ENERGY DENSITY DISTRIBUTION OF INTERFACE STATES IN AU SCHOTTKY CONTACTS TO EPITAXIAL IN0.21GA0.79ASZN LAYERS GROWN ON GAAS BY METALORGANIC VAPOR-PHASE EPITAXY

Au/p-In0.21Ga0.79As Schottky barrier diodes were fabricated by evapora tion of Au on chemically etched surfaces of Zn doped In0.21Ga0.79As ep itaxial layers grown on highly p-doped GaAs substrates by metalorganic vapor phase epitaxy (MOVPE). Room temperature current-voltage measure ments show that Au forms high quality rectifying contacts to P-In0.21G a0.79As: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 temperat ure on Au Schottky diodes made on four P-In0.21Ga0.79As:Zn samples wit h varying acceptor doping concentrations (N(A)) in a range between 5.8 X 10(14) and 4.3 X 10(17) CM-3. Under forward bias, the capacitance s howed large frequency dispersion, possibly caused by interface states in thermal equilibrium with the semiconductor. The C-f data was analyz ed in terms of Lehovec's model of an interface state continuum with a single time constant. The density and relaxation time of interface sta tes 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 betwe en 1 X 10(11) and 3.5 X 10(12) eV-1 CM-2, and the relaxation times wer e in the range of 7 X 10(-6)-6 X 10(-5) s. For samples with N(A) betwe en 1.5 X 10(17) and 4.3 X 10(17) CM-3, the interface state density inc reased 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 (N(A) = 4.3 X 10(17) cm- 3) was one order of magnitude higher than that in the lightly doped sa mples (N(A) = 5.8 X 10(14) cm-3).