Study of grown-in defects and effect of thermal annealing in Al0.3Ga0.7As and GaAs LPE layers

Studies of the grown-in deep-level defects in the undoped n-Al_xGa_1-xAs (x = 0.3) and GaAs epitaxial layers prepared by the liquid phase epitaxy (LPE) techniques have been made, using DLTS, I-V and C-V measurements. The effect of 300 °C thermal annealing on the grown-in defects was investigated as a function of annealing time. The results showed that significant reduction in these grown-in defects can be achieved via low temperature thermal annealing process. The main electron and hole traps observed in the Al_0.3Ga_0.7As LPE layer were due to the E_c-0.31 eV and E_v+0.18 eV level, respectively, while for the GaAs LPE layer, the electron traps were due to the E_c-0.42 and 0.60 eV levels, and the hole traps were due to E_v+0.40 and 0.71 eV levels. Research supported in part by the Air Force Wright Aeronautical Laboratories, Aeropropulsion Lab., Wright Patterson Air Force Base, Ohio, subcontract through SCEEE, contract F33615-81-C-2011, task-4, and in part by AFOSR grant no. 81-0187.     

Deep level studies in MBE GaAs grown at low temperature

The photo-induced current transient spectroscopy (PICTS), thermoelectric effect spectroscopy (TEES) and thermally stimulated current (TSC) spectroscopy have been used to characterize the deep levels in the GaAs materials grown at low temperature by molecular beam epitaxy. At least five hole traps and five electron traps have been identified by the TEES measurement employing a simplified sample arrangement. We have studied the behavior of various traps as a function of the growth temperature and the post-growth annealing temperature. Some of the shallower hole traps were annealed out above 650‡ C. Electron traps atE _c- 0.29 eV andE _c- 0.49 eV were present in the material, and have been identified as M3 and M4, respectively. The dominant electron trap, atE _c- 0.57 eV, is believed to be associated with the stoichiometric defect caused by the excess As in the material, and our data show evidence of forming a defect band by this trap. A possible model involving As precipitates is proposed for this trap atE _c-0.57 eV.     

Evidence of trapping in device-quality liquid-phase-epitaxial In1?xGaxAsyP1?y

Traps have been identified in epitaxial n- and p-type In1?xGaxAsyP1?y for the first time. The activation energy, capture cross-section and density of several electron traps in the quaternary composition range from InP to In0.53Ga0.47As have been determined. An electron trap similar in some characteristics to the 0.83 eV electron trap present dominantly in bulk and v.p.e. GaAs was observed in an n-type In0.71Ga0.29As0.45P0.55(Eg=0.95 eV) layer. Hole traps were not observed.     

Growth of 1‐eV GaNAsSb‐based photovoltaic cell on silicon substrate at different As/Ga beam equivalent pressure ratios

We report the performance of 1‐eV GaNAsSb‐based photovoltaic samples grown on a Si substrate using molecular beam epitaxy at different As/Ga beam equivalent pressure (BEP) ratios. The light current–voltage curve and spectral response of the samples were measured. The sample grown at an As/Ga BEP ratio of 10 showed the highest energy conversion efficiency with an open circuit voltage (V_OC) of 0.529 V and a short circuit current density of 17.0 mA/cm². This measured V_OC is the highest ever reported value in GaNAsSb 1‐eV photovoltaic cell, resulting in the lowest ever reported E_g/q‐V_OC of 0.50 eV. The increase in the As/Ga BEP ratio also resulted in an increase in the bandgap‐voltage offset value (E_g/q‐V_OC) and a decrease in quantum efficiency up to As/Ga BEP ratio of 18. Copyright © 2015 John Wiley & Sons, Ltd.     

A DLTS analysis of electron and hole traps in VPE grown n-GaAs using schottky barrier diodes

Capacitance lock-in amplifier deep level transient spectroscopy (DLTS) using Schottky barrier diodes (SBD’s) was used to characterize the electron and hole traps in VPEn-GaAs (N_D - N_A = 1 - 2 x 10¹⁵/cm³) layers grown on n⁺ (10¹⁸/cm³) GaAs substrates. The main electron traps observed were the EL2 atE _c - 0.81 eV and a level atE _c - 0.48 eV. The use of large forward bias electrical injection pulses (and no optical excitation) facilitated the detection of hole traps, of which the defect with an energy level atE _v + 0.42 eV, speculated to be Cu-related, was present in the highest concentration.     

On the carrier profiling of GaAsSb/GaAs heterostructures

Carrier profiles of MBE grown Ga(As,Sb)/GaAs heterostructures were studied. In low Sb content samples of Ga(As,Sb)/GaAs grown by MBE the experimentally measured carrier profiles exhibit double dips in concentration, whereas a single large dip is ob-tained for higher Sb content with larger lattice-mismatched samples. The capacitance voltage(C-V) carrier profile of a Schottky barriern- N heterojunction of Au/n-GaAsSb/N-GaAs has been modeled and double dips occur when nonuniform doping is present which may explain the experimentally observed double dips in a GaAs_0.95Sb_0.05/GaAs specimen. For large lattice mismatch and therefore large heterointerface charge density in the model, the accumulation peak due to ΔE_c is shown to be overwhelmed by a pro-nounced single dip as observed in higher Sb content samples such as GaAs_0.91Sb_0.09/ GaAs and GaAs/GaAs_0.9Sb_0.1.     

LPE and VPE In1-xGaxAsyP1-y/InP: Transport properties, defects, and device considerations

The electrical properties of In1-xGaxAsyP1-yalloys lattice matched to InP, grown by liquid-phase and vapor-phase epitaxial techniques, have been determined by various measurements. Several electron and hole traps, with activation energies varying from 0.26 to 0.82 eV, have been identified by transient capacitance and photocapacitance measurements and their density and capture cross section have been measured. The 0.82 electron trap has emission and capture properties identical to the dominant 0.83 eV electron trap present in bulk and VPE GaAs. Hall measurements were made on the alloys in the temperature range of 20-600 K. Analysis of the mobility data has yielded the values of several transport parameters including the alloy scattering potentialDelta Uas a function of composition. The maximum value ofDelta U simeq 0.8eV corresponding to the bandgapE_{g} simeq 0.95eV. Photo-Hall measurements at low temperatures show the presence of donor- and acceptor-like defects in the LPE and VPE alloys, respectively. These centers exhibit persistent photoconductivity at low temperatures and have a high barrier energy (∼0.2 eV) associated with electron capture. Defects, which are possibly located in the interconduction-valley region, have been identified from analysis of Hall data forT > 400K. The strong temperature dependence of the threshold current in injection lasers and the large leakage currents near breakdown in avalanche photodiodes have been discussed in the fight of the defects identified in the present investigation.     

Interface trap and interface depletion in lattice-mismatched GaInAs/GaAs heterostructures

The effects of lattice mismatch on the deep traps and interface depletion have been studied for the Ga_0.92In_0.08As(p⁺)/GaAs(N) and Ga_0.92In_0.08As(n)/GaAs(SI) heterostructures grown by molecular beam epitaxy. We have used deep level transient spectroscopy (DLTS) and admittance spectroscopy (AS) and observed two hole traps, one at an energy ranging from 0.1 to 0.4 eV and the other at 0.64 eV, and two electron traps at 0.49 and 0.83 eV in the GalnAs/GaAsp ⁺-N junction sample. The hole trap appeared as a broad peak in the DLTS data and its energy distribution (0.1 ∼ 0.4 eV) was obtained by a simulation fitting of the peak. Concentration of this distributed hole trap increased as the in-plane mismatch increased, suggesting its relation to defects induced by lattice relaxation, whereas the other traps are from the bulk. The misfit dislocations are believed to be responsible for the interface trap. For the Ga_0.92In_0.08As(n)/GaAs(SI) samples, Hall effect measurements showed an increased interface depletion width of about 0.14 Μm for the 0.5 Μm thick layer and about 0.12 /gmm for the 0.25 Μm thick layer, while a corresponding GaAs/GaAs sample had only 0.088 Μm for the interface depletion width.     

Plasma anodisation of Ga1?xInxAs (x=0.35 and 0.10) and study of MOS interface properties

Oxides have been grown on n-type Ga1?xInxAs/GaAs wafers (x=0.35 and 0.10) using plasma anodisation. According to C/V measurements, the surface can be biased into inversion and probably accumulation on Ga0.65In0.35As. The interface trap density is about 1012 cm?2eV?1 near midgap, and about 1013 cm?2eV?1 near flatband. MOS capacitors on Ga0.90In0.10As exhibit a high density of interface States 0.4?0.5 eV below the conduction band.     

Metallurgical amd electroluminescence characteristics of vapor-phase and liquid-phase epitaxial junction structures of InxGa1−xAs

In_xGa_1−xAs (x = 0.05 to 0.32) p-n junction structures have been grown on GaAs substrates by vapor-phase epitaxy (VPE) and liquid-phase epitaxy (LPE). It is shown that by step-grading the VPE material, lattice-mismatch strain can be absorbed by dislocations at the grading interfaces, leaving the final constant-composition device layers relatively dislocation free. In contrast, the dislocation density for LPE In_xGa_1−xAs increases with increasing InAs concentration. For both materials, diffusion lengths, electroluminescence efficiencies, and 77°K laser-diode parameters (threshold and efficiency) can be correlated with their dislocation densities. The VPE materials have electrical and luminescence properties that are independent of InAs concentration, and match those of their GaAs counterparts. The LPE materials exhibit properties that degrade with increasing InAs concentration. This research was supported in part by the Air Force Avionics Laboratory, WPAFB, Ohio, under Contract No. F33615-73-C-1177     

Evidence of interaction between two DX centers in N-Type AlGaAs from RDLTS and temperature dependent pulse-width DLTS measurements

Two well-separated electron traps with activation energies: E_{t 1} ≊ 0.286 eV and E_{t 2} ≊ 0.433 eV have been consistently detected in the n-type Al_0.6Ga_0.4As confinement layer of AlGaAs/GaAs single quantum well laser diodes. The physical characteristic parameters for these two traps, including capture cross section, emission time constant, and capture time constant, have been calculated. Reverse-bias pulsed deep level transient spectroscopy (RDLTS) results provide the evidence for the first time that these two traps have strong interaction during emission processes. This allows us to conclude that E_{t 1} and E_{t 2} are indeed both donor-unknown centers. Furthermore, using a temperature-dependent pulse-width method, DLTS signals from E_{t 1} alone can be obtained. The corrected activation energy appears to be a little shallower at E_{t 1} ≊ 0.265 eV.     

MBE自组织方法生长InGaAs/AlGaAs量子线FET材料

利用分子束外延 (MBE)技术在高指数面 Ga As衬底上自组织生长了应变 In Ga As/Ga As量子线材料。原子力显微镜 (AFM)观测结果表明量子线的密度高达 4× 1 0 5/cm。低温偏振光致发光谱 (PPL)研究发现其发光峰半高宽 (FWHM)最小为 9.2 me V,最大偏振度可达 0 .2 2。以 Al Ga As为垫垒 ,In Ga As/Ga As量子线为沟道 ,成功制备了量子线场效应管 (QWR-FET)结构材料 ,并试制了器件 ,获得了较好的器件结果     

Hole traps in n-type Ga1?xAlxAs grown by organometallic vapour phase epitaxy

Minority carrier traps in n-type Ga1?xAlxAs (x = 0.25 and 0.30) grown by the organometallic vapour phase epitaxy process have been investigated by minority carrier transient spectroscopy (MCTS). Hole traps with thermal activation energies of Ev + 0.35 and 0.48 eV and a deeper centre have been observed in GaAs and at Ev + 0.20, 0.26, 0.44 and 0.78 in GaAlAs. The electron and hole capture cross-sections of these centres have also been measured.     

Effect of heat treatment on the nature of traps in epitaxial GaAs

By annealing v.p.e. GaAs at increasing temperatures, the commonly observed 0.83 eV electron trap in v.p.e. and bulk GaAs is removed and a 0.64 eV hole trap, also detected in l.p.e. GaAs, is introduced. The results indicate that these electron and hole traps are related to Ga and As vacancies, respectively.     

Interpretation of profiles obtained by C(V) technique in presence of deep traps: Application to proton irradiated GaAs samples

In the present paper, we attempt to give a mathematical form to the results of the “profiles” obtained by the C(V) method. The theory is performed in the case of a donor or acceptor like trap. The results are applied to a uniform trap profile (case of electron irradiation) and a gaussian trap profile (case of ion irradiation). The temperature variation, the trap localization in the gap and the effect of the Fermi level, which gives the spatial separation between the empty and full defect, has been taken into account. The variation of the crossing point between the Fermi level and the trap level with the voltage has been evaluated in some particular cases.The theoretical results are applied to experiments on proton irradiated n type (2.10¹⁵/cm³) epitaxial VPE GaAs. In the irradiated samples, two dominant defects labeled E₂ (E_c ? 0.22 eV) and E₃ (E_c ? 0.33 eV) have been identified by DLTS technique. A good fit of experimental C(V) “profiles” by the model exposed in this paper is obtained. This result leads us to confirm E₂ (E_c - 0.22 eV) and E₃ (E_c - 0.33 eV) as acceptor like traps in n type GaAs.     

Capacitance study of electron traps in low-temperature-grown GaAs

Electron traps in GaAs grown by MBE at temperatures of 200–300°C (LT-GaAs) were studied. Capacitance deep level transient spectroscopy (DLTS) was used to study the Schottky barrier on n-GaAs, whose space-charge region contained a built-in LT-GaAs layer ∼0.1 μm thick. The size of arsenic clusters formed in LT-GaAs on annealing at 580°C depended on the growth temperature. Two new types of electron traps were found in LT-GaAs layers grown at 200°C and containing As clusters 6–8 nm in diameter. The activation energy of thermal electron emission from these traps was 0.47 and 0.59 eV, and their concentration was ∼10¹⁷ cm⁻³, which is comparable with the concentration of As clusters determined by transmission electron microscopy. In LT-GaAs samples that were grown at 300°C and contained no arsenic clusters, the activation energy of traps was 0.61 eV. The interrelation between these electron levels and the system of As clusters and point defects in LT-GaAs is discussed. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 4, 2004, pp. 401–406. Original Russian Text Copyright ? 2004 by Brunkov, Gutkin, Moiseenko, Musikhin, Chaldyshev, Cherkashin, Konnikov, Preobrazhenskii, Putyato, Semyagin.     

High resistivity interfacial layers due to compensation by Sulfur in (Al,Ga)As devices

In p-n junctions grown by LPE in the (Al,Ga)As system, high concentrations of Sulfur can accumulate on the p side of the junction. As a result, a closely compensated, high resistivity region can extend for 0.1-1.0 µm into the p layer. Since sulfur creates deep electron traps in Al0.4Ga0.6As with a thermal activation energy in bulk p-type material of 0.2 eV, both electrical and optical properties of (Al,Ga)As diode devices can be affected by the interfacial sulfur concentrations.     

Effect of composition on deep levels in heteroepitaxial GexSi1−x layers and evidence for dominant intrinsic recombination-Generation in relaxed ge layers on Si

Electron traps, hole traps, and the dominant recombination-generation (R-G) centers have been investigated with deep level transient spectroscopy and current-voltage/temperature measurements in heteroepitaxial Ge_xSi_1-x alloys with x ranging from 0.15 to 1, grown on graded Ge_y.Si_1−y/Si substrates. For all samples with compositions x < 0.85, which retain the Si-like conduction band structure, we detect a dominant electron trap and R-G center whose activation energy is ΔE = 0.5 eV, independent of composition. This energy agrees with that of electron traps previously reported for plastically deformed (PD) Si, suggesting a connection to the Si-like band structure. This 0.5 eV level dominates the reverse leakage current over a wide range of growth and annealing conditions for the 30% Ge samples, indicating that the electronic state at ΔE = 0.5 eV is a very efficient R-G center, as would be expected from its midgap position. Alternatively, for strain relaxed, pure Ge (< 1), we detect electron traps at E_c − 0.42 eV and E_c − 0.28 eV, in agreement with the literature on PD Ge and Ge bicrystals. These energies are significantly different from those observed for x < 0.85, and we conclude that these changes in activation energy are due to changes in the conduction band structure for high Ge content. Moreover, in contrast with the Si-like samples (x < 0.85), the reverse leakage current in the relaxed Ge cap layer is not controlled by deep levels, but is rather dictated by intrinsic, band-to-band generation due to the reduced bandgap of Ge as compared to Si-like alloys. Only for reverse bias magnitudes which incorporate a significant portion of the graded buffer within the depletion region do R-G centers dominate the reverse leakage current. These results confirm the high quality of the strain-relaxed, pure Ge cap region which was grown on a Ge_ySi_1−y/Si step graded heterostructure (where y was increased from 0 to 1) by ultra high vacuum chemical vapor deposition. Finally, we report for the first time, what is apparently the dislocation kink site state at E_c − 0.37 eV, in a Ge_xSi_1−x alloy.     

Controlled vapor-pressure heat-treatment effect on deep levels in liquid-encapsulated czochralski-grown GaP crystals

Photocapacitance (PHCAP) measurements have been carried out on GaP crystals grown by the liquid-encapsulated Czochralski (LEC) method with heat treatment under various phosphorus-vapor pressures at different temperatures. Electron traps of E_C−1.1 eV, E_C−1.6 eV, E_C−1.9 eV, and a hole trap of E_V+2.26 eV are mainly detected. The phosphorus-vapor pressure dependence of the E_C−1.9 eV trap density and their diffusion behavior indicate that they are interstitial phosphorus atoms. The densities of both E_C−1.1 eV and E_C−1.6 eV traps are strongly dependent on the shallow impurity concentrations. Moreover, the density of E_C−1.1 eV traps increases with increasing phosphorus-vapor pressure. From these results, we suggest that E_C−1.1 eV traps are the complexes of shallow donors and antisite phosphorus atoms. Deep-level densities in GaP crystals after annealing at 860°C or 960°C for 60 min are decreased almost one order of magnitude lower than those in untreated substrate crystals, which should have occurred via out-diffusion of interstitial phosphorus atoms. However, such an effect is not prominent for 800°C treatment for 60 min.     

Effect of Se-doping on deep impurities in AlxGa1−xAs grown by metalorganic chemical vapor deposition

We have studied the effect of Se-doping on deep impurities in Al_xGa_1−xAs (x = 0.2∼0.3) grown by metalorganic chemical vapor deposition (MOCVD). Deep impurities in various Se-doped Al_xGa_1−xAs layers grown on GaAs substrates were measured by deep level transient spectroscopy and secondary ion mass spectroscopy. We have found that the commonly observed oxygen contamination-related deep levels at E_c-0.53 and 0.70 eV and germanium-related level at E_c-0.30 eV in MOCVD grown Al_xGa_1−xAs can be effectively eliminated by Se-doping. In addition, a deep hole level located at E_y + 0.65 eV was found for the first time in Se-doped Al_xGa_1-xAs when Se ≥2 × 10¹⁷ cm⁻³ or x ≥ 0.25. The concentration of this hole trap increases with increasing Se doping level and Al composition. Under optimized Se-doping conditions, an extremely low deep level density (N_t less than 5 × 10¹² cm⁻³, detection limit) Al_0.22Ga_0.78As layer was achieved. A p-type Al_0.2Ga_0.8As layer with a low deep level density was also obtained by a (Zn, Se) codoping technique.