Surface Potential Measurements of doping and defects in p-GaN
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Surface Potential Measurements of doping and defects in p-GaN M. Losurdo, M.M. Giangregorio, G. Bruno Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR, via Orabona 4 – 70126 Bari, Italy A.S. Brown Department of Electrical and Computer Engineering, Duke University, Durham, NC 27709, USA W.A. Doolittle, Gon Namkoong Georgia Institute of Technology, Microelectronic Research Center, 791 Atlantic Dr, Atlanta, GA, USA A.J. Ptak National Renewable Energy Lab, Golden, Colorado T. H. Myers, Department of Physics, West Virginia University, Morgantown, WV 26506, USA ABSTRACT The interaction of Be-, Mg-, and Si- doped GaN epitaxial films with atomic hydrogen, produced by a remote r.f. hydrogen plasma, is investigated. The kinetics of the interaction is monitored in real time by spectroscopic ellipsometry through the measurement of the variation of the GaN pseudodielectric function. The passivation effect of hydrogen is inferred by surface potential measurements using scanning Kelvin probe microscopy (SKPM). It is found that the interaction of GaN with hydrogen is a strong function of both the type and level of the doping. Hydrogen treatment is shown to lead to a strong variation of the surface potential and, hence, of the Fermi level position, which is the result of p-dopant passivation by hydrogen. A different interaction of Mg and Be with atomic hydrogen is also observed and monitored in real time by ellipsometry. SKPM is also used for studying the interaction of defects in GaN with atomic hydrogen. INTRODUCTION Effective p-type doping of GaN is still a crucial issue for the realization of efficient optical and electronic devices. The most frequently investigated p-dopants, Mg and Be, suffer from acceptor passivation through hydrogen complex formation [1,2]. Therefore, it is important to study the interaction of atomic hydrogen with GaN films [3]. For GaN, the hydrogen diffusivity and interaction of hydrogen exposed samples have been shown to depend on the Fermi-level position [1] and on experimental conditions [4]; hence, the possibility of monitoring in real time the interaction of GaN with atomic hydrogen will be useful for understanding the interplay between doping and hydrogen. Among p-dopants, Mg and Be are characterized by a favourable substitutional incorporation, which is consistent with the strong binding in Mg3N2 and Be3N2, although it has been reported that Be is small enough to be incorporated on the interstitial site, where it acts as a double donor [5] and hence causes compensation. In this study, we use non-destructive optical and electrical probes such as spectroscopic ellipsometry and scanning Kelvin probe microscopy (SKPM) [6] in conjunction with noncontact atomic force microscopy (AFM) for investigating the interaction of Mg and Be dopants with atomic hydrogen and for characterization of the passivation of defects such as terrace steps, dislocations and micropipes with atomic hydrogen. Ga-polar GaN epitaxial films grown molecular beam epitaxy (MBE) and doped with both Be and Mg at a d
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