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저압 MOCVD법에 의한 (100)-GaAs 기판 위의 Ga_xIn(1-x)P 성장과 특성
전성란,손성진,조금재,박순규,김영기 全北大學校 基礎科學硏究所 1994 基礎科學 Vol.17 No.-
x??0.51인 Ga_xIn_(1-x)P 에피층을 저압 MOCVD 성장법으로 TEGa(triethylgallium), TMIn(trimethylindium) 등의 MO(metalorganic) 원료와 PH_3(phosphine)를 사용하여 GaAs(100) 기판 위에 성장하였다. 성장조건에 의한 표면 morphology, 결정결함, 성분비, PL spectra, 운반자 농도와 이동도 및 DLTS spectra와 같은 성장층의 특성을 관찰하였다. 650℃의 성장온도와 V/Ⅲ 비, 즉 TEGa와 TMIn 두 원료의 유량에 대한 PH_3의 유량비가 160∼220일 때 가장 좋은 성장표면을 나타내었다. 성장률은 PH_3의 유량변화에 아무런 영향을 받지 않음을 알 수 있었다. Ga_0.51In_0.49P 에피층과 기판의 격자상수 차에 의한 격자 부정합 Δa_⊥/a_0은 약 (3.7∼8.9)×10 exp (-4)이었으며 실온과 5K에서 에피층의 PL 피크 에너지는 각각 1.85 eV와 1.9 eV였다. 성장층의 운반자 농도와 이동도는 V/Ⅲ 비에 따라 달라지는데 그 비가 120에서 220으로 증가함에 따라 농도는 1.8×10 exp (16) ㎝^-3에서 8.2×10 exp (16) ㎝^-3로 증가하였고 이동도는 1010 ㎝/V·sec에서 366 ㎝/V·sec로 감소하였다. Epitaxial layers of Ga_xIn_(1-x)P with x??0.51 were grown on the GaAs substrates oriented 2℃ off (100) toward <110> by low pressure MOCVD growth technique using triethylgallium (TEGa), trimethylindium (TMIn) and phosphine (PH_3). Surface morphology, crystal defects, composition, photoluminescence spectra, carrier concentration and DLTS spectra of the grown layers were investigated. Good quality epilayers with featureless surface were obtained at growth temperature of 650℃ and V/Ⅲ ratio, i.e., PH_3 flow rate divided by the sum of TEGa and TMIn flow rates, of 160 to 220. The growth rate turned out to have no dependence on phosphine flow rate. The lattice mismatchs Δa_⊥/a_0 between grown Ga_0.51In_0.49P epilayer and GaAs substrate were (3.7∼8.9)×10 exp (-4) and the PL peak energies of the epitaxial layer at room temperature and 5K were 1.85 eV and 1.9 eV, respectively. With increasing V/Ⅲ ratio i.e., phosphine flow rate, from 120 to 220, the carrier density and mobility of undoped epitaxial layers increased from 1.8×10 exp (16) to 8.2×10 exp (16) ㎝^-3 and decreased from 1010 to 366 ㎝/V·sec, respectively.
( Seong Ran Jeon ),( Jin-oh Kim ),( Jeong-sik Byeon ),( Dong-hoon Yang ),( Bong Min Ko ),( Hyeon Jeong Goong ),( Hyun Joo Jang ),( Soo Jung Park ),( Eun Ran Kim ),( Sung Noh Hong ),( Jong Pil Im ),( S 대한간학회 2021 Gut and Liver Vol.15 No.3
Background/Aims: Although balloon-assisted enteroscopy (BAE) enables endoscopic visualization of small bowel (SB) involvement in Crohn’s disease (CD), there is no data on the changes in outcomes over time. We therefore investigated the changes in BAE use on CD patients over different time periods in terms of its role and clinical outcomes. Methods: We used a multicenter enteroscopy database to identify CD patients with SB involvement who underwent BAE (131 procedures, 116 patients). We compared BAE-related factors and outcomes between the first period (70 procedures, 60 patients) and the second period (61 procedures, 56 patients). The specific cutoff point for dividing the two periods was 2007, when BAE guidelines were introduced. Results: Initial diagnosis of SB involvement in CD was the most common indication for BAE during each period (50.0% vs 31.1%, p=0.034). The largest change was in the number of BAE uses for stricture evaluation and/or treatment, which increased significantly in the latter period (2.9% vs 21.3%, p=0.002). The diagnostic yield in patients with suspected CD was 90.7% in the first period and 95.0% in the second (p=0.695). More endoscopic interventions were performed in the second period than in the first (5.1% vs 17.6%, p=0.041). Enteroscopic success rates were high throughout (100% in the first period vs 80.0% in the second period, p>0.999). In the first and second periods, therapeutic plans were adjusted in 62.7% and 61.4% of patients, respectively. Conclusions: The overall clinical indications, outcomes, and effectiveness of BAE were constant over time in CD patients with SB involvement, with the exception that the frequency of enteroscopic intervention increased remarkably. (Gut Liver 2021;15:375-382)
Growth and Characterization of a High-quality Al0.45Ga0.55N Layer with AlGaN/AlN Superlattices
Seong Ran Jeon,박시현 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.8
We report the growth and characterization of a Si-doped, n-type AlGaN layer with 45% Alcomposition. For the application of n-type AlGaN layers with high Al compositions in ultravioletemitters, we fabricated an n-Al0.45Ga0.55N layer with high crystalline quality and high electricalconductivity by inserting Al0.85Ga0.15N/AlN superlattices (SLs) to prevent cracks prior to growingthe n-type AlGaN layer. The dislocation density in the n-AlGaN layer with a 45% Al compositionand SLs was less than 2.4 × 1010 cm−2, which was lower than the dislocation density of 5.3 × 1010cm−2 for the n-AlGaN layer without SLs. The resistivity, mobility, and free-electron concentrationin the n-type Al0.45Ga0.55N layer with SLs were 2.2 × 10−2·Ωcm, 55.0 cm2/V-s, and 5.0 × 1018cm−3 at room temperature, respectively.