Electronic structure of BAs and boride III-V alloys

Gus L. W. Hart and Alex Zunger
Phys. Rev. B 62, 13522 – Published 15 November 2000
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Abstract

Boron arsenide, the typically ignored member of the Group-III–V arsenide series BAs-AlAs-GaAs-InAs is found to resemble silicon electronically: its Γ conduction-band minimum is p-like (Γ15), not s-like (Γ1c), it has an X1c-like indirect band gap, and its bond charge is distributed almost equally on the two atoms in the unit cell, exhibiting nearly perfect covalency. The reasons for these are tracked down to the anomalously low atomic p orbital energy in the boron and to the unusually strong ss repulsion in BAs relative to most other Group-III–V compounds. We find unexpected valence-band offsets of BAs with respect to GaAs and AlAs. The valence-band maximum (VBM) of BAs is significantly higher than that of AlAs, despite the much smaller bond length of BAs, and the VBM of GaAs is only slightly higher than in BAs. These effects result from the unusually strong mixing of the cation and anion states at the VBM. For the BAs-GaAs alloys, we find (i) a relatively small (3.5eV) and composition-independent band-gap bowing. This means that while addition of small amounts of nitrogen to GaAs lowers the gap, addition of small amounts of boron to GaAs raises the gap; (ii) boron “semilocalized” states in the conduction band (similar to those in GaN-GaAs alloys); and (iii) bulk mixing enthalpies that are smaller than in GaN-GaAs alloys. The unique features of boride Group-III–V alloys offer new opportunities in band-gap engineering.

  • Received 16 June 2000

DOI:https://doi.org/10.1103/PhysRevB.62.13522

©2000 American Physical Society

Authors & Affiliations

Gus L. W. Hart and Alex Zunger

  • National Renewable Energy Laboratory, Golden, Colorado 80401

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Issue

Vol. 62, Iss. 20 — 15 November 2000

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