New process approaches to metalorganic vapor phase epitaxy of III-nitrides for high power HEMTs [Elektronische Ressource] / vorgelegt von Roger Steins

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2006
• Nombre de lectures: 14
• Langue: English
• Poids de l'ouvrage: 8 Mo

Extrait

New Process Approaches to Metalorganic Vapor
Phase Epitaxy of III-nitrides for High Power HEMTs
Von der Fakult˜at fur˜ Elektrotechnik und Informationstechnik
der Rheinisch{Westf˜alischen Technischen Hochschule Aachen
zur Erlangung des akademischen Grades eines Doktors der Ingenieurwissenschaften,
genehmigte Dissertation.
vorgelegt von
Diplom-Ingenieur
Roger Steins
aus Johannesburg, Sudafrik˜ a
Berichter: Universit˜atsprofessor Hans Luth˜
Universit˜atsprofessor Wilfried Mokwa
Tag der mundlic˜ hen Prufung:˜ 10. August 2006
Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online
verfugbar.˜2Contents
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Scope of this Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Properties of III-Nitrides and their Application in HEMTs 7
2.1 Physical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Electrical Properties of Nitrides . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.1 Spontaneous and Piezoelectric Polarization . . . . . . . . . . . . . . 10
2.2.2 HEMT-Structures Based on AlGaN/GaN Heterojunctions . . . . . 13
3 Principles of MOVPE GaN Growth 19
3.1 MOVPE Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.1.1 General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.1.2 Thermodynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.1.3 Kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.1.4 Hydrodynamics and Mass Transport . . . . . . . . . . . . . . . . . 27
3.1.5 In uence of Carrier Gases . . . . . . . . . . . . . . . . . . . . . . . 32
3.2 Sapphire as Substrate for (Al)GaN growth . . . . . . . . . . . . . . . . . . 33
3.3 MOVPE III-nitride Growth . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.3.1 Modelling of GaN Growth . . . . . . . . . . . . . . . . . . . . . . . 38
iii CONTENTS
4 Experimental Setup and Characterization Methods 41
4.1 The Horizontal MOVPE Reactor (Aix 200 RF-S) . . . . . . . . . . . . . . 41
4.2 In-situ Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.2.1 In-situ Normalized Re ectometry . . . . . . . . . . . . . . . . . . . 45
4.2.2 Pyrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.3 Ex-situ Characterization Methods . . . . . . . . . . . . . . . . . . . . . . . 52
4.3.1 Film Thickness and Homogeneity . . . . . . . . . . . . . . . . . . . 52
4.3.2 Difierential Interference Contrast Microscopy . . . . . . . . . . . . . 53
4.3.3 Atomic Force Microscopy. . . . . . . . . . . . . . . . . . . . . . . . 54
4.3.4 Photoluminescence Spectroscopy . . . . . . . . . . . . . . . . . . . 55
4.3.5 X-ray difiraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.3.6 Rutherford Backscattering Spectroscopy . . . . . . . . . . . . . . . 57
4.3.7 Contactless Sheet Resistance Measurement . . . . . . . . . . . . . . 58
4.3.8 Hall Efiect Measurement . . . . . . . . . . . . . . . . . . . . . . . . 59
5 Determination of Surface Temperature on Transparent Substrates 61
5.1 Standard Measurement Techniques vs. Emissivity Corrected Pyrometry . . 61
5.2 Conventional Calibration Methods. . . . . . . . . . . . . . . . . . . . . . . 62
5.3 New Calibration Approach with SiC Band Temperature Dependence. . . . 64
5.4 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
5.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
6 New Growth Approach for GaN 71
6.1 Morphological Development of MOVPE GaN. . . . . . . . . . . . . . . . . 71
6.2 Growth Reproducibility Issues . . . . . . . . . . . . . . . . . . . . . . . . . 75
6.3 New Process Approach: The Inverted Inlet Conflguration . . . . . . . . . . 78
6.3.1 Growth Modelling. . . . . . . . . . . . . . . . . . . . . . . . . . . . 79CONTENTS iii
6.3.2 Experimental Veriflcation: Inverted to Conventional Inlet . . . . . . 83
6.3.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
7 Optimizing GaN Growth 89
7.1 Homogeneity Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
7.1.1 Optimization Strategy . . . . . . . . . . . . . . . . . . . . . . . . . 90
7.1.2 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . 92
7.1.3 Modelling Veriflcation . . . . . . . . . . . . . . . . . . . . . . . . . 94
7.1.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
7.2 On the Efiect of N on GaN Growth . . . . . . . . . . . . . . . . . . . . . 972
7.2.1 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . 97
7.2.2 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
7.3 Electrical and Structural Optimization with Nitrogen . . . . . . . . . . . . 103
7.3.1 Aim to Prolong Coalescence in N . . . . . . . . . . . . . . . . . . . 1032
7.3.2 Role of Nitrogen in 2D Growth . . . . . . . . . . . . . . . . . . . . 105
7.3.3 Optimizing GaN . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
7.3.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
8 HEMT growth 113
8.1 AlGaN Growth in the inverted inlet . . . . . . . . . . . . . . . . . . . . . . 114
8.1.1 Thickness and Alloy Composition control . . . . . . . . . . . . . . . 114
8.1.2 Thin AlGaN/GaN layers . . . . . . . . . . . . . . . . . . . . . . . . 117
8.1.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
8.2 Highly resistive GaN bufier. . . . . . . . . . . . . . . . . . . . . . . . . . . 121
8.2.1 Strategy for Semi-Insulating GaN . . . . . . . . . . . . . . . . . . . 121
8.2.2 In uence of Carrier Gas on Resistance . . . . . . . . . . . . . . . . 123
8.2.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131iv CONTENTS
8.3 HEMT results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
9 Summary and Conclusions 137
References 141
Danksagung 149List of Figures
2.1 Stick and ball diagram of wurtzitic GaN. According to the ionic radii the
small spheres represent nitrogen while the big ones represent Gallium. . . . 8
2.2 Difierent polarities (Ga- and N faced) of wurtzite GaN [Amb98]. . . . . . . 10
2.3 Bandgaps of important binary semiconductors. . . . . . . . . . . . . . . . . 11
2.4 Sumofthemicroscopicdipoles,resultinginaspontaneouspolarization =0
in the wurtzite structure (right) and =0 in the zincblende (left). . . . . . . 12
2.5 Banddiagramoftheheterostructureformedbylightlyn-dopednarrowgap
semiconductor I and heavily n-doped wide gap semiconductor II divided
one from another (a) and together in thermodynamical equilibrium [Iba99]. 14
2.6 PolarisationinducedchargeinaGa-faced(a)andN-faced(b)AlGaN/GaN
heterostructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.7 Dependenceofthe2DEGmobilityonthetemperatureandscatteringmech-
anisms for AlGaN/GaN heterostructures [Jen01]. . . . . . . . . . . . . . . 17
3.1 Process steps in CVD reactions . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2 Typical Arrhenius plot of a CVD deposition process . . . . . . . . . . . . . 22
3.3 Schematic of the formation heat as a function of the distance along the
reaction path. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.4 Adatom motion and preferred adsorption at kinks and islands. . . . . . . . 27
3.5 Schematic diagram of the Rayleigh number versus the Reynolds number,
classifying the difierent ow behavior expected in horizontal CVD reactors
[Jen93]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.6 Structure of an epilayer under biaxial compression. Pseudomorphic (left)
and relaxed (right) with misflt dislocations.. . . . . . . . . . . . . . . . . . 34
v
6vi LIST OF FIGURES
3.7 Rhombohedral structure and surface planes of the sapphire substrate. . . . 35
3.8 Growth model for GaN on sapphire substrates. . . . . . . . . . . . . . . . . 37
3.9 Schematic of the GaN decomposition and reaction pathways. Activation
energy (kcal=mol) is shown for each reaction pathway. Here, GaN* and
Ga*areadsorptionspeciesonthesurface. BasedontheworkofMihopoulos
[Mih99] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.1 The AIX 200/4 horizontal reactor equipped with in-situ re ectometry and
pyrometry (EpiR-TT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.2 Schematic representation of the AIX 200/4 RF-S horizontal reactor em-
ployed for the MOVPE growth of group III nitrides. Note, that the inlet
of group V and III is the conventional state on this sketch. . . . . . . . . . 44
4.3 Schematicofthein-siture ectometerasusedformeasurementsonrotating
samples to detect the re ection [Hab02]. . . . . . . . . . . . . . . . . . . . 45
4.4 Schematic diagram illustrating the normalized re ectance. Layer B is nor-
malized to the re ectance of layer A [Hab02].. . . . . . . . . . . . . . . . . 46
4.5 Typical re ectance transient measured at a wavelength of 600 nm. . . . . . 47
4.6 Spectral radiance of a blackbody from Planck’s radiation law for several
temperatures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.7 Spectralradiancesforablackbodyandagraybodywithemissiv