Al1-xInxN/AlN/GaN heterostructures studied by Surface Photovoltage Spectroscopy

GaN-based high electron mobility transistors with excellent high-frequency and high-power performance characteristics obtained from AlInN/ GaN heterostructures already reached market maturity. Nearly lattice-matched AlInN/ GaN heterostructures exhibit typical 2D electron gas (2DEG) density confined at the heterointerface whose density is of the order of 1013 cm-2. Unfortunately, these electrons forming the 2DEG may suffer from poor in-plane transport properties due to alloy disorder induced scattering. AlN interlayer helps keeping the electrons better confined in the GaN channel and prevents 2DEG electrons from alloy scattering. The present contribution deals with AlInN/AlN/GaN heterojunctions grown by MOCVD with different AlN thicknesses studied by Surface Photovoltage Spectroscopy (SPS). The 2DEG at the AlN/GaN interface has been characterized by Hall effect and Current –Voltage characteristics. By Surface Photo-voltage Spectroscopy a band gap shift has been detected and its dependence on the 2DEG electron density was studied. The energy gap was found to increase as a function of the free carrier concentration at the heterointerface, which is related to the 2DEG density, due to the combined effect of Moss-Burnstein and renormalization models. Their application allows us to calculate a parameter which quantitatively accounts for the non parabolic conduction band and to evaluate the effective mass dependence on free carrier concentration. This work was supported by the EU under Project No. PITN-GA-2008 213238-RAINBOW.