Title page for ETD etd-02102011-142210


Document Type Doctoral Thesis
Author Chawanda, Albert
Email albert.chawanda@up.ac.za
URN etd-02102011-142210
Document Title Electrical and structural characterization of metal germanides
Degree PhD
Department Physics
Supervisor
Advisor Name Title
Prof FD Auret Committee Chair
Dr J M Nel Committee Co-Chair
Keywords
  • Ideality factor
  • schottky barrier height
  • temperature dependence
  • deep level transient spectroscopy
  • defects
  • scanning electron microscopy
  • e-centre
  • Richardson constant
  • germanides
  • thermal annealing
Date 2011-04-15
Availability unrestricted
Abstract
Metal-semiconductor contacts have been widely studied in the past 60 years. These structures are of importance in the microelectronics industry. As the scaling down of silicon-based complementary metal-oxide-semiconductor (CMOS) devices becomes more and more challenging, new material and device structures to relax this physical limitation in device scaling are now required. Germanium (Ge) has been proposed as a potential alternative to silicon.

In this thesis a systematic study of the thermally induced reaction of transition metals with the n-Ge substrate is outlined. Investigations in the change of the electrical properties of the metal germanide structures is studied in a wide range of temperatures. Current-voltage (I-V), capacitance-voltage (C-V), deep level transient spectroscopy (DLTS) and high-resolution Laplace-DLTS (L-DLTS) techniques have been used for the electrical characterization of the fabricated Schottky contacts. Results obtained indicate the variation of the electrical properties of these Schottky contacts can be attributed to combined effects of interfacial reactions and phase transformation during the annealing process. The barrier height distribution in identically prepared Schottky contacts on n-Ge (100) showed that the barrier heights and ideality factors varied from diode to diode even though they were identically fabricated. The properties of the n-Ge Schottky contacts have revealed a strong dependence on temperature. The current transport mechanism has been shown to be predominantly thermionic emission at high temperatures while at low temperatures, the Schottky contacts have exhibited the dominance of the generation-recombination current mechanism. The variation of the Schottky barrier heights at low temperatures have been attributed to barrier inhomogeneities at the metal-semiconductor (MS) interface. Results from defect characterization by DLTS show that the E-centre is the dominant defect introduced in n-Ge by electron beam deposition during contact fabrication and substitutional related defects are induced during the annealing process. The identification of some of the defects was achieved by using defect properties, defect signature, annealing mechanisms and annealing behaviour and comparing these properties to the results from theoretical defect models. Annealing showed that defects in Ge can be removed by low thermal budget of between 250350C.

Finally, structural characterization of these samples was performed by scanning electron microscopy (SEM) and Rutherford backscattering spectrometry (RBS) techniques. From the SEM images it can be observed that the onset temperature for agglomeration in the 30 nm Ni/n-Ge (100), and Pt/-, Ir/- and Ru/n-Ge (100) systems occur at 500600C and 600700C, respectively.

2010 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:

Chawanda, A 2010, Electrical and structural characterization of metal germanides, PhD thesis, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-02102011-142210/ >

B11/59/ag

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