Some positron annihilation studies on highly doped and supersaturated N-type silicon
Abstract of thesis entitled
SOME POSITRON ANNIHILATION STUDIES ON HIGHLY DOPED AND SUPERSATURATED N-TYPE SILICON
Submitted by HO KING FUNG
for the degree of Doctor of Philosophy
at The University of Hong Kong
in July 2004
Positron Annihilation Spectroscopy (PAS) is a non-destructive technique that can be extensively used to probe the point defect structures found in solids. The basic physics behind PAS such as implantation, transport, vacancy trapping and annihilation are reviewed together with the various experimental techniques.
Deconvolution algorithms have been applied to Coincidence Doppler Broadening Spectroscopy (CDBS) to improve the effective momentum resolution of the technique. The CDBS system instrumental resolution function is obtained using the 514-keV line from 85Sr.
The generalized least square method with Tikonov-Miller regularization, which incorporates a priori non-negativity constraints, is found to be very effective. Monte-Carlo simulations of CDBS have been used to optimize the deconvolution. The
deconvolution technique, when applied to a series of well annealed polycrystalline metals, gives results that are found to be comparable quality-wise to those obtained by one dimensional Angular Correlation of Annihilation Radiation (ACAR).
An attempt was made to evaluate the significance of ACAR data from positrons trapped in a crystal defect by defect studying the E-center (vacancy-dopant pair) in silicon. The Fourier transformation of the ACAR momentum distribution coming from positrons trapped at the E-center was studied. This gives in real-space the autocorrelation function of the positron-electron wavefunction product at the site of annihilation. Employing the ratio of the autocorrelation function for the E-center and bulk silicon, the positron binding energy to the E-center was estimated. It has been possible to approximately isolate that part of the E-centers?autocorrelation function that originates from the localized defect orbitals and to see spatial features relating to atomic positions in the E-center.
Nonequilibrium processing consisting of ion implantation followed by annealing has been employed to produce supersaturated Antimony doped silicon. The defect structure of the ion implanted region and the post-implanted region have been studied using the Variable Energy Positron Annihilation Spectroscopy (VEPAS) technique. Evidence is given that positrons are trapped into precipitates or get trapped at precipitate boundaries at annealing temperatures less than 600?. Surprisingly, new vacancy defects appear in the implanted region at annealing temperatures over 600?. This is tentatively attributed to the fact that Sb precipitates begin to dissolve at these temperatures into VSb2 type complexes.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:positron annihilation electron spectroscopy silicon crystals defects
Date of Publication:01/01/2005