Composition dependence of interband transition intensities in GaPN, GaAsN, and GaPAs alloys
- National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)
Using large (512-atom) pseudopotential supercell calculations, we have investigated the composition dependence of the momentum matrix element M{sub v,c} for transitions between the valence-band maximum and the conduction-band minimum of three semiconductor alloys: GaP{sub 1{minus}x}N{sub x} and GaAs{sub 1{minus}x}N{sub x}, exhibiting large chemical and size differences between their alloyed elements, and GaP{sub 1{minus}x}As{sub x}, which is a weakly perturbed alloy. In the composition ranges where these alloys have a direct band gap, we find that (i) in GaP{sub 1{minus}x}As{sub x}, M{sub v,c} is large (like the virtual-crystal value) and nearly composition independent; (ii) in GaAs{sub 1{minus}x}N{sub x}, M{sub v,c} is strongly composition dependent: large for small x and small for large x; and (iii) in GaP{sub 1{minus}x}N{sub x}, M{sub v,c} is only slightly composition dependent and is significantly reduced relative to the virtual-crystal value. The different behavior of GaP{sub 1{minus}x}As{sub x}, GaP{sub 1{minus}x}N{sub x}, and GaAs{sub 1{minus}x}N{sub x} is traced to the existence/absence of impurity levels at the dilute alloy limits: (a) there are no gap-level impurity states at the x{r_arrow}1 or x{r_arrow}0 limits of GaP{sub 1{minus}x}As{sub x}, (b) an isolated As impurity in GaN (GaN{underscore}:As) has a deep band gap impurity level but no deep impurity state is found for N in GaAs, and (c) GaN{underscore}:P exhibits a P-localized deep band-gap impurity state and GaP{underscore}:N has an N-localized resonant state. The existence of deep levels leads to wave-function localization in real space, thus to a spectral spread in momentum space and to a reduction of M{sub v,c}. These impurity levels are facilitated by atomic relaxations: unrelaxed GaN{underscore}:As and GaN{underscore}:P, show no deep levels, have extended wave functions, and have large interband transition elements. {copyright} {ital 1997} {ital The American Physical Society}
- Research Organization:
- National Renewable Energy Laboratory
- DOE Contract Number:
- AC36-83CH10093
- OSTI ID:
- 550386
- Journal Information:
- Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 16 Vol. 56; ISSN PRBMDO; ISSN 0163-1829
- Country of Publication:
- United States
- Language:
- English
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