Fig. 1.1. Enery bandgap and lattice constant of compound semiconductor materials. Recently the bandgap energy of InN is reported as 0.7eV. 21

Fig. 1.2. The wurtzite structure of III-nitride 22

Fig. 1.3. Atomic arrangement in Ga-face and N-face GaN. 23

Fig. 1.4. Schematic representation of the in-plane atomic arangement in the case of a (0001) GaN grown on c plane sapphire [15]. White: III-plane of GaN, black: Oplane of sapphire. 27

Fig. 1.5. Schematic illustration of the Spontaneous polarization in wurtzite GaN. The small and large spheres indicate Ga and N, respectively. The arrows indicate the directions of dipole moments, pointing from the anion (N) to the cation (Ga). 28

Fig. 1.6. Spontaneous and piezoelectric polarization effects on different faces of GaN under compressive and tensile strain. 29

Fig. 1.7. Band profiles in 5 nm GaN and 10 nm Al0.1Ga0.9N quantum wells. (a) Growth direction is assumed along (0001) direction and the polarizations fields result in a quantum confined Stark effect and poor electron-hole overlap. (b) (1100) oriented structure is free of electrostatic fields, therefore flat-band conditions are...(이미지참조) 32

Fig. 1.8. Schematic bandstructure diagram of GaInN/GaN QW oriented along different crystal axes (a, c, e). Sketch of QW plane in the hexagonal crystal structure (b, d, f). Situation of polar c-axis (a, b), non-polar m-axis (c, d), and nonpolar a-axis growth (e, f) [25]. 35

Fig. 1.9. Schematic illustration of the epitaxial relationship between GaN and r-plane sapphire. The positive GaN c-axis points in same direction as the sapphire c-axis projection on the growth surface. 36

Fig. 2.1. Crystallography of sapphire substrate 50

Fig. 2.2. Schematic growth temperature profile of (112-0) nonpolar a-plane GaN by using MOCVD(이미지참조) 51

Fig. 2.3. 1 μm × 1 μm AFM images of GaN nucleus grown on r-plane sapphire substrates with thickness of (a) 50 nm, (b) 120 nm, (c) 150 nm, and (d) 250 nm, respectively [23]. 54

Fig. 2.4. Changes of the full width at half maximum (FWHM) of the X-ray rocking curves for the (a) on-axis (112-0) and (b) off-axis (101-1) plane of a-plane GaN grown with different initial growth pressure.(이미지참조) 59

Fig. 2.5. Measurements of reflectance intensity during the a-plane GaN growth with different initial growth pressure. 61

Fig. 2.6. AFM surface morphologies for the nucleation layers grown with different initial growth pressure, (a) 200 mbar, (b) 400 mbar, (c) 500 mbar, (d) 600 mbar. The scale of AFM image is 5 μm × 5 μm. 63

Fig. 2.7. The results of X-ray diffraction (XRD) measurements with (a) 2θ-ω scan of the nucleation layers grown at 200 mbar and 600 mbar. (b) Change of the full width at half maximum (FWHM) of the X-ray rocking curves for the on-axis (112_0) plane of the nucleation layers grown at 200 mbar and 600 mbar.(이미지참조) 66

Fig. 2.8. Room temperature PL spectra of the a-plane GaN grown with different initial growth pressure. 67

Fig. 2.9. The evolution of surface morphology obtained by SEM during the early stage of direct growth of a-plane GaN 69

Fig. 2.10. AFM results of surface morphology (20 ㎛ × 20㎛) during the early stage of direct growth of a-plane GaN, corresponding to the SEM results. 70

Fig. 2.11. Plan-view TEM images revealing threading dislocation densities ((a) and (b)) and basal stacking faults ((c) and (d)) for the sample A ((a) and (c)) and B ((c) and (d)). The diffraction conditions for (a) and (b), and (c) and (d) are g=0002 and 11_00, respectively.(이미지참조) 72

Fig. 3.1. Nomarski optical microscope images of a-plane GaN films with different SiH₄ flow rates: (a) 0, (b) 6.61, (c) 64.9 and (d) 81.1 nmol/min. The images were taken at a 100× magnification. 81

Fig. 3.2. (a) On-axis full width at half maximum (FWHM) values of the X-ray rocking curves measured along c- and m-axis directions and (b) off-axis FWHM values of a-plane GaN. 83

Fig. 3.3. Room temperature carrier concentration and mobility of a-plane GaN with different SiH₄ flow rates. 84

Fig. 3.4. Room temperature photoluminescence (PL) spectra of a-plane GaN with different SiH₄ flow rates. 86

Fig. 3.5. Peak position of near band edge (NBE) emission as a function of carrier concentration with a solid guideline for the eye. 87

Fig. 4.1. Hole concentration and mobility of Mg doped a-plane GaN at room temperature as a function of growth pressure. 96

Fig. 4.2. The plan view SEM images for Mg-doped a-plane GaN layers as a function of growth pressure of (a) 100 mbar, (b) 200 mbar, and (c) 300 mabr, respectively. 98

Fig. 4.3. Hole concentration and mobility of Mg-doped a-plane GaN at room temperature with different NH₃ flow rate. 100

Fig. 4.4. The plan view SEM images for Mg-doped a-plane GaN layers with different NH₃ flow rate of (a) 6000 sccm, (b) 8000 sccm, and (c) 10000 sccm, respectively. 101

Fig. 4.5. Hole concentration and mobility of Mg-doped a-plane GaN at room temperature with increasing Cp₂Mg flow rate. 103

Fig. 4.6. The plan view SEM images for Mg-doped a-plane GaN layers with increasing Cp₂Mg flow rate of (a) 420 sccm, (b) 450 sccm, (c) 475 sccm, and (d) 500 sccm, respectively. 105

Fig. 4.7. The panchromatic CL mapping images with NH₃ flow rate of (a) 6000 sccm, (b) 10000 sccm, respectively. Plan view TEM results of Mg doped a-plane GaN with Cp₂Mg flow rate of 475 sccm. (c) The stacking faults with g vectors 11-00, and (d) the partial dislocations with g vector 0002, respectively.(이미지참조) 107

Fig. 4.8. SEM surface images of Mg-doped a-plane GaN with a growth rate of (a) 0.8 Å/sec, (b) 1.2 Å/sec, (c) 1.5 Å/sec, and (d) 2.2 Å/sec, respectively. 116

Fig. 4.9. Cross-sectional STEM images of Mg-doped a-plane GaN with a growth rate of (a) 0.8 Å/sec, (b) 1.5 Å/sec, and (c) 2.2 Å/sec, respectively. 118

Fig. 4.10. (a) A plan view SEM, and (b) panchromatic mapping CL result of Mg-doped a-plane GaN with at a growth rate of 0.8 Å/sec, and (c) crosssectional TEM image of Mg-doped a-plane GaN with a growth rate of 2.2 Å/sec. 120

Fig. 4.11. Hole concentration and mobility of Mg-doped a-plane GaN at room temperature as a function of growth rate. 123

Fig. 4.12. (a) Current-voltage (I-V) characteristics, (b) Electroluminescence (EL) intensity, and (c) EL spectra of LEDs with p-GaN growth rate of 0.8 Å/sec and 2.2 Å/sec for different drive current. 125

Fig. 5.1. High resolution TEM (HRTEM) image and CBED patterns which were obtained with Z = [1-100] from the a-plane GaN grown on r-plane sapphire.(이미지참조) 135

Fig. 5.2. The room temperature PL peak wavelength and intensity of MQWs grown at different growth pressure. 136

Fig. 5.3. The XRD ω-2θ scan for (112-0) of MQWs grown at different growth pressure.(이미지참조) 138

Fig. 5.4. The thickness of well and barrier (one pair) of MQWs grown at different growth pressure, which was obtained from XRD ω-2θ scan for (112-0) plane.(이미지참조) 139

Fig. 5.5. PL spectra of MQWs grown at 100 mbar and 400 mbar with the same thickness (18nm) of well and barrier (one pair). 140

Fig. 5.6. The variation of wafer temperature at susceptor temperature 800 ℃, and temperature difference, ΔT = susceptor temperature - wafer temperature, as a function of growth pressure. 142

Fig. 5.7. The room temperature PL spectra for MQWs grown at 100 mbar and 400 mbar with wafer temperature 667 ℃. 144

Fig. 5.8. The characteristics of room temperature PL spectra with different NH₃ flow. 147

Fig. 5.9. The characteristics of PL spectra with different well width in MQWs. 148

Fig. 5.10. The characteristics of room temperature PL spectra with different number of InGaN well. 149

Fig. 5.11. Schematic cross-section of the a-plane LED structure grown on r-plane sapphire. 152

Fig. 5.12. (a) Electroluminescence (EL) spectra, and (b) current-voltage (I-V) characteristic of LED with for different drive current, from 20 mA to 100 mA, emitting image of nonpolar LED (c) after chip process, and (d) package 153