Title page for ETD etd-02022010-134937

Document Type Doctoral Thesis
Author Nyamhere, Cloud
Email cloud.nyamhere@up.ac.za
URN etd-02022010-134937
Document Title Characterization of process and radiation induced defects in Si and Ge using conventional deep level transient spectroscopy (DLTS) and Laplace-DLTS
Degree PhD
Department Physics
Advisor Name Title
Prof. F D Auret Committee Chair
Dr W E Meyer Committee Co-Chair
  • DLTS
  • defects
  • radiation
  • silicon
  • germanium
Date 2010-04-16
Availability unrestricted
Defects in semiconductors are crucial to device operation, as they can either be beneficial or detrimental to the device operation depending on the application. For efficient devices it is important to characterize the defects in semiconductors so that those defects that are bad are eliminated and those that are useful can be controllably introduced.

In this thesis, deep level transient spectroscopy (DLTS) and high-resolution Laplace-DLTS (LDLTS) have been used to characterize deep level defects introduced by energetic particles (electrons or Ar ions) and during metallization using electron beam deposition on silicon and germanium. Schottky diodes were used to form the space-charge region required in DLTS and LDLTS measurements. From the DLTS and LDLTS measurements the activation enthalpy required to ionize a trap, ET, and defect carrier capture cross-section were deduced. LDLTS proved particularly useful since it could separate deep levels with closely spaced energy levels (the limit being defects with emission rates separated by a factor greater than 2), which was not possible by conventional DLTS.

The majority carrier traps in gallium-, boron- and phosphorus-doped silicon introduced after MeV electron irradiation and during electron beam deposition have been characterized, and several defects such as the divacancy, A-center and E-center and other complex defects were observed after the two processes. Annealing studies have shown that all deep levels are removed in silicon after annealing between 500C-600C.

Both electron and hole traps introduced in n-type germanium by electron irradiation, Ar sputtering and after electron beam deposition have been characterized using DLTS and LDLTS. The E-center is the most common defect introduced in germanium after MeV electron irradiation and during electron beam deposition. Annealing shows that defects in germanium were removed by low thermal budget of between 350C - 400C and it has been deduced that the E-center (V-Sb) in germanium anneals by diffusion.

The identification of some of the defects was achieved by using defect properties such as defect signature, introduction rates, annealing behavior and annealing mechanisms, and then comparing these properties to theoretical defect models and results from other techniques.

2009 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria.

Please cite as follows:

Nyamhere, C 2009, Characterization of process and radiation induced defects in Si and Ge using conventional deep level transient spectroscopy (DLTS) and laplace-DLTS, PhD thesis, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-02022010-134937/ >


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