Pallab K. Bhattacharya

The trend of deep states in organometallic vapor‐phase epitaxial GaAs with varying As/Ga ratios

Traps in organometallic vapor‐phase GaAs have been characterized. The dominant electron trap present in conventional vapor‐phase epitaxial GaAs is also present in organometallic GaAs with an activation energy ΔE0T +ΔEB=0.820.02 eV and a capture cross section σ∞= (1.71.0) ×10−14 cm2. A linear dependence of the trap concentration on As/Ga ratio in the material indicates the involvement of a Ga vacancy in the formation of the center. A second electron trap with an activation energy of 0.360.02 eV and hole traps with activation energies of 0.30 and 0.35 eV have been identified and their capture cross section and density determined.

Correlation of photoluminescence and deep trapping in metalorganic chemical vapor deposited AlxGa1−xAs (0≤x≤0.40)

Shallow and deep level photoluminescence (PL) in metalorganic chemical vapor deposition grown AlxGa1−xAs (0≤x≤0.40) are studied. Two sets of samples grown under different conditions are compared. The growth conditions are chosen to produce a large density of deep levels in one case and to minimize the deep level density in the other case. The 0.82‐eV EL2 electron trap and four other dominant electron traps with activation energies ET ranging from 0.25 to 0.62 eV are identified. The concentrations of the four other traps are observed to increase with Al content in those samples grown under trap‐producing conditions, and the traps are nearly absent in the other set of samples. The PL intensity is inversely proportional to trap concentrations. The trap densities are related to background contamination in the growth ambient, most likely H2O and O2, leading to the speculation that two traps with ET=0.35 eV and ET=0.25 eV involve Al and O complexes. Hole traps have also been observed but show no definite trends...

Growth and photoluminescence spectra of high‐purity liquid phase epitaxial In0.53Ga0.47As

High‐purity liquid phase epitaxial In0.53Ga0.47As has been grown on semi‐insulating (100) InP:Fe substrates. The electrical characteristics of the layers were determined from Hall measurements. Different melt‐baking schemes were used to improve the purity of the grown layers. It was found that the layers with the most desirable transport properties were obtained by a 20–40 h bakeout of the In melt followed by 20–60 h bakeout of In+InAs+GaAs under ultrapure H2 flow. Such layers were n‐type with ND and NA∼1014 cm−3 and with μ300 K and μ77 K=9000 and 55 000 cm2/V s, respectively. Some of the as‐grown layers were subsequently heat treated with an InAs proximity cap at 670 °C for 20 min under H2 flow. High‐resolution photoluminescence measurements were performed with the as‐grown and heat‐treated layers at temperatures down to 4.4 K. The spectra were correlated with the growth conditions. Measurements at different temperatures and with varying excitation intensity helped to elucidate excitonic and impurity‐rel...

Photoinduced current transient spectroscopy of semi‐insulating InP:Fe and InP:Cr

Traps in semi‐insulating InP:Fe and InP:Cr have been studied by Photo‐Induced Current Transient measurements for the first time. Hole emissions to the valence band with activation energy ΔET = 0.69±0.01 and 0.96±0.01 eV from the Fe and Cr levels, respectively, have been identified. These values of ΔET , on comparison with Hall measurement data for 350⩽T⩽600 K, indicate negligible coupling of the Fe and Cr levels with the lattice. Electron traps with ΔET = 0.68±0.01 eV, probably related to native defects, and hole traps with ΔET = 0.50±0.005 and 0.67±0.01 eV have also been detected. The thermal capture cross section related to the various electron and hole emissions have been estimated.

LPE and VPE In 1-x Ga x As y P 1-y /InP: Transport properties, defects, and device considerations

The electrical properties of In 1-x Ga x As y P 1-y alloys 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 potential \Delta U as a function of composition. The maximum value of \Delta U \simeq 0.8 eV corresponding to the bandgap E_{g} \simeq 0.95 eV. 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 for T > 400 K. 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.

Behavior of the 0.82 eV and other dominant electron traps in organometallic vapor phase epitaxial AlxGa1−xAs

Thermal emission and capture properties of three dominant electron traps in organometallic vapor phase epitaxial AlxGa1−xAs have been studied by transient capacitance measurements. The traps have activation energies ΔET = 0.82±0.01, 0.62±0.02, and 0.38±0.02 eV, which remain invariant with x. The thermal capture cross section of the traps, however, decreases with increasing x. These results, together with the annealing behavior of the traps, add more evidence to the fact that the 0.82‐eV trap, commonly known as the EL2 center, is related to a Ga vacancy. The 0.82‐ and 0.38‐eV traps exhibit barriers to electron capture ∼0.06–0.08 eV and the concentration of the 0.62‐ and 0.38‐eV traps increases with increasing x.

The role of lattice strain in the phase equilibria of III‐V ternary and quaternary semiconductors

Liquidus and solidus isotherms for ternary GaxIn1−xAs and AlxIn1−xAs and quaternary In1−xGaxAs1−yPy and In1−xGaxAs1−ySby alloy semiconductors have been calculated using the regular solution phase equilibria model for liquid phase epitaxial growth. The effect of lattice‐mismatch strain in the growing layer has been incorporated in the model. Calculations have been made in order to make comparisons with published results of previous workers for both lattice‐matched and mismatched layers. It is found that agreements are better with the inclusion of strain than with a zero‐strain model.

Photoluminescence in Si‐implanted InP

Photoluminescence measurements at various temperatures and excitation intensities have been performed with Si‐implanted InP (Fe) suitable for device applications. The implantation dose and energy of 28Si+ varied in the range (0.5–1.0)×1013 cm−3 and 100–200 keV, respectively. Post‐implantation annealing was done at 670 and 700 °C with a proximity cap. The superior optical quality of the samples were evidenced by the strength of the bound exciton doublet centered at 1.414 eV in all samples and the appearance of the free‐excitron‐polaritron transition at 1.418 eV in the spectra of some samples at low temperatures. The dominant transition centered at 1.375 eV is ascribed to Zn impurities in the starting material. Analysis of temperature‐dependent data yields an activation energy of 49.0 meV. The origin of a transition at 1.379 eV appearing in the unimplanted heat‐treated samples is not clear. A new transition, whose emission intensity increases with the implant dose, appears in the implanted samples at 1.35 e...

Interface states in GaAs/AlxGa1−xAs heterostructures grown by organometallic vapor phase epitaxy

The GaAs/AlxGa1−xAs interface grown by organometallic vapor phase epitaxy has been studied by transient capacitance techniques. No electron emissions have been observed from deep states at or near the interface of a GaAs/Al0.2Ga0.8As junction. Highly nonexponential transients were recorded for emissions near the interface, which arise from states with an apparent activation energy of 0.15 eV. Dominant deep traps were detected in the GaAs and Al0.2Ga0.8As in regions away from the interface. The implications of the results have been discussed.

Characterization of implanted and annealed vapor phase epitaxial GaAs

The electrical and optical properties of as‐grown and implanted and annealed vapor phase epitaxial GaAs have been determined and compared by photoluminescence, transient capacitance spectroscopy, and Hall measurements. The dominant electron trap level with activation energy ΔE = 0.83 eV is observed consistently in the as‐grown layers, but is not detected in the implanted layers. A second electron trap level with ΔE = 0.37±0.01 eV is also observed in some as‐grown and some implanted layers. A hole trap level with ΔE = 0.86 eV which is detected in some as‐grown layers with a low density compared to the carrier concentration and in most of the implanted layers with larger density is attributed to Cr. An electron trap level with ΔE = 0.53 eV detected in some implanted layers and a hole trap level with ΔE = 0.15 eV present in all the implanted layers are believed to be created due to the implant and anneal process. Room‐temperature Hall electron mobilities and activated surface carrier concentrations decrease ...