Ohmic Contacts Optimisation for High-Power InGaAs/AlAs Double-Barrier Resonant Tunnelling Diodes Based on a Dual-Exposure E-Beam Lithography Approach

In this paper, we report on a simple test structure which can be used to accurately extract the specific contact resistivity rho(c) associated with metal-n++ InGaAs-based low-resistance Ohmic contacts through the transfer length method (TLM). The structure was designed to avoid common measurement artifacts that typically affect standard layouts. Moreover, microfabrication was optimised to achieve an accurate short minimum gap spacing of 1 mu m through a dual-exposure step based on e-beam lithography, which is required for a reliable rho(c) estimation. Ohmic contacts based on a Ti/Pd/Au metal stack were fabricated and characterised using the proposed structure, resulting in an extracted rho(c) similar or equal to 1.37x10(-7) Omega cm(2) = 13.7 Omega mu m(2). This work will assist in increasing the quality of Ohmic contacts in high-power InGaAs/AlAs double-barrier resonant tunnelling diodes (RTDs), and so help to overcome one of the bottlenecks to the output power capability of RTD-based oscillators at terahertz frequencies.

Automated summary

This paper introduces a simple test structure for accurately extracting the specific contact resistivity of metal-n++ InGaAs-based low-resistance Ohmic contacts. The structure is designed to avoid common measurement artifacts and microfabrication was optimised to achieve a short minimum gap spacing required for reliable rho(c) estimation. The Ohmic contacts fabricated and characterised using this structure yielded a extracted rho(c) of approximately 1.37x10(-7) Omega cm(2) = 13.7 Omega mu m(2), which can improve the quality of Ohmic contacts in high-power InGaAs/AlAs double-barrier resonant tunnelling diodes and enhance the output power capability of RTD-based oscillators at terahertz frequencies.