A. Mandelis et al., NONCONTACTING MEASUREMENTS OF PHOTOCARRIER LIFETIMES IN BULK-FILM ANDPOLYCRYSTALLINE THIN-FILM SI PHOTOCONDUCTIVE DEVICES BY PHOTOTHERMAL RADIOMETRY, Journal of applied physics, 80(9), 1996, pp. 5332-5341
Laser-induced and frequency-scanned infrared photothermal radiometry w
as applied to a crystalline-Si photoconductive device, and to polysili
con thin-film photoconductors deposited on oxidized Si substrates by a
n LPCVD method. A detailed theoretical model for the radiometric signa
l was developed and used to measure the free photoexcited carrier plas
ma recombination lifetime, electronic diffusivity and surface recombin
ation velocity of these devices, with the simultaneous measurement of
the bulk thermal diffusivity. A trade-off between detectivity/gain and
frequency-response bandwidth was found via the lifetime dependence on
the wafer background temperature rise induced by Joule-heating due to
the applied bias, This effect was most serious with the bulk-Si devic
e, but was limited by the high resistivity of the LPCVD thin-film devi
ces, In the case of the bulk-Si device. the results of photothermal ra
diometry were compared with, and corroborated by, frequency-scanned ph
otocurrent measurements. More sophisticated analysis was shown to be r
equired for the interpretation of the polysilicon photoconductor frequ
ency-responses, perhaps involving the fractal nature of carrier transp
ort in these grain-structured devices. (C) 1996 American Institute of
Physics.