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.     

Structural, electrical, and optical studies of GaAs implanted with MeV As or Ga Ions

The structural properties of GaAs implanted with high doses of 2 MeV arsenic or gallium ions with subsequent annealing at different temperatures were studied by transmission electron microscopy, Rutherford backscattering spectrometry-channeling, double crystal x-ray diffraction. Optical absorption, electrical conductivity, Hall effect and time-resolved photoluminescence were applied to monitor changes in electrical and optical characteristics of the material. An important conclusion from this investigation is that there was hardly any difference between materials implanted with gallium or arsenic. For implantation of either species, a large number of point defects was introduced and for a high enough dose a buried amorphous layer was formed. Hopping conduction and high absorption below band-to-band transition were observed for both cases. After low temperature annealing of the amorphous material, a high density of stacking faults and microtwins were found. Regrowth rates at the front and back amorphous-crystalline interfaces showed a significant difference. This was attributed to differences in local nonstoichiometry of the material at the upper and lower amorphous-crystalline interfaces. Structural studies showed the presence of some residual damage (a band of polycrystalline material in the center of the regrown area) with some associated strain even after annealing at high temperatures. Recovery to the conduction band transport in annealed samples was observed but mobilities, of the order of 2000 cmWs, were still smaller than in unimplanted GaAs. These results show that, in as-implanted material and even after annealing at lower temperatures, the point defects introduced by the implantation are responsible for the very short photocarrier lifetime. *On leave from Institute of Experimental Physics, Warsaw University, Poland.     

Extremely strong and sharp photoluminescence lines from nitrogen atomic-layer-doped GaAs,AlGaAs and AlGaAs/GaAs single quantum wells

We have performed nitrogen atomic-layer doping into GaAs, AlGaAs, and AlGaAs/GaAs single quantum wells using atomic nitrogen cracked by a hot tungsten filament. While the atomic-layer-doped GaAs layers show a series of sharp and strong photoluminescence lines relating to excitons bound to nitrogen atoms at 8K, atomic-layer-doped AlGaAs layers show several broad nitrogen-related lines. For the atomic-layer-doped single quantum well at the center of the GaAs layer, the quantum well luminescence itself disappears and a dominant and sharp luminescence is observed at a longer wavelength. It is found that the As pressure during the atomic-layer doping greatly affects the luminescence characteristics.     

SI GaAS中S~+注入的电学特性

本文研究了经常规热退火和快速热退火后SIGaAs中S~+注入的电学特性.热退火后,GaAs中注入S~+的快扩散和再分布不决定于S~+或砷空位V_(AS)的扩散而决定于离子注入增强扩散.使用快速热退火方法能抑制注入S~+在GaAs中的增强扩散,明显减小S~+的再分布,可以获得适合于制造GaAs MESFET器件的薄有源层.     

Electrical properties and deep levels in bulk solution grown GaAs crystal

Electrical and photoelectrical properties, deep levels spectra and microcathodoluminescence spectra were measured for bulk high-resistivity GaAs samples grown from Ga-rich solution by a synthesis solute diffusion technique. It is shown that the main portion of the grown crystal is high-resistivity p-type with electrical properties determined by deep hole traps with the level near 0.43 eV from the valence band edge. The density of these 0.43 eV hole traps was shown to decrease with increasing distance from the crystallization front and the traps were associated with the deep hole traps observed earlier in Ga-rich liquid-phase-epitaxy-grown films. The single crystalline end portion of the crystal was semi-insulating n-type with a very low (some 10¹⁴ cm⁻³) concentration of midgap EL2 donors. This end portion of the crystal was characterized by a very high photosensitivity. Possible advantages of the use of such material in radiation detectors are briefly discussed.     

Si-implantation into GaAs grown on Si

200 keV Si implantations were performed in the dose range of 5 × 10¹² − 1 × 10¹⁴ cm⁻² in GaAs grown on Si. For comparison implants were also performed in GaAs layers grown on GaAs substrates. Implanted layers were annealed by both furnace and halogen lamp rapid thermal anneals. Significantly lower donor activations were observed in GaAs layers grown on Si substrates than in the layers grown on GaAs substrates. Extremely low dopant activations were obtained for Be implants in GaAs grown on Si. Photoluminescence and photoreflectance measurements were also performed on the implanted material.     

C掺杂GaAs外延层的MOCVD生长

以CCl4为掺杂源,利用EMCORE D125 MOCVD系统生长了不同C掺杂浓度的GaAs外延层.通过Hall、PL、DXRD以及在位监测工具Epimetric等手段研究了掺C GaAs层的电学特性、光学特性、晶体质量和生长速度等.     

MBE高掺杂n-GaAs:Si和p-GaAs:Be的光致发光谱

我们对MBE高掺杂的n-GaAs∶Si和p-GaAs∶Be进行了光致发光研究,详细比较了高掺杂n-GaAs和p-GaAs在光谱线型,峰值半宽,峰值位置等方面的差异,以及两者的发光与温度的关系.由分析得出,对于高掺杂的n-GaAs,填充在导带内较高能态(K≠0)的电子与价带顶(K=0)空穴的非竖直跃迁是主要的发光过程.而对于高掺杂的p-GaAs,则是以导带底附近(K(?)0)的电子和价带顶附近(K(?)0)的空穴竖直跃迁为主要发光过程.     

Electrical properties of low-temperature GaAs grown by molecular beam epitaxy and migration enhanced epitaxy

Measurements on low-temperature GaAs epitaxial layers (LT-GaAs) grown by molecular beam epitaxy and migration enhanced epitaxy showed that the excess arsenic incorporated during growth played a crucial role in determining their electrical properties. The electrical transport in LT-GaAs grown by a standard molecular beam epitaxy proceeded mainly via a hopping process, which showed a higher activation energy and onset temperature than those usually observed in lightly doped semiconductors. Using migration enhanced epitaxy to grow LT-GaAs, we were able to substantially reduce the density of As-rich defects and to achieve a good Hall mobility in Be-doped LT-GaAs. The study presented here indicates that, with controlled excess arsenic incorporation during growth, LT-GaAs can vary in a range of conduction properties and thus can be engineered for different device applications.     

Co-Implantation and autocompensation in close contact rapid thermal annealing of Si-implanted GaAs:Cr

Close contact rapid thermal annealing of semi-insulating GaAs:Cr implanted with Si, Si + Al, and Si + P has been studied using variable temperature Hall effect measurements and low temperature (4.2K) photoluminescence (PL) spectroscopy. Isochronal (10 sec) and isothermal (1000° C) anneals indicate that As is lost from the surface during close contact annealing at high anneal temperatures and long anneal times. Samples which were implanted with Si alone show maximum activation at an annealing temperature of 900° C, above which activation efficiency decreases. Low temperature Hall and PL measurements indicate that this reduced activation is due to increasing auto-compensation of Si donors by Si acceptors at higher anneal temperatures. However, co-implantation of column V elements can increase the activation of Si implants by reducing Si occupancy of As sites and increasing Si occupancy of Ga sites, and therebyoffset the effects of As loss from the surface. For samples implanted with Si + P, activation increases continuously up to a maximum at an anneal temperature of 1050° C, and both low temperature Hall and PL measurements indicate that autocompensation does not increase in this case as the anneal temperature increases. In contrast, samples implanted with Si + Al show very low activation and very high compensation at all anneal temperatures, as expected. The use of column V co-implants in conjunction with close contact RTA can produce excellent donor activation of Si implanted GaAs.     

Electrical properties of molecular beam epitaxial GaAs grown at 300–450°C

We use the Hall effect and a new charge-transfer technique to study molecular beam epitaxial GaAs grown at the low substrate temperatures of 300–450°C. Layers grown from 350–450°C are semi-insulating (resistivity greater than 10⁷ Ω-cm), as grown, because of an As_Ga-related donor (not EL2) at E_C-0.65 eV. The donor concentrations are about 2×10¹⁸ cm⁻³ and 2×10¹⁷ cm⁻³ at growth temperatures of 300 and 400°C, respectively, and acceptor concentrations are about an order of magnitude lower. Relatively high mobilities (∼5000 cm²/V s) along with the high resistivities make this material potentially useful for certain device applications.     

Modulation of electronic properties in liquid phase epitaxially grown p-n-p-n GaAs multilayers

Liquid phase epitaxy (LPE) is presented as an alternative method to molecular beam epitaxy (MBE) for growing p-n-p-n doped GaAs superlattices. LPE offers some advantages compared to MBE. Simple equipment, shorter growth times at comparable low growth temperatures, permits growing multilayers with a broad variety of single layer thickness 20 < d < 1000 nm at reasonably short growth times. Typical doping superlattice properties are tested in LPE multilayers, and demonstrated via some selected results: a) The simultaneous modulation of the conductivities in the n- and p-layer systems. It depends on the variation of the 2-dim. carrier concentrations and to a similar extent on the change of the mobilities with the effective channel thickness. b) The field effect transistor properties of the p-and n-doped systems are due to the special choice of doping concentrations and film thicknesses, c) The modulation of the effective band gap E _G ^ef is proved by cw and time resolved photoluminescence Good agreement is achieved between the expected shift E _G ^ef due to the LPE growth parameters and the observed shift of the peak energy of the luminescence spectra.     

Relationship between near bandedge absorption and photoluminescence efficiency in semi-insulating GaAs

We demonstrate that near bandedge photoluminescence efficiency in SI bulk GaAs can be increased by low temperature photo-quenching of native point defects in the material. These defects cause infrared absorption at photon energies just below the bandgap energy in cooled samples and their concentrations anti-correlate with those of EL2 in unannealed crystals. This absorption has been previously termed “Reverse Contrast.” The increase in PL efficiency is almost an exponential function of the photoquenching time and proportional to the Reverse Contrast absorption coefficient.     

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.     

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.     

Stoichiometry of melt-grown N-type GaAs as revealed by photoluminescence measurements

A comparative study of the 77K PL spectra of n-type GaAs single crystals, grown by the horizontal or Czochralski technique, shows that the former are crystallized from Ga-rich melts (although in equilibrium with 1 atm As-pressure) whereas the latter are pulled from As-rich melts (although the starting loads are mostly As-deficient). Besides the V_Ga, copper appears as the major compensating acceptor in these crystals. Association of Cu and/or V_Ga with V_As and/or donor atoms tends to neutralize this compensation. This work shows how the above interaction explains the empirically determined relation N_D∝(N_D-N_A), which is shown to hold for crystals of various sources.     

Effect of iso-electronic dopants on the dislocation density of GaAs

The addition of 1% In to LEC GaAs has been reported to reduce the dislocation density in this material; similar data exists for Sb doping. Several effects have been inferred to explain these phenomena, the most prevailing one stating that the solid stoichiometry is affected by an as yet unknown mechanism. Similar postulations have been made to explain the growth of semi-insulating GaAs. A thermodynamic model is described, based on earlier work, that shows a broadening of the existence region of GaAs when In or Sb are added to GaAs. Comparing the solidus phase diagrams of In- or Sb-doped GaAs to undoped GaAs shows that addition of either one of these two iso-electronic dopants has a similar effect on the solid stoichiometry as adding more As to the melt. However, the increased pressure problems in LEC growth of GaAs, normally associated with adding As, are circumvented if instead In or Sb are added to the melt. From our calculations it is also shown that the addition of the iso-electronic dopants Al or P to GaAs would not result in the same effect on the solid stoichiometry. Published experimental evidence supports this and shows that no dislocation reduction and semi-insulating GaAs is obtained with the use of these dopants. The model described in this paper explains the postulation that iso-electronic doping is of critical significance in controlling the solid stoichiometry and thereby obtaining zero dislocation density LEC GaAs and semi-insulating GaAs.     

Intentional ρ-type doping by carbon in metalorganic MBE of GaAs

We report on the intentional ρ-type doping of GaAs layers grown in an UHV system from molecular beams of arsine (AsH₃) and mixtures of frimethyl gallium (TMG) and friethyl gallium (TEG). The entire doping range between 10¹⁴ cm^-3 (growth from pure TEG) and 10²⁰ cm^-3 (growth from pure TMG) can be covered by using mixtures of TMG and TEG. As revealed by SIMS and photoluminescence (PL) carbon is the dominant acceptor in the layers. Comparison of the Hall mobility and of the PL spectra shows that the quality of our films equals that of the best LPE and MBE grown ρ-type GaAs layers.     

New photoluminescence lines in Vanadium doped GaAs grown by MOVPE

We examined the electrical and optical properties of vanadium-doped GaAs grown by metalorganic vapour phase epitaxy using vanadium tetrachloride (VCl₄) as a novel dopant source. Samples with various vanadium incorporations were investigated. All samples were n type. The electron concentration dependence on the VCl₄ flow rate was established. At 15 K, by comparison with undoped layers grown in the same conditions, photoluminescence spectra of V-doped exhibited three new emission bands: at 1.41, 1 and 0.72 eV. The 1 and 0.72 eV band emissions were attributed to V²⁺ and V³⁺ intracenter emission, while the 1.41 eV band was suggested to be a donor-bound transition. The identity of the donor is tentatively attributed to a donor complex that associates vanadium to an arsenic vacancy. From Hall effect as function of temperature, the donor ionisation energy was estimated to be about 102±5 meV.