• 한국결정성장학회지
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• 제18권1호
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• pp.1-4
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• 2008

The growth of composite-structured Nd:$GdVO_4$ single crystal rods by the double die EFG method is reported. Two crucibles are combined with an outer and inner die for ascending of different melt. The composite-structured Nd:$GdVO_4$ single crystal rods with a length of 50 mm and an outer diameter of 5 mm including of inner Nd-doped core region with diameter 3 mm were grown successfully. Nd distribution in the, radial direction has graded profile from result of EPMA. Absorption coefficient in the core region at 808 nm was $42cm^{-1}$. Finally, we demonstrated the laser oscillation using our composite crystal and 2-W output was obtained.

• 한국결정성장학회지
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• 제34권1호
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• pp.1-7
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• 2024

β-Ga₂O₃는 ~4.8 eV의 넓은 밴드 갭과 8 MV/cm의 높은 항복 전압을 가지는 물질로 전력소자의 응용 분야에서 많은 주목을 받고 있다. 또한, 대표적인 WBG 반도체 소재인 SiC, GaN, 다이아몬드 등과 비교했을 때, 높은 성장률과 낮은 제조 비용으로 단결정 성장이 가능하다는 장점을 가진다[1-4]. 본 연구에서는 다중 슬릿 구조를 이용한 EFG(Edge-defined Film-fed Growth) 법을 통해 SnO₂ 0.3 mol% 도핑된 10 mm 두께의 β-Ga₂O₃ 단결정을 성장시키는 데에 성공했다. 성장 방향과 성장 면은 각각 [010]/(001)로 설정하였으며 성장 속도는 약 12 mm/h이다. 성장시킨 β-Ga₂O₃ 단결정은 다양한 결정면(010, 001, 100, ${\bar{2}}01$)으로 절단하여 표면 가공을 진행하였다. 가공이 완료된 샘플은 XRD, UV/VIS/NIR Spec., Mercury Probe, AFM, Etching 등의 분석을 통해 결정면에 따른 특성을 비교하였다. 본 연구는 고전압 및 고온 응용 분야에서 전력반도체 기술의 발전에 기여할 것으로 기대되며 더 나은 특성의 기판을 선택하는 것은 소자의 성능과 신뢰성을 향상시키는데에 중요한 역할을 할 것이다.

• 한국전기전자재료학회논문지
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• 제35권6호
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• pp.626-630
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• 2022

A 100 mm × 50 mm-sized (100) gallium oxide (Ga₂O₃) single crystal ingot was successfully grown by edge-defined film-fed growth (EFG). The preferred orientation and the quality of grown Ga₂O₃ ingot were compatible with a commercial Ga₂O₃ substrate by showing strong (100) orientation behaviors and 246 arcsec in X-ray rocking curve. Raman characterization was also performed for both samples; thereby providing various Raman-active characteristics of Ga₂O₃ crystals. In particular, we observed A_g(5) and A_g(10) peaks of Raman active mode, directly related to the impurity of the grown Ga₂O₃ crystal. Hence, the comparison of the crystal quality and Raman analysis might be useful for further enhancement of Ga₂O₃ single crystal quality in the future.

• 한국결정성장학회지
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• 제11권5호
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• pp.203-206
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• 2001

The applicability of shaped growth of yttrium orthovanadate was approved by successful growth of rod-like single crystals with the rectangular shape. Nd-doped single crystals with content of $Nd^{3+}$ ions of 1,2,3,5 atomic % in the starting melt were grown by the EFG technique with the size up to $10^{*}10mm$ in section and up to 85 mm in length. For the testing of the multiple growth of the orthovanadates, two and three Nd-and Yb-doped $YVO_{4}$ single crystals were grown by the EFG technique simultaneously up to 110 mm in length.

• 한국결정성장학회지
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• 제34권4호
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• pp.109-116
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• 2024

β-Ga₂O₃는 4.9 eV의 넓은 밴드갭과 8 MV/cm의 높은 항복전압으로 전력 소자 응용 분야에서 많은 관심을 받고 있는 대표적인 UWBG(Ultra-wide Band-gap) 반도체이다. 또한 용액 성장이 가능하기 때문에 SiC, GaN에 비해 성장 속도가 빠르고 생산 비용이 저렴하다는 장점이 있다[1,2]. 본 연구에서는 EFG(Edge-defined Film-fed Growth) 법을 통해 Si 도핑 된 β-Ga₂O₃ 단결정을 성장시키는 데에 성공하였다. 성장 방향과 성장 주 면은 각각 [010] / (001)로 설정하였으며 성장속도는 7~20 mm/h이다. 성장시킨 β-Ga₂O₃ 단결정은 다양한 결정 면 방향(001, 100, ${\bar{2}}01$)과 off-angle(1^o, 3^o, 4^o)에 따라 절단하여 표면 가공을 진행하였고, 가공 후 HVPE(Halide vapor phase epitaxy) 법을 이용해 epi-ready 기판 위에 homoepitaxial 층을 성장시켰다. 가공 후의 샘플과 epi-layer를 성장시킨 샘플을 XRD, AFM, OM, Etching 등의 분석을 통해 결정면과 off-angle에 따른 표면 특성을 비교하였다.

• 한국결정성장학회지
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• 제33권2호
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• pp.83-90
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• 2023

최근 전력반도체 소재로 관심을 가지는 Ga₂O₃의 β-상은 열역학적으로 가장 안정한 상을 가지며 4.8~4.9 eV의 넓은 밴드갭과 8 MV/cm의 높은 절연파괴전압을 갖는다. 이러한 우수한 물리적 특성으로 인해 전력반도체 소재로 많은 주목을 받고 있다. β-Ga₂O₃는 SiC 및 GaN의 소재와는 다르게 액상이 존재하기 때문에 액상 성장법으로 단결정 성장이 가능하다. 하지만 성장한 순수 β-Ga₂O₃ 단결정은 전력 소자에 적용하기에는 낮은 전도성으로 인해 의도적으로 제어된 도핑 기술이 필요하며 도핑 특성에 관한 연구가 매우 중요하다. 이 연구에서는 Ga₂O₃ 분말과 SnO₂ 분말의 몰 비율을 다르게 첨가하여 Un-doped, Sn 0.05 mol%, Sn 0.1mol%, Sn 1.5 mol%, Sn 2 mol%, Sn 3 mol%의 혼합분말을 제조하여 EFG(Edge-defined Film-fed Growth) 방법으로 β-Ga₂O₃ 단결정을 성장시켰다. 성장된 β-Ga₂O₃ 단결정의 Sn dopant 함량에 따른 결정 품질 및 광학적, 전기적 특성 변화를 분석하였으며 Sn 도핑에 따른 특성 변화를 광범위하게 연구하였다.

• 한국세라믹학회지
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• 제41권1호
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• pp.1-8
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• 2004

The microstructural features and mechanical behavior of directionally solidified $(Y_2O_3)ZrO_2/Al_2O_3$ eutectic fibers after extended beat treatment in oxidizing environment were investigated. The fiber was grown continuously by an Edge-defined Film-fed Growth (EFG) technique. The microstructure was characterized using X-Ray Diffraction (XRD) and Scanning Electron Microscopy(SEM). The microstructure of the fiber in the as-fabricated state consists of highly oriented colonv and fine lamellar microstructure along the fiber axis. Tensile strength of the $(Y_2O_3)ZrO_2/Al_2O_3$ eutectic fiber remained unchanged with heat treatment at temperatures between $1200^{\circ}C$ and $1500^{\circ}C$ up to 300h. The weibulls modulus remained fairly constant after extended thermal exposure. The fracture toughness and crack propagation behavior were investigated. The fracture toughness ($K_{1C}$) of the $(Y_2O_3)ZrO_2/Al_2O_3$ eutectic fiber in the as-fabricated state were measured to be 3.6 ${\pm}$ 0.5 MPa${\cdot}m^{1/2}$ by an indentation technique and 2.2 ${\pm}$ 0.2 MPa${\cdot}m^{1/2}$ by assuming elliptical flaw of a semi-infinite solid, respectively. The $(Y_2O_3)ZrO_2/Al_2O_3$ eutectic fiber showed a radial (Palmqvist) crack type and exhibited an orthotropic crack growth behavior under 100 g load.

• 한국전기전자재료학회논문지
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• 제35권5호
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• pp.504-508
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• 2022

Single crystal gallium oxide (Ga₂O₃) has been an emerging material for power semiconductor applications. However, the defect distribution of Ga₂O₃ substrates needs to be carefully characterized to improve crystal quality during crystal growth. We analyzed the type and the distribution of defects on commercial (-201) Ga₂O₃ substrates to get a basic standard prior to growing Ga₂O₃ crystals. Etch pit technique was employed to expose the type of defects on the Ga₂O₃ substrates. Synchrotron white beam X-ray topography was also utilized to observe the defect distribution by a nondestructive manner. We expect that the observation of defect distribution with three-dimensional geometry will also be useful for other crystal planes of Ga₂O₃ single crystals.

• 한국전기전자재료학회논문지
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• 제32권3호
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• pp.201-206
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• 2019

This report constitutes the first demonstration in Korea of single-crystal lateral gallium oxide ($Ga_2O_3$) as a metal-oxide-semiconductor field-effect-transistor (MOSFET), with a breakdown voltage in excess of 480 V. A Si-doped channel layer was grown on a Fe-doped semi-insulating ${\beta}-Ga_2O_3$ (010) substrate by molecular beam epitaxy. The single-crystal substrate was grown by the edge-defined film-fed growth method and wafered to a size of $10{\times}15mm^2$. Although we fabricated several types of power devices using the same process, we only report the characterization of a finger-type MOSFET with a gate length ($L_g$) of $2{\mu}m$ and a gate-drain spacing ($L_{gd}$) of $5{\mu}m$. The MOSFET showed a favorable drain current modulation according to the gate voltage swing. A complete drain current pinch-off feature was also obtained for $V_{gs}<-6V$, and the three-terminal off-state breakdown voltage was over 482 V in a $L_{gd}=5{\mu}m$ device measured in Fluorinert ambient at $V_{gs}=-10V$. A low drain leakage current of 4.7 nA at the off-state led to a high on/off drain current ratio of approximately $5.3{\times}10^5$. These device characteristics indicate the promising potential of $Ga_2O_3$-based electrical devices for next-generation high-power device applications, such as electrical autonomous vehicles, railroads, photovoltaics, renewable energy, and industry.