Growth of buffer structures for AlGaN/GaN HEMT on Silicon Substrates

GaN buffers were deposited on (111)−oriented silicon (Si) by AIXTRON metal organic vapour phase epitaxy (MOVPE) reactors using a buffer structure of low temperature (LT) AlN layers and high temperature (HT) layer stacks, consisting of AlN, AlGaN and GaN. Structures with two − and three−fold LT/HT layer combinations were investigated. The films were characterized by atomic force microscopy (AFM) (minimum root mean square roughness (rms) = 0.4 nm), high resolution X−ray diffraction (HRXRD), LT photoluminescence (PL) measurements (minimum FWHM = 10 meV) and circular transmission line measurements (CTLM) (Rsheet = 0.8 − 1 M Ohm/sq). The GaN buffers were used for the subsequent deposition of AlGaN/GaN modulation−doped and undoped high electron mobility transistors (HEMT). Room temperature (RT) mobilities of up to 1170 cm2/Vs and sheet carrier concentrations of up to 1.26·1013cm−2 were measured. Round−HEMT devices (unpassivated, gate length 1 µm, gate width 150 µm) showed a maximum transconductance of 148 mS/mm at UDS = 4 V and a maximum current of 439 mA/mm at UGS = 1 V