• Journal of IKEEE
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• v.28 no.3
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• pp.360-364
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• 2024

Npn heterostructures with GaN collectors were fabricated using nanomembrane (NM) stacking. N- and p-Si NMs were transfer-printed onto the n-GaN substrates, resulting in the formation of vertical n-Si/p-Si/n-GaN heterostructures. Electrical measurements of Si/Si and Si/GaN pn heterostructures exhibited rectifying properties, indicating that the formation of bipolar junctions was feasible through NM stacking. The energy band diagram of stacking-enabled npn heterostructure was analyzed to explain the rectifying behaviors of base-emitter and collector-base junctions, as well as to suggest potential applications for bipolar junction transistors with a GaN subcollector.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.48 no.11
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• pp.1-8
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• 2011

One of the most important parameters that limit maximum output power of transistor is breakdown. InAlAs/InGaAs/GaAs Metamorphic HEMTs (MHEMTs) have some advantages, especially for cost, compared with InP-based ones. However, GaAs-based MHEMTs and InP-based HEMTs are limited by lower breakdown voltage for output power even though they have good microwave and millimeter-wave frequency performance with lower minimum noise figure. In this paper, InAlAs/$In_xGa_{1-x}As$/GaAs MHEMTs are simulated and analyzed for breakdown. The parameters affecting breakdown are investigated in the fabricated 0.1-${\mu}m$ ${\Gamma}$-gate MHEMT device having the modulation-doped $In_{0.52}Al_{0.48}As/In_{0.53}Ga_{0.47}As$ heterostructure on the GaAs wafer using the hydrodynamic transport model of a 2D commercial device simulator. The impact ionization and gate field effect in the fabricated device including deep-level traps are analyzed for breakdown. In addition, Indium mole-fraction-dependent impact ionization rates are proposed empirically for $In_{0.52}Al_{0.48}As/In_xGa_{1-x}As$/GaAs MHEMTs.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.50-50
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• 2008

ZnO has been extensively studied for optoelectronic applications such as blue and ultraviolet (UV) light emitters and detectors, because it has a wide band gap (3.37 eV) anda large exciton binding energy of ~60 meV over GaN (~26 meV). However, the fabrication of the light emitting devices using ZnO homojunctions is suffered from the lack of reproducibility of the p-type ZnO with high hall concentration and mobility. Thus, the ZnO-based p-n heterojunction light emitting diode (LED) using p-Si and p-GaN would be expected to exhibit stable device performance compared to the homojunction LED. The n-ZnO/p-GaN heterostructure is a good candidate for ZnO-based heterojunction LEDs because of their similar physical properties and the reproducibleavailability of p-type GaN. Especially, the reduced lattice mismatch (~1.8 %) and similar crystal structure result in the advantage of acquiring high performance LED devices with low defect density. However, the electroluminescence (EL) of the device using n-ZnO/p-GaN heterojunctions shows the blue and greenish emissions, which are attributed to the emission from the p-GaN and deep-level defects. In this work, the n-ZnO:Ga/p-GaN:Mg heterojunction light emitting diodes (LEDs) were fabricated at different growth temperatures and carrier concentrations in the n-type region. The effects of the growth temperature and carrier concentration on the electrical and emission properties were investigated. The I-V and the EL results showed that the device performance of the heterostructure LEDs, such as turn-on voltage and true ultraviolet emission, developed through the insertion of a thin intrinsic layer between n-ZnO:Ga and p-GaN:Mg. This observation was attributed to a lowering of the energy barriers for the supply of electrons and holes into intrinsic ZnO, and recombination in the intrinsic ZnO with the absence of deep level emission.

• Journal of Adhesion and Interface
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• v.21 no.3
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• pp.107-112
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• 2020

Recently, the atomically thin transition-metal dichalcogenide (TMD) semiconductors have attracted much attention owing to their remarkable properties such as tunable bandgap with high carrier mobility, flexibility, transparency, etc. However, because these TMD materials have a significant drawback that they are easily degraded in an ambient environment, various attempts have been made to improve chemical stability. In this research article, I report a method to improve the air stability of WSe₂ one of the TMD materials via surface passivation with an h-BN insulator, and its application to field-effect transistors (FETs). With a modified hot pick-up transfer technique, a vertical heterostructure of h-BN/WSe₂ was successfully made, and then the structure was used to fabricate the top-gate bottom-contact FETs. The fabricated WSe₂-based FET exhibited not only excellent air stability, but also high hole mobility of 150 ㎠/Vs at room temperature, on/off current ratios up to 3×10⁶, and 192 mV/decade of subthreshold swing.

• Journal of the Optical Society of Korea
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• v.1 no.2
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• pp.116-119
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• 1997

Highly quantum efficient and multi-color emissible polymer light emitting devices have been realized utilizing poly (1-dodecyloxy-4-methyl-1, 3-phenylene)(2, 5"-terthienylene)(hereafter, mPTTh polymer) as an emitting layer and tris(8-hydroxyquinoline) aluminum (Alq3) as an electron transport layer. A single layer EL device of mPTTh polymer emits orange-colored light. EL efficiency increases as the thickness of Alq3 layer increases, but the emission color becomes visually broad when the Alq3 layer thickness is greater than 30nm since the relative peak intensity of green EL from Alq3 layer grows. EL color is changed from orange to greenish orange as the thickness of Alq3 layer grows. EL color is changed from orange to greenish orange as the thickness of Alq3 layer increases. EL efficiency of the double layer device was greatly enhanced by 3000 times compared with that of a single layer device. Alq3 layer in device acts as a hole blocking electron transporting layer and an emitting layer as a function of the thickness of Alq3 layer.ayer.

• ETRI Journal
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• v.27 no.5
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• pp.551-556
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• 2005

We have demonstrated a high-power widely tunable sampled grating distributed Bragg reflector (SGDBR) laser integrated monolithically with a semiconductor optical amplifier (SOA) having a lateral tapered waveguide, which is the first to emit a fiber-coupled output power of more than 10 dBm using a planar buried heterostructure (PBH). The output facet reflectivity of the integrated SOA using a lateral tapered waveguide and two-layer AR coating of $TiO_2\;and\;SiO_2$ was lower than $3\;{\times}\;10^{-4}\;over$ a wide bandwidth of 85 nm. The spectra of 40 channels spaced by 50 GHz within the tuning range of 33 nm were obtained by a precise control of SG and phase control currents. A side-mode suppression ratio of more than 35 dB was obtained in the whole tuning range. Fiber-coupled output power of more than 11 dBm and an output power variation of less than 1 dB were obtained for the whole tuning range.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.77.1-77.1
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• 2010

반도체 나노 결정은 크기와 모양에 따라 다른 광학적 전기적 성질을 보이는 독특한 특성 때문에 태양전지, 발광 다이오드, 레이저, 바이오메디컬 레이블링 등에 응용될 수 있는 저가격의 차세대 광전기 재료의 개발을 위한 구조체로 각광받고 있다. 최근에는 하나의 나노 결정에 type-II band offset을 가지는 두 개의 물질을 결합한 이종접합 나노 결정체의 연구가 활발하게 진행되고 있는데, 이는 나노 결정 내에서 빛에 의해 생성된 전하들을 공간적으로 분리해 낼 수 있는 장점을 가지고 있기 때문에 태양전지나 광촉매로의 응용에 매우 유용하다. 우리는 나노 결정과 고분자 하이브리드 태양전지의 제작에 있어서 성분과 type-II 이종접합 반도체 나노 결정의 영향을 조사하기 위하여 CdSe, CdTe, type-II CdTe/CdSe tetrapod을 합성하였다. CdSe tetrapod과 P3HT의 블렌딩에 의해 만들어진 태양전지는 AM 1.5, 100mW/$cm^2$ 조건에서 1.03%의 가장 높은 변환 효율, 그리고 415nm에서 43%의 IPCE를 나타내었다. 그리고 CdTe/CdSe type-II tetrapod 이종접합과 P3HT 블렌딩으로 만들어진 태양전지는 CdTe를 이용하여 만든 태양전지에 비해 4.4배의 변환효율과 3.9배의 단락전류를 나타내었다.

• Journal of the Korean Chemical Society
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• v.61 no.4
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• pp.168-178
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• 2017

$La/TiO_2$ - graphene composites were synthesized in this study, and applied to the photocatalytic degradation of Rhodamine B (RhB) under UV-visible light irradiation. X-ray diffraction (XRD), surface analysis, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), and Transmission electron microscopy (TEM) analysis demonstrated that $La/TiO_2$ nanoparticles were well distributed on the surface of graphene, and formed the heterostructure of $La/TiO_2$-graphene. Compared to the pure $TiO_2$, $La/TiO_2$-graphene composites displayed much higher photocatalytic activities in RhB degradation under UV-visible light irradiation. The photocatalytic data of $La/TiO_2$-graphene composites exhibit extended light absorption in the visible light region, and possess better charge separation capability than that of pure $TiO_2$. The high photocatalytic activity was attributed to the composite's high adsorptivity, extended light absorption, and increased charge separation efficiency, due to the excellent electrical properties of graphene, and the large surface contact between graphene and $La/TiO_2$ nanoparticles.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.362.1-362.1
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• 2016

InAs nanowires were synthesized by a vapor-liquid-solid method with InAs powder. The composition and crystalline structure of nanowires were confirmed by energy-dispersive spectroscopy (EDS) and high resolution transmission electron microscopy (HRTEM), respectively. The thermal conduction of nanowires was investigated by the optical method using Raman spectroscopy: i.e., the local temperature on nanowire was determined by laser heating. As temperature increased, the Raman peaks are shifted to low frequency and broadened. The temperature dependent Raman scattering experiments was realized on InAs nanowires with different percentages of zinc-blende and wurtzite structure. The temperature dependence on the nanowire structure has been successfully obtained: the phonon scattering was more increased in InAs heretostructure nanowires, compared to the InAs nanowires with homostructure. The result strongly suggests that the thermal conduction can be effectively controlled by ordered interface without any decrease in electrical conduction.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.100-100
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• 2016

Among various two-dimensional (2D) materials, 2D semiconductors and insulators have attracted a great deal of interest from nanoscience community beyond graphene, due to their attractive and unique properties. Such excellent characteristics have triggered highly active researches on 2D materials, such as hexagonal boron nitride (hBN), molybdenum disulfide (MoS2), and tungsten diselenide (WSe2). New physics observed in 2D semiconductors allow for development of new-concept devices. Especially, these emerging 2D materials are promising candidates for flexible and transparent electronics. Recently, van der Waals heterostructures (vdWH) have been achieved by putting these 2D materials onto another, in the similar way to build Lego blocks. This enables us to investigate intrinsic physical properties of atomically-sharp heterostructure interfaces and fabricate high performance optoelectronic devices for advanced applications. In this talk, fundamental properties of various 2D materials will be introduced, including growth technique and influence of defects on properties of 2D materials. We also fabricate high performance electronic/optoelectronic devices of vdWH, such as transistors, memories, and solar cells. The device platform based on van der Waals heterostructures show huge improvement of devices performance, high stability and transparency/flexibility due to unique properties of 2D materials and ultra-sharp heterointerfaces. Our work paves a new way toward future advanced electronics based on 2D materials.