• Proceedings of the Materials Research Society of Korea Conference
• /
• 2003.11a
• /
• pp.21-21
• /
• 2003

To increase the light-emission efficiency of LED, we increased the internal and external quantum efficiency by suppressing the defect formation in the quantum well and by increasing the light extraction efficiency in LED, respectively. First, the internal quantum efficiency was improved by investigating the effect of a low temperature (LT) grown p-GaN layer on the In$\sub$0.25/GaN/GaN MQW in green LED. The properties of p-GaN was optimized at a low growth temperature of 900oC. A green LED using the optimized LT p-type GaN clearly showed the elimination of blue-shift which is originated by the MQW damage due to the high temperature growth process. This result was attributed to the suppression of indium inter-diffusion in MQW layer as evidenced by XRD and HR-TEM analysis. Secondly, we improved the light-extraction efficiency of LED. In spite of high internal quantum efficiency of GaN-based LED, the external quantum efficiency is still low due to the total internal reflection of the light at the semiconductor-air interface. To improve the probability of escaping the photons outside from the LED structure, we fabricated nano-sized cavities on a p-GaN surface utilizing Pt self-assembled metal clusters as an etch mask. Electroluminescence measurement showed that the relative optical output power was increased up to 80% compared to that of LED without nano-sized cavities. I-V measurement also showed that the electrical performance was improved. The enhanced LED performance was attributed to the enhancement of light escaping probability and the decrease of resistance due to the increase in contact area.

• Journal of the Korean Vacuum Society
• /
• v.17 no.6
• /
• pp.523-527
• /
• 2008

GaAs/AlGaAs based quantum cascade lasers were fabricated with two different types of i) the shallow mesa type which was etched up to above active region and ii) the deep mesa type which was etched through active region. While the threshold current density of shallow mesa type was $26-32\;kA/cm^2$, the one of deep mesa type was reduced drastically up to $13\;kA/cm^2$. Such lowered threshold current density at deep mesa type attributed to the reduction of current loss to the lateral directions.

• Korean Journal of Materials Research
• /
• v.31 no.9
• /
• pp.496-501
• /
• 2021

Metal halide perovskite nanocrystals, due to their high absorption coefficient, high diffusion length, and photoluminescence quantum yield, have received significant attention in the fields of optoelectronic applications such as highly efficient photovoltaic cells and narrow-line-width light emitting diodes. Their energy band structure can be controlled via chemical exchange of the halide anion or monovalent cations in the perovskite nanocrystals. Recently, it has been demonstrated that chemical exfoliation of the halide perovskite crystal structure can be achieved by addition of organic ligands such as n-octylamine during the synthetic process. In this study, we systematically investigated the quantum confinement effect of methylammonium lead bromide (CH₃NH₃PbBr₃, MAPbBr₃) nanocrystals by precise control of the crystal thickness via chemical exfoliation using n-octylammonium bromide (OABr). We found that the crystalline thickness consistently decreases with increasing amounts of OABr, which has a larger ionic radius than that of CH₃NH₃⁺ ions. In particular, a significant quantum confinement effect is observed when the amounts of OABr are higher than 60 %, which exhibited a blue-shifted PL emission (~ 100 nm) as well as an increase of energy bandgap (~ 1.53 eV).

• Nonlinear Functional Analysis and Applications
• /
• v.28 no.1
• /
• pp.11-36
• /
• 2023

In this presentation, the particles at the matter surface (metal, crystal, nano) will be considered as the control target outside the physical domain. As is well known that control problems of quantum particles at surface had been investigated in various aspects in last couple of years, but the realization of control would become rather difficult than theoretical results. Especially, whether surface control would be valid? what kind of particles at what kind of matter surfaces can be controlled? so many questions still left as the mystery in the current research literature and papers. It means that the direct control sometime does not easy. On the other hands, control outside the physical domain is quite a interest consideration in mathematics, physics and chemistry. The main plan is to take the quantum systems operator (such as Laplacian ∆) in the form of fractional operator (∆^s , 0 < s < 1), then to consider the control outside of physical domain. Fortunately, there are many published articles in the field of applied mathematics can be referred for the achievement of control outside of domain. The external quantum control would be a fresh concept to do the physical control, first in the theoretic, second in the computational, final in the experimental issues.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.21 no.6
• /
• pp.503-508
• /
• 2008

In order to reduce the piezoelectric field originated from the well layer which resides in InGaN/GaN light emitting diode, InGaN/GaN superlattice buffer layers were grown at the bottom and the top of the active layer. Measuring the photoluminescence spectra with different reverse bias voltages clearly revealed the condition of the flat band under which the transition energy is maximized and the linewidth is minimized. Accordingly, the piezoelectric field of $In_{0.15}Ga_{0.85}N$ in our sample was estimated as -1.08 MV/cm. It is less than half the value reported in the previous studies, and it is evidenced that the strain has reduced due to the superlattice buffer layers.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.07a
• /
• pp.636-639
• /
• 2001

InGaN/GaN multiple quantum wells (MQWs) grown with various growth interruptions between the InGaN well and GaN barrier by metal-organic chemical vapor deposition were investigated using photoluminescence, high-resolution transmission electron microscopy, and energy filtered transmission electron microscopy (EFTEM). The luminescence intensity of the MQWs with growth interruptions is abruptly reduced compared to that of the MQW without growth interruption. Also, as the interruption time increases the peak emission shows a continuous blue shift. Evidence of indium clustering is directly observed both by using an indium ratio map of the MQWs and from indium composition measurements along an InGaN well using EFTEM. The higher intensity and lower energy emission of light from the MQW grown without interruption showing indium clustering is believed to be caused by the recombination of excitons localized in indium clustering regions and the increased indium composition in these recombination centers.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.324-325
• /
• 2014

Quantum wells infrared photodetectors (QWIPs) have been used to detect infrared radiations through the principle based on the localized stated in quantum wells (QWs) [1]. The mature III-V compound semiconductor technology used to fabricate these devices results in much lower costs, larger array sizes, higher pixel operability, and better uniformity than those achievable with competing technologies such as HgCdTe. Especially, GaAs/AlGaAs QWIPs have been extensively used for large focal plane arrays (FPAs) of infrared imaging system. However, the research efforts for increasing sensitivity and operating temperature of the QWIPs still have pursued. The modification of heterostructures [2] and the various fabrications for preventing polarization selection rule [3] were suggested. In order to enhance optical performances of the QWIPs, double barrier quantum well (DBQW) structures will be introduced as the absorption layers for the suggested QWIPs. The DBWQ structure is an adequate solution for photodetectors working in the mid-wavelength infrared (MWIR) region and broadens the responsivity spectrum [4]. In this study, InGaAs/GaAs/AlGaAs double barrier quantum well infrared photodetectors (DB-QWIPs) are successfully fabricated and characterized. The heterostructures of the InGaAs/GaAs/AlGaAs DB-QWIPs are grown by molecular beam epitaxy (MBE) system. Photoluminescence (PL) spectroscopy is used to examine the heterostructures of the InGaAs/GaAs/AlGaAs DB-QWIP. The mesa-type DB-QWIPs (Area : $2mm{\times}2mm$) are fabricated by conventional optical lithography and wet etching process and Ni/Ge/Au ohmic contacts were evaporated onto the top and bottom layers. The dark current are measured at different temperatures and the temperature and applied bias dependence of the intersubband photocurrents are studied by using Fourier transform infrared spectrometer (FTIR) system equipped with cryostat. The photovoltaic behavior of the DB-QWIPs can be observed up to 120 K due to the generated built-in electric field caused from the asymmetric heterostructures of the DB-QWIPs. The fabricated DB-QWIPs exhibit spectral photoresponses at wavelengths range from 3 to $7{\mu}m$. Grating structure formed on the window surface of the DB-QWIP will induce the enhancement of optical responses.

• Korean Journal of Materials Research
• /
• v.12 no.4
• /
• pp.296-303
• /
• 2002

For potential application to quantum mechanical devices, nano-composite thin films, consisting of GaAs quantum dots dispersed in SiO$_2$ glass matrix, were fabricated and studied in terms of structural, chemical, and optical properties. In order to form crystalline GaAs quantum dots at room temperature, uniformly dispersed in $SiO_2$matrix, the composite films were made to consist of alternating layers of GaAs and $SiO_2$in the manner of a superlattice using RF magnetron sputter deposition. Among different film samples, nominal thickness of an individual GaAs layer was varied with a total GaAs volume fraction fixed. From images of High Resolution Transmission Electron Microscopy (HRTEM), the formation of GaAs quantum dots on SiO$_2$was shown to depend on GaAs nominal thickness. GaAs deposits were crystalline and GaAs compound-like chemically according to HRTEM and XPS analysis, respectively. From measurement of optical absorbance using a spectrophotometer, absorption edges were determined and compared among composite films of varying GaAs nominal thicknesses. A progressively larger shift of absorption edge was noticed toward a blue wavelength with decreasing GaAs nominal thickness, i.e. quantum dots size. Band gaps of the composite films were also determined from Tauc plots as well as from PL measurements, displaying a linear decrease with increasing GaAs nominal thickness.

• Smart Media Journal
• /
• v.12 no.2
• /
• pp.76-82
• /
• 2023

In the 4th industrial revolution, the blockchain that distributes and manages data through a P2P network is used as a new decentralized networking paradigm in various fields such as manufacturing, culture, and public service. However, with the advent of quantum computers, quantum algorithms that are able to break existing cryptosystems such as hash function, symmetric key, and public key cryptography have been introduced. Currently, because most major blockchain systems use an elliptic curve cryptography to generate signatures for transactions, they are insecure against the quantum adversary. For this reason, the research on the quantum-resistant blockchain that utilizes lattice-based cryptography for transaction signatures is needed. Therefore, in this paper, we propose a blind signature scheme for the blockchain in which the contents of the signature can be verified later, as well as signing by hiding the contents to be signed using lattice-based cryptography with the property of quantum resistance. In addition, we prove the security of the proposed scheme using a random oracle model.

• Proceedings of the Optical Society of Korea Conference
• /
• 1990.02a
• /
• pp.204-206
• /
• 1990