Determination of the minority-carrier lifetime in silicon ingots by photoconductivity relaxation measured at microwave frequencies

Method for the Microwave Measurement of Carrier Lifetime in Lightly Doped Silicon Ingots

“…Both the transmission and the reflection mode of measurement were employed. The experimental setup was as in our previous study [1].…”

“…An advantage of this arrangement is that it can be used with ingots as well as specially prepared specimens. This paper is a continuation of the work by Borodovskii et al [1], in which a new method was proposed for the microwave measurement of bulk lifetime in monocrystalline silicon ingots. It is again assumed that the excess conductivity as measured by absorbed microwave power is proportional to the total number of excess carriers excited by a light pulse.…”

“…Even at t p = 10 ms, we have = 2.8 ms, a value 1.78 times less than τ = 5 ms. This bulk lifetime is deduced from the point where a measured graph of U ( t )/ U (0) and a calculated graph of N ( τ )/ N (0) intersect, U ( t ) being the photoconductivity response [1].…”

“…For a light pulse approximating to the delta function, the decay of excess-carrier density is described by (1) where , τ is the bulk lifetime, α is the linear absorption coefficient for the light, S is the surface recombination velocity, and L = is the diffusion length of excess carriers [10].…”

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A further investigation is conducted into a new microwave method for evaluating bulk lifetime in silicon ingots [1]. It is shown that for lightly doped ingots transmission and reflection microwave measurements yield different values of the decay time of photogenerated excess-carrier density.

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