Optimization of ALD high-k gate dielectric to improve AlGaN/GaN MOS-HFET DC characteristics and reliability

Abstract

This presents DC electrical characteristics and reliabilities of AlGaN/GaN metal-oxide-semiconductor heterojunction-field-effect transistors (MOS-HFETs) with HfO 2 gate dielectric deposited by atomic layer deposition (ALD). Two types of oxidants were investigated, namely, water (H 2 O) 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 HfO 2 /GaN interface quality. For a 20nm ALD HfO 2 gate dielectric, MOS-HFET with O 3 oxidant has less threshold voltage (V TH ) shift with respect to HFET (1.8V), higher transconductance (112.66 mS/mm), less on-resistance, and less gate leakage (5.4×10−6 A/cm2) 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 1.7×10−4 A/cm2. 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).