A thin-film field-effect transistor has been fabricated using glow-discharge amorphous silicon as the semiconductor and silicon nitride as the insulator. The transistor operates in the electron (n type) accumulation mode and by changing the gate potential from zero to only 3 V a change in the source-drain conductance of greater than four orders of magnitude is obtained. The results imply upper limits to the density of gap states in amorphous silicon and interface states at the amorphous silicon-silicon nitride interface of 3×1016 cm−3 eV−1 and 5×1011 cm−2 eV−1, respectively.

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This paper describes work carried o u t towards achieving extrinsically doped Cd,Hg, -,Te (CMT) heterostructures grown with stable dopants and sharp junctions. Both acceptor and donor doping of CMT has been achieved in our MOVPE growth reactor using the interdiffused multilayer process at -400 "C with diethyitellurium (DET) as the tellurium alkyl source. The two dopants used were arsenic, introduced as ASH,, and iodine, as vapour from the solid element. The donor doping range has been extended by t h e use of a concentrically arranged double-injection-tube system which reduced the pre-reaction between the cadmium alkyl and the iodine vapour. investigations have been carried out into the growth of various double-layer structures which incorporate either a single dopant transition or a double transition, as in a fully doped structure. concentrations and alloy compositions of As-doped ( x = 0.3) on undoped (x = 0.21) CMT heterostructures has shown that pn structures have been produced after suitable Hg anneal treatments. Iodine-doped x = 0.2 layers on As-doped x = 0.3 layers have also exhibited pn transitions. Results from fully doped homojunction layers grown with -1 x IO" I (atomic) cm --3 n-type regions on ( 1 4 ) x IO" atoms Ascm-" p-type regions have also been obtained which show sharp electrical junctions.Depth profiling to obtain the electrical characteristics, chemical dopant

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