Showing papers on "Heterojunction published in 1992"

Physics of Semiconductors and Their Heterostructures

Abstract: Chapter 1: Free Electron PictureChapter 2: Crystalline StructuresChapter 3: Wave Diffraction From CrystalsChapter 4: Electrons in Periodic StructuresChapter 5: Semiconductor BandstructuresChapter 6: Bandstructure Modifications--Alloys and HeterostructuresChapter 7: Bandstructure Modifications: Strained StructuresChapter 8: Lattice Vibrations--PhononsChapter 9: Doped SemiconductorsChapter 10: Carrier Transport--Basic FormalismChapter 11: Carrier Scattering by DefectsChapter 12: Carrier Scattering by PhononsChapter 13: Carrier-Carrier ScatteringChapter 14: High Field TransportChapter 15: Optical Processes in SemiconductorsChapter 16: Optical Processes in Semiconductors: Excitons

Development of New a-Si/c-Si Heterojunction Solar Cells: ACJ-HIT (Artificially Constructed Junction-Heterojunction with Intrinsic Thin-Layer)

Abstract: A new type of a-Si/c-Si heterojunction solar cell, called the HIT (Heterojunction with Intrinsic Thin-layer) solar cell, has been developed based on ACJ (Artificially Constructed Junction) technology. A conversion efficiency of more than 18% has been achieved, which is the highest ever value for solar cells in which the junction was fabricated at a low temperature (<200°C).

Observation of a two‐dimensional electron gas in low pressure metalorganic chemical vapor deposited GaN‐AlxGa1−xN heterojunctions

Abstract: We have confirmed the presence of a two‐dimensional electron gas (2DEG) in a wide band‐gap GaN‐AlxGa1−xN heterojunction by observing steplike features in the quantum Hall effect. The 2DEG mobility for a GaN‐Al0.13Ga0.87N heterojunction was measured to be 834 cm2/V s at room temperature. It monotonically increased and saturated at a value of 2626 cm2/V s at 77 K. The 2DEG mobility remained nearly constant for temperatures ranging from 77 to 4.2 K. Using Shubnikov–de Haas (SdH) measurements the two‐dimensional carrier concentration was estimated to be 1×1011 cm−2. The peak mobility for the 2DEG was found to decrease with the heterojunction aluminum compositions in excess of 13%.

Graded band gap ohmic contact to p‐ZnSe

Abstract: We describe a low‐resistance quasi‐ohmic contact to p‐ZnSe which involves the injection of holes from heavily doped ZnTe into ZnSe via a Zn(Se,Te) pseudograded band gap region. The specific contact resistance is measured to be in the range of 2–8×10−3 Ω cm2. The graded heterostructure scheme is incorporated as an efficient injector of holes for laser diode and light emitting diode devices, demonstrating the usefulness of this new contact scheme at actual device current densities.

Single-electron charging of quantum-dot atoms.

Abstract: Arrays of field-effect-confined quantum dots with diameters smaller than 100 nm have been prepared starting from Al x Ga 1-x As-GaAs heterostructures. In far-infrared spectroscopy, we induce transitions between the 2-meV-separated quantum levels. We observe discrete steps in the gate-voltage dependence of the integrated absorption strength indicating directly the incremental occupation of each dot with N=1, 2, 3, and 4 electrons. From the gate-voltage dependence, we can estimate a Coulomb charging energy of about 15 meV

Empirical fit to band discontinuities and barrier heights in III–V alloy systems

Abstract: We present a figure summarizing the variation of conduction band discontinuity, valence band discontinuity, and gold Schottky barrier height for binary and ternary III–V semiconductors. This figure, which applies to unstrained material, makes use of the property of transitivity in band alignments, and the observed experimental correlation between barrier heights and band gap discontinuities, to consolidate a wide range of data. The figure should be very useful in the design of novel heterostructure electronic and optical devices.

Near‐band‐gap photoluminescence from pseudomorphic Si1−xGex single layers on silicon

Abstract: The systematic study of band‐edge luminescence in pseudomorphic Si/Si1−xGex/Si double‐heterostructure layers is reported for a wide composition range, 0.12

Silicon-based semiconductor heterostructures: column IV bandgap engineering

Abstract: The use of strained layer epitaxy to grow high-quality Ge/sub x/Si/sub 1-x//Si heterostructures and their application to a wide range of heterostructure devices are addressed. The author reviews the mechanisms of strained layer growth, the bandstructure of the resulting material, and its use in test devices, including superlattice avalanche photodiodes for fiber optic communication, intrasubband optical detectors and arrays operating in the 10-15 mu m wavelength range, mobility enhanced modulation-doped transistors, heterojunction bipolar transistors with cutoff frequencies of 75 GHz, and negative resistance devices based on resonant tunneling and real-space carrier transfer. >

Characterization of boron carbide thin films fabricated by plasma enhanced chemical vapor deposition from boranes

Abstract: We have fabricated boron carbide thin films on Si(111) and other substrates by plasma‐enhanced chemical‐vapor deposition (PECVD). The PECVD of boron carbides from nido‐cage boranes, specially nido‐pentaborane(9) (B5H9), and methane (CH4) is demonstrated. The band gap is closely correlated with the boron to carbon ratio and can range from 0.77 to 1.80 eV and is consistent with the thermal activation barrier of 1.25 eV for conductivity. We have made boron carbide by PECVD from pentaborane and methane that is sufficiently isotropic to obtain resistivities as large as 1010 Ω cm at room temperature. This material is also shown to be suitable for photoactive p‐n heterojunction diode fabrication in combination with Si(111).

UHV/CVD growth of Si and Si:Ge alloys: chemistry, physics, and device applications

Abstract: The fundamental chemical principles underlying ultra-high-vacuum chemical vapor deposition (UHV CVD) are described in this overview. A variety of unique devices and structures, e.g. high-speed graded-bandgap heterojunction bipolar transistors and n-type resonant tunneling diodes, are discussed. The role of fundamental interface chemistry in making such structures possible is considered. >

Compound semiconductor device physics

Abstract: Review of semiconductor physics, properties, and device implications mathematical treatments transport across junctions metal semiconductor field effect transistors insulator and heterostructure field effect transistors heterostructure bipolar transistors hot carrier and tunnelling structures scaling and operational limitations. Appendixes: network parameters and relationships properties of compound semiconductors physical constraints and conversion units.

Measurement of minority-carrier lifetime by time-resolved photoluminescence

Abstract: Much of the current compound semiconductor device research is based on minority-carrier devices such as heterojunction bipolar transistors and diode lasers. The improvement of minority-carrier-parameters is the focal point of much ongoing materials research. The minority-carrier lifetimes of III-V compound semiconductors are most easily characterized by time-resolved photoluminescence. This is a quick and contactless technique which directly measures the excess minority-carrier carrier density. By using a focused laser beam as the excitation source, the required sample area may be very small. In special diagnostic structures which utilize a confinement or passivating layer, the interface recombination velocity can be determined. Here I will describe the measurement theory and measurement techniques which are used in our laboratory. Recent developments in the III-V materials technology will be reviewed.

Heterojunction solar cell

Abstract: A high-efficiency single heterojunction solar cell wherein a thin emitter layer (preferably Ga 0 .52 In 0 .48 P) forms a heterojunction with a GaAs absorber layer. The conversion effiency of the solar cell is at least 25.7%. The solar cell preferably includes a passivating layer between the substrate and the absorber layer. An anti-reflection coating is preferably disposed over the emitter layer.

Band Offsets in Semiconductor Heterojunctions

Abstract: Publisher Summary This chapter presents an overview of several theoretical approaches and experimental measurement techniques for determining band offset values and discuss the experimental and theoretical data reported for a number of specific heterojunction systems. It also evaluates the credibility and accuracy of the experimental measurements and provides a tabulation of reliable band offset values for as many heterojunctions as possible. Among the most important physical parameters for a given heterojunction system are the conduction- and valence-band offsets; indeed, the quality and even the feasibility of heterojunction device concepts often depend crucially on the values of these band offsets. The band offset is defined simply as the discontinuity in the band edge at the interface between two semiconductors. A number of current theories seem to yield band offset values in reasonable agreement with experiment, even though the physical ideas underlying these theories can be quite different. These ideas include electron affinities, Schottky barrier heights, bulk band structures on the same energy scale, and the definition of effective midgap energies corresponding to charge neutrality for each bulk constituent.

Low-frequency noise properties of N-p-n AlGaAs/GaAs heterojunction bipolar transistors

Abstract: The low-frequency noise characteristics of N-p-n Al/sub x/Ga/sub 1-x/As/GaAs heterojunction bipolar transistors (HBTs) have been investigated as a function of bias current, device geometry, extrinsic-base-surface condition, Al mole fraction in the emitter, and temperature in order to identify the dominant noise mechanisms. These measurements show the existence of three distinct regions in the noise spectra: a 1/f noise line shape, a Lorentzian spectrum (noise 'bump'), and a white-noise region. The 1/f noise is attributed to fluctuations in the extrinsic-base surface recombination current. The noise bump is generated by an AlGaAs trap in the emitter-base junction. The DX center was identified as a possible candidate for this trap. It is shown that for 4- mu m*10- mu m emitter AlGaAs/GaAs HBTs, the use of a depleted, AlGaAs passivation ledge over the extrinsic-base surface typically reduced the 1/f base noise current by a factor of 10, and the reduction of the Al mole fraction from 0.3 to 0.2 decreased the magnitude of the noise bump by a factor of 3. >

Dislocation Mechanisms of Relaxation in Strained Epitaxial Films

Abstract: Advances in the methods of deposition and characterization of crystalline films of submicron thickness have been dramatic over the past two decades. A principal motivation for development of this technology has been the potential for use of thin film semiconductor materials in electronic and optoelectronic devices. The main function of these devices is to control transport of electrons in a way which permits high spatial density, and in which the carriers are highly mobile, that is, they show fast response with little power consumption. Spatial control of mobile electrons can be facilitated by combining materials, forming a material heterostructure, with one or more of these materials being a thin film. Carrier confinement is enforced by a difference in energy band structure across the interface acting as a barrier. The exploitation of this physical effect in device design is called bandgap engineering. A great deal of attention has been focused on film/substrate systems involving the III-V compounds (InGaAs/GaAs, for example), as well as on II-VI compounds for optical applications (ZnSe/GaAs, for example). Current efforts are also directed toward SiGe/Si and GaAs/Si systems to exploit well-developed silicon device technology.

Atomic layer epitaxy of compound semiconductor

Abstract: A heterojunction between In-containing compound semiconductors in which the interface thereof is controlled at an atom level is provided by a process of atomic layer epitaxy (ALE) in which hydrogen gas is utilized as a carrier gas and as a purge gas for a separation of source gases. The time for which the purge gas is supplied can be utilized for controlling the ALE.

Organic–inorganic multilayers: A new concept of optoelectronic material

Abstract: By utilizing copper phthalocyanine (CuPc) and TiOx, we report the fabrication of organic–inorganic heteromultilayer structures as a new concept of optoelectronic material. These are based on an anticipated model where charge carrier photogeneration occurs in the CuPc layers, while the TiOx layers have the role of transportation of electrons in‐plane after charge separation at the interfaces. Atomic force microscopy has confirmed the formation of layered structures for samples with an artificial period of more than 50 A. The multilayers are found to exhibit 40 times higher photoconductivity than a CuPc single layer.

Physical properties of III-V semiconductor compounds : InP, InAs, GaAs, GaP, InGaAs, and InGaAsP

Abstract: Structural Properties Mechanical, Elastic, and Lattice Vibrational Properties Thermal Properties Collective Effects and Some Response Characteristics Electronic Energy-Band Structure Electron and Hole Deformation Potentials Optical Properties Elastooptic and Electrooptic Effects Carrier Transport Properties Strain Problems in InGaAs(P)-Based Heterostructures Concluding Remarks Appendix Indexes.

14.6% efficient thin-film cadmium telluride heterojunction solar cells

Abstract: Thin-film CdS/CdTe heterojunction solar cells have been prepared by the successive deposition of thin films of fluorine-doped SnO/sub 2/, CdS, p-CdTe, and an ohmic contact on glass substrates, followed by the deposition of an antireflection coating. The properties of CdS/CdTe heterojunctions have been studied. Under global AM1.5 conditions, a solar cell of about 1 cm/sup 2/ area has an open-circuit voltage of 805+or-5 mV, a short-circuit current density of 24.4+or-0.3 mA/cm/sup 2/, and a fill factor of 70.5+or-0.5%, corresponding to a total area conversion efficiency of 14.6+or-0.3%, verified by the National Renewable Energy Laboratory. >

Article comprising a lattice-mismatched semiconductor heterostructure

Abstract: Disclosed are strained layer heteroepitaxial structures (e.g., GeSi/Si) that can have low threading dislocation density as well as a substantially planar surface. Furthermore, a large fraction (e.g., >90%) of the total surface are of the structure can be available for device processing. These advantageous features are achieved through utilization of novel "dislocation sinks" on or in the substrate whose height parameter h is less than or about equal to the thickness of the strained heteroepitaxial layer on the substrate. Exemplarily, h≧h c , where h c is the critical thickness associated with misfit dislocation generation in the substrate/overlayer combination.

Elimination of heterojunction band discontinuities by modulation doping

Abstract: Heterojunction band discontinuities have been an active field of research during the last decade’ and made possible the realization of new device concepts such as modulation-doped transistors, heterobipolar transistors, and quantum-well lasers. The physical principles of these devices are based on heterojunction band discontinuities. In other device structures, however, heterojunction band discontinuities impede the flow of charge carriers across the junction. These structures include the optical distributed Bragg reflector which consists of alternating layers of two semiconductors with different refractive index, each having a thickness of a quarter wavelength. If distributed Bragg reflectors are used for current conduction, the constituent heterojunction band discontinuities impede the current flow, which is a highly undesired concomitant effect. It is the purpose of this publication to demonstrate that unipolar heterojunction band discontinuities can be eliminated by modulation doping and compositional grading of heterojunctions. The charge carrier transport across a heterojunction is illustrated in Fig. 1, which shows the band diagram of two semiconductors “A” and “B.” Band discontinuities occur in the conduction and valence band since the fundamental gap of semiconductor B is larger than the gap of A. Such discontinuities are usually referred to as type-1 heterojunctions, which contrast to type-11 (staggered) and type-III (broken gap) heterostructures. Transport across the heterojunction barrier can occur via thermal emission or via tunneling as schematically illustrated in Fig. 1. For sufficiently thick and high barriers, tunneling and thermal emission of carriers are not efficient transport mechanisms across the barrier. It is therefore desirable to eliminate such heterojunction band discontinuities in the conduction or valence band. Modulation doping of a parabolically graded heterojunction will next be shown to result in a flat-band-edge potential. The band diagram of a parabolically graded conduction-band edge is shown in Fig. 2 (a). The energy of the band edge increases parabolically with a positive second derivative between the points z, and z,. The band edge further increases parabolically with a negative second derivative between z2 and zs. The energy of the band edge can be expressed as / -&(z,) + 2(zf~z,)‘iz - zd’

Indium phosphide and related materials : processing, technology, and devices

Abstract: Properties of InP related materials SIMS analysis of InP and related materials deep levels in InP and related materials low pressure MOVPE of InP-based compound semiconductors doping of InP as grown by metal-organic chemical vapor deposition growth of InP and related compounds by GSMBE and MOMBE ion beam processing of InP and related materials dry etching of in-based semiconductors ohmic contacts to InP and related materials issues for dielectric technology for InP MISFETs InGaAsP quantum well lasers InGaAs heterostructure bipolar transistors optimization and fabrication of metal contacts for photovoltaic solar cells.

A thermodynamic model for determining pressure and temperature effects on the bandgap energies and other properties of some semiconductors

Abstract: Semiconductor bandgap energies are shown to be equal to the difference between the sum of the standard chemical potentials of free electrons and holes and standard chemical potential of the recombined electron-hole pairs when equilibrium occurs at a given temperature and pressure. The decrease in the bandgap energies of diamond semiconductors with increasing temperature is shown to be caused by the interaction of the free electrons, holes and recombined electron-hole pairs with lattice phonons and linear expansion of the lattice constant. The determined bandgap energies and other intrinsic properties of nondegenerate GaAs are found to be in excellent agreement with experimental data as a function of temperature and pressure. The proposed model is also shown to be useful in determining the effects of temperature and pressure on the intrinsic properties of epilayers and substrate in the metal-semiconductor junctions and heterojunctions.

Confinement and single-electron tunneling in Schottky-gated, laterally squeezed double-barrier quantum-well heterostructures.

Abstract: The conductance of laterally confined double-barrier quantum-well resonant-tunneling heterostructures is investigated. The confinement is provided by a Schottky gate and can be varied in a continuous way, giving direct proof of the quantum size effect. Data for dots with nominal diameters in the submicron range are reported. Possible evidence for a modulation of the Coulomb blockade by quantum confinement is presented

Diode ideality factor for surface recombination current in AlGaAs/GaAs heterojunction bipolar transistors

Abstract: n-p-n AlGaAs/GaAs heterojunction bipolar transistors of various emitter areas have been fabricated to examine the diode ideality factor for surface recombination. These transistors are fabricated with and without exposed extrinsic base surfaces. Comparison of the measured results indicates that the base surface recombination current increases exponentially with the base-emitter voltage with an ideality factor which is closer to 1 than 2(1 >

Low‐threshold InGaAs strained‐layer quantum‐well lasers (λ=0.98 μm) with GaInP cladding layers and mass‐transported buried heterostructure

Abstract: Buried‐heterostructure quantum‐well lasers fabricated by mass transport are reported for In0.18Ga0.82As/GaAs/Ga0.5In0.5P strained‐layer structures grown by atmospheric pressure organometallic vapor‐phase epitaxy. Threshold current densities as low as 85 A/cm2 are measured for broad‐stripe lasers, and buried‐stripe devices show threshold currents as low as 3 mA and differential quantum efficiencies as high as 34% per facet without coatings.