The optical and detector properties of the PbS-Si heterojunction

Related optical and detector properties of the PbS-Si heterojunction (HJ) are presented and discussed. A direct optical bandgap at 300 K of 0.44 eV has been measured for PbS-Si versus 0.42 eV for PbS-sapphire. The HJ photocurrent frequency response has been determined to consist of two waveform components: Type A, a "spike" present only during the turn-on and turn-off stages of a radiation pulse, is bias independent; Type B, a continuous response, which increases with reverse bias. The temperature characteristic of the photocurrent has been observed to be strongly dependent on which waveform type dominates. The HJ noise current is Johnson noise limited at zero bias and 1/
f
noise limited under reverse bias. The HJ dark current is postulated to have four main generation mechanisms depending on temperature: Si-generated current, diffusion current from the PbS, PbS depletion or surface-generation current, and surface leakage. The PbS-Si HJ spectral response combines the effect of intrinsic absorption in Si and PbS and transitions between the Si and PbS valence bands. A detectivity of 1 × 10
¹¹
cm . Hz
^1/2
/W has been obtained at 3 µm.