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The effect of emitter cap growth conditions on the common-emitter current gain of InGaP/GaAs HBTs, grown by LP-MOCVD, has been studied. This work shows that the material quality of a carbon-doped base is highly dependent on the emitter cap growth. The emitter cap growth effectively serves as a source of thermal stress. This stress on the base during the emitter and cap growth causes the formation of carbon-related defects in the base that increase the base recombination and reduces the current gain. Atomic force microscopy is used to identify these carbon-related defects. Gain improvements of about 40% have been achieved by optimizing the emitter cap growth conditions to reduce the thermal stress.

Thin films of highly (100) textured fine-grain (lateral grain size ≅0.1 to 0.15 μm) PbZrxTi1−xO3 (PZT) (x = 0 to 0.7) were grown on conductive perovskite LaNiO3-buffered platinized Si substrates by metalorganic chemical vapor deposition. Domain configuration and crystalline orientation were studied using x-ray diffraction and transmission electron microscopy. The predominant domain boundaries of Ti-rich tetragonal-phase PZT and Zr-rich rhombohedral-phase PZT were found to be on the (110) planes and (100) planes, respectively. The equilibrium domain widths were observed and estimated numerically on the basis of transformation strain, grain size, and domain boundary energy. The peak value of the dielectric constant was 790 near the morphotropic boundary. Hysteresis behavior of these PZT thin films was demonstrated. A decrease in coercive field with the increment of Zr content was found; this variation was attributed to domain density and the multiplicity of polarization axes. Furthermore, the low leakage current (J ≤ 5 × 10−7 A/cm2 at V = 4 V) was observed for all samples, and the involvement of several possible conduction mechanisms was suggested.

This work describes the temperature dependence of the DC and small-signal performance of InGaP/GaAs heterojunction bipolar transistors (HBT's) with different collector thicknesses. Detailed analyses of the small-signal performance and the temperature dependence of both DC and high-frequency parameters are presented. An HBT delay-time analysis is also presented and justified empirically. In addition, the factors causing the decrease in f/sub T/ with temperature are described, and the variations in collector resistance and collector drift velocity with temperature are determined.

Ion implantation into III–V nitride materials is animportant technology for high-power and high-temperature digital and monolithic microwave integrated circuits. We report the results of the electrical, optical, and surface morphology of Si ion-implanted GaN films using furnace annealing. We demonstrate high sheet-carrier densities for relatively low-dose (natoms=5×1014 cm−2) Si implants into AlN/GaN/sapphire heteroepitaxial films. The samples that were annealed at 1150°C in N2 for 5 min exhibited a smooth surface morphology and a sheet electron concentration ns ∼9.0×1013 cm−2, corresponding to an estimated 19% electrical activation and a 38% Si donor activation in GaN films grown on sapphire substrates. Variable-temperature Hall-effect measurem entsindicate a Si donor ionization energy ∼15 meV.

We present in this article device characteristics of molecular beam epitaxy grown GaAs/AlGaAs quantum well infrared photodetectors (QWIP) on a semi-insulating GaAs substrate and on a GaAs-on-Si substrate grown by metalorganic chemical vapor deposition (MOCVD). Important issues for QWIP application such as dark current, spectral response, and absolute responsivity were measured. We find that the detector structure grown on a GaAs-on-Si substrate exhibits comparable dark current and absolute responsivity and a small blue shift in the spectral response. This is the first demonstration of long wavelength GaAs/AlGaAs quantum well infrared photodetector using MOCVD grown GaAs-on-Si substrate and the performance is comparable to a similar detector structure grown on a GaAs substrate.

Low-temperature photoluminescence spectra of Er-doped GaP grown by low-pressure organometallic vapor phase epitaxy was investigated under both above-band gap and below-band gap excitation conditions. Under all experimental conditions, similar Er-related spectra dominated by numerous sharp emission lines were obtained for the first time. The intensity dependence of the photoluminescence exhibits complicated behavior and is modeled using a unique energy-transfer process. The results obtained indicate that some Er-related luminescence centers are efficiently activated by direct excitation of electrons to some traps related to the luminescence centers.

The partial intermixing of the well and barrier materials offers unique opportunities to shift locally the bandgap of quantum-well (QW) structures. We have demonstrated redshifting and broadening of the wavelength responses of bound-to-continuum GaAs and InP based quantum-well infrared photodetectors (QWIP's) after growth via impurity-free vacancy disordering (IFVD). A comprehensive set of experiments is conducted on QWIP's fabricated from both as-grown and multiple-quantum-well (MQW) structures. Compared to the as-grown detector, the peak spectral responses of the disordered detectors were shifted to longer wavelengths. The peak absolute response of the disordered GaAs based QWIP is lower by almost a factor of four. However, the responsivity characteristics of the disordered InP based QWIP show no major degradation. In general, with the spectral broadening taken into account, the overall performance of the disordered QWIP's has not dropped significantly. Thus, the postgrowth control of the QW composition profiles by impurity-free vacancy disordering offers unique opportunities to fine tune various aspects of a photodetector's response. Theoretical calculations of the absorption coefficient spectrum are in excellent agreement with the experimental data.

High-quality InGaAs/InP quantum wells with ultra-narrow well widths (∼10A) and peak response at 4.55 µm were grown by gas source molecular beam epitaxy. These structures were characterized by cross-sectional tunneling microscopy (XSTM), double-crystal x-ray diffraction (DCXRD), and cross-sectional transmission electron microscopy (XTEM). Based on the structural parameters determined by XTEM, XSTM, and DCXRD, the field dependent photocurrent spectra were simulated using a six-band effective bond-orbital model. The theoretical calculations are in excellent agreement with experimental data. When used to fabricate p-type InGaAs/InP quantum-well infrared photodetectors (QWIPs), and combined with the high responsivity of 8.93 µm n-type InGaAs/InP QWIPs, these structures offer the possibility of dual band monolithically integrated QWIPs.

We present experimental results on the growth and characterization of n-type InGaAs/InP quantum-well intersubband photodetectors for use at 8.93 µm. High-quality InGaAs/InP multiple quantum wells were grown by gas source molecular beam expitaxy, and then characterized by double-crystal x-ray diffraction and cross-sectional transmission electron microscopy. Based upon the structural parameters determined by these methods, the photocurrent response spectra were simulated using a six-band effective bond-orbital model. The theoretical results are in excellent agreement with experimental data. Additional important device characteristics such as dark current, spectral response, and absolute responsivity are also presented.

We report the determination of band offset ratios, using photoluminescence excitation measurements, for GaInP/GaAs and AlInP/GaAs quantum wells grown by gas-source molecular beam epitaxy. To reduce the uncertainty related to the intermixing layer at heterointerfaces, the residual group-V source evacuation time was optimized for abrupt GalnP/GaAs (AlInP/GaAs) interfaces. Based upon thickness and composition values determined by double-crystal x-ray diffraction simulation and cross-sectional transmission electron microscopy, the transition energies of GalnP/GaAs and AlInP/GaAs quantum wells were calculated using a three-band Kane model with varying band-offset ratios. The best fit of measured data to calculated transition energies suggests that the valence-band offset ratio (γ band discontinuity) was 0.63 ± 0.05 for GalnP/GaAs and 0.54 ± 0.05 for AlInP/GaAs heterostructures. This result showed good agreement with photoluminescence data, indicating that the value is independent of temperature.

Data are presented on the luminescence characteristics of InGaP InAlP heterostructures with oxidized InAlP cladding layers grown by metalorganic chemical vapor deposition. The structures are grown on GaAs substrates and consist of either a 20 nm thick In 0.5 Ga 0.5 P quantum well or a 0.75 μm InGaP layer sandwiched between two InAlP bulk barriers or between two 10-period In 0.5 Al 0.5 P In x Ga 1−x P strain-modulated superlattice heterobarriers, where x varies from 0.5 to 0.45 and the period of the superlattice is ∼ 3 nm. The top InAlP cladding layer of the InAlP InGaP heterostructures is oxidized for 2–5.5 h at ∼ 500°C in an ambient of H 2 O vapor saturated in a N 2 carrier gas. Photoluminescence and time-resolved photoluminescence studies at room temperature show that, as a result of the oxidation of a portion of the top InAlP cladding layer, the photoluminescence emission intensity and lifetime from the InGaP QWs increase significantly.

Selectively red shifting the photoresponse of intersubband GaAs/Al0.25Ga0.75As multiple‐quantum‐well (MQW) infrared photodetectors (QWIPs) by furnace and rapid thermal annealing is explored. Selective interdiffusion of the MQW is achieved by dielectric encapsulating (SiO2 or Si3N4) the surface. The high dark current of annealed QWIPs is attributed to dopant out‐diffusion from the QWs into the barriers. Declining responsivities result from reduced carrier density in the QW and a red shift of the intersubband transition energy. In this work, the intersubband energy is determined by the Fourier synthesis model and compared with experimental results (further confirming the interdiffusion mechanism). Minimal dark current and responsivity degradation is observed for Si3N4‐encapsulated QWIPs red shifted by 1 μm

InGaP GaAs heterojunction bipolar transistors with various collector structures are compared. The dependence of d.c. device characteristics on the thickness of the n− GaAs spacer in the collector of composite collector devices is presented. Results indicate that the spacer thickness significantly affects the performance of the transistor. An n+ doping spike on the InGaP side of the collector heterojunction is included in the collector design of the composite collector devices. Standard single-heterojunction d.c. results are compared to abrupt double- and composite collector heterojunction devices. Optimization of the spacer thickness, in conjunction with the n+ doping spike, eliminates most of the detrimental effects associated with a double-heterojunction device while retaining the beneficial properties of a wide-gap collector. As expected, the composite collector structure produces devices with higher breakdown voltages and lower offset voltages than single heterojunction devices. In addition, optimizing the spacer thickness can reduce the collector current saturation voltage of the composite collector device below that of a single-heterojunction device. These characteristics make composite collector heterojunction bipolar transistors ideal candidates for high power microwave device applications.

Factors which influence the alloy composition and doping level of CCl4-doped In0.53Ga04.7As grown at low temperatures (450°C < Tg < 560°C) by low-pressure metalorganic chemical vapor deposition (MOCVD) have been investigated. The composition is highly dependent on substrate temperature due to the preferential etching of In from the surface during growth and the temperature-dependent growth efficiency associated with the Ga source. The lower pyrolysis temperature of TEGa relative to TMGa allows the growth of CCl4-doped InGaAs at lower growth temperatures than can be achieved using TMGa, and results in improved uniformity. High p-type doping (p ∼ 7 × 1019 cm-8) has been achieved in C-doped InGaAs grown at T = 450°C. Secondary ion mass spectrometry analysis of a Cdoping spike in InGaAs before and after annealing at ∼670°C suggests that the diffusivity of C is significantly lower than for Zn in InGaAs. The hole mobilities and electron diffusion lengths in p+-InGaAs doped with C are also found to be comparable to those for Be and Zn-doped InGaAs, although it is also found that layers which are highly passivated by hydrogen suffer a degradation in hole mobility. InP/InGaAs heterojunction bipolar transistors (HBTs) with a C-doped base exhibit high-frequency performance (ft = 62 GHz, fmax=42 GHz) comparable to the best reported results for MOCVD-grown InP-based HBTs. These results demonstrate that in spite of the drawbacks related to compositional nonuniformity and hydrogen passivation in CCl4-doped InGaAs grown by MOCVD, the use of C as a stable p-type dopant and as an alternative to Be and Zn in InP/ InGaAs HBTs appears promising.

The incorporation of residual carbon has been studied for InP grown at low temperatures using TMIn and PH3 by low‐pressure metalorganic chemical vapor deposition. n‐type conduction is observed with electron concentrations as high as 1×1018 cm−3, and the electrical activation efficiency is 5%–15%. Carbon incorporation is found to be highly dependent on substrate temperature, suggesting that the rate‐limiting step is desorption of CHy (0≤y≤3) from the surface during growth. Hydrogen is also incorporated in the layers during growth. The electron mobilities are lower for C‐doped InP than for Si‐doped InP. InP/InGaAs heterojunction bipolar transistors with C as the p‐type base dopant and either Si or C as the n‐type emitter dopant have been fabricated and compared. Devices with a carbon‐doped base and emitter showed degraded performance, likely as a result of deep levels incorporated during growth of the emitter.

Minority‐carrier electron‐diffusion coefficients and lifetimes have been measured in heavily doped p‐type GaAs using the zero‐field time‐of‐flight (ZFTOF) technique. The materials studied included C‐doped GaAs grown by molecular‐beam epitaxy (MBE) using graphite as the dopant source, C‐doped GaAs grown by metalorganic chemical‐vapor deposition (MOCVD) using CCl4 as the dopant source, and Be‐doped GaAs grown by MBE. Room‐temperature photoluminescence intensity measurements were made on the structures and the results are compared with ZFTOF measurements of lifetime. The graphite‐doped material (p∼1019 cm−3) exhibited diffusion lengths of less than 1000 A. MOCVD‐grown C‐doped GaAs, which was optimized by adjusting the growth conditions to maximize the room‐temperature photoluminescence intensity, had diffusion lengths comparable to those measured in Be‐doped GaAs for hole concentrations of 1×1019 and 5×1019 cm−3. Comparison of photoluminescence intensities also suggests that addition of In to very heavily do...

AlInAs layers lattice‐matched to InP substrates were grown by atmospheric‐pressure metal‐organic chemical vapor deposition. The residual oxygen concentration determined by secondary ion mass spectrometry ranged from 3×1016 to 3×1019 cm−3, and was high when the growth temperature was low or the V/III ratio was low. The oxygen concentration and the residual carrier concentration showed the same dependence on the V/III ratio in the high V/III ratio region. This suggests that oxygen is the origin of the residual carrier concentration. Strong correlations between the oxygen concentration and the photoluminescence intensity and reverse current through Schottky diodes suggest that oxygen creates generation‐recombination centers in AlInAs layers.

A comparison of MOCVD-grown, n-p-n In/sub 0.5/Ga/sub 0.5/P/GaAs single- and double-heterojunction bipolar transistors (SHBTs and DHBTs) with a carbon-doped base is presented. A base doping level of 2.5*10/sup 19/ cm/sup -3/ was employed in both device structures, resulting in a base sheet resistance of 500 Omega /sq. Common-emitter current gains as high as 210 and 150 were measured for the SHBTs and DHBTs, respectively. Results of a DC performance optimization study indicate that a 15- and 25-AA undoped set-back layer at the emitter-base junction provides optimal common-emitter current gain. The DHBTs exhibited a 40% improvement in common-base breakdown voltage compared to SHBTs (25 versus 18 V), indicating that In/sub 0.5/Ga/sub 0.5/P/GaAs DHBTs may prove suitable for power device applications. >

The long-range vision of the Engineering Research Center for Compound Semiconductor Microelectronics (CCSM) is focused on a new generation of high-speed communications and data-processing technology which exploits the bandwidth, immunity to electromagnetic interference, and connectivity of optical interconnects. In order to realize this vision, it will be necessary to design, fabricate, and integrate high-performance electrical and optical devices in monolithic optoelectronic integrated circuits, OEIC's. The research programs of the CCSM are focused on the development of the engineering science and technology base for fabrication of OEIC's and their application in optical interconnect systems; the education of engineers in this field; and effective transfer of this technology to industry

Carbon dopedp-type GaAs and In0.53Ga0.47As epitaxial layers have been grown by low-pressure metalorganic chemical vapor deposition using CC14 as the carbon source. Low-temperature post-growth annealing resulted in a significant increase in the hole concentration for both GaAs and In0.53Ga0.47As, especially at high doping levels. The most heavily doped GaAs sample had a hole concentration of 3.6 × 1020 cm−3 after a 5 minute anneal at ≈400° C in N2, while the hole concentration in In0.53Ga0.47As reached 1.6 × 1019 cm−3 after annealing. This annealing behavior is attributed to hydrogen passivation of carbon acceptors. Post-growth cool-down in an AsH3/H2 ambient was found to be the most important factor affecting the degree of passivation for single, uncapped GaAs layers. No evidence of passivation is observed in the base region of InGaP/GaAs HBTs grown at ≈625° C. The effect ofn-type cap layers and cool-down sequence on passivation of C-doped InGaAs grown at ≈525° C shows that hydrogen can come from AsH3, PH3, or H2, and can be incorporated during growth and during the post-growth cool-down. In the case of InP/InGaAs HBTs, significant passivation was found to occur in the C-doped base region.

Carbon‐doped GaAs with carbon concentrations ranging from 2×1017 cm−3 to 2.6×1020 cm−3 has been characterized by variable temperature Hall effect measurements, secondary ion mass spectrometry (SIMS), and double‐crystal x‐ray diffraction (DCXD). The samples studied were grown by metalorganic chemical vapor deposition (MOCVD) and by metalorganic molecular beam epitaxy (MOMBE). The hole mobility is dominated by degenerate conduction for hole concentrations ≥1×1019 cm−3, and the 77 K resistivity is typically 30%–35% lower than at 300 K in these samples. The mobilities of C‐doped p+‐GaAs are found to be significantly higher than for Zn‐ or Be‐doped p+‐GaAs for doping concentrations in excess of 2×1018 cm−3. The maximum achievable hole mobilities for C‐doped material grown by the two techniques are nearly identical, indicating that neither MOCVD nor MOMBE has an inherent advantage over the other for producing low‐resistivity p‐type GaAs. SIMS analysis and Hall effect measurements reveal that the total carbon co...

Photoluminescence (PL) measurements under different excitation powers were carried out at low temperature on tensile-strained In0.3Ga0.7As single wells of 6 nm with InGaAs barriers lattice matched to InP substrate. PL measurements taken at 2 K show a main emission band at 0.762 eV probably originating From a type-II transition. The insertion of an ultrathin InAs layer at In0.3Ga0.7As on In0.53Ga0.47As interface reveals an additional feature at 0.711 eV as well as an excited-state luminescence emission at high pump powers. The InAs insertion improves heterointerface quality, which was confirmed by an increase in PL intensity.

The effect of intermediate temperature annealing on the carbon-doped base region of InGaP/GaAs heterojunction bipolar transistors (HBTs) was studied. This work shows that the minority carrier lifetime in the samples doped at 5.5×1019 cm−3 decreases upon annealing at only 600 °C. Magnetotransport measurements were performed to obtain the minority carrier mobility, with which the minority carrier lifetime was extracted. The decrease in the direct current (dc) current gain upon annealing is attributed to the increase in the base bulk recombination. The correlation between the dc current gain and the magnetotransport measurements indicates that the annealing increases the carbon-related defects in the GaAs base, decreases the minority carrier lifetime in the carbon-doped base, and degrades the dc current gain of the InGaP/GaAs HBTs. These results are very important to the growth and postgrowth processing of InGaP/GaAs HBTs.

Classic signatures of Be diffusion were observed in InAlAs/InGaAs HBT's after elevated temperature bias stress, i.e., a positive shift in the Gummel plot, higher collector ideality, and higher offset voltage. An activation energy of 1.57 eV was calculated. Lifetimes of 3.3/spl times/106 h and 37000 h were extrapolated for low and high power operation, respectively. In contrast, an InP/InGaAs HBT with a C doped base showed no signatures of C diffusion. The results show that Be diffusion is manageable at lower power. They also support the idea that C is more stable than Be in this material system.

Variable temperature Hall effect and low temperature photoluminescence measurements have been performed on high purityp- andn-type GaAs grown at atmospheric pressure by metalorganic chemical vapor deposition. These high purity epitaxial GaAs layers were grown as a function of the arsine (AsH3) to trimethylgallium (TMG) ratio (V/III ratio). The accurate quantitative assessment of the electronic properties of thep-type layers was emphasized. Analysis of the material focussed on the variation of the concentration of the shallow impurities for different V/III ratios. Surface and interface depletion effects are included to accurately estimate the concentration of impurities. The model of the merging of the excited states of the acceptor with the valence band is used to include the dependence the activation energy of the impurity on the acceptor concentration as well as on acceptor species identity. The characteristicp- ton-type conversion with increasing V/III ratio was observed in these samples and the reason for thep- ton-type conversion is that the background acceptor concentration of carbon decreases and the germanium donor concentration increases as the V/III ratio is increased.

The thermal dissociation of PH3 and NH3 injected through a Ta‐based high‐pressure gas‐injection cell were studied. Using a quadrupole mass spectrometer, the Ta was found to effectively dissociate the PH3 into primarily P2, P4, and H2 molecules with an injector temperature as low as 550 °C. The introduction of NH3 through this same injector resulted in dissociation into N2 and H2 for an injector temperature greater than 900 °C. When NH3 and PH3 were coinjected, again P2, P4, N2, and H2 were the primary molecules produced; however, an additional dimer, PN, was also detected. The PN concentration was maximum at a cell temperature of 700 °C. This dimer was found to be an effective source for introducing nitrogen as an isoelectronic trap in GaP.

Superlattices (SLs) of Alo.3Gao.7As/GaAs grown by metalorganic chemical vapor deposition and heavily doped with carbon using CClp4 were annealed for 24 h at 825° C under a variety of ambient and surface encapsulation conditions. Photoluminescence atT = 1.7 K has been employed to determine approximate Al-Ga interdiffusion coefficients (D Ai-Ga) for different annealing conditions. For all encapsulants studiedD Al-Ga increases with increasing As4 pressure in the annealing ampoule. This result disagrees with trends reported for Mg-doped crystals, and with predictions of the charged point-defect (Fermilevel) model. The Si3N4 cap provides the most effecitve surface sealing against ambientstimulated layer interdiffusion (D Al-Ga ≈ 1.5-3.9 x 10-19 cm2/sec). The most extensive layer intermixing has occurred for an uncapped SL annealed under As-rich ambient (D Al-Ga ≈ 3.3 x 10-18 cm2/sec). These values are up to ~40 times greater than those previously reported for nominally undoped AIGaAs/GaAs SLs, implying that theC As doping slightly enhances layer intermixing, but significantly less than predicted by the Fermi-level effect. The discrepancies between the experimental data and the model are discussed. Pronounced changes in the optical properties of the annealed SLs with storage time at room temperature are also reported. These changes may indicate a degraded thermal stability of the annealed crystals due to high-temperature-induced lattice defects. A possibly related effect of the systematic failure to fabricate buried heterostructure quantum well lasers via impurity-induced layer disordering in similarly doped AIGaAs/GaAs crystals is discussed.

The magnetic properties of hydrogenic Te donors and bistable,DX-like S donors in GaAS x P1-x have been investigated. Te shows an EPR signal after cooling down, both in the dark. The EPR signal from S appears only after illumination. S does not show an EPR signal after cooling down in the dark, but after illumination when the hydrogenic state of this donor is populated. Static magnetic susceptibility measurements show however that the ground state of S in GaAs x P1-x is paramagnetic even though it does not produce an EPR signal. This is in agreement with a one-electron ground state of this bistable donor.

Laser studies carried out at the University of Illinois in 1966 showed that the shortest wavelength at which lasing could be achieved in GaAsP was dependent on then-type dopant. In particular sulfur doping was found to restrict lasing to longer wavelengths. It was suggested that this could be due to the effect of energy levels associated with the higher conduction band minima. This led in 1967 to an investigation of the effect of Te and S donor levels on the properties of GaAsP near the direct-indirect crossover. Samples throughout the composition range were studied using Hall effect measurements from 55 to 400° K and resistivity measurements under hydrostatic pressure between 0 and 7 kbar at 300, 195, and 77° K. The data on Te-doped samples fit the standard energy band models, but S doping was found to exhibit dramatic persistent photoconductivity and other compositional effects similar to the “DX-center” effects later observed in AlGaAs and other materials. This paper summarizes these results on GaAsP:S, and gives a brief overview of other early investigations in compound semiconductors where energy levels associated with higher lying minima were studied and where, in some cases, nonequilibrium effects were observed. A later study on GaAsP:S is also described which shows the effect of S-doping on LED performance. Finally, some of the implications that the existence of deep levels of this type have on light emitting device performance in other alloy systems is discussed.

Data are presented on the room-temperature, photopumped, continuous laser operation of multiple-well InGaP–GaAs quantum-well heterostructures and superlattices grown by low-pressure metalorganic chemical vapor deposition. Continuous laser operation at room temperature indicates high material quality and minimal nonradiative recombination at the heterointerfaces. The lasing wavelength near the GaAs band gap is consistent with weak bandfilling, and small quantum confinement of electrons and large confinement of holes (mh>me, ΔEv>ΔEc). Double-crystal x-ray diffraction and transmission electron microscopy data confirm the high material quality and heterointerface abruptness.

The effect of intermediate temperature annealing on the carbon-doped base region of InGaP/GaAs heterojunction bipolar transistors (HBTs) was studied. This work shows that after annealing at only 600 °C a sample doped at 5.5×1019 cm−3 displays carbon precipitation. InGaP/GaAs HBT structures were grown for the annealing study. Hall measurements were used to measure hole concentration. Atomic force microscopy was employed to identify carbon precipitation. The annealing process not only removes hydrogen from the base but also creates carbon precipitates. The dc current gain measurements imply that the carbon precipitates increase base recombination. These results are very important in the growth and postgrowth annealing of high gain HBTs.

Data are presented on the hydrogenation of Be‐doped (p‐type) and Si‐doped (n‐type) In1−xGaxP epitaxial layers grown lattice matched to GaAs (x ∼ 0.5). Low‐temperature (1.7 K) photoluminescence, electrochemical carrier concentration profiling, and scanning electron microscopy are used to study the effects of hydrogenation on carrier recombination, carrier concentration, and surface morphology. Hydrogenation is found to passivate Si donors and Be acceptors and to improve photoluminescence efficiency, but causes mild surface damage. The carrier concentration following hydrogenation is found to be lowest in acceptor‐doped material.

Interdiffusion of Al and Ga in heavily C‐doped Al0.3Ga0.7As/GaAs superlattice (SL) structures has been investigated quantitatively for a variety of ambient and surface encapsulation conditions. High‐resolution photoluminescence (PL) at T=1.7 K was employed to evaluate the extent of layer intermixing after 24‐h anneals at 825 °C. From the shifts to higher energies of the PL peaks due to n=1 electron‐to‐heavy hole transitions in the quantum wells of the annealed SLs relative to the position of this peak in the as‐grown crystal, approximate Al‐Ga interdiffusion coefficients (DAl‐Ga) have been determined for different annealing conditions. For all encapsulants studied the interdiffusion in C‐doped crystals is accelerated with increasing As4 pressure in the annealing ampoule. This result disagrees with previously observed trends for Group II‐doped p‐type structures, which have led to the charged point‐defect model (Fermi‐level effect) of Al‐Ga interdiffusion. The Si3N4 cap has provided the most effective surface sealing against ambient‐stimulated layer interdiffusion, and yielded DAl‐Ga≊1.5−3.9×10−19 cm2/s. The most extensive layer intermixing has occurred for uncapped SL annealed under As‐rich ambient (DAl‐Ga≊3.3×10−18 cm2/s). These values are up to ∼40 times greater than those previously reported for nominally undoped AlxGa1−xAs/GaAs SLs, implying that the CAs doping slightly enhances host‐atom self‐diffusion on the Group III sublattice, but significantly less than predicted by the Fermi‐level effect. The discrepancies between the experimental observations and the model, are discussed.

We report the growth of GaAs by molecular beam epitaxy (MBE), gas source molecular beam epitaxy (GSMBE), and chemical beam epitaxy (CBE) in an epitaxial III–V reactor which features high pumping speed. The system is comprised of a modified Perkin-Elmer 430P molecular beam epitaxy system and a custom gas source panel from Emcore. The growth chamber is pumped with a 7000 1/s (He) diffusion pump (Varian VHS-10 with Monsanto Santovac 5 oil). The gas source panel includes pressure based flow controllers (MKS 1150) allowing triethylaluminum (TEA), triethylgallium (TEG), and trimethylindium (TMI) to be supplied without the use of hydrogen. All source lines, including arsine and phosphine, are maintained below atmospheric pressure. The high pumping speed allows total system flow rates as high as 100 SCCM and V/III ratios as high as 100. The purity of GaAs grown by MBE in this system increases with pumping speed. GaAs layers grown by GSMBE with arsine flows of 10 and 20 SCCM have electron concentrations of 1 × 1015 cm-3 (μ77=48,000 cm2/V·) and 2 × 1014 cm-3 (μ77=78,000 cm2/V·s) respectively. El ectron concentration varies with hydride injector temperature such that the minimum in electron concentration occurs for less than complete cracking. The effect of V/III ratio and the use of a metal eutectic bubbler on residual carrier concentration in GaAs grown by CBE is presented. Intentional Si and Be doping of CBE grown GaAs is demonstrated at a high growth rate of 5.4 μm/h.

Effects of passivation and light‐induced reactivation of acceptors in high‐purity hydrogenated GaAs are investigated with low‐temperature photoluminescence. The effectiveness of both processes has been found to be strongly dependent on the chemical identity of acceptor species, thus allowing a qualitative assessment of the relative stability of different acceptor‐hydrogen passivating complexes in p‐type hydrogenated GaAs. Efficient neutralization of acceptors in high‐purity n‐type hydrogenated GaAs is also reported, in contradiction with results of recent studies on heavily doped materials where passivation of minority dopants was not observed. The implications of these experimental data on theoretical models of the [AV:acceptor passivation mechanism are discussed.

The growth of AlxGa1−xP for Al mole fractions between 0 and 1 has been achieved on (100) GaP substrates using gas source molecular beam epitaxy with elemental Ga and Al, and P2 cracked from PH3 as the source materials. The observed reflection high energy electron diffraction pattern of the GaP surface indicates that an exponential increase in the incident P2 flux is required to maintain good morphology beyond 690 °C. This temperature was found to correspond closely to the congruent vaporization temperature of Ga from the growth surface. The addition of Al on the surface was found to substantially increase the Ga congruent vaporization temperature from the GaP surface. The growth rates for AlxGa1−xP as a function of growth temperature between 600 and 750 °C were determined by transmission electron microscopy. Using elemental Si as an n‐type dopant, free electron concentrations as high as 1.65×1019 cm−3 in GaP and 1.5×1019 cm−3 in Al0.28Ga0.72P were achieved.

We report a study of a defect responsible for the ‘‘g’’ bound exciton line at 1.5112 eV that is frequently detected in photoluminescence spectra of GaAs grown by molecular beam epitaxy (MBE). A direct correlation has been observed between this line and a transition at 1.4946 eV, which is shown to result from a conduction band‐to‐acceptor recombination involving a shallow, unidentified acceptorlike defect that is labeled ‘‘A.’’ The activation energy of the defect is 24.8±0.2 meV, about 1.7 meV lower than that of CAs acceptor. Upon hydrogenation the defect is passivated more extensively than any known shallow acceptor species in GaAs. This result is analyzed in terms of a passivation model, from which it can be inferred that the A defect is not due to a simple substitutional Group II impurity on a Ga site. Incorporation of the A defect strongly affects the luminescence properties of the material. An almost complete quenching of the donor‐bound exciton lines, profound changes in the line shape and relative i...

A dilute mixture of CCl4 in H2 has recently been shown to be a suitable carbon doping source for obtainingp-type GaAs grown by metalorganic chemical vapor deposition (MOCVD) with carbon acceptor concentrations in excess of 1 × 1019cm−3. To understand the effect of growth parameters on carbon incorporation in CCl4 doped Al x Ga1−x As, carbon acceptor concentration was studied as a function of Al composition, growth temperature, growth rate, and CCl4 flow rate using electrochemical capacitance-voltage profiling. The carbon incorporation as a function of Al composition, growth temperature and CCl4 flow rate was also measured by secondary ion mass spectroscopy (SIMS). All layers were grown by low pressure MOCVD using TMGa and TMAl as column III precursors, and 100% AsH3 as the column V source. Increased Al composition reduced the dependence of carbon concentration on the growth temperature. Reduced growth rate, which resulted in substantially decreased carbon acceptor concentrations in GaAs, had an insignificant effect on the carrier concentration of Al0.4Ga0.6As. A linear relationship between hole concentration and CC14 flow rate in AlxGa1−x As for 0.0 ≤x ≤ 0.8 was observed. These results are interpreted to indicate that adsorption and desorption of CCl y (y ≤ 3) on the Al x Ga1-x As surface during crystal growth plays an important role in the carbon incorporation mechanism.

Impurity‐induced layer disordering experiments on AlxGa1−xAs‐GaAs quantum well heterostructures (QWHs) that are doped heavily with carbon are described. The data show that carbon doping retards Al‐Ga interdiffusion relative to an undoped crystal, and that interdiffusion in C‐doped QWHs is not enhanced by a Ga‐rich (versus As‐rich) annealing ambient. The data are inconsistent with most Fermi‐level‐effect models for layer disordering that do not include chemical impurity dependence or sublattice dependence, and that do not consider the possibility of inhibited Al‐Ga interdiffusion in extrinsic crystals.

The incorporation of Ge in GaAs layers grown simultaneously on (100), (311)A, and (311)B GaAs substrates by molecular‐beam epitaxy has been studied using Hall‐effect measurements, photothermal ionization spectroscopy, and photoluminescence. The quantitative analysis shows that Ge is more amphoteric than Si, but the orientation dependence of the amphoteric behavior of Ge is similar to Si. The amphoteric site preference of Ge is more selective for growth on the (311) polar orientation than on the (100) nonpolar orientation. Like Si, Ge incorporates predominantly as a donor in (311)B growth, while it incorporates predominantly as an acceptor in (311)A growth.

The implantation of Si ions into undoped high-resistivity GaN films is of interest for the realization of high-performance digital and monolithic microwave integrated circuits. We report the effect of postimplant annealing conditions on the electrical, optical, and surface morphology of Si ion-implanted GaN films. We demonstrate high activation efficiencies for low-dose Si implants into unintentionally doped GaN/sapphire heteroepitaxial films. The Si ions were implanted through an epitaxial AlN cap layer at 100 keV and a dose ∼5×1014 cm−2. Samples were subsequently annealed in an open-tube furnace for various times and temperatures. The postanneal electrical activation is correlated with the surface morphology of the film after annealing. The samples annealed at 1150 °C in N2 for 5 min. exhibited a smooth surface morphology and a sheet electron concentration ns∼6.8×1013 cm−2.

A high concentration of hydrogen in the alloy ambient slows the formation of PdGe contacts and increases the resistance of the PdGe to GaAs etchants. The effects of alloy ambient on alloy formation, specific contact resistance, and chemical reactivity of PdGe contacts on n-type GaAs have been studied. A very low specific contact resistance of

To improve electrical isolation and simplify the heterojunction bipolar transistor (HBT) fabrication process, a semi-insulating InGaP buffer layer has been employed in an InGaP/GaAs HBT. Data is presented that demonstrates this buffer layer serves as an excellent isolation material. In addition, high-frequency HBT's have been fabricated and characterized to show that the buffer layer does not degrade device performance.

In this letter, we describe the characteristics of molecular beam epitaxy GaAs/AlGaAs quantum-well infrared photodetectors (QWIP’s) grown on a GaAs substrate, and on a GaAs-on-Si substrate produced by metalorganic chemical-vapor deposition. Important issues for QWIP applications such as dark current, spectral response, and absolute responsivity are studied. We find that compared to a similar detector structure grown on a GaAs substrate, the detector grown on a GaAs-on-Si substrate exhibits similar dark current and absolute responsivity while displaying a small blueshift in the spectral response.

High-resistivity unintentionally-doped In0.49Ga0.51P lattice matched to GaAs has been grown via low-pressure metalorganic chemical vapor deposition at a reduced growth temperature. These layers have excellent surface quality and are single crystal. The resistivity increases exponentially as the growth temperature is decreased from 550 to 490 °C, resulting in a resistivity of ∼109 Ω cm for samples grown at 490 °C. In addition, the photoluminescence intensity decreases exponentially for growth temperatures below 550 °C, indicating an increase in nonradiative recombination related to an increasing trap concentration. For samples grown at 550 °C, constant capacitance deep level transient spectroscopy measurements show a strong broad peak at ∼200 °K with an ionization energy of 0.40±0.04 eV, verifying the presence of an electron trap. The gummel plot and I–V characteristics of an InGaP/GaAs heterojunction bipolar transistor (HBT) with a 2000-A-thick InGaP buffer layer grown at 500 °C are identical to that of a...

Lattice-matched InGaAs/InP quantum well intersubband photodetectors (QWIPs) have been grown on an InP substrate by gas source molecular beam epitaxy. Detection at 4.55 μm was observed for a narrow well p-type InGaAs QWIP which, when complimented by a high responsivity 8.93 μm n-type InGaAs/InP QWIP, demonstrates the possibility of dual band, monolithically integrated QWIPs on the same InP substrate. Theoretical calculations of the photocurrent spectra are in excellent agreement with the experimental data.

We have demonstrated a high-speed InP/lnGaAs heterojunction bipolar transistor with nonalloyed TiPtAu contacts on n+-InP emitter and collector contacting layers. The use of SiBr4 as a silicon doping source enabled the formation of low resistance (pc

The influence of subhydride species generated in a low‐pressure Ta‐based AsH3 cracker on the degree of H passivation of C acceptors in heavily doped (p⩾3×1019 cm−3) In0.53Ga0.47As grown by gas source and metalorganic molecular beam epitaxy has been studied. A strong correlation has been observed between the relative abundance of AsH3, AsH, and H in quadrupole mass spectra and the degree of passivation. Enhanced effects were observed at reduced growth temperatures. Design of experiments techniques have been used to study the influence of hydride cracker temperature, substrate temperature, H2 pumping speed, group III sources, AsH3 flow rate and the second order interactions on the H passivation of C acceptors. The substrate temperature, hydride cracking temperature, and H2 pumping speed, were determined to have the dominant effects, while second order interactions were dominated by substrate temperature, H2 pumping speed, and AsH3 flow rate interactions with the hydride cracking temperature. Optimized param...

Data are presented on the luminescence characteristics of GaAs layers adjacent to native‐oxide regions derived from epitaxial AlGaAs and InAlP films. The native‐oxide ‘‘window’’ layers capping the epitaxial structures are formed by the oxidation of the exposed Al0.9Ga0.1As and In0.48Al0.52P cladding layers. Extensive photoluminescence and time‐resolved photoluminescence studies performed at 300 K show that both the luminescence intensity and lifetime from GaAs ‘‘active regions’’ drop dramatically when the adjacent AlGaAs window layer is oxidized completely. However, there is a marked increase in the efficiency and decay time of the luminescence with the oxidation of InAlP window layers which are grown immediately above the GaAs layer.

A self-aligned InGaP/GaAs heterojunction bipolar transistor with a compositionally graded In/sub x/Ga/sub 1-x/As base has been demonstrated with f/sub T/=83 GHz and f/sub max/=197 GHz. To our knowledge, these results are the highest reported for both parameters in InGaP/GaAs HBT's. The graded base, which improves electron transport through the base, results in a DC current gain and a cutoff frequency which are 100% and 20% higher, respectively, than that achieved by an identical device with a nongraded base. The high f/sub max/ results from a heavily doped base, self-aligned base contacts, and a self-aligned collector etch. These results demonstrate the applicability of InGaP/GaAs HBT's in high-speed microwave applications.