Papers by Author: Prakash N.K. Deenapanray

Abstract: Oxygen-rich crystalline silicon materials doped with boron are plagued by the presence of a well-known carrier-induced defect, usually triggered by illumination. Despite its importance in photovoltaic materials, the chemical make-up of the defect remains unclear. In this paper we examine whether the presence of excess silicon self-interstitials, introduced by ion-implantation, affects the formation of the defects under illumination. The results reveal that there is no discernible change in the carrier-induced defect concentration, although there is evidence for other defects caused by interactions between interstitials and oxygen. The insensitivity of the carrier-induced defect formation to the presence of silicon interstitials suggests that neither interstitials themselves, nor species heavily affected by their presence (such as interstitial boron), are likely to be involved in the defect structure, consistent with recent theoretical modelling.

Abstract: The defects created in GaAs and AlxGa1-xAs epitaxial layers by impurity-free disordering (IFD) were studied by deep level transient spectroscopy (DLTS) and capacitance-voltage (C-V)measurements. IFD introduces three electron traps S1 (EC – 0.23 eV), S2* (EC – 0.53 eV), and S4 (EC – 0.74 eV) in n-type GaAs. 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 the superposition of two defects, which may be VGa-related, while S4 is identified as the defect EL2. The same set of defects is created in impurity-free disordered n-type AlxGa1-xAs, but with the defects either pinned relative to the conduction band or the Fermi level. In contrast to disordering in n-type GaAs, IFD of p-type GaAs results in the pronounced atomic relocation of impurities, including Zn and Cu, in the nearsurface region of the disordered layer. The redistribution of these fast diffusers poses serious constraints regarding the application of IFD to the band gap engineering of doped GaAs-based heterostructures for optoelectronic devices application. However, we will demonstrate that this impurity segregation effect can be minimized. The discussion takes a critical look at the technological viability of impurity-free disordering for the integration of GaAs-based optoelectronic devices.