GaN/AlN superlattice high electron mobility transistor heterostructures on GaN/Si(111)

In this work we report the growth of AlGaN/GaN heterostructures on silicon substrates using quasi AlGaN barrier layer formed by 6×(AlN/GaN) superlattice (SL) stack with nominal Al content of 35%. This is the first attempt of implementation of quasi AlGaN barrier layer in AlGaN/GaN heterostructure, originally proposed by Kawakami, on the Si(111) substrates by metalorganic vapor phase epitaxy (MOVPE) technique. The electrical properties of high‐electron mobility transistors (HEMT) type SL structures and conventional Al0.28Ga0.72N/GaN heterostructures grown on sapphire and silicon substrates were investigated and compared. The obtained results showed deterioration of channel resistivity in the heterostructure with SLs (1430 Ω/sq) in comparison to the alloy Al0.28Ga0.72N/GaN heterostructure (751 Ω/sq). Additional, surface and chemical structure characterizations were done by atomic force microscopy (AFM) and secondary ion mass spectrometry (SIMS) techniques. The roughness parameter Ra, estimated based on AFM scans of investigated structures was between 0.5 and 1 nm. The SIMS depth profiles of the alloy AlGaN and SL quasi AlGaN barrier did not show any significant differences between the samples deposited on sapphire and silicon substrates. The room temperature photoluminescence spectra of HEMT type SL structures revealed peaks corresponding to GaN and AlGaN band transitions, which indicates lack of sharp interfaces between AlN and GaN layers and thus formation of AlGaN transition regions in AlN/GaN SL stack.