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Electrical properties and deep traps spectra of N-polar and Ga-polar AlGaN films grown by molecular beam epitaxy in a wide composition range

The authors have examined the dependence of phase separation in thick layers (1 μm) of molecular beam epitaxially grown, thermodynamically metastable Ga(0.25)In(0.75)As(0.22)Sb(0.78) and unstable Ga(0.50)In(0.50)As(0.44)Sb(0.56) alloys on growth kinetics and strain. For the metastable alloy, which emits at 2.8 μms, they found that phase separation does not occur for any growth temperature, and the alloy grows stoichiometrically, with step flow growth and with high optical output at around 400 °C and 440–480 °C. Moreover, optical quality is robust for alloys grown up to 30 times the critical thickness, with evidence of some improvement for compressive strain. Remarkably, no relaxation of layers occurs, as evidenced in atomic force microscopy or reciprocal space maps up to 12 times the critical thickness. The unstrained unstable alloy, which emits at 3.9 μms, can be grown with optimal optical output and a low degree of phase separation by limiting adatom diffusion length with lower temperature growth (400–440 °C) than metastable alloy. At 450 °C and hotter, severe spinoidal decomposition occurs; however, the authors show that compressive strain may be employed to dramatically suppress phase separation.

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Thick 2 um Ga1-xInxAsySb1-y layers lattice-matched to (100)-GaSb were grown by molecular beam epitaxy across the compositional range x = 0 to 1. By lowering the growth temperature to the 410 – 450 C range, phase separation was suppressed throughout the miscibility gap, as evidenced in measurements such as photoluminescence, high-resolution x-ray diffraction, atomic force microscopy, and cross-sectional transmission electron microscopy. Bright photoluminescence was recorded in the sample series ranging from 1.7 to 4.9 ums.

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