In this work

we derived the formula of Dλ* of intrinsic photocon

under conditions of which τn=τp and the restriction on infinite optical absorption had been removed

but the effect of the surface recombination was taken into account.The τPEM appears in the Dλ* formula

but it’s influence

being very small

can be neglected.The calculation shows that

for normal surface recombination velocity

the optimum thickness of p-type InSb at 77°K is about 3μm. In addition

the detectivity of the sample mentioned above increases as the majority carrier concentration decreases. Owing to the BLIP limit

the excessive reduction of concentration is not only difficult but also unnecessary.