Order and Disorder in Type–II InAs/InAsSb Superlattices
Abstract
We employ cross–sectional scanning tunneling microscopy (STM) to examine
how an as–grown InAs/InAsSb superlattice differs from the intended one as regards
translational invariance in (001) planes perpendicular to the growth direction. This
requires atomic–resolution, lateral surveys paralleling the buffer/epilayer interface for up
to a micron in orthogonal (–1–10) or (1–10) cross sections, together with repeated lateral
surveys at representative vertical locations (i.e., spanned superlattice repeats) within the
multilayer stack.
We show that STM may be used to accurately map the period fluctuations
throughout this superlattice. The concept, analogous to Bragg's law in high–resolution
x–ray diffraction, relies on an analysis of the [001]–convolved reciprocal–space satellite
peaks obtained from discrete Fourier transforms of individual STM images. Properly
implemented, the technique enables local period measurements that reliably discriminate
lateral fluctuations localized to within ~ 40 nm along <110> directions in the growth
plane. While not as accurate as x–ray, the inherent, single–image measurement error
associated with the method may be made as small as 0.1%, allowing the lateral period
fluctuations contributing to inhomogeneous energy broadening and carrier localization in
these structures to be pinpointed and quantified. The direct visualization of
unexpectedly–large fluctuations on nanometer length scales is tied to a stochastic
description of correlated interface roughness.
We also introduce a new technique to automatically tabulate the crystalline
coordinates of previously–identified top–layer antimony atoms and construct the
antimony pair–correlation functions for orthogonal cross sections. Nearest–neighbor
correlations on opposing cleavage faces are inversely related, with the (–1–10) deficit at
nearest–neighbor sites balanced by a compensating (1–10) surplus. The logarithm of this
preference scales inversely with bulk antimony fraction. In more vivid physical terms,
the preferential [110]–incorporation of nearest–neighbor antimony atoms in the bulk is
traced to the inferred concentration of [110]–oriented antimony dimers at the growth
surface
Subject
Cross–Sectional ScanningTunneling Microscopy
III–V
Semiconductor
Superlattice
Alloy Order
Interface Roughness
Citation
Wood, Matthew R (2017). Order and Disorder in Type–II InAs/InAsSb Superlattices. Doctoral dissertation, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /173176.