AlGaN/GaN MBE 2DEG heterostructures [Elektronische Ressource] : interplay between surface-, interface- and device properties / vorgelegt von Martin Kočan

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• Physik

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• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2003
• Nombre de lectures: 24
• Poids de l'ouvrage: 9 Mo

Extrait

AlGaN/GaN MBE 2DEG Heterostructures:
Interplay between Surface-, Interface-
and Device-Properties
Von der Fakultät für Elektrotechnik und Informationstechnik
der Rheinisch-Westfälischen Technischen Hochschule Aachen
zur Erlangung des akademischen Grades
eines Doktors der Ingenieurwissenschaften genehmigte Dissertation
vorgelegt von
Diplom-Ingenieur
Martin Kocanˇ
aus Bratislava, Slowakei
Berichter: Universitätsprofessor Dr. H. Lüth
Univ Dr.-Ing. R. Waser
Tag der mündlichen Prüfung: 16. Juli 2003
Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfügbarContents
1 Introduction 1
2 Nitrides 5
2.1 Nitrides Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 Physical Properties . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.2 Symmetry and Polarization of III-Nitrides . . . . . . . . . . . . . 8
2.1.3 Heterostructure and 2-dimensional Electron Gas . . . . . . . . . 15
2.1.4 Electron Transport in III-V Nitrides . . . . . . . . . . . . . . . . 19
2.1.5 Principle of HEMT Device . . . . . . . . . . . . . . . . . . . . . 27
2.2 Nitride Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.2.1 Substrates for III-Nitride based Heteroepitaxy . . . . . . . . . . . 31
2.2.2 MBE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.2.3 MOCVD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
2.3 Surface and Interface Electronic Properties . . . . . . . . . . . . . . . . . 46
2.3.1 Band Offsets at SiC/AlN, SiC/GaN and GaN/AlGaN Heterostruc-
tures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.3.2 Schottky Barrier Height at Pt/GaN Ga- and N-face interfaces . . . 48
2.3.3 Impact of surface states on AlGaN/GaN HFET performance . . . 50
3 Experimental Methods 53
3.1 Auger Electron Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . 53
3.2 Low Energy Electron Diffraction . . . . . . . . . . . . . . . . . . . . . . 55
3.3 Atomic Force Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.4 X-Ray Diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
3.5 Secondary Ions Mass Spectroscopy . . . . . . . . . . . . . . . . . . . . . 62
3.6 X-ray Photoelectrony . . . . . . . . . . . . . . . . . . . . . 63
3.6.1 Core Levels and Valence Band Spectra . . . . . . . . . . . . . . 65
3.6.2 Determination of the Valence Band Offset . . . . . . . . . . . . . 67
3.7 Capacitance-Voltage Measurements . . . . . . . . . . . . . . . . . . . . 69
3.8 Magnetotransport Measurement . . . . . . . . . . . . . . . . . . . . . . 75
3.8.1 Van der Pauw Hall Measurement . . . . . . . . . . . . . . . . . . 77
iii Contents
4 Experimental Apparatus 83
4.1 MBE System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4.2 In- and ex-situ Analysis System . . . . . . . . . . . . . . . . . . . . . . 87
4.2.1 Hall Measurement Experimental Setup . . . . . . . . . . . . . . 87
4.2.2 Hall Control using a PC . . . . . . . . . . . . . . . 91
5 Band Scheme Modelling 93
5.1 Self-consistent Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . 93
5.2 Modelling of 2DEG AlGaN/GaN Heterostructures . . . . . . . . . . . . 98
5.2.1 Polarization Charge Issue . . . . . . . . . . . . . . . . . . . . . 98
5.2.2 Surface States . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
5.2.3 AlGaN Barrier Thickness and Al Alloy Composition . . . . . . . 102
5.2.4 Doped AlGaN/GaN Heterostructures . . . . . . . . . . . . . . . 105
6 Experimental Results 107
6.1 Epitaxial Growth of III-N Layers . . . . . . . . . . . . . . . . . . . . . . 107
6.1.1 Growth Rate Determination . . . . . . . . . . . . . . . . . . . . 107
6.1.2 Determination of Al Ga N Alloy Composition . . . . . . . . 111X 1¡X
6.2 Growth Optimization of Nitrides on SiC Substrate . . . . . . . . . . . . . 113
6.2.1 Substrate Preparation . . . . . . . . . . . . . . . . . . . . . . . . 113
6.2.2 Nucleation and Buffer Layer Growth . . . . . . . . . . . . . . . 115
6.2.3 Structural Properties of GaN grown on n- and i-SiC Substrate . . 117
6.2.4 Impurities in MBE Growth . . . . . . . . . . . . . . . . . . . . . 118
6.2.5 Unintentional Doping in MBE GaN Layers . . . . . . . . . . . . 121
6.2.6 Growth of a HEMT Structure . . . . . . . . . . . . . . . . . . . 122
6.2.7 HEMT Device . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
6.3 Growth Optimization of Nitrides on Si Substrate . . . . . . . . . . . . . . 132
6.3.1 Substrate Preparation . . . . . . . . . . . . . . . . . . . . . . . . 132
6.3.2 GaN Layer Growth . . . . . . . . . . . . . . . . . . . . . . . . . 134
6.3.3 Diffusion and Impurities in MBE Growth . . . . . . . . . . . . . 139
6.3.4 Growth of a HEMT structure . . . . . . . . . . . . . . . . . . . . 142
6.4 Surface and Interface Properties of AlGaN/GaN Heterostructures . . . . . 148
6.4.1 Fermi Level Pinning at Al Ga N Surfaces . . . . . . . . . . . 148X 1¡X
6.4.2 Si N Passivation . . . . . . . . . . . . . . . . . . . . . . . . . . 1543 4
7 Conclusions 157
8 Zusammenfassung 161CONTENTS iii
A Hall Measurement Program Realization 167
A.1 Device Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
A.2 Program Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
B Growth Parameters of MBE Samples 179
C Physical Constants and Periodic Table of Elements 189
List of Figures 191
List of Tables 195
Bibliography 197
Acknowledgements 211
Curriculum vitae 213iv ContentsChapter 1
Introduction
In the semiconductor technology the leading role is still played by silicon, with its well
stabilized CMOS process. All integrated circuits and chips are practically developed on
silicon basis. In the last decades also III-V semiconductors gained more and more impor-
tance, conquering well established positions in important niches. As-based (AlGaInAs)
and P-based (AlGaInP) systems are successfully used for optoelectronic applications in
the infrared, red and yellow range, as well as for high frequency devices.
There are many areas where conventional III-V semiconductors cannot be used. Short
wavelength light emitters are required for full color displays, laser printers, high density
information storage, and under water communication. High power and high temperature
transistors are needed for automobile engines, future advanced power distribution systems,
all electric vehicles and avionics. Si and conventional III-V semiconductors are not suit-
able for designing and fabricating optoelectronic devices in the violet and blue region of
the spectrum. Their band gaps are not sufficiently large. GaAs based electronic devices
can not be used at high temperatures. III-nitrides are particularly suitable for applications
in these areas. The band gaps of III-nitrides are large and direct. The band gap values vary
from 0.7 eV for InN, 3.4 eV for GaN and 6.2 eV for AlN for wurtzite semiconductors
(fig. 1.1, 2.1). Due to their wide band gaps and strong bond strength, they can be used for
violet, blue and green light emitting devices and for high temperature transistors.
In the last 10 years we assisted impressive development of the nitride semiconductor tech-
nology, where major achievements have been the fabrication of high brightness blue light
emitting devices (LEDs) and laser diodes [1–3]. In 1993 Nakamura succeeded in produc-
ing a blue LED using an InGaN/AlGaN double heterostructure, whose1 cd light intensity
is comparable with the one of an AlGaAs LED. The following intense work has led to the
brightest visible LEDs available today concerning the blue part of the spectrum (6 cd). As
far as blue LEDs were developed the interest of the research moved to blue lasers. A blue
laser, having a wavelength shorter than the lasers that are used nowadays, could greatly
increase the storage capability of CD-ROM and DVD discs, which are actually widely
used to store electronic data.
1Wavelength (nm)
2 1. Chapter Introduction
Besides optoelectronic applications, nitride heterostructures play an important role in
AlGaN/GaN based RF-high power high frequency High Electron Mobility Transistor
(HEMT) devices [4, 5], that are expected to be used in earth bound transmitter stations
for satellite communication. Specially for high power applications the GaN-based ma-
terial enables high temperature operation, reduced cooling, high frequency operation
7(10 GHz), high saturation electron velocity (2:7£10 cm/s), a larger breakdown elec-
tric field (3 MV/cm), allowing high drain-source bias voltage, a high power density of an
AlGaN/GaN HEMT over 11 W/mm, a larger conduction band discontinuity between GaN
and AlGaN and the presence of polarization fields that allow a large two dimensional elec-
tron gas (2DEG) concentration to be confined, as opposed to by remote doping induced
2DEG as in AlGaAs/GaAs modulation doped heterostructures and gate induced inversion
in silicon Metal Oxide Semiconductor Field Effect Transistors (MOSFETs).
In semiconductor technology and device physics the development of semiconductor
devices and the related process technology was intimately related to fundamental investi-
gations in surface and interface science. A recent great acknowledgment of this important
interplay was the Nobel Prize in Physics 2000 to H