Electrical and optical properties of AlGaN/GaN HEMT structures with 2-dimensional electron gas grown by MOCVD on sapphire and Si (111) substrates

High electron mobility transistors (HEMT) with a 2-dimensional electron gas (2DEG) channel formed by an AlGaN/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 AlGaN/GaN heterointerface region. The presence of this heterointerface leads to a modification of the 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.