Electronic Properties of III-Nitride Surfaces and Interfaces Studied by Scanning Photoelectron Microscopy and Spectrosco
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1202-I04-03
Electronic Properties of III-Nitride Surfaces and Interfaces Studied by Scanning Photoelectron Microscopy and Spectroscopy Cheng-Tai Kuo1, Hong-Mao Lee1, Chung-Lin Wu2, Hung-Wei Shiu1,3, Chia-Hao Chen3, and Shangjr Gwo1 1 Department of Physics, National Tsing-Hua University, Hsinchu 30013, Taiwan 2 Department of Physics, National Cheng-Kung University, Tainan 70101, Taiwan 3 National Synchrotron Radiation Research Center (NSRRC), Hsinchu 30076, Taiwan ABSTRACT We report on a method based on cross-sectional scanning photoelectron microscopy and spectroscopy (XSPEM/S) for studying electronic structure of III-nitride surfaces and interfaces on a submicrometer scale. Cross-sectional III-nitride surfaces prepared by in situ cleavage were investigated to eliminate the polarization effects associated with the interface charges/dipoles normal to the cleaved surface. In contrast to the as-grown polar surfaces which show strong surface band bending, the cleaved nonpolar surfaces have been found to be under the flat-band conditions. Therefore, both doping and compositional junctions can be directly visualized at the cleaved nonpolar surfaces. Additionally, we show that the “intrinsic” valence band offsets at the cleaved III-nitride heterojunctions can be unambiguously determined. INTRODUCTION III-nitride semiconductors such as indium nitride (InN), gallium nitride (GaN), aluminum nitride (AlN), and their alloys are pyroelectric materials, which have large spontaneous polarizations along the polar axis. The polarization effects play an important role at the IIInitride surfaces and interfaces. For example, spontaneous polarization-induced sheet charges at the surface result in the surface band bending difference between Ga- and N-polar GaN surfaces [1]. In addition, the difference in spontaneous polarization can induce a high charge density at the III-nitride heterointerface to form a two-dimensional electron (or hole) system. As a result, III-nitride heterostructures are promising materials for applications using heterojunction fieldeffect transistor (HFET) structures. Recently, ultrathin InN ion sensitive field-effect transistors (ISFETs) have been shown to have large sensitivity and fast response time for ion sensing in liquid [2]. Moreover, InN/AlN metal-insulator-semiconductor heterojunction field-effect transistor (MISHFET), which exhibits a higher sheet carrier density than conventional devices, can be attributed to a large spontaneous polarization difference at the InN/AlN interface [3]. However, due to the existence of large polarization differences at wurtzite-type III-nitride heterointerfaces, many reported valence band offset (VBO) values for III-nitride heterojunctions show a large discrepancy [4-7]. In this paper, we report on a method for measurements of electronic properties at the III-nitride surfaces and interfaces by photoelectron emissions from in situ cleaved, nonpolar cross-sectional surfaces of III-nitride multilayered structures. EXPERIMENT
All of the III-nitride expitaxial films were grown
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