III-(As, Sb) alloys are building blocks for various advanced optoelectronic devices, but the growth of their ternary or quaternary materials are commonly limited by spontaneous formation of clusters and phase separations during alloying. Recently, digital alloy growth by molecular beam epitaxy has been widely adopted in preference to conventional random alloy growth because of the extra degree of control offered by the ordered alloying. In this article, we provide a comparative study of the optical characteristics of AlAsSb alloys grown lattice-matched to GaSb using both techniques. The sample grown by digital alloy technique showed stronger photoluminescence intensity, narrower peak linewidth, and larger carrier activation energy than the random alloy technique, indicating an improved optical quality with lower density of non-radiative recombination centers. In addition, a relatively long carrier lifetime was observed from the digital alloy sample, consistent with the results obtained from the photoluminescence study.

The strain-mediated evolution of epitaxial ZnTe/ZnSe quantum structures is studied at the atomic scale using spherical aberration-corrected scanning transmission electron microscopy, coupled with electronic properties characterized by photoluminescence spectroscopy. The growth development of these buried quantum dots clearly demonstrates a homogeneous profile with similar pyramidal geometry rather than bi-modal distribution; contradicting prior reports on ZnTe/ZnSe quantum dots. The result is consistent with atomistic theoretical calculations on strain distribution and electronic structure of a modeled quantum dot of similar geometry using a valence force field model. It is also found that the transition from 2-D islands to 3-D quantum dots involves thermally activated carrier transfer process and follows up with formation of extended defects at the quantum dot surface, acting as an effective source for remnant misfit strain relaxation. The new physical understanding concerning the growth of self-assembled ZnTe/ZnSe quantum dots embedded in the active regions provides important information for the measures to control the properties of buried ZnTe quantum dots, setting up a key footstep in developing novel materials of energy conversion.