Molecular beam epitaxy of AlInAsSb alloys near the miscibility gap boundary

For many years, mid-infrared (2-5μm) semiconductor lasers operating at or near room temperature have been sought for use in LADAR, gas sensing, and spectroscopy. Smaller bandgap materials necessary for this range are more susceptible to non-radiative Auger recombination. Further, as laser structures become more complicated, like quantum cascade intersubband and interband lasers, Shockley-Read-Hall losses increase. The simplest structure is Type-I multiple quantum well (MQW), but few QW III-V heterojunction material systems capable of 2-5μm emission have a Type-I offset. One such system with InAsSb wells and AlInAsSb barriers has been unable to exceed 175K under CW operation partially due to poor carrier confinement associated with small valence band offsets. This paper describes the growth and performance of AlInAsSb/InAsSb lasers using a 0.3 mole fraction of Al in the Group III elements. Increased Al content enhances the valence and conduction band offsets, but the AlInAsSb alloy exhibits a miscibility gap above 0.06 Al mole fraction, so a digital alloy technique was used to grow high quality 0.3-2μm thick quaternary films. As Al mole fraction in the barriers was increased from 0.20 to 0.30 an 80-fold increase in photoluminescence (PL) was observed. The corresponding lasers were grown and tested demonstrating lasing at 3.9μm and 50K. Theoretical studies suggest that adding Ga to the barriers, forming an AlGaInAsSb quinary alloy, results in band structures more favorable towards minimizing Auger effects and realizing Type I offset behavior over a wider range of alloy compositions. PL structures were grown and tested, again using a digital alloy technique for the quinary alloy. Preliminary results show promise.

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Type I mid-infrared MQW lasers using AlInAsSb barriers and InAsSb wells

As one of the few Type I band offset, antimony-based material systems available for 3.3 to 4.2 micron mid-infrared multiple quantum well lasers, AlInAsSb alloys have been used as barriers with InAsSb wells. Previously, AlxIn(1-x)AsySb(1-y) quaternary alloys have been grown by MBE as random alloys up to an aluminum fraction, x = 0.10 on GaSb substrates and x = 0.15 on InAs substrates. Random alloy growth of quaternary films with increased aluminum content, although beneficial to the devices, is limited by a miscibility gap. We have used a digital alloy technique to grow stable, single phase, GaSb lattice-matched, optically smooth quaternary alloys for aluminum fractions of 0.05 to 0.5, well into the miscibility gap. DCXRD results show FWHM of 0th order alloy peaks are within 1.5 to 2 times that of the highly crystalline GaSb substrates and have well defined thickness fringes corresponding to the total film thickness and the digital alloy period. TEM images show very well ordered alloys with characteristic ultrathin superlattice structure having smooth interfaces, very little strain and atomic ordering limited to that imposed by the digital alloy technique. Photoluminescence measurements are used to fit a model for bandgap prediction from known alloy compositions. Theoretical studies have predicted that the addition of a fifth element, gallium, may help suppress Auger recombination through its effects on the subband structure. So, gallium is added to the quaternary to produce a quinternary alloy lattice-matched to GaSb. These AlGaInAsSb alloys have DCXRD and TEM results similar to the quaternary. The stable, single-phase growth of these quinternary alloys across the composition range is promising for improving the operating characteristics of mid-IR lasers.

Characterization of AlInAsSb and AlGaInAsSb MBE-grown Digital Alloys

MBE growth of InAs/InAsSb/InAlAsSb “W” quantum well laser diodes emitting near 3μm

Effect of molecular beam epitaxy growth conditions on phase separation in wide-bandgap InAlAsSb lattice-matched to InP

Al1−xInxAs1−ySby epilayers and Al1−xInxAs1−ySby/GaSb multilayers (0.5⩽y⩽1.0) have been grown by molecular beam epitaxy on GaSb (100) substrates as part of an investigation for potential use of this material’s system as kinetic heterojunctions (KHJs). Viable KHJ’s require lattice matching and a zero-conduction-band offset to GaSb, necessitating a high degree of compositional control. Therefore, a detailed study of the growth of Al1−xInxAs1−ySby epilayers has been conducted. Synthesis of the arsenide/antimonide quaternary system is problematic due to the miscibility gap throughout the composition range, therefore, the compositional dependence on the Sb:As flux, Sb:In flux, and substrate temperature has been studied. In situ reflection high-energy electron diffraction was used to monitor the surface reconstruction during growth. Crystalline quality and composition of single layer and multilayer samples have been determined by double-crystal x-ray diffraction and electron dispersion spectroscopy. Hall-effect ...

U. Kirschbaum

Papers

Al1−xInxAs1−ySby/GaSb heterojunctions and multilayers grown by molecular beam epitaxy for effective-mass superlattices