensitivity and was also able to assess coating uniformity and stress distribution over areas covering a whole wafer. Measurements of strain versus film thickness over a range of 2.5 nm to 80 nm showed that a critical thickness exists for maximum residual strain. Growth beyond this range produces stress relaxation. This non-destructive type of analysis could be employed on a wide range of film-substrate combinations.
TL;DR: In this paper, the feasibility of using laser reflectometry for in situ monitoring and control of OMVPE AlGaAs was demonstrated, and the optical constants, refractive index and extinction coefficient, of the alloys at the growth temperature were obtained for 633 nm wavelength.
Abstract: The feasibility of laser reflectometry for in situ monitoring and control of OMVPE AlGaAs was demonstrated. The optical constants, refractive index and extinction coefficient, of the AlGaAs alloys at the growth temperature were obtained for 633 nm wavelength. These data were used in closed loop control of thickness and composition during deposition of heterostructure layers. Laser reflectometry was also instrumental in the observation of unintentional composition gradients at the substrate-epilayer interfaces in atmospheric pressure vertical flow reactors.
TL;DR: In this article, the ion implantation process creates defects which affect surface state densities and recombination probabilities, leading to an overall decrease in carrier recombination at the surface which leads to an enhanced photoconductive response.
Abstract: The development of efficient thin-film solar cells based on CuInSe2 absorber layers has encouraged fundamental research on both thin films and single crystals of this chalcopyrite semiconducting compound. The resistance to radiation and ion bombardment is of technical importance particularly for a material which could find future applications in space photovoltaic power systems. In this paper results are described for an ion implantation study using CuInSe2 single crystal substrates. Oxygen, helium and neon implantations have produced significant changes in surface resistivity and photoconductivity. Also the near-surface regions ofn-type crystals have been type-converted top-type following ion implantation. It is apparent that the ion implantation process creates defects which affect surface state densities and recombination probabilities. In the case of oxygen there is an additional doping effect caused either by the introduction of acceptor states or by the reduction of the existing donor state population. Following implantation there appears to be an overall decrease in carrier recombination at the surface which leads to an enhanced photoconductive response.
TL;DR: In this article, the pyrolysis of triisopropylantimony ((C3H7)3Sb) and triallylantimony (C 3H5)3sb) was investigated in He and D2 using a SiO2 flow tube reactor at atmospheric pressure.
Abstract: The pyrolysis of triisopropylantimony ((C3H7)3Sb) and triallylantimony ((C3H5)3Sb) has been investigated mass-spectrometrically in He and D2 using a SiO2 flow tube reactor at atmospheric pressure. Both temperature and time dependencies of percent decomposition were studied and the reaction products were analyzed. The overall decomposition processes for both compounds were found to be homogeneous and first order. (C3H7)3Sb pyrolyzes at 250-350° C with no effect of the ambient gas. However, C3H6, C3H8, and C6H14 (2,3-dimethylbutane) were produced in He whereas C3H3D appeared in D2. The pyrolysis is believed to begin via bond cleavage to generate the free C3H7 radicals that, in turn, recombine and disproportionate. Isopropyl radicals react slowly with D2, producing the C3H7D detected. For (C3H5)3Sb, the pyrolysis takes place at 100-160° C. The only major product is C6H10 (1,5-hexadiene). Both the pyrolysis rate and products were independent of the ambient. Two possible mechanisms, homolysis and reductive coupling, are discussed. Assuming that homolysis is the rate-limiting step for the pyrolysis of both (C3H7)3Sb and (C3H5)3Sb, bond strengths of 30.8 and 21.6 kcal/mole for C3H7—Sb and C3H6—Sb were determined from the experimental data. When either (C3H7)3Sb or (C3H5)3Sb was mixed with trimethylindium, a nonvolatile, liquid material, probably an adduct, was formed.
TL;DR: In this article, the critical thickness of InxGa1-xAs/GaAs and GaAs/InxGa 1-xA/GaA strained-layer systems were determined by transmission electron microscopy using the lift-off technique.
Abstract: The critical thicknesses of InxGa1-xAs/GaAs and GaAs/InxGa1-xAs/GaAs strained-layer systems were determined by transmission electron microscopy using the lift-off technique. The onset of misfit dislocation generation has been observed for the first time and the geometries of the misfit dislocations in both uncapped and capped layers correspond to the predicted models. A comparison is given between the predicted and experimental critical thicknesses.