Showing papers in "Journal of Vacuum Science & Technology B in 1984"

InAsSb strained‐layer superlattices for long wavelength detector applications

Abstract: InAsSb strained‐layer superlattices (SLS’s) are proposed as novel III–V semiconductor materials with the potential for long wavelength intrinsic detector applications. Theoretical studies of the band gaps of various InAs0.4Sb0.6/InAs1−xSbx SLS’s with x > 0.6 have been carried out. The results indicate that the wavelength response of various SLS’s with x ≳ 0.73 can be extended to 12 μm at 77 K through the intentional use of layer strains. These new structures offer the metallurgical and processing advantages of III–V semiconductors for 12 μm detector applications. Further advantages include a weaker dependence of the SLS band gap on composition and reduced band‐to‐band tunneling in the SLS compared to bulk Hg0.8Cd0.2Te.

Phase equilibria in thin‐film metallizations

Abstract: The determination of stable tie lines in a ternary phase diagram through a limited number of thin‐film reactions is demonstrated. Ternary phase diagrams are then used to explain the stability of refractory metals, silicides, and nitrides during various integrated circuit processing steps. The W–Si–O, Ti–Si–O, Ti–Si–N, and Ti–Al–N systems serve as examples.

The oxidation of GaAs(110): A reevaluation

Abstract: Photoemission spectra of 3d core levels excited with synchrotron radiation reveal a multicomponent substructure which increases in complexity with oxygen exposures over the range 106–1014L (langmuir). Spectral changes are already evident for Ga at 104 L, and for As near 106 L. Two oxide components shifted by 0.45 and 1 eV relative to the bulk Ga‐3d core level are evident throughout the exposure range, but shift to 0.8 and 1.4 eV for 1014 L. With increasing exposure the As‐3d core level develops a sequential set of shifted components at 0.8, 2.3, 3.2, and 4.2 eV relative to the bulk position in GaAs, which are attributed to single through fourfold coordinated bond formation to oxygen. Both surface and bulk‐sensitive core spectra reveal a nearly equally intense oxide substructure, which indicates that contrary to previous notions subsurface oxidation is the dominant mechanism throughout the exposure range. The core spectra furthermore indicate preferential Ga oxidation—which suggests that separate Ga and As...

Adsorption of H, O, and H2O at Si(100) and Si(111) surfaces in the monolayer range: A combined EELS, LEED, and XPS study

Abstract: This paper is a summary of a series of experiments studying the exposure of hydrogen, oxygen, and water, on the (2×1) surfaces of Si(100) and Si(111). While the primary focus has been on high resolution electron energy loss (EELS) results, low energy electron diffraction (LEED) and x‐ray photoelectron spectroscopy (XPS) are also used in the studies. Both the (100) and cleavage (111) surfaces form a monohydride and a dihydride exhibiting a (2×1) and a (1×1) LEED pattern, respectively. These systems exhibit saturation, which is consistent with the model of hydrogen saturation of the dangling bonds. Upon water adsorption the Si–H and Si–OH vibronic modes are observed, indicating that water is decomposed. On the cleavage surface only, there is evidence of a very weak scissor mode, allowing for the possibility of a few percent of molecular water adsorption. Oxygen adsorption is complex. For samples formed at high temperatures (∼1000 K) the observed vibronic features are similar to those known for the Si–O–Si c...

Electrical properties of ideal metal contacts to GaAs: Schottky‐barrier height

Abstract: The electrical properties, with emphasis on Schottky‐barrier height φB, of ideal (no interfacial oxide) contacts to GaAs have been measured for a diverse group of 14 metals by using current‐voltage and capacitance–voltage methods. The contact interfaces were formed under controlled ultrahigh vacuum conditions by metal evaporation onto clean (100) surfaces of both n‐type and p‐type GaAs. The range of φB for n‐type contacts is 0.96 to 0.62 eV in the decreasing order: Cu, Pd, Ag, Au, Al, Ti, Mn, Pb, Bi, Ni, Cr, Co, Fe, and Mg. For p‐type contacts, the φB range is 0.45 to 0.62 eV. No simple correlation is apparent between φB and contact metal work function nor between φB and the metal–GaAs interface chemistry.

RHEED oscillation studies of MBE growth kinetics and lattice mismatch strain‐induced effects during InGaAs growth on GaAs(100)

Abstract: We present the first report of RHEED intensity changes and recovery as a function of monolayer and submonolayerMBE depositions of In x Ga1−x As (x≤0≤0.5) on GaAs(100) substrates. The influence of the lattice mismatch‐induced strain on the growth mechanisms and the incorporation behavior of In and Ga is suggested by new and In concentration dependent effects in the RHEED intensity waveform behavior during growth. The monolayer oscillation period is determined by the combined In and Ga fluxes. The initial growth of InGaAs on GaAs(100) is planar, but after an amount of deposition depending upon InAs content and growth conditions, a sudden change from a streaked reflection pattern to a spotty transmission pattern is observed indicating formation of 3D islands. The film thickness at which this transition occurs is strongly influenced by the step density of the GaAssurface when InGaAsgrowth is initiated. We have examined the recovery behavior of the specular spot intensity after the growth of 0.1 to 15 monolayers of GaAs on an annealed metal‐stabilized GaAs(100) surface. In this experiment, the RHEED intensity has dropped from its initial (no‐growth) value and, after termination of growth, it slowly recovers to its steady‐state value. We report RHEED intensity recovery rates as a function of the number of monolayers of GaAs deposited and compare them to recovery rates after steady‐state growth has been reached. The recovery rate is a strong function of the completeness of the surface when growth is stopped.

Thermal nitridation of silicon: An XPS and LEED investigation

Abstract: Two thermal, low pressure nitridation processes are achieved on silicon(111), using two different nitridant gases, and studied in situ by x‐ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED). The results show two different growth rates but the same evolution of the electronic and surface crystallographic stucture. A correlation is established between XPS and LEED measurements, associating the characteristic ‘‘quadruplet’’ patterns with the presence of intermediate nitrides. On the contrary, such compounds are absent when the LEED displays ‘‘8×8’’ patterns. Complementary results by reflection high energy electron diffraction (RHEED) and scanning electron microscopy (SEM), permit us to conclude that our thickest films, up to 40 A, are stoichiometric Si3N4, poorly crystallized in the β phase, presenting no surface rugosity.

Diffusion coatings of steels: Formation mechanism and microstructure of aluminized heat‐resistant stainless steels

Abstract: The effect of base‐alloy composition on the microstructure and mechanical and thermal stabilities of aluminum diffusion coatings has been studied for 316, 310, and I800H stainless steels, by optical, microprobe, transmission/scanning transmission electron microscopy, and microhardness testing. In all the diffusion aluminized alloys, two distinct coating layers form: an outer aluminide layer and an inner, interdiffusion layer. The substrate austenite stability is the single most important parameter affecting the thickness, phase distribution, and microchemistry of these two layers. TEM/STEM analyses showed that the interdiffusion layer is a ‘‘natural composite’’ made up of a uniform dispersion of the hard nickel aluminide phase (B2) in a soft ferrite matrix. Formation of this layer involves ‘‘ferritization’’ of the substrate, a process akin to pearlitic transformation in carbon steels. The interdiffusion layer demonstrated high hardness with good mechanical integrity and its thermal stability with the subs...

Hydrogenic impurity states in a quantum well wire

Abstract: A variational calculation of hydrogenic impurity binding energies in quantum well wires has been performed. The binding of the hydrogenic impurity has been calculated as a function of the transverse dimensions of the wire. It is found that the binding energy of the hydrogenic impurity increases as the ratio of the Bohr radius of the impurity in a bulk semiconductor to the transverse dimension of the wire increases. To test the sensitivity of the binding energies to the trial wave function we have used in our calculations, we use a wave function of the same type to calculate the binding energy of hydrogenic impurities confined in a quasi‐two‐dimensional quantum well as a function of well width and compare our results for the binding energies to the results obtained by Bastard [Phys. Rev. B 24, 4714 (1981)].

Thin solid films to combat friction, wear, and corrosion

Abstract: This paper deals with the relations and interactions of the substrate, the interface, and the functional hard overlay or diffusion coating deposited by chemical or physical vapor deposition, CVD or PVD, respectively, and how these structures influence the overall mechanical and physicochemical properties of the composite. Emphasis is given to the friction and wear behavior of the refractory carbides, nitrides, borides, and oxides, with and without lubrication, to the characterization of the mechanical strength of the interface as measured by the scratch test and thus, of the adhesion and cohesion properties, and to the corrosion behavior, mainly of TiC.

Barrier control and measurements: Abrupt semiconductor heterojunctions

Abstract: A brief critical review is given of diverse techniques used to measure heterojunction band lineups; they range from very reliable to worthless Another problem pertains to the heterosystems themselves: Data on systems in which two semiconductors from a different pair of columns of the periodic table are combined, should be reviewed with suspicion, although some selected pairs are probably trustworthy—but none in which a compound semiconductor was grown on an elemental one Technologies that do not lead to device‐quality interfaces also probably do not yield device‐quality lineup data A list of the most trustworthy experimental data is given The simplest possible theoretical framework for a theory of band lineups is a model of linear superpositon of atomiclike bulk potentials Such a model automatically leads to a theory that is linear and transitive, in which the band lineups are orientation independent, and in which a technology dependence of the band lineups requires a technology‐dependent deviation of the atomic arrangement from the ideal one The Harrison theory is both the simplest and the most successful theory of band lineups, although it still does not meet the needs of the device physicist The set of most reliable data selected earlier agree very well with this theory, with a largest deviation of 018 eV and a standard deviation of 013 eV

Effect of ion sputtering on interface chemistry and electrical properties of Au GaAs(100) Schottky contacts

Abstract: Auger and electron photoelectron spectroscopy were used to measure the extent of As depletion during 1 keV to 5 keV argon sputtering of GaAs surfaces. This depletion was correlated with a general decrease in the barrier height of the rectifying Au contact deposited in situ. However, nondestructive angle resolved XPS measurements showed As was depleted at the outer surface more by 1 keV than 3 keV argon. These effects are explained based on a combined work effective work function model and creation of a donor like surface damage layer. The donor layer was correlated with As depletion by sputtering. Deep level trap formation and annealing of sputtering effects were studied.

Schottky barrier heights of single crystal silicides on Si(111)

Abstract: Capacitance–voltage and current–voltage characteristics at single crystal silicide–silicon interfaces are studied. Schottky barrier heights are determined for epitaxial NiSi2 and CoSi2 layers grown under ultrahigh vacuum conditions on Si(111). These results demonstrate that there is an influence of interface structure on Schottky barrier height. This dependence suggests a reassessment of many previous interpretations or models of Schottky barriers. It also shows that experimentally measured barrier heights of metal–semiconductor systems with inhomogeneous interface structure are likely to be the averages from those associated with different regions of the interface. Homogeneous metal–semiconductor interfaces are therefore the simplest and most desirable systems for the study of Schottky barrier mechanisms. In particular, the present epitaxial silicide–silicon interfaces represent ideal candidates for detailed theoretical investigations based on experimentally obtained atomic structures.

Impurity effects in transition metal silicides

Abstract: Impurities can affect the properties of silicides directly by virtue of their presence. Impurities can also influence the processes by which silicides are formed. The effect of impurities on the reaction of transition metal films with a silicon substrate induced by thermal annealing are well documented. The interpretation of these results is discussed. It is shown that impurity redistribution is a major factor in determining how significant the effect of an impurity is. Redistribution observed for dopant impurities is also discussed.

The geometric structures of the GaAs(111) and (110) surfaces

Abstract: We present results of a reconstruction model proposed for the (2×2) GaAs(111) surface, together with a reexamination of the (1×1) GaAs(110) surface structure. Our model indicates that the reconstruction mechanisms on the (111) and (110) surfaces are similar to one another. In both cases, surface electronic energies are lowered via orbital rehybridization between nearest neighbor Ga and As atoms with dangling bonds. Reexamination of the GaAs(110) surface structure confirms our previous result of a tilt angle of ω=27°±2° and rejects a recently proposed value of ω=7°.

The growth and characterization of nominally undoped Al1−xInxAs grown by molecular beam epitaxy

Abstract: Al1−xInxAs films have been grown by molecular beam epitaxy (MBE) on InP substrates. Unintentionally doped material had a free electron concentration of the order of 1×1016 cm−3 when grown above 560 °C but was semi‐insulating when grown below 520 °C. The effects of substrate temperature and the group V to group III flux ratio during growth on the electrical properties and on the 4 K cathodoluminescence are reported. The Auger electron spectroscopy (AES) profiles through the films show that loss of indium is detectable only at temperatures in excess of 600 °C for As4/group III flux ratios of 15–20:1. The optimum MBE growth temperature for Al1−xInxAs on InP is 580 °C. Cathodoluminescence spectroscopy was used to measure the band gap of the epitaxial layers as a function of In content for values of x between 0.46 and 0.55. Over this range, at room temperature the band gap energy was found to vary as Eg(300 K)=1.450+2.29(0.523−x) eV, while at 4 K the relation was measured to be Eg(4 K)=1.508+2.22(0.523−x) eV. ...

Computer simulations of surfaces, interfaces, and physisorbed films

Abstract: We survey selected computer simulations or ‘‘experiments’’ relating to the statistical physics of surface phenomena. An introduction to the Monte Carlo and molecular dynamics simulation techniques is presented, followed by chosen computer simulation applications which have been done mainly at the IBM Research Laboratory over the last several years. The examples are taken from studies of the structure and thermodynamics of microclusters, liquid–vapor and liquid–solid interfaces and quasi‐two‐dimensional physisorbed films. An up‐to‐date bibliography of the various topics is given at the conclusion.

Electronic transport properties of TiSi2 thin films

Abstract: High purity, single‐phase TiSi2 thin films were prepared by deposition of titanium onto polycrystalline silicon layers followed by furnace annealing. Measurements of the temperature dependence of resistivity show that the material behaves as a classical metallic conductor, with an intrinsic resistivity proportional to temperature and having a room temperature value of ∼11μΩ cm. Geometrical magnetoresistance measurements on Corbino disk samples give a ‘‘representative’’mobility value (∼60 cm2/V‐s at room temperature) that mirrors the temperature dependence of resistivity. The very small Hall effect, taken together with a sizeable physical magnetoresistance, indicates the material is predominantly an electron conductor with a spectrum of mobility values for carriers on the Fermi surface because an isotropic, two‐band model cannot quantitatively account for the data.

Photoemission studies of the band bending on MBE‐grown GaAs(001)

Abstract: The band bending on GaAs(001) surfaces prepared by molecular beam epitaxy (MBE) have been studied for n‐ and p‐type materials. Surfaces with c(4×4), c(2×8), and (4×6) reconstruction ranging from As to Ga rich have been investigated. The surface symmetry was determined by reflection high energy electron diffraction (RHEED) and the position of the valence band maximum relative to the Fermi level was measured using angle resolved UV photoelectron spectroscopy (ARUPS) at normal emission. The position of the Fermi level relative to the valence band maximum was found to be ∼0.7 eV for n‐type and ∼0.5 eV for p‐type material, with a slightly increasing trend in going from Ga‐ to As‐rich surfaces. For the (4×6) reconstructed n‐type samples the growth termination method was found to have a significant influence on the band bending. The results obtained here are in very good agreement with previous measurements of the Al–GaAs(001) Schottky barrier height indicating that the electronic properties of this junction are...

Theoretical investigations of the nature of the normal and inverted GaAs–AlGaAs structures grown by molecular beam epitaxy

Abstract: We have developed an atomistic model for the growth of GaAs and AlGaAs and have simulated the MBE growth of both the normal (AlGaAs on GaAs) and the inverted (GaAs on AlGaAs) structures along (100) direction using Monte Carlo techniques. We assume the growth to occur under anion overpressure with As2 molecular species as the anion source and Ga and Al atoms as the cation sources. We find that some of the differences in the quality of the two interfaces can be explained on the basis of the surface kinetics operational for the two kinds of cations. In our model there is a considerable interlayer surface migration for the Ga atoms due to the relatively weak Ga–As bond compared to the Al–As bond. For comparable substrate temperatures the stronger Al–As bonds lower the interlayer diffusion for Al atoms. The role of this key kinetic step, namely, the interlayer surface migration on the quality of the growth front profiles of GaAs and AlGaAs as well as their interfaces is examined.

Interactions in metallization systems for integrated circuits

Abstract: Conductive films are required to provide interconnection between contacts on the devices and between devices and outside world. Aluminum has been the most popular metal. Conducting polycrystalline silicon (polysilicon) film has been the conductor for gate and interconnection. PtSi has been used as a Schottky barrier contact and also simply as a contact for deep junctions. Refractory silicides are now used as gate and interconnection metallizations. Titanium/palladium/gold or titanium/platinum/gold beam lead technology was successful in providing high reliability connection to the outside world. Several similar schemes have been suggested or used in the integrated circuits. A considerable amount of work is carried out in adopting such a metallization scheme in integrated circuits. These include a study of metallurgical and chemical interactions between various materials and effect of such interactions on the properties of the materials and devices. In this paper a review of these studies will be presented.

Oxygen redistribution during sintering of Ti/Si structures

Abstract: We have used helium backscattering spectroscopy (RBS) to trace the evolution of oxygen depth profiles after UHV sintering, in 1430 A titanium films, sputter deposited onto single crystal silicon substrates. The as‐deposited films exhibit a roughly exponential oxygen distribution, decreasing from the titanium film surface. After sintering at 350 °C, 30 min the oxygen has moved into the film and after 450 °C, 20 min the oxygen is uniformly distributed in the titanium. At higher temperatures, as silicide formation progresses, the oxygen is snowplowed back toward the surface and is completely driven from the TiSi2 film after sintering at 800 °C, 30 min. The low temperature oxygen redistribution in titanium correlates well with increases in the sheet resistance of the unreacted films, as has been suggested earlier from x‐ray diffraction results which revealed an increase in the titanium c axis after sintering at 500 °C [S. P. Murarka and D. B. Fraser, J. Appl. Phys. 51, 342 (1980)]. The sheet resistance reache...

Influence of the interfacial oxide on titanium silicide formation by rapid thermal annealing

Abstract: The interaction of titanium films with single crystal silicon during rapid thermal annealing (RTA) has been studied by Auger analysis and SEM. The diffusion of silicon in titanium to form a silicide has been investigated as a function of the thickness of the interfacial silicon dioxide between the film and the substrate. For a clean interface the diffusion is initiated at lower temperatures, approximately 600 °C. Ion beam mixing of the interface caused by the implantation of heavy ions, such a arsenic, through the titanium film helps to render the interfacial oxide ineffective and thereby facilitates Si diffusion into the film. The presence of the interfacial oxide has been shown to affect the smoothness of the final silicide layer and the silicide–silicon interface. Silicide films produced from ion‐mixed films have been found to have smoother surfaces and interfaces than nonion‐mixed samples. Application of ion‐mixed films to devices has been studied.

Nonuniform surface potentials and their observation by surface sensitive techniques

Abstract: Various models of Schottky barrier formation have been proposed in the last few years which involve metallurgical interactions at the metal–semiconductor interface. Most of these models involve nonuniform lateral variations in the surface potential. For metallic clusters and/or anion clusters, these variations involve a relatively large size scale (tens to hundreds of angstroms). For interface defect formation, the suggestion of cluster formation energy as the driving force for defect formation could also lead to a nonuniform distribution of pinning sites on a similar size scale. We have studied the effects of various spatial distributions of pinning sites (e.g., surface defects, clusters of anions and/or adsorbed metal atoms) and variations of their energy levels upon surface potentials and their depth distribution via a two‐dimensional finite difference program that integrates Poisson’s equation. Our results suggest that surface sensitive spectroscopies provide a less than exact measure of pinning level...

Summary Abstract: The MBE growth of GaAs free of oval defects

Abstract: The oval defect has been an ubiquitous problem in GaAs epitaxial layers grown by MBE. Their reported density varies from about 100 cm 2 (best case) to about 10 000 cm 2. A recent report by Calawa, et al., I shows that oval defect formation is associated with Ga droplets which appear on the epilayer surface during growth. In this paper we report for the first time the deposition of epitaxial layers of GaAs by MBE which are entirely free of oval defects. The oval-defect-free layers were grown on a 1.6 cm2 (100) semi-insulating GaAs substrate at 550 ·C, at growth rates of 0.4-1.0 Jllh. The critical factor in obtaining oval-defect-free layers was the presence of a Mg flux corresponding to a magnesium content of about 10 cm -3. A careful metallurgical inspection of these layers using Nomarski phase constrast microscopy at magnifications up to 1600X revealed no oval defects. The hole concentrations ofthese layers were approximately 10 cm-3. Layers grown without high-level Mg doping under otherwise identical conditions had oval defect densities in the 300 cm 2 range. Gallium spitting from the gallium effusion cell has long been suspected as the primary means of droplet generation. Magnesium doping should not eliminate this source, therefore we conclude that gallium spitting is not the source of gallium droplets on the substrate surface. The remaining plausible mechanism for the formation of gallium droplets on the substrate surface is the nucleation of droplets from adsorbed gallium. When the growth surface is allowed to accumulate large quantities of gallium, many droplets form and huge oval defect concentrations result. A GaAs layer grown fo]]owing exposure to about 100 monolayers of gallium had an oval defect concentration of about 10 cm -2. The growth of oval-defect-free layers indicates that this nucleation is not spontaneous under arsenic-stable conditions. Rather, sites of surface imperfections or contamination must act as nucleating centers for gallium. However, some growth irregularities indicative of surface contamination are commonly observed and are not oval defects. Thus, only certain defects or contaminants cause the oval defect. Gallium commonly requires its oxide species to wet otherwise inert surfaces, and will not wet in vacuum certain surfaces it readily wets in the presence of atmospheric oxygen and water vapor. One might expect that a precipitate at least partly composed of gallium oxides would serve as an ideal site to nucleate a gallium droplet. Mg is ap-type dopant in MBE GaAs that is known to have a lower electrical activity than is expected from the incident flux. 1Jte model most consistent with available data indicates that the reduced activity is due to the incorporation of an electrically inactive species ofMg: that species is believed to be MgO. This indicates the existence of oxygen-containing species that readily form MgO in the presence of Mg. Ga20 (gallium suboxide) is an oxide species observable in the gallium cell's effusate.2 Intentionally increasing the Ga20 flux from the Ga effusion cell has been shown 3 to markedly increase oval defect densities. Ga20 3 is formed by the disproportionation of the suboxide. It is believed that this forms oxide precipitates that nucleate gallium droplet formation, thus forming the precursor of the oval defect. Moreover, the disproportionation reaction yields unbonded Ga atoms that may trigger the Ga droplet nucleation. In the presence of large fluxes of magnesium, the gallium oxides are reduced on the sample surface, forming MgO. MgO is not wet by Ga in vacuum, thus it is unlikely that macroscopic gallium droplets will be nucleated by MgO. We performed experiments to enhance the formation of Ga20 3 precipitates in an attempt to induce Ga droplet formation and thereby increase the oval defect density. We used an independent source ofG~O, consisting of an effusion cell charged with both Ga and Ga20 3. This allowed stable control of the Ga20 flux independent of the gallium source used for growth. A Ga20 pressure of about 5 X 109 Torr at the substrate resulted in an oval defect density of lOS _106 cm 2. Optical properties were affected as well. The near-band-edge photoluminescence intensity at 2 K was reduced approximately tenfold compared to control specimens grown with the Ga20 source shuttered. These control layers exhibited oval defect densities of 200-500 cm-2. In conclusion, the role of gallium droplets in the formation of oval defects is supported. The elimination of oval defects through the use of magnesium doping indicates that these Ga droplets do not originate externally to the surface, i.e., at the gallium effusion cell. Rather, it is believed that nucleating centers on the sample surface support Ga droplet formation. It is found that a sufficient quantity of magnesium disrupts this mechanism. The reactivity of magnesium and its observed doping behavior indicates that at least some magnesium is incorporated as MgO (at the 10 cm-3 level, about 9O%!). This, in tum, suggests that in the absence of sufficient quantities of Mg, G~03 is incorporated as precipitates. Ga203 precipitates can nucleate Ga droplet formation: Enhancing oxide incorporation with an additional Ga20 source drastically increases the oval defect concentration. Gallium oxide species are eliminated via reactions with Mg fluxes. For properly prepared surfaces free from other nucleating centers, this results in oval-defect-free epilayers. Our results and interpretation are consistent with the accepted origins of the oval defect I and the observed doping

New coatings for high temperature materials protection

Abstract: The development, characterization, and performance evaluation of two new thin (≲20 μm) ceramic coatings for high temperature materials protection is reviewed. These coatings were silica produced by two vapor deposition procedures and ceria formed by sol–gel technology. The current position regarding the use of these coatings in the UK nuclear industry is described.

Influence of growth conditions and alloy composition on deep electron traps of n‐AlxGa1−xAs grown by MBE

Abstract: Two dominant deep electron traps, named ME3 and ME6, in Si‐doped AlxGa1−xAs grown by MBE have been studied by Deep Level Transient Spectroscopy (DLTS) and photoluminescence measurements. The change of the two trap concentrations with growth conditions and alloy composition, and the effects of them on photoluminescence intensity are described. The ME3 concentration shows strong alloy composition dependence and has a maximum nearly equal to the doping concentration at x of about 0.4. The ME3 concentration depends linearly on the doping concentration. The ME6 concentration depends strongly on the growth temperature above 720 °C. Group V/III beam flux ratio dependence of ME6 is less than the growth temperature dependence. The growth temperature and beam flux ratio dependences of ME3 are opposite to those of ME6. ME3 has no effect on photoluminescence intensity at room temperature, whereas ME6 reduces the photoluminescence intensity.

Thin film transistors for large area electronics

Abstract: This paper reviews thin film transistor technology with a detailed emphasis on amorphous silicon (a‐Si:H) devices. The fabrication and large area technology issues are described. The materials parameters that affect device performance are dominated by interface effects and the gate dielectric. The problem of characterizing the interfaces is discussed. Applications in liquid crystal displays (LCD) and image sensors are described. It is concluded that there is considerable promise for this rapidly expanding technology.

Reactive ion etching of GaAs in a chlorine plasma

Abstract: Chlorine was used to carry out the reactive ion etching (RIE) of GaAs. At 5 mTorr pressure and 270 V bias, it was found to etch at a rate >1 μ/min, and produced features having vertical sidewalls and a clean substrate surface. The mechanism of chlorine RIE of GaAs was studied by examining etch rates and profiles obtained using gases of different mixtures of chlorine and argon. The results are consonant with proposed mechanisms of GaAs etching by chlorine in both the plasma and reactive ion beam etching regimes.