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Title: Electronic consequences of random layer-thickness fluctuations in AlAs/GaAs superlattices

Abstract

We study the effects of a few types of atomic disorder on the electronic and optical properties of AlAs/GaAs (001) and (111) superlattices: (i) atomic intermixing across the interfaces; (ii) replacing a single monolayer in a superlattice by one containing the opposite atomic type (isoelectronic {delta} doping); and (iii) random layer-thickness fluctuations in superlattices (SL). Type (i) is an example of lateral disorder, while types (ii) and (iii) are examples of vertical disorder. Using three-dimensional empirical pseudopotential theory and a plane-wave basis, we calculate the band gaps, electronic wave functions, and optical matrix elements for systems containing up to 2000 atoms in the computational unit cell. Spin-orbit interactions are omitted. Computationally much less costly effective-mass calculations are used to evaluate the density of states and eigenstates away from the band edges in vertically disordered SLs. Our main findings are: (i) Chemical intermixing across the interface can significantly shift the SL energy levels and even change the identity (e.g., symmetry) of the conduction-band minimum in AlAs/GaAs SLs; (ii) any amount of thickness fluctuations in SLs leads to band-edge wave-function localization; (iii) these fluctuation-induced bound states will emit photons at energies below the ``intrinsic`` absorption edge (red shift of photoluminescence); (iv) monolayermore » fluctuations in thick superlattices create a gap level whose energy is pinned at the value produced by a single {delta} layer with ``wrong`` thickness; (v) (001) AlAs/GaAs SLs with monolayer thickness fluctuations have a direct band gap, while the ideal (001) superlattices are indirect for {ital n}{lt}4; (vi) there is no mobility edge for vertical transport in a disordered superlattice, because all the states are localized; however, the density of states retains some of the features of the ordered-superlattice counterpart.« less

Authors:
; ;  [1]
  1. National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
OSTI Identifier:
124285
DOE Contract Number:  
AC36-83CH10093
Resource Type:
Journal Article
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 78; Journal Issue: 11; Other Information: PBD: 1 Dec 1995
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; SUPERLATTICES; THICKNESS; ALUMINIUM ARSENIDES; EFFECTIVE MASS; ELECTRONIC STRUCTURE; ENERGY GAP; FLUCTUATIONS; GALLIUM ARSENIDES; OPTICAL PROPERTIES; RANDOMNESS

Citation Formats

Maeder, K A, Wang, L, and Zunger, A. Electronic consequences of random layer-thickness fluctuations in AlAs/GaAs superlattices. United States: N. p., 1995. Web. doi:10.1063/1.360728.
Maeder, K A, Wang, L, & Zunger, A. Electronic consequences of random layer-thickness fluctuations in AlAs/GaAs superlattices. United States. https://doi.org/10.1063/1.360728
Maeder, K A, Wang, L, and Zunger, A. 1995. "Electronic consequences of random layer-thickness fluctuations in AlAs/GaAs superlattices". United States. https://doi.org/10.1063/1.360728.
@article{osti_124285,
title = {Electronic consequences of random layer-thickness fluctuations in AlAs/GaAs superlattices},
author = {Maeder, K A and Wang, L and Zunger, A},
abstractNote = {We study the effects of a few types of atomic disorder on the electronic and optical properties of AlAs/GaAs (001) and (111) superlattices: (i) atomic intermixing across the interfaces; (ii) replacing a single monolayer in a superlattice by one containing the opposite atomic type (isoelectronic {delta} doping); and (iii) random layer-thickness fluctuations in superlattices (SL). Type (i) is an example of lateral disorder, while types (ii) and (iii) are examples of vertical disorder. Using three-dimensional empirical pseudopotential theory and a plane-wave basis, we calculate the band gaps, electronic wave functions, and optical matrix elements for systems containing up to 2000 atoms in the computational unit cell. Spin-orbit interactions are omitted. Computationally much less costly effective-mass calculations are used to evaluate the density of states and eigenstates away from the band edges in vertically disordered SLs. Our main findings are: (i) Chemical intermixing across the interface can significantly shift the SL energy levels and even change the identity (e.g., symmetry) of the conduction-band minimum in AlAs/GaAs SLs; (ii) any amount of thickness fluctuations in SLs leads to band-edge wave-function localization; (iii) these fluctuation-induced bound states will emit photons at energies below the ``intrinsic`` absorption edge (red shift of photoluminescence); (iv) monolayer fluctuations in thick superlattices create a gap level whose energy is pinned at the value produced by a single {delta} layer with ``wrong`` thickness; (v) (001) AlAs/GaAs SLs with monolayer thickness fluctuations have a direct band gap, while the ideal (001) superlattices are indirect for {ital n}{lt}4; (vi) there is no mobility edge for vertical transport in a disordered superlattice, because all the states are localized; however, the density of states retains some of the features of the ordered-superlattice counterpart.},
doi = {10.1063/1.360728},
url = {https://www.osti.gov/biblio/124285}, journal = {Journal of Applied Physics},
number = 11,
volume = 78,
place = {United States},
year = {1995},
month = {12}
}