Conduction and valence band states for the highly mismatched alloy (HMA) Ge:C are projected onto Ge crystal states, Ge vacancy states, and Ge/C atomic orbitals, revealing that substitutional carbon not only creates a direct bandgap but also the new conduction band is optically active. Overlap integrals of the new Ge:C conduction band state with states from unperturbed Ge show that the new band cannot be attributed to any single Ge band but is a mixture of multiple Ge states. The Ge Γ conduction band valley state plays the largest single role, but L and X valley states collectively contribute a larger share than Γ due to the multiplicity of degenerate states. C sites structurally resemble uncharged vacancies in the Ge lattice, similar to Hjalmarson's model for other HMAs. C also perturbs the entire Ge band structure even at the deepest crystal core energy levels, particularly if staggered supercells are used to mimic a disordered alloy. Projection onto atomic sites shows a relatively weak localization compared with other HMAs, but it does show a strong anisotropy in probability distribution. L-valley conduction band states in Ge contribute to the conduction band minimum in Ge:C, but the optical transition strength in Ge:C remains within a factor of 2 of the direct gap transition in Ge.
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7 February 2021
Research Article|
February 02 2021
The carbon state in dilute germanium carbides
Special Collection:
Highly Mismatched Semiconductors Alloys: from Atoms to Devices
Istvan A. Gulyas
;
Istvan A. Gulyas
1
Department of Physics, Texas State University
, San Marcos, Texas 78666, USA
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Chad A. Stephenson
;
Chad A. Stephenson
b)
2Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA
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Qian Meng
;
Qian Meng
3Electrical & Computer Engineering Department,
University of Texas at Austin
, Austin, Texas 78705, USA
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Seth R. Bank
;
Seth R. Bank
3Electrical & Computer Engineering Department,
University of Texas at Austin
, Austin, Texas 78705, USA
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Mark A. Wistey
Mark A. Wistey
a)
1
Department of Physics, Texas State University
, San Marcos, Texas 78666, USA
a)Author to whom correspondence should be addressed: [email protected]
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a)Author to whom correspondence should be addressed: [email protected]
b)
Present address: Sandia National Laboratory, Albuquerque, NM 87185.
Note: This paper is part of the Special Topic on Highly Mismatched Semiconductors Alloys: from Atoms to Devices.
J. Appl. Phys. 129, 055701 (2021)
Article history
Received:
June 10 2019
Accepted:
January 09 2021
Citation
Istvan A. Gulyas, Chad A. Stephenson, Qian Meng, Seth R. Bank, Mark A. Wistey; The carbon state in dilute germanium carbides. J. Appl. Phys. 7 February 2021; 129 (5): 055701. https://doi.org/10.1063/1.5112057
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