Femtosecond response of a free-standing LT-GaAs photoconductive switch.
We present a novel, free-standing low-temperature GaAs (LT-GaAs) photoconductive switch and demonstrate its femtosecond performance. A 1-microm-thick layer of a single-crystal LT-GaAs was patterned into 5-10-microm-wide and 15-30-microm-long bars, separated from their GaAs substrate and, subsequently, placed across gold coplanar transmission lines deposited on a Si substrate, forming a photoconductive switch. The switch was excited with 110-fs-wide optical pulses, and its photoresponse was measured with an electro-optic sampling system. Using 810-nm optical radiation, we recorded an electrical transient as short as 360 fs (1.25 THz, 3-dB bandwidth) and established that the photo-carrier lifetime in our LT-GaAs was 150 fs. Our free-standing devices exhibited quantum efficiency of the order of approximately 7%, and their photoresponse amplitude was a linear function of the applied voltage bias, as well as a linear function of the excitation power, below a well-defined saturation threshold.
Zheng
Xuemei
X
Department of Electrical and Computer Engineering and the Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14627-0231, USA. xuzheng@ece.rochester.edu
Xu
Ying
Y
Sobolewski
Roman
R
Adam
Roman
R
Mikulics
Martin
M
Siegel
Michael
M
Kordos
Peter
P