Defect Engineering and Atomic Relocation Processes in Impurity-Free Disordered GaAs and AlGaAs
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Defect Engineering and Atomic Relocation Processes in Impurity-Free Disordered GaAs and AlGaAs P. N. K. Deenapanray, M. Krispin1, W. E. Meyer2, H. H. Tan, C. Jagadish and F. D. Auret2 Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT 0200, Australia 1 Lehrstuhl für Experimentalphysik IV, Institut für Physik, Universität Augsburg, 86135 Augsburg, Germany 2 Department of Physics, University of Pretoria, Pretoria 0002, South Africa ABSTRACT Impurity-free disordering (IFD) of GaAs and AlxGa1-xAs epitaxial layers using SiOx capping in conjunction with annealing was studied by deep level transient spectroscopy (DLTS) and capacitance-voltage (C-V) measurements. Three dominant electron traps S1 (EC – 0.23 eV), S2* (EC – 0.53 eV), and S4 (EC – 0.74 eV) are created in disordered n-type GaAs. The electron emission rate of S1 is enhanced in the presence of an externally applied electric field. We propose that S1 is a defect that may involve As-clustering or a complex of arsenic interstitials, Asi, and the arsenic-antisite, AsGa. S2* is shown to be the superposition of two defects, which may be VGa-related. S4 is identified as the defect EL2. Our preliminary results indicate that the same set of defects is created in disordered n-type AlxGa1-xAs, with S1 pinned to the conduction band edge, while S2* and S4 are pinned relative to the Fermi level. In contrast to disordering in n-type GaAs, IFD of p-type GaAs results in the pronounced increase in the free carrier concentration in the near-surface region of the disordered layer. Two electrically active defects HA (EV + 0.39 eV) and HB2 (EV + 0.54 eV), which we have attributed to Cu- and Asi/AsGarelated levels, respectively, are also observed in the disordered p-GaAs layers. IFD causes segregation of Zn dopant atoms and Cu towards the surface of IFD samples. This atomic relocation process poses serious limitations regarding the application of IFD to the band gap engineering of doped GaAs-based heterostructures. INTRODUCTION Impurity-free disordering (IFD) has been actively researched for the past two decades regarding its potential application in optoelectronic devices integration [1,2]. The technique makes use of a dielectric capping layer (eg. SiO2 or anodic oxides of GaAs) on the semiconductor structure, that acts as a sink for Ga atoms during a high temperature annealing step [1-13]. The resulting injection of an excess of Ga vacancies, VGa, below the semiconductor surface then promotes disordering, and hence a change in the band gap of the semiconductor heterostructure. In the GaAs-based system, there is evidence that IFD proceeds via the diffusion of point defects on the group III sublattice [9,10,14]. Hence, IFD can be seen as a two-step process involving (1) the creation of VGa, and (2) the diffusion of VGa away from the dielectric/semiconductor interface. Pépin et al. [15] have demonstrated that both steps become energetically favorable during a high temperature anne
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