Optimization of ALD High-k Gate Dielectric to Improve AlGaN/GaN MOS-HFET DC Characteristics and Reliability

This presents DC electrical characteristics and reliabilities of AlGaN/GaN metal oxide semiconductor heterojunction-field-effect transistors (MOS-HFETs) with HfO2 gate dielectric deposited by atomic layer deposition (ALD). Two types of oxidants were investigated, namely, water (H2O) and ozone (O-3) for the ALD deposition. The comparison study reveals that GaN MOSHFETs with O-3 oxidant results in overall better device performance and reliability than water based oxidant due to improved HfO2/GaN interface quality. For a 20nm ALD HfO2 gate dielectric, MOS-HFET with O-3 oxidant has less threshold voltage (Vim) shift with respect to HFET (1.8V), higher transconductance (112.66 mS/mm), less on-resistance, and less gate leakage (5.4x10(-6) A/cm(2)) compared to MOS-HFET with water oxidant where V-TH shift with respect to HFET is 9.15V, transconductance is 81.38 mS/mm and gate leakage is 1.7x10(-4) A/cm(2). Moreover, significant improvement in device reliability (V-TH shift is less than 0.5V) is observed with O-3 oxidant at high-temperature reverse bias (HTRB).