Positron annihilation study of
equilibrium point defects in GaAs
Dissertation
zur Erlangung des akademischen Grades
Dr. rerum naturlalium (Dr. rer. nat.)
vorgelegt der
Mathematisch-Naturwissenschaftlich-Technischen Fakultät
(mathematisch-naturwissenschaftlicher Bereich)
der
Martin-Luther-Universität Halle-Wittenberg
von Herrn
Vladimir Bondarenko
geb. am 15.02.1978 in Sumy, Ukraine
Gutachter:
(1) Prof. Dr. R. Krause-Rehberg
(2) Prof. Dr. U. M. Gösele
(3) Prof. Dr. P. Masher
urn:nbn:de:gbv:3-000006446
[http://nbn-resolving.de/urn/resolver.pl?urn=nbn%3Ade%3Agbv%3A3-000006446]
Halle(Saale), November 2003
verteidigt am 30.01.2004
Table of contents
1.Introduction ____________________________________________________ 1
2.
3.
Thermodynamics of native point defects in GaAs_____________________ 3
2.1
GaAs system at melting point _____________________________________ 3
2.2
Defects chemistry in GaAs________________________________________ 5
2.3
Tan model and Fermi-level effect __________________________________ 7
2.4
Quantum mechanical calculations _________________________________ 9
2.5
Electrical compensation in n-type GaAs ___________________________ 11
Experimental methods _________________________________________ 13
3.1
3.1.1
3.1.2
3.2
3.2.1
3.2.2
4.
Positron annihilation lifetime spectroscopy _________________________ 13
Physical background of positron trapping ________________________________ 13
Measurement principle and trapping model ______________________________ 14
Temperature dependence of positron trapping in semiconductors ______ 16
Theory ___________________________________________________________ 16
Model of positron trapping for experimental data fitting ____________________ 21
3.3
Coincidence Doppler-broadening spectroscopy _____________________ 24
3.4
Procedure of positron annihilation measurements ___________________ 26
3.5
Other methods ________________________________________________ 27
Vacancy formation in n-type silicon-doped GaAs ___________________ 29
4.1
Introduction __________________________________________________ 29
4.2
Heavily silicon doped GaAs ______________________________________ 31
4.2.1
4.2.2
4.2.3
Experimental ______________________________________________________ 31
Defect identification by means of positron annihilation _____________________ 31
Model of the compensation mechanism _________________________________ 33
4.3
Influence of dislocations on the lateral distribution of SiGaVGa complexes in
Si-doped VGF GaAs wafers ___________________________________________ 35
4.3.1 Experimental details ________________________________________________ 36
4.3.2 Correlation between photoluminescence and positron annihilation investigations of
silicon doped VGF GaAs ___________________________________________________ 37
4.3.3 Lateral variation of the compensation degree in VGF GaAs:Si _______________ 41
4.4
4.4.1
4.4.2
4.4.3
4.5
Identification of the 0.95 eV luminescence band in VGF GaAs:Si ______ 44
Experimental ______________________________________________________ 44
Cathodoluminescence spectroscopy ____________________________________ 45
Defect identification by positron annihilation _____________________________ 47
Discussion: defects formation in VGF GaAs:Si______________________ 49
5. Vacancy formation in semi-insulating and silicon-doped GaAs under
equilibrium conditions_____________________________________________ 51
5.1
Experimental__________________________________________________ 51
5.2
Defects detected by PALS in annealed GaAs________________________ 53
5.2.1
5.2.2
5.2.3
5.3
5.3.1
5.3.2
5.3.3
5.3.4
6.
Si-doped GaAs_____________________________________________________ 53
Undoped semi-insulating GaAs________________________________________ 54
Reproducibility of results for annealed SI GaAs ___________________________ 55
Defect identification in annealed n-type and SI GaAs ________________ 59
Identification of vacancies____________________________________________ 59
Identification of shallow traps in undoped annealed GaAs ___________________ 62
Charge state of the VAs complex _______________________________________ 64
Gibbs free energy of VAs formation_____________________________________ 66
Defects study in intentionally undoped VCz-grown GaAs _____________ 67
6.1
Growth method________________________________________________ 67
6.2
Carbon controlled growth _______________________________________ 69
6.3
Influence of the melt stoichiometry and unintentional doping on vacancy
formation___________________________________________________________ 71
6.4
6.4.1
6.4.2
6.4.3
Results of PALS measurements __________________________________ 73
Semi-insulating GaAs _______________________________________________ 73
p-type GaAs_______________________________________________________ 75
n-type GaAs_______________________________________________________ 77
6.5
Validity of positron annihilation for determination of vacancy
concentration _______________________________________________________ 79
6.6
7.
On the temperature dependence of positron trapping in GaAs _________ 82
7.1
GaAs:Si vs GaAs:Te____________________________________________ 83
7.2
Positron trapping in GaAs doped with Si and Te simultaneously _______ 85
7.2.1
7.2.2
7.2.3
7.3
8.
Summary _____________________________________________________ 80
Experimental ______________________________________________________ 85
Results of temperature-dependent PALS measurements _____________________ 86
Discussion ________________________________________________________ 87
Systematization of results _______________________________________ 89
Summary____________________________________________________ 93
References ______________________________________________________ 95
Eidesstattliche Erklärung
Curriculum Vitae
Acknowledgments