C-V Characteristics of GaP MOS diode with anodic oxide film

Gallium phosphide was anodically oxidized in an aqueous H
2
O
2
solution and MOS diodes were fabricated by the evaporation of aluminum. The resistivity and electric breakdown strength were higher than 10
¹⁴
Ω.cm and 6 × 10
⁶
V/cm, respectively. Almost no frequency dispersion was observed in the C-V curves from 100 Hz to 1 MHz. The C-V curve showed the injection-type hysteresis. From the hysteresis window, the transferred charged carriers were estimated to be about 9 × 10
¹¹
/cm
²
. By leaving the diode biased at negative voltage or by shining light with energy higher than 1.8 eV, the curve shifted to negative voltage direction. The results indicate that the density of the fast interface states which follow the 100-Hz signal is very low but there exist deep electron traps with activation energy higher than 1.8 eV near the surface in the oxide film and the shallower electron traps which cause the hysteresis in the dark.