Photoresponse of 3-5 µm p-channel MISFETs

Abstract

Photoresponse of 3 -5 /um p- channel MISFETsS.C. Gupta and B.L.SharmaSolid State Physics Laboratory,Lucknow Road, Delhi -110007, IndiaAbstractPhotogenerated current at 77K, when the transparent gate of an Hgl_xCdxTe(x =0.29) andInSb p- channel MISFETs is illuminated with infrared radiation, have been evaluatedtheoretically as a function of gate voltage. To process of excitation are considered,namely, an electron -hole pair generation across the bandgap in the depletion layer of thefield induced junction and an electron excitation through interface states at the semi -conductor -SiO2 interface. The photocurrent is primarily due to the later process. Forsake of comparison, the drain - source current without illumination has also been calculatedas function of gate voltage.IntroductionThe remote sensing by infrared technology has led to enormous development in thefield of narrow band semiconductor devices.1'2 Amongst the semiconducting infraredmaterials in 3 -5 /um atmospheric window, InSb and Hgl- xCdxTe(x= 0.29)are the two mostimportant materials and have been used to fabricate photoconductors, photovoltaic detectors,metal -insulator- semiconductor (MIS) photodiodes, charge coupled devices(CCDs), chargeinjection devices (CIDs) and metal- insulator - semiconductor field effect transistors(MISFETs).3,4,5 The MISFETs can be used for signal processing and for CCD interfacing.6Both n and p- channel MISFETs of InSb and n- channel of Hg1- xCdxTe(x =0.29) have been latelyrealized. In this paper, the results of photoresponse calculations at 77K when thetransparent gate of an Hgl_xCdxTe(x =0.29) and an InSb p- channel MISFETs, is illuminatedwith infrared radiation of varying intensities, are reported and compared. As thep- channel MIS technology3 is somewhat simpler then the n- channel, calculations arerestricted to p- channel MISFET only. The MISFET configuration used here consists ofsemitransparent In gate having SiO2 as the gate insulator.Theoretical FormulationThe schematic representation of an Hgl- xCdxTe(x =0.29) or an InSb p- channel MISFETis shown in Figure 1. The expression for the drain - source current ID for such a MISFET isgiven by7