Electroreflectance and deep-level transient spectroscopy studies of metal/n-InP interfaces

Abstract

Electroreflectance (ER) and deep-level transient spectroscopy (DLTS) were used to study the effect of surface treatment and substrate temperature on the characteristics of metal/n-InP. The Franz–Keldysh oscillations (FKO) were observed for all samples. From the period of the FKO, the surface electric field ξ was calculated and found to be a function of reverse dc bias, Vdc, but not ac modulating voltage, Vac. Surface potential and carrier concentration were determined from the plot of ξ2 vs Vdc. The Schottky barrier height φB and surface carrier concentration were found to be 0.46 eV and 8.0×1015/cm3 for the metal-semiconductor (MS) diode deposited at room temperature (RT=300 K). With a thin layer of thermal oxide, the φB was increased to 0.70 eV. For a MS diode deposited at low temperature (LT=77 K), φB was found to be as high as 0.96 eV. DLTS studies of InP MS diodes revealed two extra interface traps on RT diodes and a much higher trap density compared with the LT diode. The results clearly show the effect of surface treatment and substrate temperature during metal deposition on the behavior of MS and metal-insulator-semiconductor interfaces. It is demonstrated that the ER technique can be utilized as an optical Mott–Schottky method. It permits an independent confirmation of surface electric field, doping concentration, and barrier height.