Diffusion length of holes in a-Si:H by the surface photovoltage method

Abstract

The diffusion length L for holes in undoped a-Si:H films has been measured by using a variation of the surface photovoltage method. Values of L in the range 0.33–0.45 μ were found for samples prepared at substrate temperatures Ts = 240 °C and Ts = 330 °C. After prolonged illumination, a reduction to L<0.2 μ was observed; the original value of L was restored after annealing at 200 °C.

Surface photovoltage phenomena: theory, experiment, and applications

“…The purpose of the latter was to shrink w to the range where L ) w is valid [465,469,471]. Except in the very ®rst SPV-based L measurement of a-Si:H [464], L app was indeed found to decrease with increasing photo-bias, as shown in Fig. 66, typically saturating at $1 sun illumination.…”

“…Some relatively recent applications may be found in [435,436,453± 463]. Speci®cally, throughout the 1980s and early 1990s, much attention has been devoted to a-Si:H. These studies were pioneered by Dresner, Goldstein, and Szostak [464], and were followed by many other research groups [304,465±485]. Measurements of a-Si:H are presented in Section 5.1.3 as part of the discussion of the limitations of the SPV approach.…”

“…In addition, long surface-state-related transients following illumination may cause similar effects. For example, in the ®rst a-Si:H diffusion length SPV studies, slow surface trapping effects precluded chopped light measurements and a Kelvin probe was used [464,471,473].…”

Stability and electronic properties of amorphous silicon p-i-n devices fabricated using ECR plasma enhanced chemical deposition

“…ESR measurements show that during illumination the dangling bond density increases from low starting value of about 10^^ cm"3 up to values of about 10^^ cm*^ and thus reduces the minority carrier diffusion length [21].…”

Electron spin-lattice relaxation in hydrogenated amorphous semiconductors

“…Although the Staebler-Wronski effect reduces the recombination lifetime [48], it is not a significant problem at present as far as the stability of a-Si:H solar cells is concerned. The shelf life of a-Si:H solar cells appears to be excellent even when unencapsulated [49].…”