Pakistan Research Repository Home

Title of Thesis

Abdul Majid
Institute/University/Department Details
Department of Physics/ Quaid-i-Azam University, Islamabad
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
deep levels, heavy transition metals, mocvd gaas, gaas epilayers, metal organic chemical vapor deposition, rhodium, ruthenium, osmium, deep level transient spectroscopy, bandgap

Deep levels have been characterized in n- and p-type GaAs epilayers grown by metal organic chemical vapor deposition (MOCVD), doped in situ with heavy. transition metals, rhodium, ruthenium from the 4d series and osmium from the 5d series, by using the deep level transient spectroscopy (DLTS) technique. A broad band of deep levels is found to be associated with Rh impurity in n-type GaAs in the upper half bandgap. The band of electron emitting deep levels is shown to extend from 0.57-0.67 eV below the conduction band edge. The observed variation of the peak profile with the capture time for the electron emission band support a band-like-extended-defect nature of this deep level band. In p-type GaAs:Rh, a composite peak consisting of emission signals from at least two deep levels in the lower half bandgap is identified with Rh. This peak is resolved using double-correlation DL TS . (DDL TS) measurements, providing the clear energy positions of the Rh-related deep levels as E,.+ 0.35 eV (RhA) and E,.+ 0.51 eV (RhB). Detailed study of the various deep-levels characteristics has been carried out for all the Rh-related levels. All of these are found to exhibit electric field dependent them1.al emission rates for the respective charge carriers. Detailed experimental data have been obtained on this field dependence wherever possible and theoretical analysis of these data has been carried out in the light of available models to obtain physical insight into the nature of respective deep levels.

DLTS investigations on Ru transition-metal impurity in MOCYD grown GaAs shows a prominent deep level at Ec - 0.39 eV (Ru1E) associated with ruthenium in n-GaAs. In p-type samples, three deep levels are identified with Ru impurity in the lower-half bandgap of GaAs with energy positions E,. -+- 0.38 eV (RuA), E,. + 0.52 eV (RuB) and E,. + 0.65 eV (RuC). RuC is found to have an electric field dependent emission rate signature. In minority carrier emission spectra of p-type GaAs: Ru, a broad peak is observed in Ru doped samples with the peak position corresponding to a deep-level at Ec - 0.66 eV (Ru1). Measurements with varied minority carrier injection conditions indicate that this electron emission DLTS signal probably arises from a band of deep levels, rather than a well-defined single-energy deep level.

Deep level transient spectroscopy (DLTS) technique has been employed to investigate the electrical characteristics of Os-related deep levels. Two prominent deep levels have been identified with Os at Ec - 0.28 eV (Osl) and Ec - 0.41 eV (Os2) in the upper-half bandgap of GaAs. Both the levels are found to exhibit a significant dependence of thermal emission rate on the junction electric field. While Osl does not allow accurate quantitative investigations of this field dependence due to its relatively low concentration, detailed quantitative data on the field dependence of the level, Os2, are reported. Analysis of these data in the light of the available theoretical models allows us to conclude that Os2 is probably a substitutional donor type defect in GaAs. In p-type GaAs: Os, osmium is clearly shown to introduce two prominent deep levels in the lower-half bandgap of GaAs at energy positions Ev + 0.42 eV (OsA) and Ev + 0.72 eV (OsB). A prominent electron-emitting deep level band is also observed in our p-type samples which is not seen in the n-type samples.

Download Full Thesis
3349.64 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
368.87 KB
2 1 Introduction 1
324.6 KB
  1.1 111-V Compound Semiconductors 1
  1.2 Metal Organic Chemical Vapour Deposition (MOCVD) Of GaAs 3
  1.3 GaAs And Its Properties 4
  1.4 Defects In Semiconductors 10
  1.5 Transition-Metal Related Deep Levels In Compound Semiconductors 10
  1.6 Motivation 12
  1.7 Scheme Of The Thesis 13
  1.8 References 14
3 2 Defects In Semiconductors 16
361.52 KB
  2.1 Lattice Defects In Semiconductors 17
  2.2 Shallow- And Deep-Level Defects 24
  2.3 Defects Introduced By Transition Metals 26
  2.4 Some Distinct Characteristics Of Defects 27
  2.5 References 30
4 3 Carrier Kinetics Of Semiconductor Defects 33
385.29 KB
  3.1 Deep Levels As Trap Centers 33
  3.2 Deep Levels As Generation And Recombination Centers 34
  3.3 The Principle Of Detailed Balance 35
  3.4 Deep Level Kinetics 35
  3.5 Carrier Capture 39
  3.6 Electric Field Dependence Of Thermal Emission Rates 40
  3.7 References 54
5 4 Deep Level Transient Spectroscopy 56
309.45 KB
  4.1 Capacitance Associated With Depletion Region 57
  4.2 Junction Capacitance Transients 59
  4.3 Working Principle Of DLTS 64
  4.4 Analysis Of Deep Level Transient Parameters 68
  4.5 References 77
6 5 Experimental Details 79
156.9 KB
  5.1 Samples 79
  5.2 Current-Voltage Measurements 81
  5.3 Capacitance-Voltage Measurements 81
  5.4 DLTS Measurements 82
  5.5 References 86
7 6 Deep Level Defects In MOCVD-Grown GaAs :Rh 88
669.08 KB
  6.1 C-V Analysis Of n- GaAs :Rh 88
  6.2 Results Of Deep Level Transient Spectroscopy Of n- GaAs :Rh 88
  6.3 C-V Analysis Of P- GaAs :Rh 108
  6.4 Results Of Deep Level Transient Spectroscopy Of p- GaAs :Rh 108
  6.5 Discussion 123
  6.6 Conclusions 128
  6.7 References 130
8 7 Deep Level Defects In MOCVD-Grown GaAs :Ru 131
200.39 KB
  7.1 C- V Analysis Of N- GaAs :Ru 131
  7.2 Results Of Deep Level Transient Spectroscopy Of n- GaAs :Ru 133
  7.3 Results Of Deep Level Transient Spectroscopy Of p- GaAs :Ru 140
  7.4 Discussion 147
  7.5 Conclusions 148
  7.6 References 150
9 8 Deep Level Defects In MOCVD Grown GaAs : Os 151
481.21 KB
  8.1 C-V Analysis Of N- GaAs : Os 151
  8.2 Results Of Deep Level Transient Spectroscopy Of n- GaAs : Os 151
  8.3 Results Of Deep Level Transient Spectroscopy Of P- GaAs : Os 174
  8.4 Conclusions 182
  8.5 References 184
10 9 Epilogue 185
343.26 KB
  9.1 Midgap Levels 185
  9.2 Special Features 188
  9.3 Comparison Of Heavy TM Deep-Levels In Different Semiconductors 189
  9.4 References 196