Studies on Al/ZrO2/GaAs metal-oxide-semiconductor capacitors and determination of its electrical parameters in the frequency range of 10 kHz–1 MHz

Abstract

Aluminum (Al)/zirconium oxide (ZrO2)/GaAs metal-oxide-semiconductor (MOS) capacitors were fabricated on p-GaAs. The carrier concentration of n-GaAs was varied by metal organic chemical vapor deposition. The ZrO2 gate dielectrics were prepared by the sol-gel process and then spin-coated onto GaAs substrates. Three different thicknesses of the ZrO2 layer, viz., 25, 40 and 50 nm, were used to study the effect of oxide thickness on different MOS parameters. Sulfur (S) passivation of the GaAs surface was done to control the interface state densities before ZrO2 deposition. It was found that S passivation resulted in both low hysteresis and high accumulation capacitance of the device. Frequency dependent studies on the dielectric characterizations were made in the frequency range of 10 kHz–1 MHz. It was found that within this frequency range dispersion of the oxide capacitance was 2%/decade. It was observed that interface trap densities (Dit) increased with an increase in the carrier concentration of n-GaAs from a value of 1.5×1012 cm−2 eV−1 at 1×1014 cm−3 to a value of 3.8×1012 cm−2 eV−1 at 3×1016 cm−3 doping concentration of the semiconductor. It was also found that Dit increased with an increase in the oxide thickness from a value of 0.75×1012 cm−2 eV−1 at 25 nm to a value of 2.4×1012 cm−2 eV−1 at 50 nm thickness of the oxide layer. Studies on temperature dependent current densities indicated that the leakage current decreased by three orders of magnitude with the change in temperature from 290 to 80 K. Leakage current was also found to decrease with an increase in the thickness of the dielectric layer due to a decrease in the transmission probability. Loss tangent was found to decrease with frequency, whereas the ac conductivity showed an opposite trend. Considering different MOS parameters investigated in the present study, it was observed that ZrO2 could be a potential candidate for GaAs based MOS devices.