Cleaning of GaN(2¯110) surfaces

Abstract

The cleaning of GaN(2¯110) surfaces was investigated by x-ray photoelectron spectroscopy, scanning tunneling microscopy, and low-energy electron diffraction. Two different two-step cleaning methods, performed under ultrahigh-vacuum conditions, were carried out and compared. The first cleaning step of both methods is thermal degassing. The second step is either the deposition of metallic gallium followed by redesorption or an exposure to active nitrogen from a radio frequency nitrogen plasma source. Upon storage in a glovebox (N2 atmosphere) and transfer to ultrahigh vacuum under dry nitrogen, carbon and oxygen were identified as the major contaminants. A significant decrease in oxygen and carbon was achieved by thermal degassing at 750 °C under ultrahigh-vacuum conditions. By applying a subsequent Ga deposition/redesorption or N2-plasma cleaning step, a further reduction in oxygen and carbon could be achieved. In comparison, the Ga deposition/redesorption cleaning showed a better performance in oxygen removal, whereas the N2 plasma exhibits a better efficiency in carbon removal. Furthermore scanning tunneling microscopy and low-energy electron diffraction investigations showed a drastic improvement of the morphology and atomic structure of the clean surfaces in contrast to the sample surfaces after N2 storage and transfer.