Showing papers on "Heterojunction published in 1988"

Silicon-germanium base heterojunction bipolar transistors by molecular beam epitaxy

Abstract: The devices were fabricated using molecular-beam epitaxy (MBE), low-temperature processing, and germanium concentrations of 0, 6%, and 12%. The transistors demonstrate current gain, and show the expected increase in collector current as a result of reduced bandgap due to Ge incorporation in the base. For a 1000-AA base device containing 12% Ge, a six-times increase in collector current was measured at room temperature, while a 1000-times increase was observed to 90 K. The temperature dependence of the collector current of the Si/sub 0.88/Ge/sub 0.12/ base transistor is consistent with a bandgap shrinkage in the base of 50 meV. For the homojunction transistors, base widths as thin as 800 AA were grown, corresponding to a neutral base width of no more than 400 AA. >

Migration-Enhanced Epitaxy of GaAs and AlGaAs

Abstract: Surface migration is effectively enhanced by evaporating Ga or Al atoms onto a clean GaAs surface under an As-free or low As pressure atmosphere. This characteristic was utilized by alternately supplying Ga and/or Al and AS4 to the substrate surface for growing atomically-flat GaAs-AlGaAs heterointerfaces, and also for growing high-quality GaAs and AlGaAs layers at very low substrate temperatures. The migration characteristics of surface adatoms have been investigated through reflection high-energy electron diffraction measurements. It was found that different growth mechanisms are operative in this method at both high and low temperatures. Both these mechanisms are expected to yield flat heterojunction interfaces. By applying this method, GaAs layers and GaAs-AlGaAs single quantum-well structures with excellent photoluminescence were grown at substrate temperatures of 200 and 300degC, respectively.

Advanced Theory of Semiconductor Devices

Abstract: Preface. Acknowledgments. A Brief Review of the Basic Equations. The Symmetry of the Crystal Lattice. The Theory of Energy Bands in Crystals. Imperfections of Ideal Crystal Structure. Equilibrium Statistics for Electrons and Holes. Self--Consistent Potentials and Dielectric Properties. Scattering Theory. The Boltzmann Transport Equation. Generation--Recombination. The Heterojunction Barrier. The Device Equations of Shockley and Stratton. Numerical Device Simulations. Diodes. Laser Diodes. Transistors. Future Semiconductor Devices. Appendix A: Tunneling and the Golden Rule. Appendix B: The One Band Approximation. Appendix C: Temperature Dependence of the Band Structure. Appendix D: Hall Effect and Magnetoresistance. Appendix E: The Power Balance Equation. Appendix F: The Self--Consistent Potential at a Heterojunction. Appendix G: Schottky Barrier Transport. Index. About the Author.

Heterojunction bipolar transistor

Abstract: In a first heterojunction bipolar transistor (HBT) of the present invention, base layers and collector layers are respectively divided into a plurality of layers and one of the base layers provided closer to the collector layer reiogn is set lower in impurity concentration than the other thereof provided closer to an emitter layer, thus solving a problem that thermal histories during epitaxial growth or during processes cause a set impurity distribution to be destroyed due to diffusion and thus a heterojunction is shifted from a p-n junction. Since minority carriers in the base can smoothly flow toward the collector, there can be realized an excellent HBT having a very high current gain and a very high cut-off frequency. In a second HBT of the invention, a base region comprises a first base layer of a low concentration having the same energy band gap as an emitter region and to be changed to a complete depletion layer in a thermally balanced state and a graded second base layer of a high concentration, and the first and second base layers form a heterojunction, thereby realizing an excellent HBT having a high speed performance which can exhibit a sufficient grading effect while preventing deterioration of an emitter-base voltage withstanding characteristic.

Temperature dependence of photoluminescence from GaAs single and multiple quantum‐well heterostructures grown by molecular‐beam epitaxy

Abstract: The photoluminescence (PL) from GaAs/AlxGa1−xAs single and multiple quantum well (QW) heterostructures grown by molecular‐beam epitaxy (MBE) has been studied in the temperature range 10

Carbon doping in molecular beam epitaxy of GaAs from a heated graphite filament

Abstract: Carbon doping of GaAs grown by molecular beam epitaxy has been obtained for the first time by use of a heated graphite filament. Controlled carbon acceptor concentrations over the range of 10 to the 17th-10 to the 20th/cu cm were achieved by resistively heating a graphite filament with a direct current power supply. Capacitance-voltage, p/n junction and secondary-ion mass spectrometry measurements indicate that there is negligible diffusion of carbon during growth and with postgrowth rapid thermal annealing. Carbon was used for p-type doping in the base of Npn AlGaAs/GaAs heterojunction bipolar transistors. Current gains greater than 100 and near-ideal emitter heterojunctions were obtained in transistors with a carbon base doping of 1 x 10 to the 19th/cu cm. These preliminary results indicate that carbon doping from a solid graphite source may be an attractive substitute for beryllium, which is known to have a relatively high diffusion coefficient in GaAs.

Lead salt quantum effect structures

Abstract: Lead salt (IV-VI) compounds have been grown epitaxially by a variety of growth techniques, such as molecular-beam epitaxy and hot-wall epitaxy. Recently, compositional superlattices and quantum-well heterostructures have been grown that exhibit strong quantum optical effects. These structures have been used to fabricate midinfrared diode lasers with greatly improved operating temperatures. Thus, it appears that these devices will continue to maintain a significant advantage over II-VI and III-V compound diode lasers. Doping superlattices have been made which possess enhanced minority carrier properties. Ferromagnetic ordering in PbSnTe-MnTe alloys suggests potential areas for future work in magnetic field sensitivity devices. Lead salt quantum-effect structures are included. >

Double Heterostructure GaAs Tunnel Junction for a AlGaAs/GaAs Tandem Solar Cell

Abstract: A double hetero (DH) GaAs tunnel diode which consists of a GaAs tunnel junction sandwiched between AlxGa1-xAs layers has been grown by molecular beam epitaxy, and its annealing characteristics studied. DH tunnel diodes have the advantage that a decrease in the tunnel peak current density due to annealing is greatly suppressed compared to conventional GaAs diodes without AlGaAs layers. In-depth profiles of dopants indicate that the AlGaAs layers act as blocking layers against Be diffusion, which causes a degradation of the diodes. An Al0.4Ga0.6As/GaAs tandem solar cell incorporating the DH tunnel junction as interconnectors has achieved a conversion efficiency of 20%.

Fundamental studies and device application of δ-doping in GaAs Layers and in AlxGa1−xAs/GaAs heterostructures

Abstract: In addition to the realization of atomically abrupt interfaces in III–V semiconductors by molecular beam epitaxy, the confinement of donor and acceptor impurities to an atomic plane normal to the crystal growth direction, calledδ-doping, is important for the fabrication of artifically layered semiconductor structures. The implementation ofδ-function-like doping profiles by using Si donors and Be acceptors generates V-shaped potential wells in GaAs and AlxGa1−xAs with a quasi-two-dimensional (2D) electron (or hole) gas. In this review we define three areas of fundamental and device aspects associated withδ-doping. (i) The prototype structure ofδ-doping formed by a single atomic plane of Si donors in GaAs allows to study the 2D electron gas by magnetotransport and tunneling experiments, to study the metal-insulator transition, and to study central-cell and multivalley effects. In addition, non-alloyed ohmic contacts to GaAs and GaAs field-effect transistors (δ-FETs) with a buried 2D channel of high carrier density can be fabricated fromδ-doped material. (ii) GaAs sawtooth doping superlattices, consisting of a periodic sequence of alternating n- and p-typeδ-doping layers equally spaced by undoped regions, emit light of high intensity at wavelengths of 0.9 <λ <1.2 [μm], which is attractive for application in photonic devices. The observed carrier transport normal to the layers due to tunneling indicates the feasibility of this superlattice as effective-mass filter. (iii) The confinement of donors (or acceptors) to an atomic (001) plane in selectively doped AlxGa1−xAs/GaAs heterostructures leads to very high mobilities, to high 2D carrier densities, and to a reduction of the undesired persistent photo-conductivity. Theseδ-doped heterostructures are thus important for application in transistors with improved current driving capabilities.

Optical and structural properties of GaAs grown on (100) Si by molecular‐beam epitaxy

Abstract: GaAs epitaxial layers (0.5 μm

Band offsets and excitons in CdTe/(Cd,Mn)Te quantum wells.

Abstract: The question of band offsets and details of exciton binding are investigated in the CdTe/(Cd,Mn)Te heterostructure in the quantum-well limit. Photoluminescence excitation spectroscopy in external magnetic fields is used to vary the quantum-well potential depths in this moderately strained (0.6% lattice mismatch) diluted magnetic semiconductor heterostructure. Large Zeeman splittings are observed at all the principal quantum-well transitions and at the barrier band gap for a structure of CdTe well thicknesses of 50 A\r{} and a Mn-ion concentration in the barrier layer of x=0.24. A variational theory is developed for excitons, especially accounting for the possibility of a small valence-band offset. Good agreement between theory and experiment is obtained and a band offset of 25 meV is deduced for the heavy-hole valence band, corresponding to a conduction- to valence-band offset ratio of about 14:1. This implies that the valence-band offset in a hypothetical strain-free case is virtually zero. The accuracy of the offset determination is believed to be better than 10 meV. Exciton binding energies are found to vary appreciably in the magnetic field; the zero-field value is approximately twice that for bulk CdTe.

A new effect at high currents in heterostructure bipolar transistors

Abstract: Large current densities in heterostructure bipolar transistors with heterostructure collectors are shown to cause an excess electron barrier leading to an increase in minority-carrier charge storage in the base and a decrease in current gain of the device. This effect occurs at current densities where the mobile charge in the collector depletion region significantly reduces the electrostatic field, thus exposing an electron chemical potential barrier due to bandgap grading at the junction. The effect appears at lower current densities than the Kirk effect and should occur in wide-gap heterostructure collector devices. The effect is demonstrated using experimental data and analyzed using device modeling; solutions are suggested for its elimination. >

Growth and diffusion of abrupt zinc profiles in gallium arsenide and heterojunction bipolar transistor structures grown by organometallic vapor phase epitaxy

Abstract: The growth and diffusion of abrupt Zn profiles in undoped gallium arsenide (GaAs), silicon‐doped GaAs, and heterojunction bipolar transistor structures grown by organometallic vapor phase epitaxy have been studied using secondary ion mass spectrometry depth profiling. The depth profiles indicate that abrupt (within 100 A) turn‐on of Zn doping to levels approaching 1020 cm−3 are obtainable, while abrupt turn‐off is limited to about two orders of magnitude due to dopant tailing toward the surface resulting from residual Zn in the reactor. The sharp diffusion fronts resulting from post‐growth anneals indicate that the Zn diffusion coefficient has a concentration dependence. However, the diffusion of Zn at high concentrations appears to be inhibited by crystal defect kinetics resulting in a relatively concentration‐independent Zn diffusion coefficient. The V/III growth ratio did not have an effect on Zn diffusion in undoped or silicon‐doped GaAs. The diffusion of Zn in heterojunction bipolar transistor struct...

Noise spectroscopy of deep level (DX) centers in GaAs‐AlxGa1−xAs heterostructures

Abstract: We have measured the generation‐recombination noise from the donor‐related DX centers in current biased GaAs/AlxGa1−xAs heterostructures from 1 Hz to 25 kHz and from 77 to 330 K. A significant noise contribution from these traps is observed even at Al mole fractions below 0.2, where the trap level is resonant with the conduction band. The activated behavior of the noise spectrum from this resonant level is very similar to that observed at higher Al mole fractions, when the level lies deep in the fundamental gap. This result can be predicted, based on the recently elucidated relationship of the trap level to the band structure of AlxGa1−xAs. In accordance with other experimental results, the noise spectra demonstrate that the emission and capture kinetics of the level are unperturbed by its resonance with the conduction band. We briefly discuss some implications of these results for heterostructure transistor design.

Stability and epitaxy of NiAl and related intermetallic films on III‐V compound semiconductors

Abstract: The cubic transition metal‐gallium and transition metal‐aluminum intermetallic compounds with the CsCl structure (e.g., NiGa and CoAl) have been identified as candidate materials for stable and epitaxical contacts to III‐V semiconductors. Fabrication of these stable and epitaxical contacts using only conventional vacuum deposition (e.g., electron gun evaporation) has been demonstrated for the NiAl/GaAs system. It is expected that this unique class of contact materials will find application in III‐V‐based field‐effect transistors as well as novel electronic and photonic devices based on multiple semiconductor/metal heterojunctions.

Realization of a quasi‐three‐dimensional modulation‐doped semiconductor structure

Abstract: We report the realization of a modulation‐doped quasi‐three‐dimensional electron system. The structure consists of a 2000‐A‐wide undoped AlxGa1−xAs well bounded by undoped (spacer) and doped layers of AlyGa1−yAs (y>x) on both sides. The alloy composition in the well (x) is varied quadratically so that the combined potentials due to the AlxGa1−xAs and the electric charge in the well produce a square potential well with a nearly uniform carrier density. Magnetotransport data reveal that the system contains ≂2.5×1011 cm−2 electrons, which occupy four electric subbands and have a low‐temperature mobility in excess of 1×105 cm2/V s indicating the high quality of the structure.

Molecular beam epitaxial growth of ultrathin buried metal layers: (Al,Ga)As/NiAl/(Al,Ga)As heterostructures

Abstract: We report the first growth of epitaxial NiAl metallic layers buried within monocrystalline GaAs/AlAs/NiAl/AlAs/GaAs heterostructures deposited entirely within a molecular beam epitaxy growth chamber. The layer growth sequence is monitored by reflection high‐energy electron diffraction. Cross‐sectional transmission electron microscopy shows that the metal layers and the III‐V overgrowth are monocrystalline and of high quality. Thin, buried NiAl layers over the entire thickness range investigated (3–100 nm) are electrically continuous (69 μΩ cm at 3 nm). The heterostructures formed by this process can be used for the fabrication of thin‐metal buried‐layer devices utilizing ballistic transport or quantum mechanical tunneling across thin metal bases.

Amorphous SiC/Si three-color detector

Abstract: A hydrogenated amorphous SiC/hydrogenated amorphous Si heterojunction photodetector whose peak response could be voltage adjusted to three wavelengths, i.e., 480, 530, and 575 nm, by applying a small bias within ±2 V has been successfully fabricated. The basic principle is to use two back‐to‐back p‐i‐n junction diodes (or an n‐i‐p‐i‐n transistor) in which photons with wavelength λ<500 nm (blue) are mainly collected in the front a‐SiC:H/a‐Si:H heterojunction and the rest (green and red) are absorbed in the rear a‐Si:H homojunction. To further distinguish the green from the red, two undoped a‐Si:H layers, deposited at different conditions, were used in the rear homojunction to obtain two distinct collection regions. It is found that the required voltage to select one of the collection regions is less than 2 V. This detector shows a very high rejection ratio at various responses and thus is good for distinguishing the entire color spectrum.

One‐dimensional electronic systems in ultrafine mesa‐etched single and multiple quantum well wires

Abstract: Ultrafine mesa‐etched structures with lateral geometrical dimensions of 250 to 550 nm have been prepared in modulation‐doped AlGaAs/GaAs heterostructures and multiple quantum well systems. From magnetotransport measurements at low temperatures (T=2.2 K) on these single and multiple quantum well wire structures we find that the lateral carrier confinement leads to the formation of one‐dimensional electronic subbands of typically 2 meV energy separation. The width of the electron channel is smaller than the geometrical width, indicating a lateral depletion length of about 100 to 150 nm at the mesa edge.

Envelope-function matching conditions for GaAs/(Al,Ga)As heterojunctions

Abstract: By comparing model calculations and experimental results from photoluminescence excitation spectra, we determine that for GaAs/(Al,Ga)As quantum wells the appropriate matching conditions are the continuity of the envelope function (F) and ${m}^{\mathrm{\ensuremath{-}}1}$dF/dz across the interface.

beta -SiC/Si heterojunction bipolar transistors with high current gain

Abstract: The combination of single-crystalline beta -SiC and Si permits the fabrication of a heterojunction bipolar transistor (HBT) in which the conventional poly-Si or single-crystalline Si emitter is replaced with a single-crystalline SiC emitter, a technique compatible with existing Si technology. A common-emitter current gain of 800 is attained with this device. The value of the ideality factor n of the base current is 1.1, which suggests that diffusion current is dominant. The large number of misfit dislocations at the SiC/Si heterojunction are ineffective as recombination centers and do not deteriorate the characteristics of the HBT. >

Metalorganic chemical vapor deposition

Abstract: Sophisticated technologies1–19 for the growth of high-quality epitaxial layers of compound semiconductor heterostructure materials on single crystal semiconductor substrates are becoming increasingly important to the development of the semiconductor electronics industry. Historically, germanium was used in the invention of the point contact transistor and was the first material used in commercial applications. The drawback of germanium, however, is that it does not have a stable native oxide to eliminate surface effects. Silicon, with its extraordinary native oxide providing electronic and planar processing opportunities unavailable in other material systems, eventually replaced germanium and now dominates the semiconductor industry. As high speed electronic devices approach the fundamental limits of silicon and as optical and optoelectronic semiconductor devices become important. the HI-V compound semiconductors have become the state-of-the-art material. The advantages of the 111-V compounds are...

Kink effect in submicrometer-gate MBE-grown InAlAs/InGaAs/InAlAs heterojunction MESFETs

Abstract: The authors report the influence of the kink effect on the DC and microwave performance of i-InAlAs heterojunction doped-channel MESFETs lattice matched to an InP substrate with submicrometer gates. Kink effects were observed at room temperature as well as at 77 K in the DC measurement. The kinks seem to be related to deep-level electron trapping, and are not present at microwave frequencies. Measured results are presented showing that the existence of kinks at low operating frequencies does not seem to degrade the microwave performance of the devices. >

Electronic Properties and Modeling of Lattice-Mismatched and Regrown GaAs Interfaces Prepared by Metalorganic Vapor Phase Epitaxy

Abstract: In order to study and model non-ideal semiconductor-semiconductor interfaces, three kinds of GaAs interfaces, i.e., (i) a slightly mismatched InGaAs / GaAs interface, (ii) a highly mismatched GaAs / InP interface and (iii) an air-exposed GaAs / GaAs interface, were prepared by MOVPE. Their electronic properties were studied through measurements of C-V characteristics, carrier concentration profiles, DLTS spectra and I-V characteristics. By a novel interpretation of C-V characteristics and DLTS spectra, all the experimental results were explained consistently by a common model involving a U-shaped interface state continuum. The origin of the interface state continuum is explained by the disorder induced gap state (DIGS) model recently proposed for insulator-semiconductor and metal-semiconductor interfaces. This model seems to serve as a universal model for non-ideal S-S interfaces.

Semiconductor device with crystalline silicon-germanium-carbon alloy

Abstract: The present invention discloses a semiconductor device comprising a semiconductor layer being made of monocrystalline silicon or silicon-germanium alloy and a semiconductor layer being made of silicon-germanium-carbon alloy formed thereon, wherein the two layers form a heterojunction therebetween. In such a device, no lattice mismatch occurs between the layers or even if lattice mismatch occurs, it is only slight, so that the silicon-germanium-carbon alloy layer is in no danger of causing misfit dislocation therein.

Heterojunction acoustic charge transport devices on GaAs

Abstract: We have demonstrated a new type of buried‐channel acoustic charge transport device in which charge is transported in an (Al,Ga)As/GaAs/(Al,Ga)As heterojunction channel. Traveling‐wave potential wells, associated with a surface acoustic wave (SAW) propagating on the 〈100〉 surface of a GaAs crystal, transport electrons at the SAW velocity by means of a large‐signal acoustoelectric interaction. Heterojunction acoustic charge transport (HACT) delay lines have been fabricated, and the transport of charge demonstrated. Charge packets with up to 16×106 electrons/cm were measured in a delay 1.4 μs long. The HACT device is much simpler, the transport channel is more reliably produced (by molecular beam epitaxy or metalorganic chemical vapor deposition), and the device has potential for higher dynamic range when compared to the previously developed acoustic charge transport technology. This new device type is useful for the implementation of high‐speed monolithic signal processors.