Impact of recess etching and surface treatments on ohmic contacts regrown by molecular-beam epitaxy for AlGaN/GaN high electron mobility transistors

Abstract

Ohmic contacts fabricated by regrowth of n+ GaN are favorable alternatives to metal-stack-based alloyed contacts in GaN-based high electron mobility transistors. In this paper, the influence of reactive ion dry etching prior to regrowth on the contact resistance in AlGaN/GaN devices is discussed. We demonstrate that the dry etch conditions modify the surface band bending, dangling bond density, and the sidewall depletion width, which influences the contact resistance of regrown contacts. The impact of chemical surface treatments performed prior to regrowth is also investigated. The sensitivity of the contact resistance to the surface treatments is found to depend upon the dangling bond density of the sidewall facets exposed after dry etching. A theoretical model has been developed in order to explain the observed trends.

AlGaN/GaN High Electron Mobility Transistors on Semi-Insulating Ammono-GaN Substrates with Regrown Ohmic Contacts

“…The etched sidewalls are at a 56 angle to the c-plane (0001). The sidewall angle is close to the optimal 62 angle at which the density of dangling bonds on the etched surface is similar to a c-plane surface [ 22 ].…”

Improvement of Ohmic Contact for InAlGaN/AlN/GaN HEMTs with Recess Etching

“…However, as the gate length is reduced, the performance of the device becomes dominated by parasitic resistance and short channel effects, which have to be minimized . The main contribution of the parasitic resistance is provided by the access and contact resistance of the Ohmic contacts .…”

Improved Ohmic Contact by Pre‐Metallization Annealing Process in Quaternary In0.04Al0.65Ga0.31N/GaN HEMTs

“…In order to enhance the power and high frequency performance of GaN HEMTs, high performance ohmic contacts are required. To achieve the better ohmic contact performance than that of the conventional Ti/Al‐based contacts, various approaches including Au‐free contacts, recessed ohmic contacts, pre‐metallization surface treatments, and regrown contacts have been investigated.…”