Investigation of ICPECVD Silicon Nitride Films for HgCdTe Surface Passivation

In this paper, we report results of a study of SiN (x) thin films for surface passivation of HgCdTe epitaxial layers. The hydrogenated amorphous SiN (x) 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 (80A degrees C to 100A degrees C). A series of SiN (x) 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 SiN (x) films. To investigate SiN (x) 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 D (it) 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 SiN (x) films deposited at 100A degrees C by ICPECVD exhibit electrical characteristics suitable for surface passivation of HgCdTe-based devices, that is, interface trap densities in the range of mid-10(10) cm(-2) eV(-1) and fixed negative interface charge densities of similar to 10(11) 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 SiN (x) 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.