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1Space-and-time current spectroscopy of high-resistive photoconductors: techniques and applications
M.A. Bryushinin*, I.A. Sokolov
Ioffe Institute, St. Petersburg, Russia
Space charge distributions define operation of the most photonic and electronic devices. Space-and-time current spectroscopy is one of the holography-related techniques for the investigation of space charge evolution in wide-bandgap semiconductors - functional materials for photonics and electronics. The technique is based on the so-called effect of non-steady-state photo-EMF, but not restricted by its classical realization. The effect manifests itself as an alternating electric current arising in a semiconductor illuminated by an oscillating interference pattern. The current is resulted from the interaction of the photoconductivity and space-charge field gratings (Fig. 1); and the signal amplitude is defined by the drift component of this current 0.
Lock-in voltmeter,
Laser
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P(x,t)
Esc(x,t)
Sample
Jdr
. A=2rn/K
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Jdr-
Fig. 1. Experimental setup for the investigation of non-stedy-state photo-EMF (on the left) and distributions of the light intensity, photoconductivity, space-charge density and electric field producing the electric current (on the right).
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We present characterization of a wide group of photoconductive and photorefractive materials, such as Bii2SiO20, SnS2, AlN, Ga2O3, etc. The main photoelectric parameters, such as the type and value of specific photoconductivity, its relaxation time, diffusion length of carriers are extracted from dependencies of the photo-EMF signal versus light intensity, spatial and temporal frequencies. Several advanced techniques related to the conventional non-steady-state photo-EMF, namely, the combined excitation of running space-charge and photoconductivity gratings, photo-EMF excitation by the frequency-modulated light are demonstrated as well. We briefly present applications of the non-steady-state photo-EMF and its variety for detection of phase- and frequency modulated optical signals, including laser-based adaptive vibrometry.
[1] S. Stepanov, in Handbook of Advanced Electronic and Photonic Materials and Devices, Vol. 2, edited by H.S. Nalwa (Academic Press) pp. 205-272, (2001).
[2] I.A. Sokolov and M.A. Bryushinin, Optically induced space-charge gratings in wide-bandgap semiconductors: techniques and applications (Nova Science Publishers, Inc., 2017).
