Role of AlN spacer layer and GaN back barrier on the optoelectronic properties of AlGaN/AlN/InGaN/GaN high electron mobility transistors

摘要

Effect of AlN spacer layer thickness on the optoelectronic properties of AlGaN/AlN/InGaN/GaN heterostructures has been presented. A peculiar variation in the values of carrier concentration/mobility for the structure with thicker spacer layer is observed. Significance of the optimum value for the spacer layer thickness in these heterostructures is examined. Above the optimum thickness, a decrease in carrier mobility of the channel layer, despite being better isolated from ionized impurity scattering, occurs due to deterioration of the interface structural quality. TOF- SIMS depth profile analysis revealed presence of Si and O impurity which serves as donors and accounts for the higher carrier concentration in the structure with spacer layer thickness (d_s) 3.7 nm compared to that with d_s 2 nm. Photoluminescence spectra showed a reduction in emission efficiency of the InGaN channel layer which provides a coordinating evidence to the improvement in the electron mobility of the channel.