Material and device characterizations of AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors with reactive-sputtered HfO{sub}2 gate dielectric

摘要

Metal-oxide-semiconductor (MOS) structure with high-k gate dielectric has recently been incorporated into AlGaN/GaN high electron mobility transistors (HEMTs) to suppress high Schottky gate leakage, current collapse associated with (Al)GaN surface states, and also to alleviate the significant threshold voltage (V{sub}(th)) shift and large device transconductance (g{sub}(m,max)) decrease due to the insertion of a gate dielectric [1]. HfO{sub}2, with a high dielectric constant (～20) and a large energy bandgap (～5.6 eV), is considered as a promising gate dielectric in Si MOSFETs. In this study, we report using reactive sputtered HfO{sub}2 as the gate dielectric for AlGaN/GaN MOS-HEMTs. The schematic cross section of AlGaN/GaN MOS-HEMT is illustrated in Figure 1. The Al(GaN) epi-layers were grown by MOCVD on (111) Si substrate. Room temperature Hall measurements have revealed a free electron concentration of 8.53 × 10{sup}12cm{sup}(-2) and a mobility of 1140 cm{sup}2/V·s. After device isolation by ICP etching, a 23 nm HfO{sub}2 layer was deposited by sputtering pure Hf in O{sub}2 ambient at 200°C. Ti/Al/Pd/Au ohmic contact was then formed on openings in HfO{sub}2, etched by BCl{sub}3 plasma. Samples were subsequently annealed at 700°C for 30 s in N{sub}2. Gate metals Ni/Au with a gate area of 1.5 × 40μm{sup}2 were optically defined by lift-off.