2.1 Band structures of direct and indirect semiconductors . . . 5 2.2 Temperature-dependent (a) charge carrier density and (b) Fermi
en-ergy in a semiconductor . . . 7 2.3 Energy diagram of a semiconductor with a deep trap in its band gap 9 2.4 Theoretical electron mobility as a function of the electron
concentra-tion at 300 K . . . 13 2.5 Phonon dispersion of the acoustical and optical phonon mode of a
linear crystal . . . 14 2.6 Dependence of the phonon energy on the charge carrier concentration
due to phonon-plasmon coupling at the Γ-point . . . 16 2.7 Energy band diagram of a metal and semiconductor forming a
Schot-tky contact on an n-type semiconductor . . . 17 3.1 Schematic of the operating mode of the van der Pauw method . . . . 20 3.2 Schematic of the van der Pauw method for a square shaped sample . 20 3.3 Schematic of the Hall measurement method for a square shaped sample 21 3.4 Energy band diagram of a Schottky barrier diode for the biasing
con-ditions during the DLTS measurement . . . 24 3.5 The DLTS measurement principal shown for a box car analysis. . . . 26 3.6 The correlation function of the b1 Fourier coefficient of the DLTFS
method . . . 27 3.7 Scheme of the Raman scattering process in the quantum mechanical
description . . . 30 3.8 Scheme of some vibrational modes in a linear chain with two different
atoms and inversion symmetry and their polarizability . . . 31 4.1 Scheme of the monoclinic unit cell of β-Ga2O3 . . . 37 4.2 Band structure for β-Ga2O3 calculated by Peelaers et al. using DFT . 38 4.3 Scheme of a Czochralski growth furnace . . . 39 4.4 Photographic image of Czochralski grown β-Ga2O3 single crystals
doped with various impurities . . . 40 4.5 Illustration of the preparation fromβ-Ga2O3 bulk crystal to the
epi-ready substrate . . . 40 4.6 Illustration of the metal-organic vapor-phase epitaxy (MOVPE) process 41 4.7 Illustration of the halide-vapor phase epitaxy (HVPE) process . . . . 42 5.1 The monoclinic unit cell ofβ-Ga2O3and a scheme of a plate capacitor
structure . . . 47 5.2 The relative static dielectric constant versus the temperature
perpen-dicular to (100), (010) and (001) between 25 K and 500 K . . . 48 5.3 Room-temperature Raman spectra from n-type silicon dopedβ-Ga2O3
crystals with different electron concentrations . . . 51
B.1 List of Figures
5.4 Room temperature Raman spectra from the silicon doped β-Ga2O3
crystal with n = 8×1018cm−3 excited at different wavelength . . . . 52 5.5 Temperature-dependent Raman spectra from the silicon doped β
-Ga2O3 crystal with n= 8×1018cm−3 . . . 53 5.6 Low-temperature Raman spectra (5 K) from the β-Ga2O3 crystals
heavily doped either with silicon or tin . . . 54 5.7 Raman spectra from the heavily silicon doped β-Ga2O3 crystal with
n = 8×1018cm−3 in dependence on a magnetic field . . . 54 5.8 Low-temperature Raman spectrum (20 K) from the β-Ga2O3 crystal
heavily doped with silicon (n= 8×1018cm−3) excited at 632.8 nm . . 55 5.9 Absorption spectra of (100)-oriented, Cr-doped β-Ga2O3 crystals . . . 60 5.10 Overview of the Absorption coefficient α over the Cr concentration
NCr in Cr-doped β-Ga2O3 . . . 61 5.11 I-V characteristic of a SBD on β-Ga2O3:Cr,Si at room temperature
and current density over the average electric field in the SBD . . . 63 5.12 Photographic image, spectrum and intensity over leakage current of
the EL generated in a SBD . . . 64 5.13 Temperature dependence of the Cr3+ electroluminescence . . . 65 5.14 Spectrum and pseudo-Stark splitting in the EL at 7 K . . . 66 5.15 Energy-level scheme of the free Cr3+ ion and the splitting of the levels
under the influence of the present crystal field and an external electric field . . . 67 5.16 Schematic representation of the inversion symmetry relation in the
monoclinic unit cell of β-Ga2O3 . . . 68 6.1 Band diagram of homoepitaxial β-Ga2O3 layers on semi-insulating
substrates doped with Mg or Fe . . . 72 6.2 SIMS profile of Si in homoepitaxialβ-Ga2O3 layer on semi-insulating
substrates doped with Mg or Fe . . . 73 6.3 Net doping profile of a β-Ga2O3 layer homoepitaxially grown by
MOVPE on a conductive, (100)-oriented substrate . . . 73 6.4 Band diagram of homoepitaxial β-Ga2O3 layer on semi-insulating
substrates doped with Mg or Fe including a Si interface peak . . . 74 6.5 Electron Hall mobility as a function of the electron Hall concentration
at 300 K for β-Ga2O3 homoepitaxially grown by MOVPE on (100) oriented substrates . . . 77 6.6 Electron Hall concentration n at 300 K as a function of the silicon
atomic concentration measured by SIMS forβ-Ga2O3 layers homoepi-taxially grown by MOVPE on (100) oriented substrates . . . 77 6.7 DLTS spectrum of an (100) oriented, conductive β-Ga2O3 substrate
and of a layer grown by MOVPE on such a substrate . . . 77 6.8 Electronmicroscopic investigation of MOVPE homoepitaxially grown
layers on (100) on substrates . . . 79 6.9 Scheme of the distribution of incoherent twin boundaries (ITBs) . . . 80 6.10 Scheme of the band bending due to dangling bonds introducing
ac-ceptor states in an n−type semiconductor . . . 81
B.1 List of Figures
6.11 Scheme of the charge depletion zones forming around incoherent twin boundaries . . . 82 6.12 Electron Hall mobility as a function of the electron Hall concentration
at 300 K for β-Ga2O3 homoepitaxially grown by MOVPE on (100) oriented substrates . . . 84 6.13 Electron Hall concentration n at 300 K as a function of the silicon
atomic concentration measured by SIMS forβ-Ga2O3 layers homoepi-taxially grown by MOVPE on (100) oriented substrates . . . 84 6.14 AFM and TEM images of substrates and layers with miscut-angles
of 0.1◦, 2◦, 4◦ and 6◦ towards [001] direction . . . 86 6.15 Electron Hall mobility as a function of the electron Hall
concentra-tion at 300 K for β-Ga2O3 homoepitaxially grown by MOVPE on substrates oriented (100) with a miscut of 6◦ along c . . . 87 6.16 TEM images of layers grown on substrates with a miscut either
to-wards [00¯1] or [001] . . . 88 6.17 Electron Hall mobility as a function of the electron Hall
concentra-tion at 300 K for β-Ga2O3 homoepitaxially grown by MOVPE on substrates oriented (100) with a miscut either towards [00¯1] or [001]
and the incoherent twin boundary model . . . 89 6.18 Scheme of the growth modes depending on the effective diffusion
length during MOVPE growth . . . 90 6.19 AFM images ofβ-Ga2O3layers homoepitaxially grown by MOVPE on
(100) substrates with 6◦ and 4◦ miscut for optimized growth parameters 91 6.20 AFM image of a β-Ga2O3 layer homoepitaxially grown by MOVPE
on a (100) substrate with 2◦ miscut for optimized growth parameters 92 6.21 Electron Hall mobility as a function of the electron Hall
concentra-tion at 300 K forβ-Ga2O3 homoepitaxially grown by MOVPE on sub-strates oriented (100) with different miscut angles and the incoherent twin boundary model . . . 93 6.22 DLTS spectrum and AFM image of a layer grown by MOVPE on a
substrate with 6◦ miscut and an (100) oriented, conductive β-Ga2O3
substrate . . . 94 6.23 Charge carrier concentration over inverse temperature of a β-Ga2O3
layer grown by MOVPE on a substrate with 6◦ miscut . . . 95 6.24 AFM and TEM images of an (010)-oriented substrate and a layer
grown by MOVPE on it . . . 96 6.25 Electron Hall mobility as a function of the electron Hall concentration
at 300 K for β-Ga2O3 homoepitaxially grown by MOVPE on (010)-oriented substrates . . . 97 6.26 DLTS spectra of a MOVPE layer on an (010)-oriented, conductive
β-Ga2O3 substrate for different rate windows . . . 99 6.27 Arrhenius plots of the measured temperature dependence of the
elec-tron emission times of the traps from the DLTS spectra of Fig. 6.26. . 99 6.28 Charge carrier concentration over inverse temperature of twoβ-Ga2O3
layer grown by MOVPE on (010)-oriented substrates . . . 100