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Abstract: Time-resolved transmission change of Er-doped InAs quantum dots (QDs) embedded in strain-relaxed In0.45Ga0.55As barriers has been studied using different excitation wavelengths to understand the QD-size dependence of the photocarrier relaxation. Each measured temporal profile was well reproduced by a sum of three exponential decays. Ultrafast and fast ( ) components are dominant in the initial stage of decay, and then the slow component due to the radiative recombination in the QDs appears to be seen. The first two components come from photocarrier relaxation into the nonradiative centers related to Er dopants or the lattice relaxation. The difference is considered to result from whether the nonradiative centers are positioned inside or outside the QDs. The decay time for the outside case becomes shorter as the excitation wavelength is shortened, which might be due to the weaker confinement of photocarriers in the smaller-size QDs. Suppression of the QDs contributing to the radiative recombination is also more significant for the smaller-size QD excitation. [Copyright &y& Elsevier]

Abstract: Self-assembled InAs quantum dots (QDs) embedded in strain-relaxed barriers were grown on GaAs (100) substrates by molecular beam epitaxy. Relaxation of lattice strain in the nucleation layer was monitored by in situ reflection high-energy electron diffraction. Self-assembled InAs QDs were successfully formed on the strain-relaxed barrier. Twenty-layer stacked InAs QDs showed optical absorption in the wavelength range of 1350–1650nm. A fast decay of 18ps was observed in the temporal profile of absorption saturation measurement at a wavelength of 1540nm, which is expected to be useful for ultrafast nonlinear optical switching applications operating in the waveband. [Copyright &y& Elsevier]

Abstract: Effects of erbium doping on photocarrier lifetime have been investigated for self-assembled InAs quantum dots (QDs) embedded in strain-relaxed In0.35Ga0.65As barriers grown on (100) GaAs substrates by molecular beam epitaxy. Time-resolved transmission change measurements were performed on 20-layer stacks of the Er-doped InAs QDs at room temperature using 0.1ps laser pulses with the center wavelength of . Fast and slow decay components were observed in the temporal profile of each Er-doped InAs QD sample. The slow decay component attributed to the radiative recombination process in the QDs was well suppressed by increasing Er-doping density. Moreover, the decay time of the fast component due to the nonradiative process was markedly reduced by the incorporation of Er dopants during the QD formation. A decay time of 3.5ps was obtained for the Er-doped InAs QD sample with a sheet density of incorporated Er dopants per QD layer of . [Copyright &y& Elsevier]

In order to characterize interface roughness scattering, two-dimensional electron gas (2DEG) mobility in (4 1 1)A and (1 0 0) selectively-doped In0.53Ga0.47As/In0.52Al0.48As quantum well (QW) HEMT structures, which were grown on InP substrates by molecular beam epitaxy, with a gate contact was measured at 20 K as a function of sheet electron concentration (Ns) by changing gate bias. Thickness of the QW was designed to be rather small (6 nm) for enhancing the interface roughness scattering for both samples. 2DEG mobilities of the (4 1 1)A sample were 21,000–51,400 cm2/V s in the range of Ns=0.7–1.7×1012 cm−2, which are about more than 2 times higher than the mobilities (8,700–25,400 cm2/V s) of the conventional (1 0 0) sample. 2DEG mobility was calculated by taking into account interface roughness scattering and ionized remote impurity scattering. By fitting the calculated results to the observed ones, lateral size (Λ) and height (Δ) of the interface roughness of the (4 1 1)A sample were determined to be 3.5 and 0.23 nm, respectively, which are 30% and 50% smaller than the corresponding values (Λ=5.0 nm and Δ=0.43 nm) of the (1 0 0) sample. [Copyright &y& Elsevier]

Two-color surface-emitting lasers were fabricated using a GaAs-based coupled multilayer cavity structure grown by molecular beam epitaxy. InGaAs/GaAs multiple quantum wells were introduced only in the upper cavity for two-mode emission in the near-infrared region. Two-color lasing of the device was successfully demonstrated under pulsed current operations at room temperature. We also observed good temporal coherence of the two-color laser light using a Michelson interferometer. A coherent terahertz source is expected when a wafer-bonded coupled cavity consisting of (0 0 1) and non-(0 0 1) epitaxial films is used for the two-color laser device, in which the difference-frequency generation can be enabled by the second-order nonlinear response in the lower cavity. [ABSTRACT FROM AUTHOR]

InAs quantum dots (QDs) were introduced as efficient nonlinear materials into a GaAs/AlAs coupled multilayer cavity, which was recently demonstrated as a novel THz emission device based on difference-frequency generation (DFG) of the two cavity modes. The couple multilayer cavity containing QDs was grown by molecular beam epitaxy and the THz-DFG was measured using femtosecond laser pulses. [ABSTRACT FROM AUTHOR]