Analysis of thin CdS layers on InP for improved metal–insulator–semiconductor devices

Cadmium sulfide (CdS) layers were deposited from an aqueous solution of thiourea, cadmium sulfate, and ammonia on (100) n-InP at 60–95 °C. X-ray photoelectron spectroscopy showed that the deposition process effectively removes native oxides on InP and forms a protective layer for subsequent dielectric deposition. Surface analysis also showed that the InP surface is not P deficient following oxide deposition on CdS-treated InP. Capacitance–voltage and conductance–voltage measurements of metal–insulator–semiconductor (MIS) capacitors were used to compare samples with and without CdS films between InP and a deposited insulator. Capacitance–voltage response of CdS-treated MIS structures showed well-defined regions of accumulation, depletion, and inversion. The interface-state density at midgap was reduced from 5×1011 to 6×1010 eV−1 cm−2 with CdS treatment. Depletion-mode MIS field-effect transistors made using this new passivation technique exhibited superior device performance to that of untreated samples.