Monolayer-by-monolayer compositional analysis of InAs/InAsSb superlattices with cross-sectional STM

Abstract

a b s t r a c tWe use cross-sectional scanning tunneling microscopy (STM) to reconstruct the monolayer-bymonolayer composition profile across a representative subset of MBE-grown InAs/InAsSb superlattice layers and find that antimony segregation frustrates the intended compositional discontinuities across both antimonide-on-arsenide and arsenide-on-antimonide heterojunctions. Graded, rather than abrupt, interfaces are formed in either case. We likewise find that the incorporated antimony per superlattice period varies measurably from beginning to end of the multilayer stack. Although the intended antimony discontinuities predict significant discrepancies with respect to the experimentally observed high-resolution x-ray diffraction spectrum, dynamical simulations based on the STM-derived profiles provide an excellent quantitative match to all important aspects of the x-ray data.

Measurement of InAsSb bandgap energy and InAs/InAsSb band edge positions using spectroscopic ellipsometry and photoluminescence spectroscopy

“…[23][24][25][26] Therefore, to evaluate the impact of unintentional Sb in the InAs layer, the X-ray diffraction data are further analyzed using a model with a small amount of Sb in the InAs layer. Under the strain-balanced condition, this results in a reduced level of tensile strain in the InAs layer and corresponding larger reduction in the compressive strain of the InAsSb layer that is typically not as thick as the InAs layer.…”

Time-resolved measurements of charge carrier dynamics in Mwir to Lwir InAs/InAsSb superlattices

“…In InAs binary alloy, it forms as the antibonding A 1 state and is about 30 meV below the conduction band edge of InAs which holds the same position in strain. This state is within 4 meV of the reported SRH recombination The Sb A s antisites related to the Sb diffusion at the SL interfaces could cause localized defect states, however, the energy level of these antisites is more than an eV below the InAs valence band edge[97].4.3.2.2 Radiative RecombinationThe calculated radiative coefficients are in range of 1.5 − 3× 10 −10 cm 3 /s for the samples with 30 % and 40 % Sb content in their alloy layers at 77 K. These coefficients gradually decrease to 2 − 5× 10 −11 cm 3 /s at 200 K. The radiative recombination coefficients of all the InAs/InAsSb T2SLs examined in this sample set, were found to be essentially insignificant at high excess carrier densities for the temperatures ranging[49], low surface leakage[98], and high material quality[13], they unfortunately suffer from relatively high Auger recombination rates[9,22,45]. For materials that are not limited by Shockley-Read-Hall (SRH) recombination, intrinsic Auger recombination rates typically define a photodetectors maximum attainable carrier lifetime and, hence best case dark diffusion current[99].…”

“…Another important advantage is that the band splitting in valence and conduction bands eliminates the final states for Auger processes, leading to a smaller Auger coefficient. [13,20,105]. The measurement of local Sb compositional profiles across the superlattices using electron energy-loss spectroscopy and 002 dark-field imaging revealed asymmetric Sb distribution, with the InAs-on-InAsSb interface being chemically graded.…”

“…Another consideration was Sb diffusion from the InAsSb into the InAs layers, which would produce more pronounced effects in the high-Sb alloy content samples, especially for samples with thinner SL periods. An estimated 2-3 % Sb diffusion from the InAsSb to InAs layer was observed using TEM measurements by Wood et al [13] for 200 nm SL period samples with 35 % Sb content in their alloy layers. When the Sb alloy content decreases, Sb diffusion into the InAs layer is expected to decrease as well.…”

“…1.1, the MWIR and LWIR wavelength ranges are indicated and will be associated with narrow bandgap semiconductors in this dissertation. In the past two decades, enormous progress has been made towards development of IR detectors with Ga-free materials [4][5][6][7][8][9][10][11][12][13][14][15][16]. This progress resulted in orders-of-magnitude reduction in detector dark-current density, a substantial increase in quantum efficiency (QE), and minority carrier (MC) lifetime, as well as the demonstration of high-quality MWIR and LWIR infrared FPAs.…”