• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.1
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• pp.89-93
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• 1999

The properties and effects of the electrodeposited CdTe compound film on the porous silicon. To find ways to achieve good mechanical contact on the nanostructure porous silicon layer while keeping the interface transparent, we tried to electrodeposit a CdTe compound film on the porous silicon surface. The CdTe compound film was fabricated with -2.3V vs. Ag/AgCl potential difference in the electrolyte solution containing 1M of $CdSO_4$and 1 mM of $TeO_4$. X-ray diffraction results confirmed the existence of CdTe compound film on the porous silicon surface. Auger depth profile showed that Cd and Te were uniformly distributed up to a 80 nm distance from the surface. The photoluminescence of the sample with a CdTe compound film was weaker in intensity than that without the film and the maximum wavelength was shifted to the higher energy. These results indicate that the contacting CdTe compound film was infiltrated to the nanostructure of porous silicon.

• Current Photovoltaic Research
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• v.4 no.1
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• pp.25-29
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• 2016

$Eu^{3+}$-activated $MgMoO_4$ phosphor thin films were grown at $400^{\circ}C$ on quartz substrates by radio-frequency magnetron sputter deposition from a 15 mol% Eu-doped $MgMoO_4$ target. After the deposition, the phosphor thin films were annealed at several temperatures for 30 min in air. The influence of thermal annealing temperature on the structural and optical properties of $MgMoO_4:Eu^{3+}$ phosphor thin films was investigated by using X-ray diffraction (XRD), photoluminescence (PL), and ultraviolet-visible spectrophotometry. The transmittance, optical band gap, and intensities of the luminescence and excitation spectra of the thin films were found to depend on the thermal annealing temperature. The XRD patterns indicated that all the thin films had a monoclinic structure with a main (220) diffraction peak. The highest average transmittance of 91.3% in the wavelength range of 320~1100 nm was obtained for the phosphor thin film annealed at $800^{\circ}C$. At this annealing temperature the optical band gap energy was estimated as 4.83 eV. The emission and excitation spectra exhibited that the $MgMoO_4:Eu^{3+}$ phosphor thin films could be effectively excited by near ultraviolet (281 nm) light, and emitted the dominant 614 nm red light. The results show that increasing RTA temperature can enhance $Eu^{3+}$ emission and excitation intensity.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.191.2-191.2
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• 2015

Details of carrier dynamics in self-assembled quantum dots (QDs) with a particular attention to nonradiative processes are not only interesting for fundamental physics, but it is also relevant to performance of optoelectronic devices and the exploitation of nanocrystals in practical applications. In general, the possible processes in such systems can be considered as radiative relaxation, carrier transfer between dots of different dimensions, Auger nonradiactive scattering, thermal escape from the dot, and trapping in surface and/or defects states. Authors of recent studies have proposed a mechanism for the carrier dynamics of time-resolved photoluminescence CdTe (a type II-VI QDs) systems. This mechanism involves the activation of phonons mediated by electron-phonon interactions. Confinement of both electrons and holes is strongly dependent on the thermal escape process, which can include multi-longitudinal optical phonon absorption resulting from carriers trapped in QD surface defects. Furthermore, the discrete quantized energies in the QD density of states (1S, 2S, 1P, etc.) arise mainly from ${\delta}$-functions in the QDs, which are related to different orbitals. Multiple discrete transitions between well separated energy states may play a critical role in carrier dynamics at low temperature when the thermal escape processes is not available. The decay time in QD structures slightly increases with temperature due to the redistribution of the QDs into discrete levels. Among II-VI QDs, wide-gap CdZnTe QD structures characterized by large excitonic binding energies are of great interest because of their potential use in optoelectronic devices that operate in the green spectral range. Furthermore, CdZnTe layers have emerged as excellent candidates for possible fabrication of ferroelectric non-volatile flash memory. In this study, we investigated the optical properties of CdZnTe/ZnTe QDs on Si substrate grown using molecular beam epitaxy. Time-resolved and temperature-dependent PL measurements were carried out in order to investigate the temperature-dependent carrier dynamics and the activation energy of CdZnTe/ZnTe QDs on Si substrate.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.257.1-257.1
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• 2015

Cu(In,Ga)Se2 (CIGS) 박막 태양 전지에서 buffer layer는 CIGS 흡수층과 TCO 사이의 밴드갭 차이에 대한 문제점과 lattice mismatch를 해결하기 위해 필수적이다. 흔히 buffer layer 물질로는 CdS가 가장 많이 사용되고 있으나 Cd의 독성에 관한 문제가 야기되고 있다. 따라서 ZnS(O, OH) buffer layer가 친환경 물질로 기존의 CdS 버퍼 층의 대체 물질로 각광 받고 있으며, 단파장 범위에서 높은 투과율로 인해 wide band gap의 Chalcopyrite 태양 전지에 응용되는 buffer layer로 많은 연구가 이루어지고 있다. 또한 buffer layer를 최적화 하여 carrier lifetime과 양자 효율이 증가시킬 수 있는 특성을 가지고 있다. 이 연구에서는 Cu(In,Ga)Se2 (CIGS) 박막에 화학습식공정 (CBD) 방법을 이용하여 최적화된 ZnS(O, OH)의 증착 조건을 찾고, 고품질의 buffer layer를 제조하기 위한 실험에 초점을 맞췄다. 또한, buffer layer의 막질을 개선하고 균일한 막을 제조하기 위해 processing parameters인 시약의 농도, 제조 시간 및 온도 등의 다양한 변화를 통해 실험을 진행하였다. 그 후 최적화된 ZnS(O, OH) buffer layer의 특성 분석을 위해 X-ray diffraction(XRD), photoluminescence (PL), scanning electron microscope (SEM) and GD-OES을 이용하였고, 이를 통해 제조된 CIGS 박막 태양전지는 light induced current-voltage (LIV) and external quantum efficiency (EQE)를 통해 특성 분석을 실시 하였다. 결과적으로, 제조된 ZnS(O, OH) buffer layer의 $ZnSO4{\cdot}7H2O$의 농도는 0.16 M, Thiourea는 0.5 M, NH4OH는 7.5 M, 그리고 반응 온도는 77.5 oC의 조건 하에 CIGS 기판 위에 균일하고 균열이 없는 ZnS(O, OH) 박막을 제조하였으며 이때 제조된 태양전지의 소자 특성은 Voc = 0.478 V, Jsc = 35.79 mA/cm2, FF = 47.77%, ${\eta}=8,18 %$이다.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.197.1-197.1
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• 2015

현재 화합물 반도체 나노구조는 적외선 검출기, 레이저, 발광 다이오드, 단전자 트랜지스터, 태양전지 등과 같은 고효율 광전자 소자에서의 응용을 위해 활발한 연구가 진행 되고 있다. 특히 양자점은 3차원으로 구속되어 있는 상태 밀도를 갖고 있어 레이저 응용 시 낮은 문턱 전류 밀도, 높은 이득, 높은 열적 안정성을 기대되고 있다. 하지만 양자점의 크기가 불규칙적이고 운반자 수집의 한계로 인하여 기대 이하의 온도 안정성을 갖고 있어 이를 극복하기 위해 양자점의 크기와 운반자 수집을 제어하기 위해 다양한 방법이 연구되고 있다. 본 연구에서는 분자 선속 에피 성장법(Molecular Beam Epitaxy; MBE)과 원자 층 교대 성장법(Atomic Layer Epitaxy; ALE)으로 크기가 다른 CdTe/ZnTe 이중 양자점을 ZnTe 장벽층의 두께에 변화하면서 성장 후 광학적 특성을 연구하였다. 저온 광루미네센스 측정(Photoluminescence; PL) 측정 결과 장벽층 두께가 작아질수록 작은 양자점의 광 루미네센스의 세기가 감소하면서 큰 양자점의 세기가 증가하는 것을 관찰할 수 있었는데, 이는 장벽층 두께가 작아질수록 작은 양자점의 운반자들이 큰 양자점으로 이동되는 양이 많아지기 때문이다. 또한 장벽층 두께가 작아질수록 큰 양자점의 반치폭(Full Width at Half Maximum; FWHM)이 단층 양자점의 반치폭 보다 감소하는 것을 관찰 할 수 있었는데 이는 작은 양자점과 결합된 큰 양자점이 작은 양자점의 strain을 받아 크기의 균일함이 증가했기 때문이다. 이와 같은 결과 두 양자점이 결합된 이중 양자점 구조가 단층 양자점의 한계인 운반자 수집과 크기의 균일함을 향상할 수 있는 좋은 구조임을 제시하고 있다.

• Bulletin of the Korean Chemical Society
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• v.30 no.9
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• pp.1933-1938
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• 2009

New $\pi$-conjugated polymer with vinylene linkage, poly((10-hexyl-3,7-phenothiazine)-alt-(4-(4-butyl-phenyl)- 3,5-diphenyl-4H-[1,2,4]triazole)-3,5-vinylene) (PTV-TAZ) was synthesized by the Heck coupling reaction. The photoluminescence (PL) maximum wavelength and the band gap energy of PTV-TAZ film were 555 nm and 2.41 eV, respectively. The HOMO energy level of PTV-TAZ was -4.99 eV, which was slightly lower than that of PTV (-4.89 eV). Electron deficient aromatic 1,2,4-triazole (TAZ) in the polymer backbone does not affect the HOMO energy level significantly. The maximum efficiency and brightness of double layer structured electroluminescent (EL) device (ITO/PEDOT (30 nm)/PTV-TAZ (60 nm)/Al) were 0.247 cd/A and 553 cd/$m^2$, respectively, which were significantly higher than those of the device based PTV (1.65 ${\times}\;10^{-4}$ cd/A and 4.3 cd/$m^2$). This is due to that TAZ unit improves electron transporting ability in the emissive layer. The turn-on voltage (defined as the voltage required to give a luminescence of 1 cd/$m^2$) of brightness of the device based on PTV-TAZ was 12.0 V, which was similar to that the based on PTV (11.5 V). This is due to that the ionization potential of PTV-TAZ is very similar to that of PTV.

• Journal of the Korean Vacuum Society
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• v.15 no.2
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• pp.186-193
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• 2006

In this study, we analyzed the electrical and optical properties of metalorganic chemical vapor deposition grown InGaAs/InGaAsP/InP quantum dot(QD) molecules by using photoluminescence and deep-level transient spectroscopy. From these resulte, the energy levels of the large QDs are located at deeper region from the conduction band edge of the barrier than that of the small QDs, The large QDs seem to have the energy states more than two, and these energy levels of the QD molecules are located at 0.35, 0.42, and 0.45 eV from conduction band edge under -4 V reverse bias conditions. The energy levels are closely coupled under low reverse bias, and then decoupled as the bias voltage is increased.

• Journal of Sensor Science and Technology
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• v.15 no.3
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• pp.216-221
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• 2006

ZnO thin films prepared by PLD method exhibit an excellent optical property, but may have some problems such as incomplete surface roughness and crystallinity. In this study, undoped ZnO buffer layers were deposited on (0001) sapphire substrates by ultra high vacuum pulse laser deposition (UHV-PLD) and molecular beam epitaxy (MBE) methods, respectively. After post annealing of ZnO buffer layer, undoped ZnO thin films were deposited under different oxygen pressure ($35{\sim}350$ mtorr) conditions. The Arsenic-doped (1, 3 wt%) ZnO thin layers were deposited on the buffer layer of undoped ZnO by UHV-PLD method. The optical property of the ZnO thin films was analyzed by photoluminescence (PL) measurement. The ${\theta}-2{\theta}$ XRD analysis exhibited a strong (002)-peak, which indicates c-axis preferred orientation. Field emission-scanning electron microscope (FE-SEM) revealed that microstructures of the ZnO thin films were varied by oxygen partial pressure, Arsenic doping concentration, and deposition method of the undoped ZnO buffer layer. The denser and smoother films were obtained when employing MBE-buffer layer under lower oxygen partial pressure. It was also found that higher Arsenic concentration gave the enhanced growing of columnar structure of the ZnO thin films.

• Korean Journal of Materials Research
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• v.14 no.7
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• pp.482-488
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• 2004

$SiO_2$ nanowires were synthesized using the vapor evaporation method. Grown nanowires had a different shapes by kind of substrates. Diameters and lengths of the nanowires increased with increasing growth temperature and time. Mean diameters and lengths of $SiO_2$ nanowire were different by kind of substrates. These variations were attributed to nanowire densities on the substrates. The kind of substrates affected microstructure and PL properties of grown nanowires. In case of $Al_{2}O_3$ and quartz substrates, additional $O_2$ were supported during growth stages, and made a nucleation site. Therefore relative narrow nanowire was grown on $Al_{2}O_3$ and quartz substrates. Optical property were measured by photoluminescence spectroscopy. Relatively broad peak was obtained and mean peak positioned at 450 and 420nm. however in case of quartz substrates, mean peak positioned at 370nm. These peak shift was contributed to the size and substrate effects.

• Korean Journal of Materials Research
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• v.21 no.5
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• pp.273-276
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• 2011

Ultraviolet (UV) light emitting diodes (LEDs) were grown on a patterned n-type GaN substrate (PNS) with 200 nm silicon-di-oxide (SiO2) nano pattern diameter to improve the light output efficiency of the diodes. Wet etched self assembled indium tin oxide (ITO) nano clusters serve as a dry etching mask for converting the SiO2 layer grown on the n-GaN template into SiO2 nano patterns by inductively coupled plasma etching. PNS is obtained by n-GaN regrowth on the SiO2 nano patterns and UV-LEDs were fabricated using PNS as a template. Two UV-LEDs, a reference LED without PNS and a 200 nm PNS UV-LEDs were fabricated. Scanning Electron microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Photoluminescence (PL) and Light output intensity- Input current- Voltage (L-I-V) characteristics were used to evaluate the ITO-$SiO_2$ nanopattern surface morphology, threading dislocation propagation, PNS crystalline property, PNS optical property and UVLED device performance respectively. The light out put intensity was enhanced by 1.6times@100mA for the LED grown on PNS compared to the reference LED with out PNS.