Kunishige Oe

Energy band‐gap shift with elastic strain in GaxIn1−xP epitaxial layers on (001) GaAs substrates

It is demonstrated that the energy band gap in epitaxial layers is changed by biaxial elastic strains which are produced by lattice mismatches in heterostructures. The epitaxial layers used in this work were Gax In1−xP layers grown on (001) GaAs substrates by liquid phase epitaxy. The energy band‐gap shifts were determined by comparing the photoluminescence peak energies of the as‐grown GaxIn1−xP layers with those from free‐standing layers removed from the GaAs substrates. It was experimentally found that the energy band gap shifts linearly with the elastic strain in the layer. Assuming that the lattice mismatch was accommodated only by the elastic distortion, the energy band‐gap shifts in Ga0.5In0.5P alloys were also calculated. The calculated results are 6.0 eV or 4.9×10−12 eV/dyn cm−2 per unit strain or stress, respectively, for the [100] and [010] biaxial elastic stress. These values are in quite good agreement with the experimental results.

Temperature Dependence of GaAs1-xBix Band Gap Studied by Photoreflectance Spectroscopy

We performed photoreflectance (PR) spectroscopy in order to investigate the fundamental band gap of GaAs1-xBix alloys. The temperature dependence of the band gap energy was evaluated by analyzing of the Franz–Keldysh oscillation in the PR spectra. With increasing Bi content, the band gap energy of GaAs1-xBix alloy is reduced, which shows a large optical bowing. The temperature coefficient of the band gap decreases appreciably in alloys with increasing Bi content. For x=0.026, the temperature coefficient near room temperature is -0.15 meV/K which is 1/3 of the value for GaAs.

New Semiconductor Alloy GaAs1-xBix Grown by Metal Organic Vapor Phase Epitaxy

A new semiconductor alloy material, GaAs1-xBix has been created by Metal Organic Vapor Phase Epitaxial (MOVPE) growth. A low growth temperature, such as 365°C, is required to obtain the alloy. X-ray diffraction measurements of alloy layers reveal that the diffraction patterns are satisfactory. The maximum GaBi content in the GaAsBi alloy estimated from the lattice constant is around 2%, which is consistent with that estimated from secondary ion mass spectroscopy (SIMS) measurements. In a photoluminescence (PL) measurement, a single peak spectrum is observed from 10 to 300 K. The temperature variation of the PL peak energy is as small as 0.1 meV/K.

Characteristics of Semiconductor Alloy GaAs1-xBix

The characteristics of GaAs1-xBix semiconductor alloy layers grown by metalorganic vapor phase epitaxy (MOVPE) have been studied. GaAs1-xBix epilayers were obtained on GaAs substrates. The lattice constants of the alloy were found to increase with the addition of Bi. The uniformity and the reproducibility of the solid composition of the GaAs1-xBix epilayers are good in spite of the difficulty of epitaxial growth. Although layer growth was performed at a low temperature (365°C), the stability of GaAs1-xBix alloy was sufficient for device processing, which was demonstrated by annealing in an arsenic atmosphere at 560°C for 30 min. The photoluminescence (PL) spectra show that the PL peak energy of the GaAs1-xBix alloy shifts to a longer wavelength with increasing Bi content. The temperature dependence of the PL peak energy is much weaker than the temperature variation of the band gap of GaAs; the temperature dependence of the PL peak energy of the GaAs0.974Bi0.026 layer is less than one-third the temperature variation of the band gap of GaAs. The results obtained in this research support the hypothesis that III–V alloy semiconductors consisting of semiconductor and semimetal components have a temperature-insensitive band gap.

Metastable GaAsBi Alloy Grown by Molecular Beam Epitaxy

GaAs1-xBix has been grown at a substrate temperature (Tsub) between 350 and 410°C by molecular beam epitaxy. The relationship between GaBi molar fraction (x) evaluated by Rutherford backscattering spectroscopy and the lattice constant showed good linearity. To achieve Bi incorporation into the epilayer, As flux was adjusted in a limited range on the brink of As shortage on the growing surface. The Bi incorporation was saturated at a large Bi flux, probably due to a low miscibility of Bi with GaAs. The value of x increased up to 4.5% with decreasing Tsub to 350°C.

Molecular-beam epitaxy and characteristics of GaNyAs1-x-yBix

GaNyAs1−x−yBix alloys were grown by molecular-beam epitaxy using solid Ga, Bi, and As sources and nitrogen radicals generated from nitrogen gas in rf plasma. Changing the growth temperature is found to be a convenient method for controlling the GaBi molar fraction in the alloy reproducibly. The photoluminescence (PL) spectra show that the PL peak energy of GaNyAs1−x−yBix alloy decreased with increasing GaBi and GaN molar fractions. The redshift coefficients of ∼62meV∕%Bi and ∼130meV∕%N at the PL peak energy of GaNyAs1−x−yBix were observed at room temperature. The temperature dependence of the PL peak energy in the temperature range of 150–300K is much smaller than the temperature dependence of the band gap of InGaAsP. The temperature coefficients of GaAs1−xBix and GaNyAs1−x−yBix band gaps are governed by the GaBi molar fraction and they decrease with increasing GaBi molar fraction. GaNyAs1−x−yBix alloys with different PL peak energies and lattice matched to GaAs substrates were obtained. The photoluminesc...

Monolithic integrated coherent receiver on InP substrate

The fabrication of a monolithic integrated coherent receiver with a wavelength-tunable DFB laser as local oscillator, a 3-dB waveguide directional coupler for mixing, and p-i-n photodiodes for detection is discussed. Optical heterodyne detection with a clear beat signal was experimentally observed using this monolithic integrated coherent receiver. Since an n-type substrate was used in this device, the two p-i-n photodiodes were not implemented in a balanced mixer configuration. Balanced mixing might be possible if the same structure were fabricated on a semi-insulating substrate. The results obtained suggest the possibility of applying this type of monolithic integrated coherent receiver to optical communication systems.<<ETX>>

GaInAsP lateral current injection lasers on semi-insulating substrates

GaInAsP lateral current injection lasers have been fabricated on semi-insulating InP substrates. The lasers exhibit good lasing characteristics such as 10 mA threshold current, 10 mW maximum cw output power, and cw oscillation up to 70/spl deg/C. The laser has very low capacitance of 0.5 pF at zero bias voltage. This performance shows, for the first time, that the lateral current injection laser is a promising candidate for OEIC light sources.<<ETX>>

New III-V Compound Semiconductors TlInGaP for 0.9 μm to over 10 μm Wavelength Range Laser Diodes and Their First Successful Growth

New III–V compound semiconductors TlInGaP (thallium indium gallium phosphide) lattice-matched to InP are proposed for 0.9 µm to over 10 µm wavelength range laser diodes and their first successful growth is reported by gas-source molecular beam epitaxy. A type-I band lineup and a larger band discontinuity in the conduction band than in the valence band are expected for their heterostructures. They also have the potential to exhibit a temperature-independent band-gap energy (wavelength), which is promising for the fabrication of lasers that can be used in wavelength division multiplexing (WDM) optical fiber communication. Grown layers exhibit (2×4) surface reconstruction and have mirror-like surfaces. Phase separation is not observed in this material system by X-ray diffraction measurement.

GaxIn1−xP liquid phase epitaxial growth on (100) GaAs substrates

We have performed Gax In1−xP liquid phase epitaxial (LPE) growth on (100) GaAs substrates at a growth temperature of 785 °C. The P atom fraction in the growth melts was kept constant every LPE growth run. The lattice mismatch Δa⊥/a0 between the Gax In1−xP layer and GaAs substrate normal to the wafer surface and photoluminescence (PL) of the alloy layer were measured. It was found that Δa⊥/a0 and the PL peak energy vary linearly from +0.47 to −0.13% and from 1.869 to 1.921 eV at room temperature, depending on the Ga atom fraction in the growth melts, respectively. This means that the so‐called composition pulling phenomenon does not occur in LPE growth of Gax In1−xP on (100) GaAs substrates.