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Impact of various cleaning procedures on p-GaN surfaces

Schaber, J.; Xiang, R.; Arnold, A.; Ryzhov, A.; Teichert, J.; Murcek, P.; Zwartek, P.; Ma, S.; Michel, P.


This work discusses the influence of different cleaning procedures on p-GaN grown on sap-phire by metal-organic chemical vapor deposition. The cleaned p-GaN surface was trans-ferred into an ultra-high vacuum chamber and studied by an X-ray photoelectron spectrome-ter, revealing that a cleaning with a so-called „piranha“ procedure results in low carbon and oxygen concentrations on the p-GaN surface. Contrary, a cleaning that solely uses ethanol represents a simple cleaning, but leads to an increase of carbon and oxygen contaminations on the surface. Afterward, the cleaned p-GaN samples underwent a subsequential vacuum thermal cleaning at various temperatures to achieve an atomically clean surface. XPS meas-urements revealed residual oxygen and carbon on the p-GaN surface. Thus, a thermal treat-ment under a vacuum did not entirely remove these organic contaminations, although the thermal cleaning reduced their peak intensities. The complete removal of carbon and oxygen contaminants was only achieved by argon ion sputtering, which is accompanied by a strong depletion of the nitrogen on the p-GaN surface. The treatments cause a large number of sur-face defects preventing the formation of a negative electron surface when the p-GaN is acti-vated with a thin layer of cesium.

Keywords: p-GaN; photocathode; sputtering damage; surface cleaning; damage effects

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