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International Journal of Material Science Innovations
IJMSI 2021, 11 pages - Article ID: IJMSI-2106282112360
Steady State Photo-carrier Grating (SSPG) for minority carrier diffusion length analysis in silicon thin films
a Advanced Materials & Device Metrology Division, CSIR – National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi, India 110012
b Academy of Scientific and Innovative Research (AcSIR), CSIR-NPL Campus, New Delhi, Dr. K.S. Krishnan Marg, New Delhi, India 110012
c Gautam Buddha University, Greater Noida, Uttar Pradesh, India 201312
ABSTRACT
The ambipolar diffusion length (Ld) is an estimation of the diffusion length of less mobile charge carriers (presumably holes) which determines the performance of solar cells. The Steady State Photo-carrier Grating (SSPG) technique measures ambipolar diffusion length in mobility photoconductive semiconductor films. This technique also provide access to the minority carrier transport properties as diffusion length is proportional to the product of mobility (μ) and lifetime (τ) of charge carriers. SSPG measures the interference pattern created by the superposition of two coherent laser beams (L1 and L2). A brief description of this method was presented. Furthermore, efforts were made to understand the larger attenuated intensity of the laser beam (L2) for the interference fringes can lead to large errors in the measured diffusion length. Moreover, estimation of minority carrier transport in hydrogenated amorphous silicon (a-Si:H) and micro/nano-crystalline thin film (nc-Si:H/μc-Si:H), deposited by PECVD process was carried out. The ambipolar diffusion length in a-Si:H films found to vary from 0.23 ─ 0.11 μm for different photo-gain (ï¾ 6 x 104 to 8 x 102) and in nc-Si:H/μc-Si:H vary from 0.190 ─ 0.080 μm for different crystalline fraction (43 % - 22 %). From these results, Ld were observed to be maximum for the film having high photo-gain in a-Si:H and high crystalline fraction in nc-Si:H/μc-Si:H.
SSPG; intensity of the probe laser beam; a-Si:H/ nc-Si:H/μc-Si:H thin film; ambipolar diffusion length .