Effects of surface states on electrical characteristics of InN and In1-xGaxN

Surface states are known to pin the Fermi level in InN and In1-xGaxN, strongly affecting charge distribution and transport on the surface and at interfaces. By solving Poisson's equation over a range of bias voltages for an electrolyte-based capacitance-voltage measurement configuration, we have calculated the band bending and space charge distribution in this system and developed an electronic model generally applicable to both p- and n-type group-III-nitride thin films. Both conduction band nonparabolicity and band renormalization effects due to the high surface electron concentration were included. The calculated space charge distributions, using the majority dopant concentration as a fitting parameter, are in excellent agreement with experimental data. The model quantitatively describes increasingly strong n-type electrical characteristics on the surface due to electron accumulation in p-type In1-xGaxN for decreasing values of x. This also provides a general understanding of the effect of mobile carriers on capacitance-voltage measurements.