High performance Ge Schottky PMOSFETs with ternary-phase alloy

Abstract

This work demonstrates high-performance Ge p-channel metal-oxide-semiconductor field-effect transistors (PMOSFETs) [1] with ternary-phase NiGePt alloy Schottky source/drain (S/D) by low-temperature microwave-activated annealing (MWA) [2]. Process flow of Shcottky junctions is shown in Fig. 1. Interestingly, the formed NiGePt alloy is nearly single crystalline. We found the formation of ternary-phase alloy NiGePt seems very helpful in suppressing the off-leakage of junction, as shown in Fig. 2. The fabricated NiGePt/N-Ge Schottky junction depicted an impressive effective barrier height (ΦBn) of ∼0.59 eV for electrons, leading to a high junction current ratio of >105 at the applied voltage of |Va|= 1 V. Slight increase with increasing deposited Pt thickness can be explained by the improved series resistance, as shown in Fig. 2. The lower process temperature of MWA as compared to the conventional thermal annealing is beneficial for eliminating surface roughness, reducing alloy agglomeration of Schottky contact S/D. As a consequence, we employed the advantages of low-temperature MWA to fabricate the Schottky S/D PMOSFETs. With forming gas annealing, the Ge PMOSFET (L = 4 µm) showed a very high output current of 33.5 µA/µm at VGS−VT= −2.4 and VDS = −2 V. Our ternary Schottky PMOSFET exhibited a high ION/IOFF ratios of ∼ 3.7×103 (ID) and ∼ 1.3×105 (IS), and a moderate subthreshold swing of 126 mV/dec, as shown in Figs. 3.