Characterization of AlInAsSb and AlGaInAsSb MBE-grown Digital Alloys
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Characterization of AlInAsSb and AlGaInAsSb MBE-grown Digital Alloys Leslie G. Vaughn1, L. Ralph Dawson1, Huifang Xu, Yingbing Jiang and Luke F. Lester1 Earth and Planetary Science Department, University of New Mexico, Albuquerque, NM 87131 1 Center for High Technology Materials, University of New Mexico, 1313 Goddard SE, Albuquerque, NM 87106, U.S.A. ABSTRACT 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. INTRODUCTION The search for materials systems that will produce high power, room temperature midinfrared (IR) semiconductor diode lasers operating between 2 and 5 microns has been of particular interest over the last 15 years. Potential applications include field communications and laser radar, pollution monitoring, remote toxic gas sensing and molecular spectroscopy. There are some inherent challenges to achieving this goal. Longer wavelength materials have smaller bandgaps and are more susceptible to Auger recombination, so must be operated well below room temperature to decrease the probability of this multi-step process. Further, most of the materials systems capable of this wavelength range have a Type II or broken band offset, leading to lower efficiencies than Type I or nested band offset systems. AlInAsSb/InAsSb is one of the few materials systems with a predicted Type I band offset. Results o
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