Low-Resistance Alloyed Metal Contacts to 2D and Bulk Semiconductor Materials

Stanford researchers in the Pop Lab have developed a method of making low resistance, good conductivity, temperature tolerant, CMOS processing compatible contacts for 2d semiconductor materials based on transition metal dihalcogenides (TMD's). The method alloys a low melting temperature metal (e.g., In, Sn, or Bi) with a stable, non-oxidizing noble metal (e.g., Au), which minimizes the damage to the fragile monolayer 2D semiconductor and forms excellent contact to a monolayer 2D semiconductor. The alloy is formed by depositing a thin, low melting temperature metal (In, Sn or Bi), capping it with a high melting temperature metal (Pd, Pt, Ni, or Au), and annealing at a temperature higher than the melting point of the low melting temperature metal to form the alloy. A prototype using In/Au alloys fabricated using the technique, had a contact resistance of 190 ??µm on monolayer MoS2, a widely studied 2D semiconductor, which is among the lowest currently reported values. This technique is a step closer to producing manufacturable contacts for next generation 2D transistors.

Stage of Development – Prototype
The Pop Lab temperature-resistant, stable prototype with In/Au contacts demonstrated a contact resistance of 190 ??µm on monolayer MoS2.

Future research plans include:
• Prototypes with fully CMOS compatible contacts using manufacturing-friendly alternatives like Pd, Pt or Ni.
• Fabrication of hole-injecting p-type contacts for PMOS transistors.
• Improving the intrinsic quality of the 2D semiconductor material, as synthesized.
• Minimization of material variability across a chip and wafer to improve device reliability and yield.