• Journal of the Optical Society of Korea
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• v.12 no.1
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• pp.42-48
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• 2008

The relative intensity noise (RIN) characteristics in 405 nm blue laser diodes grown on wurtzite AlGaInN multiple quantum well structures were investigated using the rate equations with the quantum Langevin noise model. The device parameters were extracted from the optical gain properties of the MQW active region using the self-consistent numerical method developed for calculating the multiband Hamiltonian in the strained wurtzite crystal. These methods have been applied to laser diodes for various conditions including the external feedback and the high frequency current injection.

• Electronics and Telecommunications Trends
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• v.3 no.4
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• pp.3-12
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• 1988

Epilayer growing process has been recognized as a key technology for successful GaAs based devices and integrations. These may include HEMT, multiple quantum well structures, band gap engineering, and quantum confinement heterostructures. The fabrication of epilayers in these devices must meet very stringent requirements in terms of crystallinity, composition, film thickness and interface quality. In particular, the quality of interfaces is getting more important because the film thickness, and flatness, roughness and stability at interface of ultrathin films cause critical effects on the device performance. This article reviews the current status of modern epitaxial techniques which have been developed in the last few years. First, the new techniques PLE, GI, MEE, TSL based on MBE technique will be reviewed and their technical importance will be stressed. Secondly, MOMBE, GSMBE, CBE which combine the advantages of MBE and MOCVD will also be discussed. Thirdly, the new sophisticated epitaxial technique, ALE, of which mechanism is totally different from others, will also be reviewed. Finally, areas which should be exploited more extensively to accomplish these techniques will be addressed.

• Current Optics and Photonics
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• v.1 no.6
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• pp.579-586
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• 2017

In this paper, we theoretically demonstrate that semiconductor optical amplifiers (SOAs) with strong wavelength dependence of gain and phase are capable of all-optical inverted and non-inverted wavelength conversion (WC) over a wide range, with the assistance of an optical filter. First, the gain dynamics and phase dynamics in a common quantum well (QW) SOA with the $In_{0.53}Ga_{0.47}As/In_{0.7322}Ga_{0.2678}As_{0.5810}P_{0.4190}$ material system are found to be strongly dependent on wavelength, which is mainly related to the wavelength dependence of the differential gain and the differential refractive-index change. Second, the wavelength dependence in an all-optical wavelength converter based on the QW SOA cascaded with a detuning band pass filter is studied. Simulations show that the quality of the converted signal has little dependence on the operation wavelength. Both inverted and non-inverted WC can be achieved, over a large wavelength range. Therefore, although the gain and phase change are strongly wavelength-dependent, the effects of this dependence can be erased by appropriate optical filtering.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.1280-1282
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• 1993

We investigated theoretically the current-voltage characteristics of resonant tunneling diodes with a single quantum well structure, using a self-consistent method. This method is a numerical analysis which is able to include the effects of the undoped spacer layer and the band bending by charge accumulation and depletion on the contact layers, so that it is better suited to explain experimental results. The structure used is an $Al_{0.5}Ga_{0.5}$As/GaAs/$Al_{0.5}Ga_{0.5}As$ single quantum well. In this work, we estimate the theoretical current-voltage characteristics, and then, the dependence of the current-voltage curves on the thickness of undoped spacer layers.

• Journal of Sensor Science and Technology
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• v.30 no.6
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• pp.441-445
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• 2021

The components affecting the extrinsic transconductance (g_{m_ext}) in In_0.7Ga_0.3As quantum-well (QW) high-electron-mobility transistors (HEMTs) on an InP substrate were investigated. First, comprehensive modeling, which only requires physical parameters, was used to explain both the intrinsic transconductance (g_{m_int}) and the g_{m_ext} of the devices. Two types of In_0.7Ga_0.3As QW HEMT were fabricated with gate lengths ranging from 10 ㎛ to sub-100 nm. These measured results were correlated with the modeling to describe the device behavior using analytical expressions. To study the effects of the components affecting g_{m_int}, the proposed approach was extended to projection by changing the values of physical parameters, such as series resistances (R_S and R_D), apparent mobility (𝜇_{n_app}), and saturation velocity (𝜈_sat).

• Korean Journal of Optics and Photonics
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• v.9 no.2
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• pp.111-116
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• 1998

Thirteen InGaAs/InGaAsP separate-confinement heterostructure multiple quantum well lasers were designed such that the strain in the active layer from 0.9% compressive strain to 1.4% tensile, and their threshold current density was caluculated to see the effects of strain on the threshold current density. The well width was adjusted such that the bandgap of the quantum well is 1.55 ${\mu}{\textrm}{m}$, For the calculation of the band structure and transition matrix element needed for the gain calculation, a block diagonalized 8$\times$8 second-order $\to{k}.\to{p}$ Hamiltonian was used to incorporate the conduction band nonparabolicity and the valence band mixing. The threshold current density shows discontinuity at 0.4% tensile strain where the first heavy-hole subband and the first light-hole subband cross and at 0.5% tensile strain where the second conduction subband begins to exist. The threshold current density at room temperature has a maximum around these 0.4-0.5% tensile strains, and as strain varies in either direction it decreases first and then increases a little after a local minimum. This calculated trend is consistent with the other reported experimental results. We discussed the results of this calculation in comparison with other theoretical or experimental papers on the effect of strain.

• Bulletin of the Korean Chemical Society
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• v.16 no.2
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• pp.96-101
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• 1995

The optical properties of individual 3-to 14-micron diameter CdS crystalline spheres embedded in poly(methyl methacrylate) were studied using elastic scattering. The presence of well defined sharp peaks in the 550 to 600 nm elastic scattering spectra confirmed that each microcrystal acts as an optical cavity with cavity quality factors exceeding 104. Such natural resonator microcrystals should lead to greatly enhanced local field effects near the surface of CdS, quantum electrodynamic modification of optical transition rates of nearby species and altered photochemistry. Absorptive heating following high intensity laser irradiation was found to induce a transient washout of the high Q modes.

• Journal of the Korean Vacuum Society
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• v.7 no.4
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• pp.328-333
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• 1998

Lattice-matched InAIAs epilayers were grown on (001) InP substrate by low pressure metalorganic chemical vapor deposition. The effects of growth conditions on the properties of InAIAs were analyzed, and InGaAs/InAIAs single and multiple quantum wells were successfully grown. It was observed that the optical property of InAIAs epilayers was improved in the temperature range of 620~$700^{\circ}C$ as the growth temperature increased due to the reduction of oxygen incorporation, however, the crystallinity decreased at temperatures higher than $750^{\circ}C$ due to the degraded crystallinity of the bufter layers. The enhanced incorporation of AI into epilayer was observed at high $AsH_3$flow rates and it was explained in terms of the differences in bond strengths of AI-As and In-As. The measured photoluminescence peak energies from InGaAs/InAIAs single quantum wells were consistent with the calculated ones based on transfer matrix method. High-order satellite peaks and fine thickness fringes were observed by high-resolution x-ray diffraction, implying that the high-quality multiple quantum wells with abrupt heterointerfaces were grown.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.313-313
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• 2012

In recent years there have been many studies of InGaN/GaN based light emitting diodes (LEDs) in order to progress the performance of luminescence. Many previous literatures showed the performance of LEDs by changing the LED structures and substrates. However, the studies carried out by the researchers so far were very complicated and sometimes difficult to apply in practice. Therefore, we propose one simple method of changing the thickness and the numbers of multiple quantum wells (MQWs) in order to optimize their effects. In our research, we investigated electrical and optical properties by changing the well thickness and the number of quantum well (QW) pair in LED structures by growing the structure -inch Si (111) wafer. We defined the samples from LED_1 to LED_3 according to MQW structure. Samples LED_1, LED_2 and LED_3 consist of 5-pair InGaN/GaN (3.5 nm/ 4.5 nm), 5-pair InGaN/GaN (3 nm/4.5 nm) and 7-pair InGaN/GaN (3.5 nm/4.5 nm), respectively. We characterized electrical and optical properties by using electroluminescence (EL) measurement. Also, Efficiency droop was analyzed by calculating external quantum efficiency (EQE) with varying injection current. The EL spectra of three samples show different emission wavelength peaks, FWHM and the blueshift of wavelength caused by screening the internal electric field because of the effect of different MQW structure. The results of optical properties show that the LED_2 sample reduce the internal electric field in QW than LED_1 from EL spectra. the increase in the number of QW pairs reduces the strain and increase the In composition in MQW. And, the points of efficiency droop's peak show different trend from LED_1 to LED_3. It is related with the carrier density in active region. Thus, from the results of experiments, we are able to achieve high performance LEDs and a reduction of efficiency droop and emission wavelength blueshift by optimizing MQWs structure.

• Korean Journal of Optics and Photonics
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• v.12 no.1
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• pp.40-47
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• 2001

The structural dependence of the performance of an 1.55 $1.55{\mu}m$ InGaAsPIInGaAsP MQW electro-absorption modulator for highspeed digital fiber communication was systematically investigated. The effects of n-doped SCH region length $t_n$ as well as the general structure parameters including quantum well number $N_w$, well-thickness $t_w$, detuning wavelength $\Delta\lambda$, and device length L were thoroughly analyzed. Thereby, a high-pelfoIDlance electro-absorption modulator with device length L of $100{\mu}m$ was successfully designed. The designed structure showed excellent characteristics that have residual loss less than -1.5 dB, operational voltage from 0 V to -2V, and extinction ratios of -2.92 dB at $V_{\alpha}$=-1 V and -10 dB at $V_{\alpha}$=-2V.X>=-2V.