HgCdTe surface passivation using electrochemical CdTe deposition

Abstract

In this thesis, electrochemical CdTe deposition process for HgCdTe surface passivation have been proposed and studied. The deposition range of CdTe was predicted through theoretical calculation of Gibbs’ free energy change and achieved by cyclic voltammetry experiments with various bath compositions. After that, constant step potentials are applied to HgCdTe substrates to electrochemically deposit CdTe from ethylene glycol based electrolyte. To improve the surface morphology and crystallinity of electrodeposited CdTe thin films by suppressing the unwanted reduction process from dissolved oxygen in electrolyte, nitrogen bubbling process was introduced before electrodeposition of CdTe. Thus, stoichiometric and highly oriented CdTe film was formed at deposition potential range between -0.4 and -0.55 V/SCE. After CdTe electrodeposition, MIS capacitors (Ni / ZnS / electrodeposited CdTe / MCT) were formed and its capacitance-gate voltage characteristics were measured at the temperature and frequency of 80 K and 1 MHz. Best C-V result was obtained when CdTe films were electrodeposited at -0.5 V/SCE. However, C-V curve showed that there was high density of fixed insulator charge density and high interface trapped charge density. The constant current deposition method was introduced to reduce high interface trapped charge density by control deposition current density. However, C-V curve was hardly modulated with applied gate voltage because of initial deposition potential of -0.2 V/SCE more positive than deposition potential of -0.5 V/SCE, where Te rich CdTe would be electrodeposited. Thus, the constant potential deposition technique was introduced and good CdTe films, which were well modulated with gate voltage and showed fixed charge density of 6.34×10^{10} /㎠, could be electrodeposited. Effect of Te ion concentration in electrolyte was also examined. As Te ion concentration in electrolyte grew thinner from 10 mM Te to no Te ion, deposition current density became...