Structural studies of natural superlattices in group III-V alloy epitaxial layers

Abstract

Structural studies have been performed using transmission electron microscopy and diffraction on Ill-V ternary and quaternary alloy epitaxial layers. The results revealed that 'natural superlattice' structures had spontaneously formed in some of the layers by phase separation and/or atomic ordering which occurred at the surface during growth. The structure of these natural superlattices and the growth conditions for their occurrence are described and their effect on the electrical and optical properties of the layers, e.g. bandgap narrowing, and possible mechanisms of formation are briefly discussed.

Magnetotransport and Magnetooptics of InAs1-xSbxand Heterojunctions Combinations Formed Between InAs and GaSb, AlSb Or InAs1 -xSbx

“…The ordering becomes stronger as the growth temperature is reduced, reaching a maximum at about 400°C and below about 400°C phase separation occurs. Below this temperature and for 0.3 < x < 0.7 a natural superlattice is formed during MBE growth by a form of self-assembly associated with the miscibility gap [5]. The mobilities are a strong function of growth temperature with the highest mobilities being obtained between 430°C and 470°C [6].…”

Self-organized growth of alloy superlattices

“…The possibility of "natural" superlattices has been suggested previously, based on layered structures seen in epitaxial growth of alloys that are unstable against spinodal decomposition [5]. How-ever, only one instance of well-organized growth has been reported in such systems [6], and theoretical explanations remain speculative [7,8].…”

Self-Organized Vertical Superlattices in Epitaxial GaInAsSb

“…While atomic ordering and VCM were simultaneously observed in InAsSb and GaAsSb [5], VCM without ordering was reported for GaInP [16]. The periodicity of the VCM was 10 to 12 nm.…”

“…The length scale of these ordered phases ranges from the atomic scale, e.g. CuPt ordering as observed in GaInP [2], GaAsP [3], GaAsSb, [4], and InAsSb [5], to microscopic dimensions on the order of ~50 nm, e.g. composition modulation.…”

“…The NSL period was 2 to 3 nm for both of these materials systems, and a model based on step-flow growth and local strain fields that are modulated during growth were developed to explain the phenomena [13]. In addition, InAsSb and GaAsSb [5,14] were reported to spontaneously form a periodic structure that consisted of platelets of alternating composition and periodicity on the order of 20 to 50 nm. Both InAsSb and GaAsSb exhibit miscibility gaps [15], and this larger scale modulation was attributed to the tendency for these alloys to phase separate.…”