Development of Optimized Deconvoluted Coincidence Doppler Broadening Spectroscopy and Deep Level Transient Spectroscopies with Applications to Various Semiconductor Materials

This dissertation, "Development of Optimized Deconvoluted Coincidence Doppler Broadening Spectroscopy and Deep Level Transient Spectroscopies With Applications to Various Semiconductor Materials" by Jingdong, Zhang, 張敬東, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled DEVELOPMENT OF OPTIMIZED DECONVOLUTED COINCIDENCE DOPPLER BROADENING SPECTROSCOPY AND DEEP LEVEL TRANSIENT SPECTROSCOPIES WITH APPLICATIONS TO VARIOUS SEMICONDUCTOR MATERIALS Submitted by Zhang Jing Dong for the degree of Doctor of Philosophy at The University of Hong Kong in September 2006 Both Positron Annihilation Spectroscopy (PAS) and Deep Level Spectroscopy (DLS) are techniques used to study defect structures in solids. The former is a non-destructive technique particularly useful for studying vacancy type defects in condensed matter. DLS, on the other hand, is an electrical characterization tool for investigating deep energy levels of defects inside the energy band gap of a semiconductor. In this thesis, the basic physics behind PAS and DLS was reviewed together with the various experimental set-ups required to implement them. A full description was provided of a newly constructed digital DLS spectrometer that can perform both DLTS (Deep Level Transient Spectroscopy) and DLOS (Deep Level Optical Spectroscopy). Coincidence Doppler Broadening Spectroscopy (CDBS) is one of the popular PAS techniques due to its ability to measure the high electron momentum components in bulk and defect states. At low momentum, however, it suffers from the problem of poor instrumental resolution. Various CDBS deconvolution algorithms have been investigated to enhance the resolution at low momentum. It was shown that the Richardson-Lucy (RL) algorithm gives CDBS deconvolution results approaching the quality of 1D angular correlation or annihilation radiation (ACAR) spectroscopy, with the advantages of retaining the high momentum components and requiring no complex tent function corrections. The RL-CDBS technique has been tested against theory and 1D-ACAR results for different metals and found to obtain slightly superior results than other existing algorithms while using far less computer resources. Major PAS studies have been carried out on bulk and 10MeV electron irradiated Si and 300keV and 1.5MeV SiC. For bulk Si, the different shapes of the low momentum densities for different directions have been well recovered using RL-CDBS. The different momentum distributions recovered for the Si-P monovacancy and the Si divacancy were shown to agree well with theoretical predictions. For the electron irradiated SiC the carbon vacancy V and the silicon vacancy V have been identified according to the electron energies and according to Si the high energy momentum components seen by CDBS. More complex semiconductor systems such electron irradiated GaN and hydrothermally grown ZnO have also been studied by RL-CDBS and Positron Lifetime Spectroscopy. Because GaN materials are widely used in opto-electronic industry the digitized DLS setup has been used to study the defect levels in electron irradiated GaN. For the CDBS and RL-CDBS studies on GaN, SiC and ZnO various methods of "fingerprinting" different defects such as "ratio curves," "difference curves" have been tested. The "autocorrelation function" method has also been used extensively and found to provide novel and useful information on the nature of defects. DOI: 10.5353/th_b3827901 Subjects: Deep level transient spectroscopy Positron annihilation Spectrum analysis - Deconvolution Se