Electrical and optical properties of AlGaN/GaN hemt structures with 2-dimensional electron gas grown by mocvd on sapphire and Si (III) substrates

High electron mobility transistors (HEMT) with a 2-dimensional electron gas (2DEG) channel formed by an AIGaN/GaN heterointerface were fabricated from MOCVD-grown heterostructures on Si (111) and sapphire substrates. The electrical characterization including C-V profiling and DC as well as RF measurements evidenced good transistor properties of all structures under study. Typically, comparable structures on Si (111) show output characteristics up to 50 V in drain-source voltage and cut-off frequencies of f₁/ f_max=7 GHz / 12 GHz. Optical characterization by means of PL and reflection spectroscopy demonstrated the high quality of the samples and allowed to estimate the values of strain in the AlGaNlGaN heterointerface region. The presence of this heterointerface leads to a modification ofthe reflection spectra compared to an uncapped GaN layer surface, which may be a future basis for understanding and estimating the interface parameters such as surface charge density or the field distribution in the vicinity of the 2DEG channel.