Fabrication and comparative study of DC and low frequency noise characterization of GaN/AlGaN based MOS-HEMT and HEMT

This work presents the effect of Al mole fraction and gate oxide on the direct current and low frequency noise characterization of GaN/AlGaN high electron mobility transistor (HEMT). Metal–oxide–semiconductor (MOS)-HEMT with SiO2 in the gate stack improved the Id(on)/Id(off) ratio up to more than 8 orders, compared to fabricated HEMT without oxide. It was shown that the gate leakage and isolation leakage suppression efficiency improved dramatically with the gate oxide. Subthreshold swing of MOS-HEMTs with different Al mole fractions (from 20% to 35%) varies slightly from 72 mV/decade to 79 mV/decade. Low frequency noise study revealed the difference in transport mechanism between HEMT and MOS-HEMTs. By using carrier number fluctuation model on the measured data, it was found that the noise is predominantly coming from the surface states. While generation-recombination is very prominent in HEMT, it is very insignificant in both MOS-HEMTs at much higher frequencies. This study reveals that very high number of surface states, assisting the tunneling in Schottky/AlGaN barrier is responsible for unusually high leakage and higher noise level in HEMT without oxide. Leakage level is improved from mA/mm range for HEMT to pA/mm range for MOS-HEMTs. Leakage suppression improvement and minimization of noise level can be mainly attributed by to high quality SiO2. Hooge's constant was on the order of 5–6 × 10−3, which is 5 × 10−2 for HEMT without oxide.