Surface preparation and Mn states of (Ga,Mn)As investigated by means of soft and hard x-ray photoemission spectroscopy [Elektronische Ressource] / vorgelegt von Benjamin Schmid

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• Physik

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• Publié par: julius-maximilians-universitat_wurzburg
• Publié le: 01 janvier 2010
• Nombre de lectures: 23
• Langue: English
• Poids de l'ouvrage: 13 Mo

Extrait

Surface preparation and Mn states of
(Ga,Mn)As investigated by means of soft-
and hard x-ray photoemission spectroscopy
Dissertation zur Erlangung des
naturwissenschaftlichen Doktorgrades
der Bayerischen Julius-Maximilians-Universit at Wurzbur g
vorgelegt von
Benjamin Schmid
aus Augsburg
Wurzburg 2010Eingereicht am:
bei der Fakult at fur Physik und Astronomie
Gutachter der Dissertation:
1. Gutachter: Prof. Dr. R. Claessen
2. Gutachter: Prof. Dr. K. Brunner
Prufer im Promotionskolloquium:
1. Prufer: Prof. Dr. R. Claessen
2. Prufer: Prof. Dr. K. Brunner
3. Prufer: Prof. Dr. E. M. Hankiewicz
Tag des Promotionskolloquiums:
Doktorurkunde ausgeh andigt am:"Ist der Soldat auf sich alleine gestellt, muss er in der Lage sein, im Sinne
des Auftrags zu handeln."
Zentrale Dienstvorschrift der Bundeswehr 3/11, Gefechtsdienst aller Truppen (zu Lande),
Blatt 101, Bundesministerium fur Verteidigung, Bonn (1988).Contents
1 Introduction 1
2 Diluted magnetic semiconductors 3
2.1 Gallium Arsenide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1 Physical properties of GaAs relevant for spintronic applications . 3
2.1.2 Natural oxide layer on GaAs . . . . . . . . . . . . . . . . . . . . . 7
2.1.3 Thermal desorption of oxides . . . . . . . . . . . . . . . . . . . . 8
2.1.4 Wet-chemical etching of GaAs . . . . . . . . . . . . . . . . . . . . 9
2.1.5 Dry etching (ion beam etching) . . . . . . . . . . . . . . . . . . . 13
2.2 Gallium Manganese Arsenide . . . . . . . . . . . . . . . . . . . . . . . . 14
2.2.1 Crystallographical and transport properties of (Ga,Mn)As . . . . 14
2.2.2 The valence band { RKKY picture . . . . . . . . . . . . . . . . . 18
2.2.3 The impurity band { double exchange picture . . . . . . . . . . . 21
2.2.4 Post-growth annealing of (Ga,Mn)As . . . . . . . . . . . . . . . . 23
3 Aspects of photoemission spectroscopy 27
3.1 Photoelectric e ect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.1.1 Basic theory of PES . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.1.2 Resonant photoemission spectroscopy . . . . . . . . . . . . . . . . 30
3.2 Many-body e ects and energy loss structures . . . . . . . . . . . . . . . . 31
3.2.1 Plasmon excitations . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.2.2 Charge-transfer satellites . . . . . . . . . . . . . . . . . . . . . . . 36
3.2.3 Multiplet splitting . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.2.4 Background corrections . . . . . . . . . . . . . . . . . . . . . . . . 39
3.2.5 Qualitative and quantitative analysis of spectra . . . . . . . . . . 40
3.3 Inelastic mean free path, information depth and e ective attenuation length 43
3.3.1 Inelastic mean free path . . . . . . . . . . . . . . . . . . . . . . . 43
3.3.2 Information depth . . . . . . . . . . . . . . . . . . . . . . . . . . 48
3.3.3 Overlayer thickness . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.3.4 Attenuation length . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.3.5 Experimental case study of inhomogeneous depth distribution and
elastic scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
iContents
4 Surface preparation of (Ga,Mn)As 63
4.1 E ects of tempering on . . . . . . . . . . . . . . . . . . . . . 63
4.2 Sputtering of (Ga,Mn)As . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.3 Wet-chemical etching of (Ga,Mn)As . . . . . . . . . . . . . . . . . . . . . 74
4.4 Combination of wet-chemical etching, ion-milling, and thermal treatment 77
5 Electronic structure of (Ga,Mn)As 87
5.1 Thermally activated surface segregation of manganese in (Ga,Mn)As . . . 87
5.2 Manganese valency in . . . . . . . . . . . . . . . . . . . . . . 94
5.3 Resonant photoemission spectroscopy on (Ga,Mn)As . . . . . . . . . . . 102
5.4 Investigation of the Mn 2p core level spectra . . . . . . . . . . . . . . . . 108
6 Temperature dependent transport measurements on (Ga,Mn)As 115
6.1 Doping dependence of the resistivity . . . . . . . . . . . . . . . . . . . . 115
6.2 Annealing dependence of they . . . . . . . . . . . . . . . . . . . 116
6.3 Low temperature behavior of the resistivity . . . . . . . . . . . . . . . . . 118
7 Conclusion and outlook 123
Bibliography 125
iiList of Figures
2.1 Crystal structure and band diagram of GaAs . . . . . . . . . . . . . . . . 4
2.2 Band of GaAs . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 Ternary Ga-As-O phase diagram . . . . . . . . . . . . . . . . . . . . . . . 8
2.4 Sketch of wet-chemical etching of GaAs . . . . . . . . . . . . . . . . . . . 12
2.5 Crystal structure and band diagram of (Ga,Mn)As . . . . . . . . . . . . 15
2.6 Phase diagram of (Ga,Mn)As . . . . . . . . . . . . . . . . . . . . . . . . 16
2.7 Doping dependence of the resistivity of as-grown (Ga,Mn)As . . . . . . 17
2.8 Relation between Curie temperature T and carrier concentration p inc
as-grown (Ga,Mn)As . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.9 Sketch of Friedel oscillations . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.10 Sketch of the impurity band in (Ga,Mn)As . . . . . . . . . . . . . . . . . 22
2.11 Dependence of on the annealing time of as-grown (Ga,Mn)As samples
with various lm thicknesses . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.12 Thermal activated surface segregation of interstitial Mn in (Ga,Mn)As . . 25
3.1 Sketch of the geometry of a PES experiment . . . . . . . . . . . . . . . . 28
3.2 Sketch of the energy diagram of a PES experiment . . . . . . . . . . . . 29
3.3 Sketch of ResPES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.4 Sketch of the di erence between single electron and many-body system
PES spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.5 Sketch of a plasmon excitation . . . . . . . . . . . . . . . . . . . . . . . . 33
3.6 Energy loss spectra of GaAs from the literature . . . . . . . . . . . . . . 34
3.7 Sketch of initial state, unscreened nal state and well-screened nal state
of Mn in MnO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.8 Multiplet splitting of the Mn 3s core level in heavily oxidized (Ga,Mn)As 38
3.9 Example of a Shirley-background correction . . . . . . . . . . . . . . . . 40
3.10 Calculations of the IMFP for GaAs . . . . . . . . . . . . . . . . . . . . . 44
3.11 of the for various materials . . . . . . . . . . . . . . . 46
3.12 Sketch of the mean escape depth and information depth . . . . . . . . . . 49
3.13 Deconvolution of overlayer and substrate intensities . . . . . . . . . . . . 50
3.14 Sketches of idealized and realistic trajectories of photoelectrons in solids . 53
3.15 Refraction of the photoelectrons at the inner potential . . . . . . . . . . 55
3.16 Reduced oxide layer thickness of Ga Mn As . . . . . . . . . . . . . . . 571 x x
3.17 Comparison of the reduced oxide layer thickness in Si/SiO and Ge/GeO 592 2
iiiList of Figures
3.18 Chemical composition of the Ga Mn As surface . . . . . . . . . . . . . 621 x x
4.1 Evolution of the oxide layer thickness and the contaminations of (Ga,Mn)As
during long-term tempering at 200 C . . . . . . . . . . . . . . . . . . . . 64
4.2 Long time changes of the stoichiometry in the course of tempering of
(Ga,Mn)As at 200 C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.3 As and Ga 3d core levels in the course of sputtering of (Ga,Mn)As at 500 eV 68
4.4 Oxide layer thickness and stoichiometry in the course of sputtering of
(Ga,Mn)As at 500 eV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.5 Long time changes of the stoichiometry in the course of sputtering of
(Ga,Mn)As at 600 eV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.6 O and C 1s core levels in the course of sputtering of (Ga,Mn)As at 1000 eV 72
4.7 As and Ga 3d core levels in the course of sputtering of (Ga,Mn)As at
1000 eV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.8 Stoichiometry in the course of sputtering of (Ga,Mn)As at 1000 eV . . . . 73
4.9 Sketch of the glove bag used for etching under protective Ar atmosphere 74
4.10 As and Ga 3d core level treated with various acids . . . . . . . . . . . . . 75
4.11 As 2p core level treated with H SO . . . . . . . . . . . . . . . . . . . 763=2 2 4
4.12 As and Ga 2p of (Ga,Mn)As in the course of a combination of wet-3=2
etching, ion-milling, and tempering cleaning procedure . . . . . . . . . . 79
4.13 O and C 1s core levels of (Ga,Mn)As in the course of combined wet-
etching, ion-milling, and tempering clean procedure . . . . . . . . . . . . 79
4.14 Evolution of the stoichiometry during a combined wet-chemical, ion-milling,
and tempering treatment of (Ga,Mn)As . . . . . . . . . . . . . . . . . . . 80
4.15 In uence of the combined wet-chemical, ion-milling, and tempering prepa-
ration of (Ga,Mn)As on the Mn 2p doublet . . . . . . . . . . . . . . . . . 82
4.16 LEED patterns of (Ga,Mn)As at 33:7 eV and 35:6 eV . . . . . . . . . . . 84
4.17 AFM picture of a surface after a combined surface preparation 85
5.1 Evolution of the As 2p line shape upon annealing . . . . . . . . . . . . 883=2
5.2 Ev of the Mn 2p line shape upon . . . . . . . . . . . 903=2
5.3 Angle dependence of the Mn 2p line shape for an as-grown and an3=2
annealed (Ga,Mn)As sample . . . . . . . . .