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.
Noncontact mode electrostatic force microscopy was employed to investigate cleaved sections of a GaSb-based quantum cascade laser structure. The technique enabled us to determine the surface potential distribution, at equilibrium and under applied external field, and to locate precisely the zone which is at the origin of failure in laser characteristics when a breakdown voltage is applied to the device.
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