Optimum conditions for measuring the minority carrier in semicondector wafers (Si), using a contactless photoconductive decay method were examined. The analysis ontains wafer factors detetmined by the characteristics of semiconductor wafers and external factors determined by a contactless measurement system. The influence of wafer factors, namely, bulk lifetime (τ
b) surface recombination velocity (
s), wafer tihckness (
W), resistivity (ρ) and diffusion coefficient (
D) are analyzed. While the influence of externel factors, namely, absorption coefficient (α) and pulse width are analyzed under a condition where the microwave frequency is 10 GHz. As a result of the present study it is found, for instance, in case of the measuremnt of recombination rate near a surface of a wafer,
W, τ
b and α should be large and the incidence surface of microwaves should be the same as the illuminate surface. Experimental results for various values of wafer thickness and pulse width correspond qualitatively well to the calculated results.
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