Si(111) as alternative substrate for AlGaN/GaN HEMT
Abstract
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. The films were characterized by atomic force microscopy (AFM) (root mean square roughness (rms) = 0.4 nm), high resolution X-ray diffraction (HRXRD), LT photoluminescence (PL) measurements (FWHM = 10 meV) and circular transmission line measurements (CTLM) (Rsheet = 0.8–1 MΩ/sq). The GaN buffers were used for the subsequent deposition of AlGaN/GaN modulation- and undoped high electron mobility transistor (HEMT) structures. Room temperature (RT) mobilities up to 1170 cm2/Vs and sheet carrier concentrations up to 1.26 × 1013 cm−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 420 mA/mm at UGS = 1 V.
