B. V. Dutt

Deep radiative levels in InP

Results of a detailed photoluminescence study of deep radiative transitions in InP crystals prepared by the bulk and epitaxial techniques are reported. In order to understand the origin of the photoluminescence (PL) spectra, bulk samples were subjected to isothermal anneals at different partial pressures of phosphorus. Similarly, the liquid phase epitaxy (LPE) wafers were grown with and without phosphorus in the gas stream. The electrical nature of some of the species responsible for the PL emission was inferred by a study of Cd diffused bulk samples. Based on these experiments the following tentative assignments are proposed. The photoluminescence band at 0.99 eV, common to all samples, is due to emission from a donorlike level related to the P vacancy. Bands at 1.21 and 1.14 eV appear to be due to emission to native acceptor levels associated with the In vacancy. The 1.08‐eV band is attributed to emission to a complex of the donor (0.99 eV) and acceptor (1.21 eV) species. The relationship between these ...

Spinodal decomposition in InGaAsP epitaxial layers

Abstract In GaAsP epitaxial layers emitting in the 1.25−1.37 μm wavelength region have been evaluated using transmission electron microscopy, X-ray diffraction and photoluminescence. Electron diffraction patterns show elongation of the 400 spots in the direction and diffuse intensity on the low angle as well as on the high angle side. This observation is consistent with the extra scattering observed close to the 400 Bragg peaks by X-ray diffraction. Furthermore, microstructures exhibit quasi periodic fine scale structure having a wavelength of ≈ 150 A, rectilinear boundaries and a weakly developed basket-weave pattern. These observations are compatible with the occurrence of spinodal decomposition in the layers. In addition, photoluminescence studies indicate that the presence of the fine scale composition modulations does not adversely affect the luminescence properties of these materials.

Photoluminescence study of native defects in InP

A photoluminescence (PL) study of native defects and their distribution in polycrystalline ingots of melt‐grown InP is reported. Three bands with peak positions at 0.99, 1.08, and 1.21 eV were found with systematic intensity changes along the length of the ingots. The PL bands were identified with the help of isothermal anneals as due to a donorlike P vacancy (0.99 eV), acceptorlike In vacancy or P interstitial (1.21 eV), and their complex (1.08 eV). The temperature dependence of the PL intensity compares well with the D‐function potential model of Lucovsky.

Electrical characteristics of InAsSb/GaSb heterojunctions

Heterojunctions of n‐type InAs0.95Sb0.05 grown by metalorganic chemical vapor deposition on n‐type GaSb substrates were studied by capacitance‐voltage and current‐voltage measurements. The n‐n heterojunctions are strongly rectifying and behave like metal‐(n) GaSb Schottky diodes with a barrier height of 0.80±0.02 eV. These measurements establish that the band lineup in this system is of the broken gap variety. We measure the valence‐band offset, Ev(GaSb)−Ev(InAs0.95Sb0.05), to be 0.67±0.04 eV.

An integrated laboratory-reactor MOCVD safety system

Abstract A comprehensive MOCVD safety interlock system has been designed and implemented which provides continuous monitoring of critical reactor and laboratory systems. Operator response to system alarms is limited to a single rule — immediate evacuation of the laboratory. The safety interlock system automatically aborts reactor and laboratory operation to predetermined latched states, provides audible and visual indication of the alarm condition, and identifies the detector and location giving rise to the alarm. Computer control of all operating systems enables additional safety to be programmed through interactive software design that eliminates most operator-based errors and provides for safe and reliable reactor operation. A full description is presented of the safety concepts incorporated into the design and construction of the laboratory and reactor system. Since its installation during the past year, the safety interlock system has operated successfully through several power failures and has demonstrated its effectiveness for ensuring a dependable fail-safe environment.

Formation of p+‐p−‐n− junctions in InP by Cd diffusion

A study was made of the diffusion of Cd into nominally undoped (4×1016 cm−3) n‐type InP using elemental sources consisting of (Cd and In) or (Cd and P). Two diffusion fronts whose depths are controlled by the amount of P or In in the diffusion source were delineated by etching. Electron beam induced current profiles and photoluminescence measurements revealed the formation of a  p+‐ p−‐ n− junction, with the  p− region bounded by the two diffusion fronts. Mesa p+‐ p−‐ n− diodes, 150 μm in diameter, fabricated from a wafer with the p+‐ p− and p−‐ n− junctions at 3.1 and 20.0 μm, respectively, have reverse breakdown voltages between 90 and 220 V and reverse leakage currents from 5 to 10 pA at half breakdown. The I‐V characteristics of these p+‐p−‐n− diodes exceed those of state of the art, abrupt p+‐n− InP avalanche photodiodes because of the formation of the p− region.

Room‐temperature operation of optically pumped InGaAsSb/AlGaAsSb double‐heterostructure laser at ≂2 μm

Optically induced room‐temperature lasing at ≂2 μm of the InGaAsSb/AlGaAsSb double heterostructures is reported. The growth of the quaternary antimonide structures lattice matched to GaSb substrates by liquid phase epitaxy is described. The optical thresholds and their temperature dependence are comparable to the InGaAsP devices operating at 1.55‐μm wavelength regions.

Elemental arsenic in native oxide films on AlxGa1−xAs

Surface reflection Raman scattering has been used to detect the presence of elemental arsenic in native oxide films grown on epitaxial (100) AlxGa1−xAs layers. Oxide films formed either by direct thermal oxidation in air at 450 °C or by electrochemical anodization followed by thermal aging (450 °C, in vacuo) were both found to contain elemental arsenic. Anodic films which were not subjected to a heat treatment showed no evidence for elemental arsenic inclusions within the detection limits of the technique. These observations are consistent with the occurrence of a thermally induced interfacial reaction involving As2O3 in the anodic film and the substrate.

Influence of ambient media on the out‐diffusion of S from InP:S

Liquid‐encapsulated Czochralski‐grown InP:S samples annealed for short times of 30 min in various ambients at 550 °C show diffusion fronts suggesting an extremely rapid out‐diffusion of S. In phosphorus ambient, the effective diffusion coefficient is inversely proportional to the phosphorus vapor pressure. Such a strong dependence on phosphorus vapor pressure is at variance with the generally accepted substitutional‐interstitial model. The out‐diffusion is fastest in vacuum, followed by hydrogen and forming gas mixtures. In inert gas medium (He), it is substantially slower. Annealing in air suggests the rapid formation of an oxide mask with little or no out‐diffusion. An Arrhenius plot of the temperature dependence of the diffusion coefficient D in vacuum anneals, yields a D of 4×105 exp(−2.16 eV/kT) in the temperature range of 350–500 °C. Anneals in vacuum at 450 °C with different orientations showed that the out‐diffusion is nearly orientation independent except for the observed absence of diffusion fro...

A novel multi-slice LPE boat: I. Preliminary results on InGaAs alloys

Abstract A novel graphite boat for depositing multi-layer structures by liquid phase epitaxy, simultaneously on sixteen large area substrates was developed and tested for initial experiments on InP/InGaAs alloys. The starting melts undergo aliquanting and can be either near equilibrium liqiuds or two-phase melts containing saturating solids in excess of equilibrium compositions. Special features include reservoirs for containing a suitable source of phosphorus vapor to prevent the thermal dissociation of the InP substrates. Preliminary experiments on two-layer structures of InP/InGaAs alloys simultaneously deposited on four InP substrates demonstrated the successful operation of the boat. The average layer thicknesses, and the composition in different wafers are uniform. These results promise a large throughput economical liquid phase epitaxy system for preparing multi-layered structures.