UV Laser Photocarrier Radiometry of c-Silicon with Surface Thin Hydrogenated Amorphous Si Film

Abstract

Photocarrier radiometry (PCR) with 355 nm laser excitation was used for the study of c-Si covered with intrinsic thin hydrogenated amorphous Si (i-a-Si:H) on one, or both, sides, with thicknesses ranging from 10 nm to 90 nm. Short wavelength excitation allows one to resolve the contribution of the upper i-a-S layer to the PCR signal due to the very small absorption depth (tens of nm) of the excitation beam. As a result, fundamental transport parameters of the composite structure can be evaluated from the PCR frequency dependence. A theoretical model has been developed to describe the diffuse carrier density wave (CDW) in this two-layer system. The model of the one-dimensional CDW fields for composite electronic solids involves front, interface, and back surface recombination velocities, the diffusion coefficient, recombination lifetimes in the upper and lower layers, and the unoccupied trap density at the interface. Simulations of the transport parameter influence on the PCR signal were performed, and the theoretical model was able to describe the experimental data accurately, therefore, making it possible to evaluate the transport parameters of i-a-Si:H and c-Si as well as to elucidate the role of interface electronic traps in the PCR frequency dependence under short wavelength excitation.