TY - JOUR
T1 - Effects of oxidation on surface chemical states and barrier height of AlGaN/GaN heterostructures
AU - Higashiwaki, Masataka
AU - Chowdhury, Srabanti
AU - Swenson, Brian L.
AU - Mishra, Umesh K.
N1 - Funding Information:
The authors would like to thank Dr. M. S. Miao and Professor C. G. Van de Walle (University of California, Santa Barbara) for their productive discussion on the first-principles calculation and Dr. T. Nagata (National Institute for Materials Science) for technical advice on the XPS measurement. This work was partially supported by ONR MINE program monitored by P. Maki, and supported by the Toyota Motor Corporation. It also made use of a research grant from JST PRESTO.
PY - 2010/11/29
Y1 - 2010/11/29
N2 - The effects of oxidation on the surface structure and chemical bonding states of AlGaN/GaN heterostructures were investigated using x-ray photoelectron spectroscopy (XPS). In comparing Al 2p core-level XPS spectra among as-grown and annealed samples, we found that Al atoms on the surface were highly oxidized after rapid thermal annealing (RTA) at high temperature; not only in an O 2 but also in an N2 gas atmosphere. The Al oxidation level was almost identical for the samples annealed at 800 °C, irrespective of the annealing atmosphere and time; yet there was a strong dependence on the annealing temperature. The dependence of surface barrier height on the annealing condition is associated with Al oxidation behavior. Before the RTA, the barrier height increased together with the AlGaN thickness, indicating an unpinned Fermi level and the existence of low-density and distributed surface donor states. After the high-temperature RTA, however, the height is maintained at a certain value, regardless of the thickness, due to Fermi level pinning by high-density donor states. These results can be explained by the formation of two types of oxide structures providing different types of donor states.
AB - The effects of oxidation on the surface structure and chemical bonding states of AlGaN/GaN heterostructures were investigated using x-ray photoelectron spectroscopy (XPS). In comparing Al 2p core-level XPS spectra among as-grown and annealed samples, we found that Al atoms on the surface were highly oxidized after rapid thermal annealing (RTA) at high temperature; not only in an O 2 but also in an N2 gas atmosphere. The Al oxidation level was almost identical for the samples annealed at 800 °C, irrespective of the annealing atmosphere and time; yet there was a strong dependence on the annealing temperature. The dependence of surface barrier height on the annealing condition is associated with Al oxidation behavior. Before the RTA, the barrier height increased together with the AlGaN thickness, indicating an unpinned Fermi level and the existence of low-density and distributed surface donor states. After the high-temperature RTA, however, the height is maintained at a certain value, regardless of the thickness, due to Fermi level pinning by high-density donor states. These results can be explained by the formation of two types of oxide structures providing different types of donor states.
UR - http://www.scopus.com/inward/record.url?scp=78650655943&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=78650655943&partnerID=8YFLogxK
U2 - 10.1063/1.3522649
DO - 10.1063/1.3522649
M3 - Article
AN - SCOPUS:78650655943
SN - 0003-6951
VL - 97
JO - Applied Physics Letters
JF - Applied Physics Letters
IS - 22
M1 - 222104
ER -