Processing for Highly Efficient AlGaN/GaN Emitters

The fabrication of high-quality ohmic contacts on n- and p-type Al,InGaN is essential for improving the performance of optoelectronic devices, such as blue light emitting diodes, metal-semiconductor field effect transistors, HEMTs, and laser diodes. In particular, to realize solid-state UV emitters for chembioagent detection and general lighting, the formation of reliable ohmic contact systems for both n- and p-AlGaN with relatively high Al contents are indispensable. In conjunction with efforts to achieve low-resistance ohmic contacts to GaN using low work-function metal contacts, surface treatment techniques have also been proposed as an additional route to improve ohmic contacts, as the nature of the GaN surface is crucial to the formation of high quality ohmic contacts. gallium oxide is formed on GaN and AlGaN surfaces when epilayers are exposed to ambient atmosphere. This native oxide acts as a thin insulating layer over the conducting epilayer. Metal contacts deposited on such semiconductors with surface oxides form a metal-insulator semiconductor structure instead of a metal-semiconductor junction. Thus, it is imperative to remove the native oxide prior to metal deposition on the semiconductor to form low resistance ohmic contacts. Apart from the removal of native oxides prior to metallization, plasma treatment techniques have been described for improving ohmic performance of contacts on GaN-based semiconductors. We investigated the effects of SiCl4 plasma treatment and subsequent cleaning in BOE, HCl, and NH4OH solutions on n-GaN and n- AlGaN surfaces using XPS and AES. The efficacy of the different surface treatment schemes were compared by monitoring the oxygen concentrations on the surface of the GaN and AlxGa1-xN materials.