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Identification of Carbon-related Bandgap States in GaN Grown by MOCVD

Published online by Cambridge University Press:  01 February 2011

A. Armstrong ,
A. R. Arehart ,
S. A. Ringel ,
B. Moran ,
S. P. DenBaars ,
U. K. Mishra  and
J. S. Speck
A. Armstrong
Affiliation:
Department of Electrical Engineering, The Ohio State University, Columbus, OH 43210
A. R. Arehart
Affiliation:
Department of Electrical Engineering, The Ohio State University, Columbus, OH 43210
S. A. Ringel
Affiliation:
Department of Electrical Engineering, The Ohio State University, Columbus, OH 43210
B. Moran
Affiliation:
Materials Department and Electrical and Computer Engineering Department, University of California, Santa Barbara, CA 93016
S. P. DenBaars
Affiliation:
Materials Department and Electrical and Computer Engineering Department, University of California, Santa Barbara, CA 93016
U. K. Mishra
Affiliation:
Materials Department and Electrical and Computer Engineering Department, University of California, Santa Barbara, CA 93016
J. S. Speck
Affiliation:
Materials Department and Electrical and Computer Engineering Department, University of California, Santa Barbara, CA 93016
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Abstract

Carbon doping of GaN is of great interest in part because it has been shown to result in semi-insulating (SI) behavior. However, determination of the bandgap states and hence the exact mechanism responsible for the SI behavior is, to date, an unresolved issue. A key impediment is that the presumed C acceptor levels are likely near the minority carrier (valence) bandedge of otherwise background n-type GaN, and hence their precise detection by usual methods is difficult. In this paper, we exploit the inherent ability of deep level optical spectroscopy (DLOS) to detect states near the minority carrier band edge, as well as potentially deep states associated with C in background n-type GaN. This is accomplished by comparing unintentionally doped (uid) GaN grown by atmospheric pressure (AP) MOCVD, which has residual n-type conductivity, with LP MOCVD GaN that incorporates a large concentration of C for both uid and intentionally Si co-doped conditions. The results show the emergence of a shallow state at Ec - 3.28 eV (Ev + 0.16 eV) for the LP samples with a minimum concentration of 3.6 × 1016 cm-3 that efficiently compensates Si donors for the co-doped sample, and results in semi-insulating behavior for the uid-LP sample. In contrast, this state is not observed for the AP GaN material, which incorporates a factor of ∼10 times less C, and instead only the expected residual Mg acceptor level at Ec - 3.22 eV is observed. Additionally, a state at Ec - 1.35 eV, near the theoretically expected C split-interstitial level in n-type GaN, is observed to increase significantly in concentration with increased C concentration.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 798: Symposium Y – GaN and Related Alloys , 2003 , Y5.38
Copyright
Copyright © Materials Research Society 2004

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References

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