• Journal of the Korea Academia-Industrial cooperation Society
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• v.5 no.4
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• pp.354-358
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• 2004

In this thesis, an analytical model for Ⅰ-Ⅴ characteristics of an n-AlGaAs/GaAs Delta doped HEMT is proposed. 2-dimensional electron gas density, and conduction band edge profile are calculated from a self-consistent iterative solution of the Poisson equation. Parameters, e.g., the saturation velocity, 2-dimensional electron gas concentration, thickness of the doped and undoped layer(AlGaAs, GaAs, spacer etc.,) are in good agreement with the independent calculations.

• JSTS:Journal of Semiconductor Technology and Science
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• v.13 no.4
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• pp.342-354
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• 2013

The aim of this work is to investigate and study the quantum effects in the modeling of nanoscale symmetric double-gate InAlAs/InGaAs/InP HEMT (High Electron Mobility Transistor). In order to do so, the carrier concentration in InGaAs channel at gate lengths ($L_g$) 100 nm and 50 nm, are modelled by a density gradient model or quantum moments model. The simulated results obtained from the quantum moments model are compared with the available experimental results to show the accuracy and also with a semi-classical model to show the need for quantum modeling. Quantum modeling shows major variation in electron concentration profiles and affects the device characteristics. The two triangular quantum wells predicted by the semi-classical model seem to vanish in the quantum model as bulk inversion takes place. The quantum effects thus become essential to incorporate in nanoscale heterostructure device modeling.

• Korean Journal of Optics and Photonics
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• v.9 no.6
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• pp.428-432
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• 1998

We fabricated 1$\times$8 array of GaAs/AlGaAs quantum well infrared photodetectors for the long wavelength infrared detection which is based on the bound-continuum intersubband transition, and characterized its electrical and optical properties. The device was grown on SI-GaAs(100) by the molecular beam epitaxy and consisted of 25 period of 40 ${\AA} $ GaAs well and 500 ${\AA} $ $Al_{0.28} Ga_{0.72}$ As barrier. To reduce the possibility of interface states only the center 20 ${\AA} $ of the well was doped with Si ($N_D=2{\times}10^{18} cm^{-3}$). We etched the sample to make square mesas of 200$\times$200 $\mu\textrm{m}^2$ and made an ohmic contact on each pixel with Au/Ge. Current-voltage characteristics and photoresponse spectrum of each detector reveal that the array was highly uniform and stable. The spectral responsivity and the detectivity $D^＊$ were measured to be 180,260 V/W and $4.9{\times}10^9cm\sqrt{Hz}/W$ respectively at the peak wavelength of $\lambda$ =7.8 $\mu\textrm{m}$ and at T=10 K.

• Advances in nano research
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• v.5 no.4
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• pp.303-311
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• 2017

The continuum elasticity model is applied to investigate quantitatively the growth features and nucleation mechanism of quantum dots, nanopits, and joint QDs-nanopits structures in GaInAlN quasyternary systems. We have shown that for GaInAlN material system at the critical strain of ${\varepsilon}^*=0.039$ the sign of critical energy and volume is changed. We assume that at ${\varepsilon}={\varepsilon}^*$ the mechanism of the nucleation is changed from the growth of quantum dots to the nucleation of nanopits. Obviously, at small misfit (${\varepsilon}$ < ${\varepsilon}^*$), the bulk nucleation mechanism dominates. However, at ${\varepsilon}$ > ${\varepsilon}^*$, when the energy barrier becomes negative as well as a larger misfit provides a low-barrier path for the formation of dislocations, the nucleation of pits becomes energetically preferable. The free energy of mixing for $Ga_{1-x-y}In_xAl_yN$ quasiternary system was calculated and studied and its 3D sketch was plotted.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.2
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• pp.81-92
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• 1990

We developed the technologies of wuperlattice and HEMT structures grown by MOCVD, and their characterization. In the case of GaAs/AlGaAs superlattice, the periodicity, interface abruptness and Al compositional uniformity were confirmed through the shallow angle lapping technique and double crystal x-ray measurement. Photoluminesence spectra due to quantum size effect of isolated quantum wells were also observed. The heterojunction abruptness was estimated to be within 1 monolayer fluctuation by the analysis of the relation between PL FWHM(Full Width at Half Maximum) and well width. HEMT structure was successfully grown by MOCVD. The 2 dimensional electron gas formation at heterointerface in HEMT structure were evidenced through the C-V profile, SdH (Shubnikov-de Haas)oscillation and low temperature Hall measurement. Low field mobility were as high as $69,000cm^2/v.sec$ for a sheet carrier density of $5.5{\times}10^{11}cm^-2$ at 15K, and $41,200cm^2/v.sec$ for a sheet carrier density of $6.6{\times}10^{11}cm^-2$ at 77K. In addition, well defined SdH oscillation and quantized Hall plateaues were observed.

• 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.

• Journal of the Korean Vacuum Society
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• v.19 no.3
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• pp.211-216
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• 2010

The luminescence properties of $In_{0.5}Ga_{0.5}As/In_{0.5}Al_{0.5}As$ multiple quantum wells (MQWs) grown on $In_{0.5}Al_{0.5}As$ buffer layers have been studied by using photoluminescence (PL) and time-resolved PL measurements. A$1-{\mu}m$ thick $In_{0.5}Al_{0.5}As$ buffer layers were deposited on a 500 nm thick GaAs layer, followed by the deposition of the InGaAs/InAlAs MQWs. In order to investigate the effects of InAlAs buffer layer on the optical properties of the MQWs, four different temperature sequences are used for the growth of InAlAs buffer layer. The growth temperature for InAlAs buffer layer was varied from 320^{\circ}C to $580^{\circ}C$. The MQWs consist of three $In_{0.5}Ga_{0.5}$As wells with different well thicknesses (2.5 nm, 4.0 nm, and 6.0 nm thick) and 10 nm thick $In_{0.5}Al_{0.5}$As barriers. The PL spectra from the MQWs with InAlAs layer grown at lower temperature range ($320-580^{\circ}C$) showed strong peaks from 4 nm QW and 6 nm QW. However, for the MQWs with InAlAs buffer grown at higher temperature range ($320-480^{\circ}C$), the PL spectra only showed a strong peak from 6 nm QW. The strongest PL intensity was obtained from the MQWs with InAlAs layer grown at the fixed temperature of $480^{\circ}C$, while the MQWs with buffer layer grown at higher temperature from $530^{\circ}C$ to $580^{\circ}C$ showed the weakest PL intensity. From the emission wavelength dependence of PL decay times, the fast and slow decay times may be related to the recombination of carriers in the 4 nm QW and 6 nm QW, respectively. These results indicated that the growth temperatures of InAlAs layer affect the structural and optical properties of the MQWs.

• Journal of the Korean Vacuum Society
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• v.20 no.6
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• pp.449-455
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• 2011

The luminescence properties of $In_{0.5}Ga_{0.5}As/In_{0.5}Al_{0.5}As$ multiple quantum wells (MQWs) grown on $In_{0.4}Al_{0.6}As$ buffer layer have been investigated by using photoluminescence (PL) and time-resolved PL measurements. A 1-${\mu}m$-thick $In_{0.4}Al_{0.6}As$ buffer layers were deposited at various temperatures from $320^{\circ}C$ to $580^{\circ}C$ on a 500-nm-thick GaAs layer, and then 1-${\mu}m$-thick $In_{0.5}Al_{0.5}As$ layers were deposited at $480^{\circ}C$, followed by the deposition of the InGaAs/InAlAs MQWs. In order to study the effects of $In_{0.4}Al_{0.6}As$ layer on the optical properties of the MQWs, four different temperature sequences are used for the growth of $In_{0.4}Al_{0.6}As$ buffer layer. The MQWs consist of three $In_{0.5}Al_{0.5}As$ wells with different well thicknesses (2.5-nm, 4.0-nm, and 6.0-nm-thick) and 10-nm-thick $In_{0.5}Al_{0.5}As$ barriers. The PL peaks from 4-nm QW and 6-nm QW were observed. However, for the MQWs on the $In_{0.4}Al_{0.6}As$ layer grown by using the largest growth temperature variation (320-$580^{\circ}C$), the PL spectrum only showed a PL peak from 6-nm QW. The carrier decay times in the 4-nm QW and 6-nm QW were measured from the emission wavelength dependence of PL decay. These results indicated that the growth temperatures of $In_{0.4}Al_{0.6}As$ layer affect the optical properties of the MQWs.

• Korean Journal of Optics and Photonics
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• v.32 no.2
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• pp.55-61
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• 2021

The lateral-mode characteristics of 850-nm GaAs/(Al,Ga)As multiple-quantum-well laser diodes and their influence on the kinks in output optical power are investigated. For the investigation, self-consistent electro-thermal-optical simulation and measurement of fabricated devices are used. From this investigation, the optimal P-cladding thickness that provides single-lateral-mode operation is determined, so that high beam quality can be achieved even at high output powers.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.234-234
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• 2010

The PR transitions in asymmetric dot-in-double-quantum-well (DdWELL) photodetector is identified by bias-dependent spectral behaviors. Discrete n-i-n infrared photodetectors were fabricated on a 30-period asymmetric InAs-QD/[InGaAs/GaAs]/AlGaAs DdWELL wafer that was prepared by MBE technique. A 2.0-monolayer (ML) InAs QD ensemble was embedded in upper combined well of InGaAs/GaAs and each stack is separated by a 50-nm AlGaAs barrier. Each pixel has circular aperture of 300 um in diameter, and the mesa cell ($410{\times}410\;{\mu}m^2$) was defined by shallow etching. PR measurements were performed in the spectral range of $3{\sim}13\;{\mu}m$ (~ 100-400 meV) by using a Fourier-transform infrared (FTIR) spectrometer and a low-noise preamplifier. The asymmetric photodetector exhibits unique transition behaviors that near-/far-infrared (NIR/FIR) photoresponse (PR) bands are blue/red shifted by the electric field, contrasted to mid-infrared (MIR) with no dependence. In addition, the MIR-FIR dual-band spectra change into single-band feature by the polarity. A four-level energy band model is proposed for the transition scheme, and the field dependence of FIR bands numerically calculated by a simplified DdWELL structure is in good agreement with that of the PR spectra. The wavelength shift by the field strength and the spectral change by the polarity are discussed on the basis of four-level transition.