Free-carrier generation in amorphous semiconductors by intense subgap excitation

Abstract

Photoconduction spectra in three amorphous semiconductors have been measured as a function of light intensity. In As2S3, shrinkage of photoconductive response peak from 2.7 to 2.0 eV occurs with an increase in the light intensity from 10−3 to 108 W/cm2. In a-Si:H, intense illumination just enhances photocurrents, and intermediate features appear in As2Se3. The anomalous red shift of the photoconduction spectrum discovered in As2S3 can be accounted for as arising from a wide valence-band tail and slow hole transport.

Photo-induced phenomena in chalcogenide glasses

“…How can we interpret such spectral intensity dependence? Tanaka (2000Tanaka ( , 2003a has proposed a model, which is consistent with marked photocurrents (Tanaka, 1998) and structural modifications (Tikhomirov et al, 2006) in As 2 S 3 under intense Urbach-edge light. We assume that the Urbach edge is governed by localized states, reflecting spatial fluctuation of inter-molecular (layer) distances, above the valence band.…”

Optical and Electrical Characterization of Hydrogen-Plasma-Damaged Silicon Surface Structures and Its Impact on In-line Monitoring

“…Two factors are considered for this mechanism. One is an increase in the number of carrier trap sites [27][28][29][30][31][32][33][34][35][36][37] (Si dangling bonds 8,38) ). The other is an increase in the thickness of the SiO 2 overlayer.…”

Transient Absorption in As2Se3and Ag(Cu)-Doped As2Se3Glasses Photoinduced at 1.06 µm

“…Considering the following reasons as well as imperceptible photocurrent, we conclude that the origin of the CNL at 1.064 mm is not the free-carrier effect. The free-carrier recombination lifetime of As 2 Se 3 glass reported to date is 50 -100 ns 14) or 4 ms, 18) which are much shorter than the measured response time of 15 ms. A simple free-carrier or Drude's model indicates that the refractive index change is always negative ( r < 0) and the absorption change is positive ( ab > 0). 19) In the case of crystalline Si, 10) we actually had r < 0 and ab > 0 at 1.064 mm (see Table I) and were able to explain the nonlinearity by the model.…”

“…In fact, it has been reported that a red shift of the photoconduction spectrum is observed in As 2 S 3 and As 2 Se 3 glasses under intense light excitation, i.e., the photoconduction can take place even at sub-gap wavelengths. 14) Therefore, we must reconsider the possibility of free-carrier effects as the origin of the CNL. In this work, we investigate the relaxation of photoinduced absorption and the generation of photocurrent in As 2 Se 3 and Ag(Cu)-doped As 2 Se 3 glasses under intense excitation at 1.064 mm and discuss the origin of the CNL.…”

“…Although the sensitivity can be improved by averaging over many oscilloscope traces, as described in ref. 14, we did not attempt to improve it. The sample's gap was illuminated using the pulsed laser beam shown in Fig.…”