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Time-Resolved Reflectivity Studies of Electric Field Effects in III-Nitride Semiconductors

Published online by Cambridge University Press:  01 February 2011

M. Wraback ,
H. Shen ,
A. V. Sampath ,
C. J. Collins ,
G. A. Garrett ,
W. L. Sarney ,
Y. Fedyunin ,
J. Cabalu  and
T. D. Moustakas
M. Wraback
Affiliation:
U.S. Army Research Laboratory, Sensors and Electron Devices Directorate, AMSRD-ARL-SE-EM, 2800 Powder Mill Road, Adelphi, MD 20783
H. Shen
Affiliation:
U.S. Army Research Laboratory, Sensors and Electron Devices Directorate, AMSRD-ARL-SE-EM, 2800 Powder Mill Road, Adelphi, MD 20783
A. V. Sampath
Affiliation:
U.S. Army Research Laboratory, Sensors and Electron Devices Directorate, AMSRD-ARL-SE-EM, 2800 Powder Mill Road, Adelphi, MD 20783
C. J. Collins
Affiliation:
U.S. Army Research Laboratory, Sensors and Electron Devices Directorate, AMSRD-ARL-SE-EM, 2800 Powder Mill Road, Adelphi, MD 20783
G. A. Garrett
Affiliation:
U.S. Army Research Laboratory, Sensors and Electron Devices Directorate, AMSRD-ARL-SE-EM, 2800 Powder Mill Road, Adelphi, MD 20783
W. L. Sarney
Affiliation:
U.S. Army Research Laboratory, Sensors and Electron Devices Directorate, AMSRD-ARL-SE-EM, 2800 Powder Mill Road, Adelphi, MD 20783
Y. Fedyunin
Affiliation:
ECE Department, Photonics Center, Boston University, 8 St. Mary's Street, Boston MA, 02215
J. Cabalu
Affiliation:
ECE Department, Photonics Center, Boston University, 8 St. Mary's Street, Boston MA, 02215
T. D. Moustakas
Affiliation:
ECE Department, Photonics Center, Boston University, 8 St. Mary's Street, Boston MA, 02215
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Abstract

Comparison of room temperature, frequency degenerate and nondegenerate femtosecond pump-probe reflectivity measurements reveal an additional component in the transient reflectivity (ΔR) decays for near bandgap probe in GaN that is attributed to a reduction of bandedge broadening due to screening of internal electric fields by photogenerated carriers. Pump-probe measurements with pulses spectrally centered at 363 nm show a ΔR component with a nanosecond decay time that is essentially absent from data obtained from nondegenerate experiments performed under identical pumping conditions, but with a probe at 385 nm far enough from the bandedges to minimize the electric field contribution and monitor primarily the carrier lifetime in the band states. The observation of significantly shorter decay times for 385 nm probe suggests that the carriers leave the band states on a picosecond time scale, but the slow decay of the field screening observed with 363 nm probe implies that they recombine from trap states at longer times. In addition, this field screening provides a mechanism for generation and detection of strain pulses in strained GaN and AlGaN epilayers that is used to measure the longitudinal sound velocity in bulk GaN and AlGaN with up to 0.4 Al content.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 798: Symposium Y – GaN and Related Alloys , 2003 , Y6.10
Copyright
Copyright © Materials Research Society 2004

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References

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