Low-thermal-budget n-type ohmic contacts for ultrathin Si/Ge superlattice materials

Abstract

Thermal budget is always a vital element in Si-based superlattice materials processing. In this work, a novel n-type ohmic contacting scheme with a low processing thermal budget is developed by combining the high-dose ion implantation and low-temperature alloying techniques. The optimized specific contact resistivity (ρc) is reduced to 6.18×10-3 Ω·cm² at a low thermal budget of 400 °C, and this is a result of the efficient low-temperature electrical activation in amorphous substances. It is indicated that both the high doping concentration and the formation of NiSi(Ge) alloy phase contribute to the linear ohmic contacting behavior. The ohmic contact resistance dependency on processing temperature is further revealed by a detailed Ni/Si(Ge)-alloying model. A minimum ρc of 2.51×10−4 Ω·cm² is achieved at a thermal budget of 450 °C, which is related to the high bonding intensity at metal/semiconductor interface. Note that this technique is compatible with standard Si-based CMOS process flow, and meanwhile can be applied in high-performance insulated-gate field-effect transistor (IGFET) fabrication. Furthermore, it is verified in our IGFETs that Si/Ge superlattice structures can serve as an efficient potential barrier to constrain electrons.

Gate-controlled hysteresis curves and dual-channel conductivity in an undoped Si/SiGe 2DEG structure

“…A schematic of a typical strained Si QW structure is depicted in figure 1(b), including a 2 nm-thick Si cap layer, a 30 nmthick relaxed SiGe barrier layer, and a strained Si QW with a thickness of ∼ 12 nm on top of a Si 0.75 Ge 0.25 virtual substrate. Then, enhancement-mode Hall bar-shaped field effect transistors (FETs) were patterned on the heterostructure following a standard fabrication process similarly described in a previous study [22], and the key steps of the integration flow are shown in figure 1(a). The source/drain contact regions were defined by heavy phosphorus ion implantation at a dose of 5 × 10 15 cm −2 , followed by a Ni/Al (10/200 nm) metal bilayer as the contact electrodes by e-beam evaporation.…”

Modulation Doping of Silicon Nanowires to Tune the Contact Properties of Nano‐Scale Schottky Barriers

“…Thus, Ohmic contacts providing a negligible resistance are desired for most silicon technologies. [10,11] However, achieving a near-perfect Ohmic contact with a nanoscale semiconductor is generally difficult. If brought in contact with moderately doped silicon most metals form a Schottky contact rather than an Ohmic contact.…”