• Korean Journal of Materials Research
• /
• v.16 no.3
• /
• pp.183-187
• /
• 2006

We present the effects of rapid thermal annealing (RTA) temperature on the structural and optical properties of self-assembled InAs quantum dot (QD) structures grown on GaAs substrates by molecular beam epitaxy (MBE). The photoluminescence (PL) measurements are performed in a closed-cycle refrigerator as a function of temperature for the unannealed and annealed samples. RTA at higher temperature results in the increase in island size, the corresponding decrease in the density of islands, and the redshift in the PL emission from the islands. The temperature dependence of the PL peak energy for the InAs QDs is well expressed by the Varshni equation. The thermal quenching activation energies for the samples unannealed and annealed at $600^{\circ}C$ are found to be $25{\pm}5meV$ and $47{\pm}5$ meV, respectively.

• Journal of the Optical Society of Korea
• /
• v.10 no.4
• /
• pp.184-187
• /
• 2006

For resonant excitation of the ground state $1s^e-1S^h_{3/2}$, dynamics of 'the electron-hole pair in a CdSe quantum dot was investigated by degenerate pump-probe measurement. At low e-h pair densities, the decay of $1s^e-1S^h_{3/2}$ state is dominated by radiative recombination. As the number of the electron-hole pairs increases, new decay features become significant. Theoretical comparison suggests this is attributed to the bi-molecular and Auger-type scattering.

• Journal of the Korean Vacuum Society
• /
• v.18 no.4
• /
• pp.266-271
• /
• 2009

We have investigated the lasing characteristics of GaAs-based 1300 nm wavelength region InAs Quantum Dot Laser Diode grown by Migration Enhanced Molecular Beam Epitaxy. Under a pulsed and CW operation, we observed the state switching of lasing wavelength from ground state (1302 nm) to excited state (1206 nm) due to the gain saturation of ground state. Under a pulsed operation, $J_{th}=92A/cm^2$, $\lambda_L=1311\;nm$ and under a CW operation, $J_{th}=247A/cm^2$, $\lambda_L=1320\;nm$.

• Bulletin of the Korean Chemical Society
• /
• v.32 no.4
• /
• pp.1282-1292
• /
• 2011

The biotin-attached G8 molecular transporter (5) was synthesized and used together with quantum dots in preparing the complexes (QD-MT). The QD-MT complexes were studied in terms of the cellular uptake and the internalization mechanism in live HeLa cells with the aid of various known endocytosis inhibitors. It has been concluded that the QD-MT complex is internalized largely by macropinocytosis. The mouse tissue distribution of the QD-MT complex by i.p. and i.v. routes showed some organ selectivity and a good ability to cross the BBB.

• Journal of the Korean Vacuum Society
• /
• v.16 no.5
• /
• pp.371-376
• /
• 2007

We have investigated the lasing characteristics of the InGaAs quantum dot laser diode (QD-LD) and InGaAs quantum well laser diode (QW-LD) operated at the 980 nm wavelength range. The 980-nm lasers are used as a pumping source for a erbium-doped fiber amplifier (EDFA) and it shows high efficiency in long-haul optical fiber network. We have compared the threshold current density, the characteristic temperature, the optical power and the internal efficiency of QD-LD and QW-LD under a pulsed current condition. The QD-LD shows superior performances to the QW-LD. Further optimization of a LD structure is expected to the superior performances of a QD-LD.

• Korean Journal of Materials Research
• /
• v.29 no.9
• /
• pp.542-546
• /
• 2019

We investigate the characteristics of self-assembled quantum dot infrared photodetectors(QDIPs) based on doping level. Two kinds of QDIP samples are prepared using molecular beam epitaxy : $n^+-i(QD)-n^+$ QDIP with undoped quantum dot(QD) active region and $n^+-n^-(QD)-n^+$ QDIP containing Si direct doped QDs. InAs QDIPs were grown on semi-insulating GaAs (100) wafers by molecular-beam epitaxy. Both top and bottom contact GaAs layer are Si doped at $2{\times}10^{18}/cm^3$. The QD layers are grown by two-monolayer of InAs deposition and capped by InGaAs layer. For the $n^+-n^-(QD)-n^+$ structure, Si dopant is directly doped in InAs QD at $2{\times}10^{17}/cm^3$. Undoped and doped QDIPs show a photoresponse peak at about $8.3{\mu}m$, ranging from $6{\sim}10{\mu}m$ at 10 K. The intensity of the doped QDIP photoresponse is higher than that of the undoped QDIP on same temperature. Undoped QDIP yields a photoresponse of up to 50 K, whereas doped QDIP has a response of up to 30 K only. This result suggests that the doping level of QDs should be appropriately determined by compromising between photoresponsivity and operating temperature.

• Applied Science and Convergence Technology
• /
• v.23 no.6
• /
• pp.387-391
• /
• 2014

Self-assembled InAlAs/AlGaAs quantum dots (QDs) on GaAs substrates were grown by using modified molecular epitaxy beam in Stranski-Krastanov method. In order to study the structural and optical properties of InAlAs/AlGaAs QDs, atomic force microscopy (AFM) and photoluminescence (PL) measurements are conducted. The size and uniformity of QDs have been observed from the AFM images. The average widths and heights of QDs are increased as the deposition time increases. The PL spectra of QDs are composed of two peaks. The PL spectra of QDs were analyzed by the excitation laser power- and temperature-dependent PL, in which two PL peaks are attributed to two predominant sizes of QDs.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.288.2-288.2
• /
• 2014

InP quantum dots were grown by using the molecular beam epitaxy technique. Quantum dots are connected and composed string-like one-dimensional structure due to the strain field along [110] crystal direction. Two prominent photoluminescence transitions from normal quantum dots and string-like one-dimensional structure were observed which show strong optical anisotropy along [1-10] and [110] crystal directions. Both peaks also showed blue-shift while rotating emission polarization from [1-10] to [110] direction. Such optical transition behaviors are the consequence of the valence band mixing caused by strain field along the [110] crystal direction.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2006.08a
• /
• pp.371-374
• /
• 2006

We developed new quantum chemical molecular dynamics and kinetic Monte Carlo programs to simulate the destruction processes of MgO protecting layer in plasma display panel. Our simulation results proposed that MgO(111) surface with nano-dot structures covered by (001) facets has the highest stability, which is against the previous knowledge. The formation of nano-dot structures on the MgO(111) surface covered by (001) facets was found to be the reason for the high stability of the MgO(111) surface. Furthermore, the effect of grain boundary on the stability of MgO surfaces was also clarified.

• Bulletin of the Korean Chemical Society
• /
• v.30 no.4
• /
• pp.857-862
• /
• 2009

We model lattice-mismatched group III-V semiconductor $In_{x}Ga_{1-x}$ alloys with the three-parameter anharmonic Kirkwood-Keating potential, which includes realistic distortion effect by introducing anharmonicity. Although the potential parameters were determined based on optical properties of the binary parent alloys InAs and GaAs, simulated dielectric functions, reflectance, and Raman spectra of alloys agree excellently with experimental data for any arbitrary atomic composition. For a wide range of atomic composition, InAs- and GaAs-bond retain their respective properties of binary parent crystals despite lattice and charge mismatch. It implies that use of the anharmonic Kirkwood-Keating potential may provide an optimal model system to investigate diverse and unique optical properties of quantum dot heterostructures by circumventing potential parameter searches for particular local structures.