Al1-xInxN/AlN/GaN Heterostructures Investigated by Surface Photovoltage Spectroscopy

GaN based heterostructures have recently gained increased interest due to their applications for High Electron Mobility (HEMT) transistors with excellent high-frequency (GHz) and high-power performance characteristics. Nearly lattice-matched (LM) AlInN/ GaN heterostructures exhibit typical 2D electron gas (2DEG) density confined at the heterointerface whose density is of the order of 1.0 × 1013 cm-2, but these electrons forming the 2DEG show poor mobilities due to alloy disorder induced scattering. The insertion of AlN interlayer helps keeping the electrons better confined in the GaN channel and prevents 2DEG electrons from alloy scattering within the AlInN barrier [1]. In this work AlInN/AlN/GaN heterojunctions grown by MOCVD with different AlN (interlayer) thicknesses have been investigated by Surface Photovoltage Spectroscopy (SPS). The density of the two dimensional electron gas forming at the interface has been measured by Hall effect. A band gap shift has been detected by SPS and its dependence on the 2DEG electron density at the AlN/GaN interface has been analyzed on the basis of the Moss Burstein and renormalization effects. The application of the model allowed us to calculate a parameter which quantitatively account for the non parabolic conduction band (E*) and to evaluate the effective mass dependence on free carrier concentration.