Silicon based microcavity enhanced light emitting diodes [Elektronische Ressource] / von Jaroslava Potfajova

Silicon based microcavity enhanced light emitting diodes [Elektronische Ressource] / von Jaroslava Potfajova

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Silicon based microcavity enhancedlight emitting diodesDissertationvorgelegt derFakult at Mathematik und NaturwissenschaftenTechnische Universit at DresdenvonIng. Jaroslava Potfajovageboren am 26. M arz 1980 in Trencin, SlowakeiEingereicht am 30. Juli 2009Verteidigt am 7. Dezember 20091. Gutachter: Prof. Dr. Manfred Helm2. Gutachter: Prof. Dr. Thomas DekorsyIt is better to light a candle, than to curse the darkness.KonfuziusAbstractRealising Si-based electrically driven light emitters in a process technology compati-ble with mainstream microelectronics CMOS technology is key requirement for the im-plementation of low-cost Si-based optoelectronics and thus one of the big challenges ofsemiconductor technology. This work has focused on the development of microcavityenhanced silicon LEDs (MCLEDs), including their design, fabrication, and experimentalas well as theoretical analysis. As a light emitting layer the abrupt pn-junction of a Sidiode was used, which was fabricated by ion implantation of boron into n-type silicon.Such forward biased pn-junctions exhibit room-temperature EL at a wavelength of 1138nm with a reasonably high power e ciency of 0.1% [1].

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Silicon based microcavity enhanced
light emitting diodes
Dissertation
vorgelegt der
Fakult at Mathematik und Naturwissenschaften
Technische Universit at Dresden
von
Ing. Jaroslava Potfajova
geboren am 26. M arz 1980 in Trencin, SlowakeiEingereicht am 30. Juli 2009
Verteidigt am 7. Dezember 2009
1. Gutachter: Prof. Dr. Manfred Helm
2. Gutachter: Prof. Dr. Thomas DekorsyIt is better to light a candle, than to curse the darkness.
KonfuziusAbstract
Realising Si-based electrically driven light emitters in a process technology compati-
ble with mainstream microelectronics CMOS technology is key requirement for the im-
plementation of low-cost Si-based optoelectronics and thus one of the big challenges of
semiconductor technology. This work has focused on the development of microcavity
enhanced silicon LEDs (MCLEDs), including their design, fabrication, and experimental
as well as theoretical analysis. As a light emitting layer the abrupt pn-junction of a Si
diode was used, which was fabricated by ion implantation of boron into n-type silicon.
Such forward biased pn-junctions exhibit room-temperature EL at a wavelength of 1138
nm with a reasonably high power e ciency of 0.1% [1]. Two MCLEDs emitting light
at the resonant wavelength about 1150 nm were demonstrated: a) 1 MCLED with the
resonator formed by 90 nm thin metallic CoSi mirror at the bottom and semitranparent2
distributed Bragg re ector (DBR) on the top; b) 5:5 MCLED with the resonator formed
by high re ecting DBR at the bottom and semitransparent top DBR. Using the appoach
of the 5:5 MCLED with two DBRs the extraction e ciency is enhanced by about 65%
compared to the silicon bulk pn-junction diode.
Keywords
microcavity, resonant cavity, Fabry-Perot resonator, distributed Bragg re ector, silicon
light emitter, silicon diode, LED, MCLED
5Contents
List of Abbreviations and Symbols 9
1 Introduction and motivation 13
2 Theory 15
2.1 Electronic band structure of semiconductors . . . . . . . . . . . . . . . . . 15
2.2 Light emitting diodes (LED) . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.2.1 History of LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.2.2 Mechanisms of light emission . . . . . . . . . . . . . . . . . . . . . 18
2.2.3 Electrical properties of LED . . . . . . . . . . . . . . . . . . . . . . 23
2.2.4 LED e ciency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.3 Si based light emitters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.4 Microcavity enhanced light emitting pn-diode . . . . . . . . . . . . . . . . 33
2.4.1 Bragg re ectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.4.2 Fabry-Perot resonators . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.4.3 Optical mode density and emission enhancement in coplanar Fabry-
Perot resonator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
2.4.4 Design and optical properties of a Si microcavity LED . . . . . . . 43
3 Preparation and characterisation methods 55
3.1 techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3.1.1 Thermal oxidation of silicon . . . . . . . . . . . . . . . . . . . . . . 55
3.1.2 Photolithography . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.1.3 Wet chemical cleaning and etching . . . . . . . . . . . . . . . . . . 58
3.1.4 Ion implantation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
3.1.5 Plasma Enhanced Chemical Vapour Deposition (PECVD) of silicon
nitride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.1.6 Magnetron sputter deposition . . . . . . . . . . . . . . . . . . . . . 61
3.2 Characterization techniques . . . . . . . . . . . . . . . . . . . . . . . . . . 63
3.2.1 Variable Angle Spectroscopic Ellipsometry (VASE) . . . . . . . . . 63
3.2.2 Fourier Transform Infrared Spectroscopy (FTIR) . . . . . . . . . . 64
3.2.3 Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
3.2.4 Electroluminescence and photoluminescence measurements . . . . . 69
4 Experiments, results and discussion 73
4.1 Used substrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
4.1.1 Silicon substrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
4.1.2 Silicon-On-Insulator (SOI) substrates . . . . . . . . . . . . . . . . . 74
4.2 Fabrication and characterization of distributed Bragg re ectors . . . . . . . 76
7CONTENTS
4.2.1 Deposition and characterization of SiO . . . . . . . . . . . . . . . . 762
4.2.2 Dep of Si . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
4.2.3 Distributed Bragg Re ectors (DBR) . . . . . . . . . . . . . . . . . 84
4.2.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
4.3 Design of Si pn-junction LED . . . . . . . . . . . . . . . . . . . . . . . . . 90
4.4 Resonant microcavity LED with CoSi bottom mirror . . . . . . . . . . . . 912
4.4.1 Device preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.4.2 Electrical Si diode characteristics . . . . . . . . . . . . . . . . . . . 94
4.4.3 EL spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.4.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
4.5 Si based microcavity LED with two DBRs . . . . . . . . . . . . . . . . . . 95
4.5.1 Test device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.5.2 Device fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.5.3 LED on SOI versus MCLED . . . . . . . . . . . . . . . . . . . . . . 104
4.5.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
5 Summary and outlook 121
5.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
5.2 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
A Appendix 127
A.1 The parametrization of optical constants . . . . . . . . . . . . . . . . . . . 127
A.1.1 Kramers-Kronig relations . . . . . . . . . . . . . . . . . . . . . . . . 127
A.1.2 Forouhi-Bloomer dispersion formula . . . . . . . . . . . . . . . . . . 127
A.1.3 Tauc-Lorentz dispersion formula . . . . . . . . . . . . . . . . . . . . 128
A.1.4 Sellmeier dispersion formula . . . . . . . . . . . . . . . . . . . . . . 128
A.2 Wafer holder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
List of publications 141
Acknowledgements 143
Declaration / Versicherung 145
8List of Abbreviations and Symbols
Abbreviations
AFM atomic force microscopy
BHF bu ered hydro uoric acid
BOE oxide etch
BOX buried oxide
CCD charge coupled device
CMOS complementary metal oxide semiconductor
DBR distributed Bragg re ector
DC direct current
EDX energy dispersive X-ray spectroscopy
EL electroluminescence
EZ emitting zone
FSR free spectral range
FTIR Fourier transform infrared spectroscopy
FWHM full width at half maximum
H high refractive index material
HVEM high voltage electron microscopy
IC integrated circuit
L low refractive index material
LED light emitting diode
MBE molecular beam epitaxy
MCLED micocavity light emitting diode
MIS metal-insulator-semiconductor
MOS metal-oxide-silicon
NA numerical aperture
NBOHC non-bridging oxygen hole center
NBS National Bureau of Standards
NC nanocrystals
ODC oxygen de ciency center
OLED organic light emitting diode
OX oxide
PECVD plasma enhanced chemical vapour deposition
PL photoluminescence
PS porous silicon
9List of Abbreviations and Symbols
RCLED resonant cavity light emitting diode
RF radio frequency
SEM scanning electron microscopy
SIMOX separation by implantation of oxygen
SOI silicon on insulator
SUB substrate
TEM transmission electron microscopy
TIR total internal re ector
TTV total thickness variation
VASE variable angle spectroscopic ellipsometry
VCSEL vertical-cavity surface-emitting lasers
VSL variable stripe length
Symbols
A area
a amplitude
1c speed of light (299 792 458 ms )
d thickness
D carrier mobilityn;p
19e elementary charge (1.60217646 10 coulombs)
E energy
F nesse
G integrated emission enhancementint
G spectral enhancemente
34 2 1h Planck’s constant (6.626068 10 m kgs ) h = 2h
I current
k wave vector
L length, thickness
l optical mode
m mass
n refractive index
N Avogadro’s constantA
p momentum
P power
Q quality factor
R resistivity, re ectance
r re ectivity
T temperature, transmittance
t time, transmisivity
V voltage, bias
W transition rate
W width of depletion zoneD
permitivity
e ciency
10