Misorientation angle에 따른 r-plane 사파이어위에 성장한 무분극 a-plane n-type, p-type GaN 특성 연구 = The characterizations of misorientation angle effects of nonpolar a-plane n-type, p-type GaN films grown on r-plane sapphire substrates

다국어 초록 (Multilingual Abstract)

III-nitride wide band gap semiconductors have been extensively investigated for optoelectronic applications such as laser diodes and light-emitting diodes (LEDs) for the green, blue, and violet spectral regions. However, conventional c-plane gallium nitride (GaN) LEDs are suffered by strong internal fields originating from strain-induced piezoelectric and spontaneous polarizations in the [0001] direction. This polarization-related field has been reported to induce the spatial separation of electrons and holes in quantum wells (QWs), which leads to the reduction of radiative recombination rates in QWs. In a recent decade, several groups have studied nonpolar and semipolar GaN LEDs which emerged as promising candidate to overcome this problem. Heteroepitaxial non-polar a-plane (11-20) GaN LEDs has been demonstrated. However, it is still far from high performance.
In this paper, we investigated the characterizations of misorientation angle effects of nonpolar a-plane (11-20) n-type, p-type GaN films grown on (1-102) r-plane sapphire substrates. For the initial layer of the high quality a-plane GaN template using the multi buffer layer technique, a 180 nm thick nucleation layer was grown in mixed atmosphere of N2 and H2 at 1050 ？C on r-plane sapphire substrate with -0.4 ~ +0.4？ off-axis orientations by metalorganic chemical vapor deposition (MOCVD). By inserting SiNx interlayer, extended defects were further reduced. A thin SiNx interlayer was used because excessive amount of SiNx makes poor surface morphology. In +0.2 off-axis orientations sample, The XRC FWHM was measured as 417 arc sec along c-axis direction, and rms roughness was 1.545 nm at 10 ？ 10 ？. On the GaN template, we grew a 1.5 Si-doped (3.0 ？ 1018 cm-3) n-type GaN layer and 1 Mg-doped (6.58 ？ 1019 cm-3) p-type GaN layer with the sapphire substrate tilted of +0.15 〬, -0.15 〬, +0.2 〬, -0.2 〬, +0.4 〬, -0.4 〬 with c-axis [0001] direction. We achieve smooth and pit-free surface with +0.2 off-axis orientations sample. With further increase in off-axis angle of more than +0.2？, it was difficult to control surface morphology in the a-plane n , p -type GaN. So we believe that misorientation angle of the sapphire substrate is optimized with +0.2 off-axis orientations in our experiment.
LED chips with an area of 200 ？ 500 2 were formed through conventional photolithography, followed by dry etching techniques. Cr/Au and Ni/Au were used as n , p-type GaN contacts, respectively. The optical output power tested on-wafer of 1.24 mW and EQE of 2.37% were measured at a drive current of 20 mA, and the FWHM of the EL emission at 475.1 nm was 32 nm. A maximum output power of 4.45 mW and an EQE of 1.7% were obtained at the bias condition of 100 mA.

목차 (Table of Contents)

• 제 1 장 서론..1
• 제 2 장 이론적 고찰..5
• 2.1 LED (Light Emitting Diode) 개요 ......................................................5
• 2.1.1 LED 소자이론 .....................................................................................6
• 2.1.2 LED의 전기적, 광학적 특성 ..............................................................7
• 2.2 GaN (Gallium nitride) ...........................................................................9
• 2.3 무분극 GaN LED (nonpolar GaN LED) ...............................................12
• 2.3.1 무분극 GaN의 물리적 특성 ...............................................................12
• 2.4 Misorientation angle에 따른 주요 연구 이슈 .......................................17
• 제 3 장 실험 및 결과 19
• 3.1 r 면 (r-plane) 위에 성장한 무분극 a 면 (a-plane) 저결함 GaN를 위한 완충층 연구 ..............................................................................19
• 3.1.1 실험개요 ............................................................................................19
• 3.1.2 실험방법 ............................................................................................20
• 3.1.3 실험결과 ............................................................................................20
• 3.2 Misorientation angle에 따른 r 면 (r-plane) 위에 성장한 무분극 a 면 (a-plane) n-type GaN 특성 연구 ........................................................25
• 3.2.1 실험개요 ............................................................................................25
• 3.2.2 실험방법 ............................................................................................26
• 3.2.3 실험결과 ............................................................................................27
• 3.3 Misorientation angle에 따른 r 면 (r-plane) 위에 성장한 무분극 a 면 (a-plane) p-type GaN 특성 연구.................................................30
• 3.3.1 실험개요 ............................................................................................30
• 3.3.2 실험방법 ............................................................................................31
• 3.3.3 실험결과 ............................................................................................32
• 3.4 r 면 (r-plane) 위에 성장한 무분극 a 면 (a-plane) GaN LED Device 연구 .........................................................................................39
• 3.4.1 실험방법 ............................................................................................39
• 3.4.2 실험결과 ............................................................................................40
• 제 4 장 결 론44참고 문헌 .........................................................................................................46
• 감사의 글 .........................................................................................................48