• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.243.1-243.1
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• 2016

Recently, many groups have attempted to fabricate 3-dimensional (3D) structures of GaN such as pyramids, rods, stripes and annulars. Since quantum structures on non-polar and semi-polar planes of 3D structures have less influence of internal electric filed, multi quantum wells (MQWs) formed on those planes have high quantum efficiency. Especially, pyramidal and annular structures consist of various crystal planes with different emission wavelength, providing a possibillity of phosphor-free white light emtting diodes (WLEDs).[1] However, it still has problem to obtain high color rendering index (CRI) number because of narrow-band emission and poor indium composition caused by the formation of few number of facets during metal-organic chemical vapor deposition growth.[2] If we can fabricate 3D structure having more various facets, we can make broad-band emittied WLEDs and improve CRI number. In this study, we suggest a simple method to fabricate 3D structures having various facet and containing high indium composition by means of a combination of metal-organic chemical vapor deposition and wet chemical etching techniques.

• Transactions on Electrical and Electronic Materials
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• 제18권1호
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• pp.7-12
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• 2017

This work takes place in the context of the development of a transport phenomena simulation based on group III nitrides. Gallium and boron nitrides (GaN and BN) are both materials with interesting physical properties; they have a direct band gap and are relatively large compared to other semiconductors. The main objective of this paper is to study the effect of boron content on the electron transport of the ternary compound $B_xGa_{(1-x)}N$ and the effect of the temperature of this alloy at x=50% boron percentage, specifically the piezoelectric, acoustic, and polar optical scatterings as a function of the energy, and the electron energy and drift velocity versus the applied electric field for different boron compositions ($B_xGa_{(1-x)}N$), at various temperatures for $B_{0.5}Ga_{0.5}N$. Monte carlo simulation, was employed and the three valleys of the conduction band (${\Gamma}$, L, X) were considered to be non-parabolic. We focus on the interactions that do not significantly affect the behavior of the electron. Nevertheless, they are introduced to obtain a quantitative description of the electronic dynamics. We find that the form of the velocity-field characteristic changes substantially when the temperature is increased, and a remarkable effect is observed from the boron content in $B_xGa_{(1-x)}N$ alloy and the applied field on the dynamics of holders within the lattice as a result of interaction mechanisms.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.146-146
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• 2011

The blue light emitting diode (LED) structure based on non-polar a-plane (11-20) GaN which was coated TiO2 nanoparticles using spin coating method was grown on r-plane (1-102) sapphire substrates to improve light extraction efficiency. We report on the emission and structural properties with temperature dependence of photoluminescence (PL) and x-ray rocking curves (XRC). From PL results at 13 K of undoped GaN samples, basal plane stacking fault (BSF) and near band edge (NBE) emission peak were observed at 3.434 eV and 3.484 eV, respectively. We also found the temperature-induced band-gap shrinkage, which was fitted well with empirical Varshini's equation. The PL intensity of TiO2 nanoparticles ?coated multiple quantum well (MQW) sample is decayed slower than that of no coating sample with increasing temperature. The anisotrophic strain and azimuth angle dependence in the films were shown from XRC results. The full width at half maximum (FWHM) along the GaN [11-20] and [1-100] directions were 564.9 arcsec and 490.8 arcsec, respectively. A small deviation of FWHM values at in-plane direction is attributed to uniform in-plane strain.

• 한국결정성장학회지
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• 제21권5호
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• pp.187-192
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• 2011

비극성 a-GaN의 성장 시 기판의 경사각은 GaN epi의 품질을 결정하는 중요한 변수로서 양질의 a-GaN 성장을 위해서는 R-면 기판의 경사각이 정밀하게 제어된 기판이 요구된다. 본 연구에서는 R-면 기판의 경사각 ${\alpha}$와 ${\beta}$의 목표값이 각각 0, -0.1, -0.15, -0.2, -0.4, $-0.6^{\circ}$와 -0.1, 0, $0.1^{\circ}$인 절단기판을 제조하였다. 절단기판의 경사각을 x-ray를 이용하여 측정하고 통계적인 분석을 통해 기판의 경사각 제어공정에 대한 신뢰성을 평가하였으며, R-면 기판의 경사각의 공차는 ${\pm}0.03^{\circ}$의 값을 가졌다. R-면 기판은 상대적으로 큰 이방성에 의해 c-면 기판에 비해 휨(BOW)과 두께편차(TTV)가 상대적으로 큰 분포를 갖는 것으로 나타났다. AFM을 이용하여 기판 표면을 관찰한 결과, 측정된 R-면기판의 step 높이는 0.2~0.4 nm로 거의 일정한 값을 가졌으며 step 너비는 경사각 ${\alpha}$가 증가함에 따라 156 nm에서 26 nm로 감소하였으며 이와같은 R-면 기판의 step 구조의 변화는 epi 성장에 큰 영향을 미치는 것으로 판단된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.358-359
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• 2012

최근 분극 특성이 상이한 무분극 GaN 에피성장에 관한 심도 있는 연구와 함께 전자-전공 캐리어의 주입 및 캐리어의 거동, 방출되는 편광 특성 및 다양한 물리적 특성들에 대해 보고되고 있으며, 광학적 특성 및 물리적 특성의 확보를 위한 많은 연구가 활발히 진행 중이다 [1]. GaN의 ohmic 접촉(ohmic contact)의 형성은 발광 다이오드(light emitting diode), 레이저 다이오드(Laser), 태양전지(solar cell)와 같은 고신뢰도, 고효율 광전자 소자를 제조하기 위해서는 매우 중요하다 [2]. 그러나 이와 함께 병행 되어야 할 무분극 p-GaN 의 ohmic contact에 관한 연구는 많이 이루어지고 있지 않는 실정이다. 따라서 본 논문에서는 r-plane 사파이어 기판 상에 성장된 p-GaN에서의 ohmic 접촉 형성 연구를 위하여 Ni/Au ohmic 전극의 접촉저항 특성을 연구하였다. 본 실험에서는 성장된 a-plane GaN의 Hole농도가 $3.09{\times}1017cm3$ 인 시편을 사용하였다. E-beam evaporation 장비를 이용하여 Ni/Au를 각각 20 nm 그리고80 nm 증착 하였으며 비접촉저항을 측정하기 위해 Circle-Transfer Length Method (C-TLM) 패턴을 사용하였다. 샘플은 RTA (Rapid Thermal Annealing)를 사용하여 $300^{\circ}C$에서 $700^{\circ}C$까지 온도를 변화시키며 전기적 특성을 비교하여 그림 1(a) 나타내었다. 그림에서 알 수 있듯이 $400^{\circ}C$에서 가장 낮은 비접촉저항 값인 $6.95{\times}10-3{\Omega}cm2$를 얻을 수 있음을 발견하였다. 이 때의 I-V curve 도 그림1(b)에 나타낸 바와 같이 열처리에 의해 크게 향상됨을 알 수 있다. 그러나, $500^{\circ}C$ 이상 온도를 증가시키면 다시 비접촉 저항이 증가하는 것을 관찰하였다. XRD (x-Ray Diffraction) 분석을 통하여 $400^{\circ}C$ 이상열처리 온도가 증가하면 금속 표면에 $NiO_2$가 형성되며, 이에 따라 오믹특성이 저하 된다고 사료된다. 또한 $Ni_3N$의 존재를 확인 하였으며 이는 nonpolar surface의 특성으로 인해 nitrogen out diffusion 현상이 동시에 발생하여 계면에는 dopant로 작용하는 질소 공공을 남기고 표면에 $Ni_3N$을 형성하여 ohmic contact의 특성이 저하되기 때문인 것으로 사료된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.327.1-327.1
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• 2014

Nitrides-on-silicon structures are considered to be an excellent candidate for unique design architectures and creating devices for high-power applications. Therefore, a lot of effort has been concentrating on growing high-quality III-nitrides on Si substrates, mostly Si(111) and Si(001) substrates. However, there are several fundamental problems in the growth of nitride compound semiconductors on silicon. First, the large difference in lattice constants and thermal expansion coefficients will lead to misfit dislocation and stress in the epitaxial films. Second, the growth of polar compounds on a non-polar substrate can lead to antiphase domains or other defective structures. Even though the lattice mismatches are reached to 16.9 % to GaN and 19 % to AlN and a number of dislocations are originated, Si(111) has been selected as the substrate for the epitaxial growth of nitrides because it is always favored due to its three-fold symmetry at the surface, which gives a good rotational matching for the six-fold symmetry of the wurtzite structure of nitrides. Also, Si(001) has been used for the growth of nitrides due to a possible integration of nitride devices with silicon technology despite a four-fold symmetry and a surface reconstruction. Moreover, Si(110), one of surface orientations used in the silicon technology, begins to attract attention as a substrate for the epitaxial growth of nitrides due to an interesting interface structure. In this system, the close lattice match along the [-1100]AlN/[001]Si direction promotes the faster growth along a particular crystal orientation. However, there are insufficient until now on the studies for the growth of nitride compound semiconductors on Si(110) substrate from a microstructural point of view. In this work, the microstructural properties of nitride thin layers grown on Si(110) have been characterized using various TEM techniques. The main purpose of this study was to understand the atomic structure and the strain behavior of III-nitrides grown on Si(110) substrate by molecular beam epitaxy (MBE). Insight gained at the microscopic level regarding how thin layer grows at the interface is essential for the growth of high quality thin films for various applications.