Investigation of ICPECVD Silicon Nitride Films for HgCdTe Surface Passivation

© 2015, The Minerals, Metals & Materials Society. In this paper, we report results of a study of SiNx thin films for surface passivation of HgCdTe epitaxial layers. The hydrogenated amorphous SiNx films under study were deposited by a SENTECH SI500D inductively coupled plasma-enhanced chemical vapor deposition (ICPECVD) system with a high-density and low-ion-energy plasma source at relatively low substrate temperatures (80°C to 100°C). A series of SiNx films were first deposited on CdTe/GaAs and Si substrates under different deposition conditions to examine the influence of ICP power, deposition temperature, and NH3/SiH4 ratio on properties of the SiNx films. To investigate SiNx deposition conditions suitable for surface passivation of HgCdTe, the SiNx/n-Hg0.68Cd0.32Te interface characteristics were investigated employing capacitance–voltage measurements, and the corresponding interface trap densities Dit were extracted from the high-frequency and low-frequency characteristics. Analysis of SiNx/n-Hg0.68Cd0.32Te metal–insulator–semiconductor (MIS) structures indicated that Si-rich SiNx films deposited at 100°C by ICPECVD exhibit electrical characteristics suitable for surface passivation of HgCdTe-based devices, that is, interface trap densities in the range of mid-10¹⁰ cm⁻² eV⁻¹ and fixed negative interface charge densities of ∼10¹¹ cm⁻². In addition, the relationship between bond concentration and surface passivation performance has been explored based on infrared (IR) absorbance spectra. The Si–H and N–H bond concentrations were found to be directly correlated with passivation performance, such that SiNx films with a combination of high [Si–H] and low [N–H] bond concentrations were found to be suitable as electrical passivation layers on HgCdTe.