Gate Bias Dependent Two Layer Conduction in InAlN/AlN/GaN Heterostructures

We studied InAlN/AlN/GaN heterostructures with In compositions near 17{\%} grown by Organo-Metallic Vapor Phase Epitaxy. These structures are free of strain and provide the confinement needed for a relatively high density and high mobility two-dimensional electron gas. The cross-sectional TEM images indicate the presence of an inadvertent GaN layer formed between the InAlN and AlN layers during the growth. Using Shubnikov-de Haas and Hall measurements performed on gated Hall bar samples at 4.2 K, we find that this additional GaN layer acts as a parasitic conduction channel. The quantitative mobility spectrum analysis of our data indicates that this parasitic channel has a very low mobility, and can be depleted by the application of a negative gate voltage.