MeV energy sulfur implantation in GaAs and InP

Room temperature and elevated temperature sulfur implants were performed into semi-insulating GaAs and InP at variable energies and fluences. The implantations were performed in the energy range 1–16 MeV. Range statistics of sulfur in InP and GaAs were calculated from the secondary ion mass spectrometry atomic concentration depth profiles and were compared with TRIM92 values. Slight in-diffusion of sulfur was observed in both InP and GaAs at higher annealing temperatures for room temperature implants. Little or no redistribution of sulfur was observed for elevated temperature implants. Elevated temperature implants showed higher activations and higher mobilities compared to room temperature implants in both GaAs and InP after annealing. Higher peak electron concentrations were observed in sulfur-implanted InP (n ≈ 1 × 10¹⁹ cm⁻³) compared to GaAs (n ≈ 2 × 10¹⁸ cm⁻³). The doping profile for a buried n⁺ layer (n ≈ 3.5 × 10¹⁸ cm⁻³) of a positive-intrinsic-negative diode in GaAs was produced by using Si/S coimplantation.     

The growth of GaAs,AIGaAs, InP and InGaAs by chemical beam epitaxy using group III and V alkyls

The growth kinetics of chemical beam epitaxy (CBE) were investigated with the growth of GaAs, AIGaAs, InP, and InGaAs. Results obtained with epilayers grown by using trimethylarsine (TMAs) and triethylphosphine (TEP) instead of arsine (AsH3) and phosphine (PH₃) were reviewed with some additional results. The CBE grown epilayers have similar optical quality to those grown by molecular beam epitaxy (MBE). Superlattices of GaAs/AlGaAs with abrupt interfaces have been prepared. Since trimethylindium (TMIn) and triethylgallium (TEGa) used in the growth of InGaAs emerged as a single mixed beam, spatial composition uniformity was automatically achieved without the need of substrate rotation in the InGaAs epilayers grown. Lattice-mismatch Δα/α< 1 x 10^-3 have been reproducibly obtained. For epilayers grown with high purity TMAs source, room-temperature electron mobility as high as 9000 cm²/V sec and concentrations of ˜7 x 10¹⁵ cm^-3 were produced. In general, the electron mobilities were as good as those obtained from low-pressure metalorganic chemical vapor deposition. (MO-CVD). Unlike MBE, since the In and Ga were derived by the pyrolysis of TMIn and TEGa molecules at the heated substrate surface, respectively, oval defects observed in MBE grown epilayers due to Ga splitting from Ga melt were not present in CBE grown epilayers. This is important for integrated circuit applications. Unlike MO-CVD, the beam nature of CBE allows for selective area growth of epilayers with well-defined smooth edges using mask shadowing techniques. Typically, growth rates of 2-5μm/h for InP, 2-6μm/h for GaAs and AIGaAs, and 2-5μm/h for InGaAs were used.     

A study of chemical beam epitaxy of GaAs using tris-dimethylaminoarsenic

The growth of GaAs by chemical beam epitaxy using triethylgallium and trisdimethylaminoarsenic has been studied. Reflection high-energy electron diffraction (RHEED) measurements were used to investigate the growth behavior of GaAs over a wide temperature range of 300–550°C. Both group III- and group Vinduced RHEED intensity oscillations were observed, and actual V/III incorporation ratios on the substrate surface were established. Thick GaAs epitaxial layers (2–3 μm) were grown at different substrate temperatures and V/III ratios, and were characterized by the standard van der Pauw-Hall effect measurement and secondary ion mass spectroscopy analysis. The samples grown at substrate temperatures above 490°C showed n-type conduction, while those grown at substrate temperatures below 480°C showed p-type conduction. At a substrate temperature between 490 and 510°C and a V/III ratio of about 1.6, the unintentional doping concentration is n ∼2 × 10¹⁵ cm⁻³ with an electron mobility of 5700 cm²/V·s at 300K and 40000 cm²/V·s at 77K.     

InP-on-CdS thin film heterostructures

Thin films of InP were deposited on single crystals and thin films of CdS by the planar reactive deposition technique. Good local epitaxy was observed on single crystals of CdS as well as InP and GaAs. The electrical evaluation of unintentionally doped films on semi-insulating InP substrates show them to be n-type with room temperature electron concentrations ranging from 5 × 1016 cm⁻³ to 5 × 10¹⁷ cm⁻³ and mobilities up to 1350 cm²/Vsec. For films intentionally doped with Mn and Be, p-type films were obtained. For Mn doping (deep acceptor level), room temperature mobilities as high as 140 cm²/Vsec and free carrier concentrations as low as 5 × 10¹⁶ cm⁻³ (with dopant level of 3 × 10¹⁸ cm⁻³) were obtained. For Bedoped films, free carrier concentrations of about 5 × 10¹⁸ cm⁻³ and mobilities of 20 cm²/Vsec were found. Scanning electron microscope and microprobe pictures show appreciable interdiffusion between the InP/CdS thin-film pair for InP deposited at 450°C. The loss of Cd from the CdS and the presence of an indium-cadmium-sulfur phase at the InP/CdS interface were observed. Interdiffusion is alleviated for InP deposition at lower temperatures. Supported in part by ERDA and AFOSR.     

Electrical characterization of self-assembled In0.5Ga0.5As/GaAs quantum dots by deep level transient spectroscopy

We have investigated electron emission from self-assembled In_0.5Ga_0.5As/GaAs quantum dots (QDs) grown by molecular-beam epitaxy (MBE). Through detailed deep level transient spectroscopy comparisons between the QD sample and a reference sample, we determine that trap D, with an activation energy of 100 meV and an apparent capture cross section of 5.4×10⁻¹⁸ cm², is associated with an electron quantum level in the In_0.5Ga_0.5As/GaAs QDs. The other deep levels observed, M1, M3, M4, and M6, are common to GaAs grown by MBE.     

Comparison of InGaSb/InAs superlattice structures grown by MBE on GaSb, GaAs, and compliant GaAs substrates

This paper contains the characterization results for indium arsenide/indium gallium antimonide (InAs/InGaSb) superlattices (SL) that were grown by molecular beam epitaxy (MBE) on standard gallium arsenide (GaAs), standard GaSb, and compliant GaAs substrates. The atomic force microscopy (AFM) images, peak to valley (P-V) measurement, and surface roughness (RMS) measurements are reported for each sample. For the 5 μm×5 μm images, the P-V heights and RMS measurements were 37 ? and 17 ?, 12 ? and 2 ?, and 10 ? and 1.8 ? for the standard GaAs, standard GaSb, and compliant GaAs respectively. The high resolution x-ray diffraction (HRXRD) analysis found different 0^th order SL peak to GaSb peak spacings for the structures grown on the different substrates. These peak separations are consistent with different residual strain states within the SL structures. Depending on the constants used to determine the relative shift of the valance and conduction bands as a function of strain for the individual layers, the change in the InAs conduction band to InGaSb valance band spacing could range from +7 meV to −47 meV for a lattice constant of 6.1532 ?. The cutoff wavelength for the SL structure on the compliant GaAs, control GaSb, and control GaAs was 13.9 μm, 11 μm, and no significant response, respectively. This difference in cutoff wavelength corresponds to approximately a −23 meV change in the optical gap of the SL on the compliant GaAs substrate compared to the same SL on the control GaSb substrate.     

P-type doping of GaAs by carbon implantation

The electrical properties of C-implanted <100> GaAs have been studied following rapid thermal annealing at temperatures in the range from 750 to 950°C. This includes dopant profiling using differential Hall measurements. The maximum p-type activation efficiency was found to be a function of C-dose and annealing temperature, with the optimum annealing temperature varying from 900°C for C doses of 5 × 10¹³ cm⁻² to 800°C for doses ≥5 × 10¹⁴cm⁻². For low dose implants, the net p-type activation efficiency was as high as 75%; while for the highest dose implants, it dropped to as low as 0.5%. Moreover, for these high-dose samples, 5 × 10¹⁵ cm⁻², the activation efficiency was found to decrease with increasing annealing temperature, for temperatures above ∼800°C, and the net hole concentration fell below that of samples implanted to lower doses. This issue is discussed in terms of the amphoteric doping behavior of C in GaAs. Hole mobilities showed little dependence on annealing temperature but decreased with increasing implant dose, ranging from ∼100 cm²/V·s for low dose implants, to ∼65 cm²/V·s for high dose samples. These mobility values are the same or higher than those for Be-, Zn-, or Cd-implanted GaAs.     

GaAs on Si substrate with dislocation filter layers for wafer-scale integration

GaAs on Si grown via metalorganic chemical vapor deposition is demonstrated using various Si substrate thicknesses and three types of dislocation filter layers (DFLs). The bowing was used to measure wafer-scale characteristics. The surface morphology and electron channeling contrast imaging (ECCI) were used to analyze the material quality of GaAs films. Only 3-μm bowing was observed using the 725-μm-thick Si substrate. The bowing shows similar levels among the samples with DFLs, indicating that the Si substrate thickness mostly determines the bowing. According to the surface morphology and ECCI results, the compressive strained indium gallium arsenide/GaAs DFLs show an atomically flat surface with a root mean square value of 1.288 nm and minimum threading dislocation density (TDD) value of 2.4 × 10⁷ cm⁻². For lattice-matched DFLs, the indium gallium phosphide/GaAs DFLs are more effective in reducing the TDD than aluminum gallium arsenide/GaAs DFLs. Finally, we found that the strained DFLs can block propagate TDD effectively. The strained DFLs on the 725-μm-thick Si substrate can be used for the large-scale integration of GaAs on Si with less bowing and low TDD.     

Growth and characterization of large diameter undoped semi-insulating GaAs for direct ion implanted FET technology

The growth of large diameter, semi-insulating GaAs crystals of improved purity by Liquid Encapsulated Czochralski (LEC) pulling from pyrolytic boron nitride (PBN) crucibles and characterization of this material for direct ion implantation technology, is described. Three-inch diameter, 〈100〉-oriented GaAs crystals have been grown in a high pressure Melbourn crystal puller using 3 kg starting charges synthesized in-situ from 6/9s purity elemental gallium and arsenic. Undoped and Cr-doped LEC GaAs crystals pulled from PBN crucibles exhibit bulk resistivities in the 10⁷ and 10⁸ Ω cm range, respectively. High sensitivity secondary ion mass spectrometry (SIMS) demonstrates that GaAs crystals grown from PBN crucibles contain residual silicon concentrations in the mid 10¹⁴ cm^?3 range, compared to concentrations up to the 10¹⁶ cm^?3 range for growths in fused silica containers. The residual chromium content in undoped LEC grown GaAs crystals is below the SIMS detection limit for Cr (4 × 10¹⁴ cm^?3).The achievement of direct ion implanted channel layers of near-theoretical mobilities is further evidence of the improved purity of undoped, semi-insulating GaAs prepared by LEC/PBN crucible techniques. Direct implant FET channels with (1–1.5) × 10¹⁷ cm^?3 peak donor concentrations exhibit channel mobilities of 4,800–5,000 cm²/V sec in undoped, semi-insulating GaAs substrates, compared with mobilities ranging from 3,700 to 4,500 cm²/V sec for various Cr-doped GaAs substrates. The concentration of compensating acceptor impurities in semi-insulating GaAs/PBN substrates is estimated to be 1 × 10¹⁶ cm^?3 or less, and permits the implantation of 2 × 10¹⁶ cm^?3 channels which exhibit mobilities of 5,700 and 12,000 cm²/V sec at 298K and 77K, respectively.Discrete power FET's which exhibit 0.7 watts/mm output and 8 dB associated gain at 8 GHz have been fabricated using these directly implanted semi-insulating GaAs substrates.     

Hall and drift mobilities in molecular beam epitaxial grown GaAs

A series of nominally undoped and Si-doped GaAs samples have been grown by molecular beam epitaxy (MBE) with Hall concentrations ranging from 10¹⁵ to 10¹⁹ cm⁻³ and mobilities measured at 77 and 300K by Hall-van der Pauw methods. Drift mobilities were calculated using the variational principle method and Hall scattering factors obtained from a relaxation-time approximation to permit cross-correlation of experimental data with drift or Hall mobilities and actual or Hall electron concentrations. At 77K, both high purity and heavily doped samples are well represented by either drift or Hall values since piezoelectric acoustic phonon scattering and strongly screened ionized impurity scattering hold the Hall factor close to unity in the respective regimes. Between n≊10¹⁵ and 10¹⁷ cm⁻³, where lightly screened ionized impority scattering predominates, Hall mobility overestimates drift mobility by up to 50 percent and Hall concentration similarly underestimates n. At 300K, polar optical phonons limit mobility and a Hall factor up to 1.4 is found in the lowest doped material, falling close to unity above about 10¹⁶ cm⁻³. Our calculation also agrees remarkably well with the Hall mobility of the highest purity MBE grown sample reported to date.     

Comparison of OMVPE Grown GaAs/AlGaAs and GaAs/InGaP HEMT and PHEMT structures

Symmetric δ-doped InGaP and AlGaAs PHEMT structures have been grown by organometallic vapor phase epitaxy with properties that approach those of MBE grown AlGaAs structures. The 300 and 77K carrier concentrations for the InGaP PHEMT were 2.72 and 2.56 × 10¹² cm^{2 −2} and the mobilities were 5,920 and 22,000 cm^{2 2}/V.s. These excellent values suggest that problems associated with switching the anion at the channel heterojunction have been overcome. The corresponding values for the AlGaAs PHEMT were 2.51 and 2.19 × 10¹² cm^{2 −2} and 6,500 and 20,400 cm²/V.s. The uniformity in the indium concentration in the InGaAs layer as determined by photoluminescence, photoreflection, double crystal x-ray diffraction, and Rutherford backscattering was found to be good, but the percent In in the AlGaAs pseudo-morphic high electron mobility transistor (PHEMT) was less than that in the InGaP PHEMT even though the programmed values were the same. The uniformity in the doping distribution as determined by secondary ion mass spectroscopy and electrochemical capacitance-voltage measurements was found to be good, but it decreased with distance from the center of the susceptor. Also, most of the dopants in the δ-doped InGaP and AlGaAs layers were activated.     

分子束外延AlGaN/GaN异质结场效应晶体管材料

用自组装的氨源分子束外延 (NH3-MBE)系统和射频等离子体辅助分子束外延 (PA-MBE)系统在 C面蓝宝石衬底上外延了优质 Ga N以及 Al Ga N/Ga N二维电子气材料。Ga N膜 (1 .2 μm厚 )室温电子迁移率达3 0 0 cm2 /V· s,背景电子浓度低至 2× 1 0 1 7cm- 3。双晶 X射线衍射 (0 0 0 2 )摇摆曲线半高宽为 6arcmin。 Al Ga N/Ga N二维电子气材料最高的室温和 77K二维电子气电子迁移率分别为 73 0 cm2 /V·s和 1 2 0 0 cm2 /V· s,相应的电子面密度分别是 7.6× 1 0 1 2 cm- 2和 7.1× 1 0 1 2 cm- 2 ;用所外延的 Al Ga N/Ga N二维电子气材料制备出了性能良好的 Al Ga N/Ga N HFET(异质结场效应晶体管 ) ,室温跨导为 5 0 m S/mm(栅长 1 μm) ,截止频率达 1 3 GHz(栅长 0 .5μm)。该器件在 3 0 0°C出现明显的并联电导 ,这可能是材料中的深中心在高温被激活所致     

Electrical and photoluminescence properties of Ge-doped n-type GaAs Grown by molecular beam epitaxy

Ge-doped n-type MBE GaAs has been studied for the doping range 6.7 × 10¹⁵ to 1.5 × 10²⁰cm^-3 and the compensation ratio inferred from the mobility variation with free-carrier concentration. The doping achieved for a given Ge source temperature is an order of magnitude greater than generally reported and this is attributed to use of a source of large surface area. Photoluminescence studies at 4°K for lightly doped specimens show the usual bound exciton, band-to-C_AS and band-to-Ge_AS peaks and their LO phonon replicas. However, with Ge doping exceeding 10¹⁸cm^-3 broad deep-level peaks develop centered at 1.3257 eV moving towards 1.255 eV, with half widths of about 115 meV. Whether these peaks are related to the broad-band photoluminescence centered at 1.20 eV (20°K) that has been reported earlier for Ge doped Bridgmangrown and epitaxially vapor grown GaAs, is not known. Since the energy displacement is considerable, it is possible that the centers responsible differ in the MBE grown material.     

Growth condition dependence for GaAs selective epitaxial growth by molecular beam epitaxy

GaAs selective epitaxial growth by conventional molecular beam epitaxy (MBE) was studied while varying its growth conditions, such as substrate temperature. As pressure, growth rate, and Si or Be doping. Selectivity is improved with the increase in substrate temperature, and with the decrease in As pressure or growth rate. Si and Be were doped up to 3 x 10¹⁸ and 3 × 10¹⁹ cm⁻³, respectively. While no Si doping influence was observed, Be doping degraded the surface morphology. Selective epitaxial growth by conventional MBE with appropriate growth conditions will be applicable to device fabrication.     

Rapid capless annealing of28Si,64Zn,and9Be implants in GaAs

We report the use of tungsten-halogen lamps for rapid (−10 s) thermal annealing of ion-implanted (100) GaAs under AsH₃/Ar and N₂ atmospheres. Annealing under flowing AsH₃/Ar was carried out without wafer encapsulation. Rapid capless annealing activated implants in GaAs with good mobility and surface morphology. Typical mobilities were 3700–4500 cm²/V-s for n-layers with about 2×10¹⁷cm⁻³ carrier concentration and 50–150 cm²/v-s for 0.1–5xl0¹⁹ cm⁻³ doped p-layers. Rapid thermal annealing was performed in a vertical quartz tube where different gases (N₂, AsH₃/H₂, AsH₃/Ar) can be introduced. Samples were encapsulated with SiO when N₂ was used. Tungsten-halogen lamps of 600 or 1000 W were utilized for annealing GaAs wafers ranging from 1 to 10 cm² in area and 0.025 to 0.040 cm in thickness. The transient temperature at the wafer position was monitored using a fine thermocouple. We carried out experiments for energies of 30 to 200 keV, doses of 2×10¹² to 1×10¹⁵ cm⁻², and peak temperatures ranging from 600 to 1000‡C. Most results quoted are in the 700 to 870‡C temperature range. Data on implant conditions, optimum anneal conditions, electrical characteristics, carrier concentration profiles, and atomic profiles of the implanted layers are described. Presented at the 25th Electronic Materials Conference, Burlington, VT, June 22, 1983.     

Growth of tin-doped indium antimonide for magnetoresistors

Magnetoresistors made from n-type indium antimonide are of interest for magnetic position sensing applications. In this study, tin-doped indium antimonide was grown by the metalorganic chemical vapor deposition technique using trimethylindium, trisdimethylaminoantimony, and tetraethyltin in a hydrogen ambient. Using a growth temperature of 370°C and a pressure of 200 Torr, it was found that the electron density in tin-doped films varied from 3.3×10¹⁶ cm⁻³ to 4.0×10¹⁷ cm⁻³ as the 5/3 ratio was varied from 4.8 to 6.8. From secondary ion mass spectroscopy (SIMS) studies, it was found that this variation is not caused by a change in site occupancy of the tin atoms from antimony to indium lattice sites, but rather to a change in the total tin concentration incorporated into the films. This dependence of tin incorporation on stoichiometry could be used to rapidly vary the doping level during growth. Undoped films grown under similar conditions had electron densities of about 2×10¹⁶ cm⁻³ and electron mobilities near 50,000 cm²V⁻¹s⁻¹ at room temperature for films that were only 1.5 μm thick on a gallium arsenide substrate. Attempts to grow indium antimonide at 280°C resulted in p-type material caused by carbon incorporation. The carbon concentration as measured with SIMS increased rapidly with increasing growth rate, to above 10¹⁹ cm⁻³ at 0.25 μm/h. This is apparently caused by incomplete pyrolysis of a reactant at this low growth temperature. Growth at 420°C resulted in rough surface morphologies. Finally, it was demonstrated that films with excellent electron mobility and an optimized doping profile for magnetoresistors can be grown.     

Optical and transport properties of δ-doped pseudomorphic AlGaAs/InGaAs/GaAs structures

We investigate the effects of spacer layer thickness on the optical and transport properties of the n-typeδ-doped pseudomorphic Al_0.30Ga_0.70As/In_0.15Ga_0.85As / GaAs structures. Aδ-doped AlGaAs/InGaAs/GaAs structure with a 6nm spacer layer yields a sheet carrier concentration of 1.5×10¹² cm^?2 at 77K with electron mobility of 6.4×10³ cm²/Vs, 3.11×10⁴ cm²/Vs, and 3.45×10⁴ cm²/Vs at room temperature, 77 and 20K, respectively. The effects of the different scattering mechanisms on luminescence linewidth and electron mobility have also been discussed.     

Molecular beam epitaxial growth of HgCdTe on CdZnTe(311)B

A series of n-type, indium-doped Hg_1−xCd_xTe (x∼0.225) layers were grown on Cd_0.96Zn_0.04Te(311)B substrates by molecular beam epitaxy (MBE). The Cd_0.96Zn_0.04Te(311)B substrates (2 cm × 3 cm) were prepared in this laboratory by the horizontal Bridgman method using double-zone-refined 6N source materials. The Hg_1−xCd_xTe(311)B epitaxial films were examined by optical microscopy, defect etching, and Hall measurements. Preliminary results indicate that the n-type Hg_1−xCd_xTe(311)B and Hg_1−xCd_xTe(211)B films (x ∼ 0.225) grown by MBE have comparable morphological, structural, and electrical quality, with the best 77 K Hall mobility being 112,000 cm²/V·sec at carrier concentration of 1.9×10⁺¹⁵ cm⁻³.     

Low oxygen and carbon incorporation in AIGaAs using tritertiarybutylaluminum in organometallic vapor phase epitaxy

High-quality AIGaAs epilayers have been grown by low pressure organometallic vapor phase epitaxy with a new aluminum precursor tritertiarybutylaluminum (TTBAl). Layers grown at 650°C have a featureless mirror surface morphology and strong room temperature photoluminescence. Carbon was not detectable in chemical analysis by secondary ion mass spectroscopy, nor in low temperature (4K) photoluminescence spectra. Oxygen concentration in Al_0.25Ga_0.75As is as low as ∼2−3 × 10¹⁷ cm⁻³. Nominally undoped AIGaAs layers exhibit n-type conductiv-ity with electron concentrations at ∼ 1−1.5 × 10¹⁶ cm⁻³. A high degree of compo-sitional uniformity over 5 cm diam substrates (0.268 ±0.001) was obtained. These results indicate the potential for TTBA1 as an aluminum precursor for low temperature growth of Al-containing III-V alloys.     

Zinc-doping of InP during chemical beam epitaxy using diethylzinc

Diethylzinc was used as ap-type dopant source during InP growth by chemical beam epitaxy. In InP, electrically activated Zn saturated at a concentration of ∼2.0 × 10¹⁸ cm⁻³ for epilayers grown at 540‡ C. Higher role concentrations were obtained by lowering the growth temperature. However, measurements with SIMS indicated that very serious Zn diffusion occurred when the Zn concentration appeared to reduce the pyrolysis efficiency of trimethylindium. This caused a reduction in the InP growth rate and InAs mole fraction in InGaAs epilayers. No Zn “memory effect≓ was detected in our system. Undoped InP epilayers maintained an n-type background of ∼5 × 10¹⁵ cm⁻³.