Electrical Characterization of Defect States in Local Conductivity Domains in ZnO:N,As Layers
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0957-K08-03
Electrical Characterization of Defect States in Local Conductivity Domains in ZnO:N,As Layers Andre Krtschil, Armin Dadgar, Annette Diez, and Alois Krost Institute of Experimental Physics, Otto-von-Guericke-University Magdeburg, PO Box 4120, Magdeburg, 39016, Germany
ABSTRACT P- and n-type conductivity domains in dual-doped ZnO:As+N layers grown by metal organic vapor phase epitaxy on GaN/sapphire templates were electrically microcharacterized by scanning capacitance (SCM) and scanning surface potential microscopy (SSPM) techniques with respect to their defect states. The p-type domains were found to be dominated by two acceptors with thermal activation energies of about 80 and 270 meV as observed by transient SCM scans at different temperatures. Optically excited SSPM scans revealed defect-to-band-transitions at 400, 459, and 505 nm omnipresent in both domain types as well as a shallower transition at 377 nm exclusively in the p-type regions. According to the similar energy levels the optical transitions at 377 and 400 nm are assigned to acceptor states, whereby the 80meV-acceptor is probably responsible for the conversion from n- to p-type in the domains. INTRODUCTION Because of some unique material properties, e.g., a very high exciton binding energy of ~60 meV in combination with a large direct band gap of about 3.37 eV at room temperature, ZnO is regarded as an extremely potential material system for optoelectronics in the UV/blue/green spectral range. However, before the commercial realization of ZnO-based light emitters can start, the question of successful p-type doping of ZnO has to be solved. In the last years a couple of different acceptor doping approaches were tested, reaching from the exploitation of intrinsic Zn vacancy acceptors [1] via conventional mono-doping with group-I elements (Li, Na, K) on Zn-sites [2] or group-V elements (N, P, As) on O-sites [3,4] up to co- and cluster-doping with N and Ga simultaneously [5,6]. However, despite of this variety of approaches and some promising reports on successful acceptor doping the problems to achieve reproducible, controllable and long-time stable p-type ZnO remain. In a recent work [7] we studied the effect of conventional mono-doping with nitrogen and arsenic as well as the simultaneous doping with both acceptor species (in the following labeled dual-doping) by scanning capacitance microscopy (SCM). As the main result we pointed out, that these doping approaches result in the formation of local n- and p-type conductivity domains induced by structural inhomogeneities instead of uniformly doped p-type ZnO layers. Moreover, in this study we observed for the dual-doped ZnO:As+N samples in dependence on the doping parameters dominant p-type regions and good surface morphology only locally disturbed by minor defect/grain-related n-type parts. Similar domain formation is already known from GaN [8] and attributed to selective dopant incorporation. In the present paper we will go a step further. In order to get more information on the defects whic
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