High-Quality Schottky Contacts for Limiting Leakage Currents in Ge-Based Schottky Barrier MOSFETs

Abstract

Abstract-Schottky barrier (SB) Ge channel MOSFETs suffer from high drain-body leakage at the required elevated substrate doping concentrations to suppress source-drain leakage. Here, we show that electrodeposited Ni-Ge and NiGe/Ge Schottky diodes on highly doped Ge show low off current, which might make them suitable for SB p-MOSFETs. The Schottky diodes showed rectification of up to five orders of magnitude. At low forward biases, the overlap of the forward current density curves for the as-deposited Ni/n-Ge and NiGe/n-Ge Schottky diodes indicates Fermi-level pinning in the Ge bandgap. The SB height for electrons remains virtually constant at 0.52 eV (indicating a hole barrier height of 0.14 eV) under various annealing temperatures. The series resistance decreases with increasing annealing temperature in agreement with four-point probe measurements indicating the lower specific resistance of NiGe as compared to Ni, which is crucial for high drive current in SB p-MOSFETs. We show by numerical simulation that by incorporating such high-quality Schottky diodes in the source/drain of a Ge channel PMOS, a highly doped substrate could be used to minimize the sourceto-drain subthreshold leakage current.

Observation of Negative Differential Conductance in a Reverse-Biased Ni/Ge Schottky Diode

“…Square Ni pads with 400-μm sides were fabricated using electrodeposition. Details on the fabrication and measurement can be found in our recent work [6]. The low-temperature measurements down to 50 K were performed using a Bio-Rad DL 4960 cryostat.…”

“…By extrapolation from the exponential forward-bias region, an SB height φ of 0.53 eV is obtained. Taking the image-force lowering and the substrate doping density N d of 8.7 × 10 14 cm −3 (obtained by C-V method [6]) into account, the theoretical fitting characteristic is shown as a solid line in Fig. 1.…”

Comparative investigation of Schottky barrier height of Ni/n-type Ge and Ni/n-type GeSn

“…The resulting SBH is plotted in Figure 3 It shows that for the Ge wafer, the SBH is 0.55eV, which is consistent with that reported in the literature. [11][12][13][14] For the GeSn film, the SBH decreases as the annealing temperature increases up to an annealing temperature of 390°C, as indicated by the solid line. The SBH remains almost constant the annealing temperature further increases, as indicated by the dashed line.…”

Silicon-compatible high-hole-mobility transistor with an undoped germanium channel for low-power application

“…1,[7][8][9] Although the smaller energy bandgap (E g ¼ 0.8 eV at the C valley and 0.66 eV at the L valley) of Ge offers the opportunity for fabricating photonic components in the infrared regime, it has a drawback in that it makes it more difficult to realize higher electrical reliability and endurance in metal-oxide-semiconductor field-effect transistors (MOSFETs). [10][11][12] Also, efforts are required prior to gate oxide deposition to passivate the surface to suppress the interface leakage induced by the instability of Ge dangling bonds. [13][14][15] In the present study, a high-hole-mobility transistor (HHMT) with an undoped Ge channel is designed and characterized by device simulation.…”