Energy density distribution of interface states in Au Schottky contacts to epitaxial In0.21Ga0.79As:Zn layers grown on GaAs by metalorganic vapor phase epitaxy

Abstract

Au/p-In0.21Ga0.79As Schottky barrier diodes were fabricated by evaporation of Au on chemically etched surfaces of Zn doped In0.21Ga0.79As epitaxial layers grown on highly p-doped GaAs substrates by metalorganic vapor phase epitaxy (MOVPE). Room temperature current-voltage measurements show that Au forms high quality rectifying contacts to p-In0.21Ga0.79As:Zn with an ideality factor of 1.2. High frequency capacitance-voltage (C-V) and capacitance-frequency (C-f ) measurements over a wide frequency range (1 kHz<f<1 MHz) were carried out at room temperature on Au Schottky diodes made on four p-In0.21Ga0.79As:Zn samples with varying acceptor doping concentrations (NA) in a range between 5.8×1014 and 4.3×1017 cm−3. Under forward bias, the capacitance showed large frequency dispersion, possibly caused by interface states in thermal equilibrium with the semiconductor. The C-f data was analyzed in terms of Lehovec’s model of an interface state continuum with a single time constant. The density and relaxation time of interface states were obtained in an energy range between 0.40 and 0.65 eV from the top of the valence band. The density of interface states varied between 1×1011 and 3.5×1012 eV−1 cm−2, and the relaxation times were in the range of 7×10−6–6×10−5 s. For samples with NA between 1.5×1017 and 4.3×1017 cm−3, the interface state density increased exponentially with interface energy in the range of 0.65 and 0.40 eV, from midgap towards the top of the valence band. The density of interface states in the highly doped samples (NA=4.3×1017 cm−3) was one order of magnitude higher than that in the lightly doped samples (NA=5.8×1014 cm−3).