Abstract ........................................................ i
Zusammenfassung ............................................... iii
1 Introduction: Silicon for photonic applications .............. 1
1.1 Moore's Law - a problem? ................................ 2
1.2 Silicon photonics - the solution? ....................... 4
1.2.1 Fundamentals ..................................... 4
1.2.2 Recent progress on silicon-based light sources ... 8
1.3 Objective and structure of this thesis ................. 10
2 Photonic crystal nanocavities for enhanced light emission ... 11
2.1 Theory & Motivation .................................... 12
2.1.1 Cavity theory ................................... 12
2.1.2 Enhanced cavity mode emission ................... 14
2.2 Photonic crystal structures ............................ 16
2.2.1 2D photonic crystal slabs ....................... 16
2.2.2 2D photonic crystal slab cavities ............... 20
2.2.3 Woodpile 3D photonic crystals ................... 23
2.2.4 Woodpile 3D photonic crystal cavities ........... 25
2.3 Summary ................................................ 29
3 2D silicon photonic crystal structures ...................... 31
3.1 Sample design .......................................... 32
3.1.1 Layer structure ................................. 32
3.1.2 Photonic crystal structure ...................... 33
3.2 Fabrication ............................................ 36
3.2.1 Fabrication overview ............................ 36
3.2.2 Electron-beam resist: PMMA vs. ZEP .............. 38
3.2.3 Electron-beam lithography ....................... 38
3.2.4 Reactive ion etching ............................ 41
3.2.5 Creation of freestanding membranes .............. 43
3.3 Experimental techniques ................................ 44
3.3.1 Photoluminescence setup ........................ 45
3.3.2 Measurement preparation and execution ........... 46
3.4 Silicon as light emitting material ..................... 47
3.5 Investigation of 2D silicon photonic crystal cavities .. 49
3.5.1 Cavity mode emission ............................ 49
3.5.2 Mode pumping mechanism .......................... 54
3.5.3 Indications for Purcell-enhancement ............. 57
3.6 Summary ................................................ 64
4 Germanium-islands in 2D silicon photonic crystal
structures .................................................. 65
4.1 Fundamentals of germanium-islands ...................... 66
4.1.1 Hetero-epitaxial growth ......................... 66
4.1.2 Island morphologies ............................. 69
4.1.3 Electronic structure of germanium-islands in
silicon ......................................... 71
4.2 Sample design .......................................... 73
4.2.1 Layer structure ................................. 73
4.2.2 Photonic crystal structure ...................... 74
4.3 Wafer thinning and growth of germanium-islands ......... 76
4.4 Germanium-islands as light emitter ..................... 78
4.5 Investigation of germanium-islands in 2D photonic
crystal cavities ....................................... 80
4.5.1 Unpatterned region .............................. 80
4.5.2 Cavity mode emission: Intensity versus
quality-factor .................................. 82
4.5.3 Influence of free carrier absorption ............ 90
4.6 Summary ................................................ 93
5 Germanium-islands in 3D silicon photonic crystal
structures .................................................. 95
5.1 Sample design .......................................... 96
5.1.1 Woodpile lattice ................................ 96
5.1.2 Woodpile defect cavity .......................... 98
5.1.3 Layer-by-layer structure ........................ 99
5.2 Fabrication ........................................... 102
5.2.1 Wafer thinning and growth ...................... 102
5.2.2 Electron-beam lithography ...................... 104
5.2.3 Creation of freestanding membranes ............. 105
5.3 Micromanipulation ..................................... 105
5.4 Experimental techniques ............................... 111
5.4.1 Photoluminescence setup ........................ 111
5.4.2 Superconducting single photon detector ......... 113
5.5 Investigation of germanium-islands in 3D photonic
crystal cavities ...................................... 114
5.5.1 Continuous wave measurements ................... 114
5.5.2 Time-resolved measurements ..................... 118
5.6 Summary ............................................... 120
Summary and Conclusion ..................................... 123
6 Outlook: Germanium-islands in silicon p-i-n diodes ......... 127
6.1 Fabrication ........................................... 128
6.1.1 Wafer structure and growth ..................... 128
6.1.2 Mesa etching ................................... 129
6.1.3 Deposition and patterning of insulating layer .. 131
6.1.4 Gold contacts .................................. 131
6.2 Investigation of germanium-islands in silicon p-i-n
diodes ................................................ 135
6.2.1 Diode characteristic ........................... 135
6.2.2 Micro-photoluminescence ........................ 138
6.2.3 Micro-electroluminescence ...................... 139
6.2.4 Micro-photocurrent ............................. 140
6.3 Summary ............................................... 144
6.4 Recommendation for future developments ................ 145
A Photonic crystal theory & numerical modeling ............... 149
A.l Photonic crystal theory ............................... 149
A.2 Numerical modeling of photonic crystal structures ..... 153
A.2.1 Planewave-expansion method ..................... 153
A.2.2 Finite-difference time-domain method ........... 156
A.2.3 Planewave-expansion vs. finite-difference
time-domain method ............................. 157
B Sample processing .......................................... 161
B.1. Photonic crystals ..................................... 161
B.2. p-i-n diodes .......................................... 164
List of samples ............................................... 171
Bibliography .................................................. 175
List of figures ............................................... 195
List of publications .......................................... 199
Acknowledgements .............................................. 203
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