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Title of Thesis

Zulfiqar Ali
Institute/University/Department Details
Quaid-i-Azam University/Physics
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
thermal evaporation, doping, semiconductors, electron beam vacuum evaporation, closed space sublimation, two-sourced thermal evaporation

The II-VI compound semiconductors thin films (CdS, ZnTe and ZnSe) have been prepared by different methods such as electron beam vacuum evaporation, closed space sublimation and two-sourced thermal evaporation. The choice of the deposition method was based on the quality of the films required for specific Application. The effects of deposition parameters, such as electron beam power (in case of electron beam evaporation); substrate temperature and annealing of the film, on the structural, optical and electrical properties have been studied. In spite of that the main goal is to get comparatively high electrical conductivity of the films, the optical properties of the films were also very important from the application point of view so that the improvement of the film conductivity should not associated with drastic change in the optical and structural properties of the films. In addition to that, the structure and the composition of the resulting films were of the basis of this study.

The structure of the films was studied by X-ray diffraction and the composition of the resulting films was measured by electron micro probe analysis (EMPA). A model was used for the calculation of optical parameters (refractive index, absorption coefficient, film thickness and optical band gap) from the optical transmission spectra recorded by spectrophotometer. For reducing the resistively of II-VI group semiconductor thin films, doping with different materials were performed. These films have been doped with (Cu, Ag) dopant to make it p-type with different methods. Since Cu and Ag dopant in II-VI group compounds act as an accepter.

The ion exchange process is a very simple, and low cost technique. In this technique the dopant has to be in the form of ion in a solution, where the pre-prepared films are to be immersed, i.e. Ag(NO3) solution in case of silver doping and Cu(NO3) solution in case of copper doping. The ion exchange parameters such as solution temperature, concentration and immersion time, and its effect on the speed of the process and further on the status of the resulting films was carefully determined and analyzed. Also the effect of post heat treatment, on the physical properties and the composition of the resulting films were studied. Ag and Cu doping of the ZnTe as well as ZnSe thin films were successfully achieved and the conductivity of the films was converted to p-type.

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1044.58 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
147.35 KB
2 1 Introduction 1
55.91 KB
  1.1 Deposition Process 1
  1.2 Thermal Evaporation 2
  1.2.1 Vapor Sources 3
  1.2.2 Deposition Parameters 4
3 2 Properties Of Ii-Vi Semiconductors 6
111.35 KB
  2.1 Cds Thin Films 6
  2.2 Zn Te Thin Films 8
  2.3 Znse Thin Films 10
  2.1 References 12
4 3 Characterization Methods And Experimental Setup 15
224.79 KB
  3.1 X-Ray Diffraction 15
  3.2 Sem And Empa 16
  3.3 Optical Calculations 18
  3.3.1 Non-Linear Curve Fitting 20
  3.3.2 Models used for n and α 21
  3.4 Spectrophotometer 23
  3.5 Glass Substrates 23
  3.6 Resistivity And Conduction Mechanism 24
  3.7 Conductivity Type 28
  3.8 Deposition System 29
  3.8.1 Electron Beam Evaporation 29
  3.8.2 Two Sourced Evaporation 30
  3.8.3 Closed Space Sublimation 32
5 4 Cds Thin Films And Effects Of Doping 36
108.75 KB
  4.1 Cds By Electron Beam Evaporation 36
  4.1.1 Structural Properties 37
  4.1.2 Optical Properties 38
  4.1.3 Electrical Properties 39
  4.2 Cds By Css Method 40
  4.2.1 Structural Properties 41
  4.2.2 Optical Properties 42
  4.2.3 Electrical Properties 43
  4.3 Comparison Between The Two Methods 45
6 5 Zn Te Thin Films And Effects Of Doping 47
253.57 KB
  5.1 Zn Te By Two Sourced Thermal Evaporation 47
  5.1.1 Structural Properties 49
  5.1.2 Optical Properties 52
  5.1.3 Electrical Properties 57
  5.2 Ag Doped Zn Te Thin Films 58
  5.2.1 Structural Properties 58
  5.2.2 Optical Properties 60
  5.2.3 Electrical Properties 62
  5.3 Cu Doped Zn Te Thin Films 65
  5.3.1 Structural Properties 65
  5.3.2 Optical Properties 66
  5.3.3 Composition Analysis 68
  5.3.4 Electrical Properties 71
  5.4 Comparison Between Ag And Cu Doped Zn Te 72
7 6 Zn Se Thin Films And Effects Of Doping 74
260.19 KB
  6.1 Zn Se By Two Sourced Evaporation 74
  6.2 Ag Doped Znse Thin Films 74
  6.2.1 Structural Properties 75
  6.2.2 Optical Properties 75
  6.2.3 Composition Analysis Of Doped Znse (Ag) Thin Films 81
  6.2.4 Electrical Properties 83
  6.3 Cu Doped Znse Thin Films 84
  6.3.1 Structural Properties 85
  6.3.2 Optical Properties 87
  6.3.3 Composition Analysis Of Doped Znse (Cu) Thin Films 90
  6.3.4 Electrical Properties 93
  6.4 Znse Thin Films By Css 94
  6.4.1 Structural Properties 95
  6.4.2 Optical Properties 98
  6.4.3 Electrical Properties 101
  6.5 Comparison Between The Two Methods 101
8 7 Conclusions 103
33.94 KB