The passivation of GaAs by laser CVD

In this study, properties of GaAs passivation films formed by laser CVD method are investigated. In order to develop GaAs devices, it is necessary to form insulators with good chemical stability, dielectric and interface properties on the GaAs surface in view of application to surface passivation and devices fabrication. SiN films were photolytically deposited by excimer laser with 193 nm wave length on P type (100) GaAs wafer in SiH₄, NH₃ and N₂ gas mixture by varying the substrate temperature from 100°C to 300°C. The thickness and refractive index of the films as a function of substrate temperature were measured by a nanoscope and ellipsometer respectively. The chemical depth profiles of SiN films were obtained using Auger depth spectroscopy. In order to investigate interface properties of the SiN-P GaAs, MIS structure is made by Al electrode evaporation on SiN films and high frequency C-V and DLTS (Deep Level Transient Spectroscopy) measurements were carried out. And also, surface leakage current was measured between two Au/Ge evaporated electrodes separated 10 μm apart on P type GaAs wafer before and after SiN film formation. As the result, deposition rate of SiN films increases as substrate temperature increases, which is due to generation of more reactive species with increasing substrate temperature. Auger depth profiles indicate that diffusion length of Ga and As atoms toward SiN films is reduced as substrate temperature decreases. From the high frequency C-V curve, the hysteresis effect is reduced as substrate temperature decreases and interface trap density obtained from DLTS signals is lowered to 10¹²-10¹³ in the substrate temperature ranging from 100°C to 200°C. In addition the passivated SiN film on GaAs by laser CVD shows less surface leakage current compared with non-passivated GaAs