• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.51-51
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• 2010

Group III-nitride semiconductors have been widely studied as the materials for growth of light emitting devices. Currently, GaN devices are predominantly grown in the (0001) c-plane orientation. However, in case of using polar substrate, an important physical problem of nitride semiconductors with the wurtzite crystal structure is their spontaneous electrical polarization. An alternative method of reducing polarization effects is to grow on non-polar planes or semi-polar planes. However, non-polar and semipolar GaN grown onto r-plane and m-plane sapphire, respectively, basically have numerous defects density compared with c-plane GaN. The purpose of our work is to reduce these defects in non-polar and semi-polar GaN and to fabricate high efficiency LED on non/semi-polar substrate. Non-polar and semi-polar GaN layers were grown onto patterned sapphire substrates (PSS) and nano-porous GaN/sapphire substrates, respectively. Using PSS with the hemispherical patterns, we could achieve high luminous intensity. In case of semi-polar GaN, photo-enhanced electrochemical etching (PEC) was applied to make porous GaN substrates, and semi-polar GaN was grown onto nano-porous substrates. Our results showed the improvement of device characteristics as well as micro-structural and optical properties of non-polar and semi-polar GaN. Patterning and nano-porous etching technologies will be promising for the fabrication of high efficiency non-polar and semi-polar InGaN LED on sapphire substrate.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.23-23
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• 2009

GaN-based nitride semiconductors have attracted considerable attention in high-brightness light-emitting-diodes (LEDs) and laser diodes (LDs) covering from green to ultraviolet spectral range. LED and LD heterostructures are usually grown on (0001)-$Al_2O_3$. The large lattice mismatch between $Al_2O_3$ substrates and the GaN layers leads to a high density of defects(dislocations and stacking faults). Moreover, Ga and N atoms are arranged along the polar [0001] crystallographic direction, which leads to spontaneous polarization. In addition, in the InGaN/GaN MQWs heterostructures, stress applied along the same axis can also give rise to piezoelectric polarization. The total polarization, which is the sum of spontaneous and piezoelectric polarizations, is aligned along the [0001] direction of the wurtzite heterostructures. The change in the total polarization across the heterolayers results in high interface charge densities and spatial separation of the electron and hole wave functions, redshifting the photoluminescence peak and decreasing the peak intensity. The effect of polarization charges in the GaN-based heterostructures can be eliminated by growing along the non-polar [$11\bar{2}0$] (a-axis) or [$1\bar{1}00$] (m-axis) orientation instead of thecommonly used polar [0001] (c-axis). For non-polar GaN growth on non-polar substrates, the GaN films have high density of planar defects (basal stacking fault BSFs, prismatic stacking fault PSFs), because the SFs are formed on the basal plane (c-plane) due to their low formation energy. A significant reduction in defect density was recently achieved by applying blocking layer such as SiN, AlN, and AlGaN in non-polar GaN. In this work, we were performed systematic studies of the defects in the nonpolar GaN by conventional and high-resolution transmission electron microscopy.

• JSTS:Journal of Semiconductor Technology and Science
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• 제6권2호
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• pp.79-86
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• 2006

N-polar, Ga-polar, and non-polar GaN was grown by MBE and MOVPE using various substrates and influence of polarity has been investigated. The GaN growth by MOVPE is along cplane (0001), c-plane (0001), and a-plane (11-20) direction on c-plane (0001), a-plane (11-20) and r-plane (1-102) sapphire substrate respectively. The polarity of the film has a strong influence on the morphology and the optical properties of PA-MBE grown As-doped GaN layers. Strong blue emission from As-doped GaN was observed only in the case of N-polarity (000-1) layers, which was attributed to the highest concentration of Ga dangling bonds for this polarity of a GaN surface.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2006년도 추계학술발표대회 및 제11회 신소재 심포지엄
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• pp.3.2-3.2
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• 2006

• JSTS:Journal of Semiconductor Technology and Science
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• 제14권5호
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• pp.557-565
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• 2014

We report the effect of basal-plane stacking faults (BSFs) on X-ray diffraction (XRD) of non-polar (11$\underline{2}$0) a-plane GaN films with different $SiN_x$ interlayers. Complete $SiN_x$ coverage and increased three-dimensional (3D) to two-dimensional (2D) transition stages substantially reduce BSF density. It was revealed that the Si-doping profile in the Si-doped GaN layer was unaffected by the introduction of a $SiN_x$ interlayer. The smallest in-plane anisotropy of the (11$\underline{2}$0) XRD ${\omega}$-scan widths was found in the sample with multiple $SiN_x$ layers, and this finding can be attributed to the relatively isotropic GaN mosaic resulting from the increase in the 3D-2D growth step. Williamson-Hall (WH) analysis of the (h0$\underline{h}$0) series of diffractions was employed to determine the c-axis lateral coherence length (LCL) and to estimate the mosaic tilt. The c-axis LCLs obtained from WH analyses of the present study's representative a-plane GaN samples were well correlated with the BSF-related results from both the off-axis XRD ${\omega}$-scan and transmission electron microscopy (TEM). Based on WH and TEM analyses, the trends in BSF densities were very similar, even though the BSF densities extracted from LCLs indicated that the values were reduced by a factor of about twenty.

• 한국결정성장학회지
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• 제19권1호
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• pp.1-5
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• 2009

본 연구에서는 metal organic vapor phase epitaxy(MOVPF) 방법으로 $8^{\circ}$-off (100) Si 기판 위에 분극이 완화된(1-101) GaN를 성장한 후 광소자로서의 가능성을 확인하고자 (1-101) GaN 위에 InGaN/GaN MQW 구조를 제작하였으며 암모니아 유량, TMI 유랑 그리고 성장 온도 등 다양한 성장 조건에 따른 구조적, 광학적인 특성을 scanning electron microscopy(SEM)와 cathodoluminescence(CL)을 통하여 관찰하였다. (1-101) GaN 성장시 암모니아 유량이 적을수록 관통전위가 현저히 줄어드는 것을 확인하였다. (1-101) GaN stripe 위에 성장 시킨 InGaN/GaN MQW 구조를 이용하여 성장조건에 따라서 391.5nm부터 541.2nm에 이르는 넓은 영역의 범위에서 발광 스펙트럼을 조절할 수 있음을 확인하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.279.2-279.2
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• 2016

InGaN/GaN multiple quantum wells (MQWs) have been attracted much attention as light-emitting diodes (LEDs) in the visible and UV regions. Particularly, quantum efficiency of green LEDs is decreased dramatically as approaching to the green wavelength (~500 nm). This low efficiency has been explained by quantum confined Stark effect (QCSE) induced by piezoelectric field caused from a large lattice mismatch between InGaN and GaN. To improve the quantum efficiency of green LED, several ways including epitaxial lateral overgrowth that reduces differences of lattice constant between GaN and sapphire substrates, and non-polar method that uses non- or semi-polar substrates to reduce QCSE were proposed. In this study, graded short-period InGaN/GaN superlattice (GSL) was grown below the 5-period InGaN/GaN MQWs. InGaN/GaN MQWs were grown on the patterned sapphire substrates by vertical-metal-organic chemical-vapor deposition system. Five-period InGaN/GaN MQWs without GSL structure (C-LED) were also grown to compare with an InGaN/GaN GSL sample. The luminescence properties of green InGaN/GaN LEDs have been investigated by using photoluminescence (PL) and time-resolved PL (TRPL) measurements. The PL intensities of the GSL sample measured at 10 and 300 K increase about 1.2 and 2 times, respectively, compared to those of the C-LED sample. Furthermore, the PL decay of the GSL sample measured at 10 and 300 K becomes faster and slower than that of the C-LED sample, respectively. By inserting the GSL structures, the difference of lattice constant between GaN and sapphire substrates is reduced, resulting that the overlap between electron and hole wave functions is increased due to the reduced piezoelectric field and the reduction in dislocation density. As a results, the GSL sample exhibits the increased PL intensity and faster PL decay compared with those for the C-LED sample. These PL and TRPL results indicate that the green emission of InGaN/GaN LEDs can be improved by inserting the GSL structures.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제37회 하계학술대회 초록집
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• pp.169-169
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• 2009

• 한국결정성장학회지
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• 제18권3호
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• pp.97-100
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• 2008

HVPE 법에 의해 성장시킨 GaN 박막이 기판에 따라서 극성과 비극성 특성의 변화에 대해 연구하였다. A-plane($11{\bar{2}}0$), C-plane(0001) and M-Plane($10{\bar{1}}0$) 사파이어 기판을 이용하여 $10\;{\mu}m$ 두께의 GaN 박막을 성장하였다. 광학현미경 및 원자력간 현미경(OM, AFM)을 이용해 표면 구조를 관찰하고, HRXD를 통해 이들은 모두 wurtzite 구조를 갖고 C-plane으로 성장시에는, 극성 특성을, A-plane 및 M-plane 성장 시에는 비극성 특성을 가짐을 확인하였으며, Photoluminescence (PL)측정 결과 3.4 eV에서 발광 피크, 2.2 eV에서 yellow luminescence peak를 확인하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.229-229
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• 2010

We report a high crystalline nonpolar a-plane (11-20) GaN on r-plane (1-102) sapphire substrates with $+0.15^{\circ}$, $-0.15^{\circ}$, $+0.2^{\circ}$, $-0.2^{\circ}$ and $+0.4^{\circ}$ misoriented by metalorganic chemical-vapor deposition (MOCVD). The multi-quantum wells (MQWs) active region is consists of 5 periods the nonpolar a-plane InGaN/GaN (a-InGaN/GaN) on a high quality a-plane GaN (a-GaN) template grown by using the multibuffer layer technique. The full widths at half maximum (FWHMs) of x-ray rocking curve (XRC) obtained from phiscan of the specimen that was grown up to nonpolar a-plane GaN layers with double crystal x-ray diffraction. The FWHM values of $+0.4^{\circ}$ misoriented sapphire substrate were decreased down to 426 arc sec for $0^{\circ}$ and 531 arc sec for $-90^{\circ}$, respectively. Also, the samples were characterized by photoluminescence (PL).