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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]

We investigated flatness of growth-interrupted InAlAs and InGaAs surfaces using In0.53Ga0.47As/In0.52Al0.48As quantum wells (QWs) with well widths (Lw) of 0.6–12 nm grown on a (4 1 1)A-oriented InP substrate by molecular beam epitaxy. In the (4 1 1)A QWs with growth interruption (GI) at the InGaAs/InAlAs interface (InAlAs surface), full width at half maximum (FWHM) of a photoluminescence peak of the 1.2-nm-thick InGaAs well was as narrow as 15.6 meV, which was almost the same as that of the corresponding well without GI (14.4 meV). On the other hand, the FWHM of the (1 0 0) QWs with GI at the InAlAs surface was 24.1 meV (Lw=1.2 nm), which was 55% larger than that of the (4 1 1)A QWs with GI at the InAlAs surface. This result indicates that the effectively atomically flat interfaces [(4 1 1)A super-flat interfaces] are successfully kept in spite of introducing GI, while GI makes the (1 0 0) interface much rough. [Copyright &y& Elsevier]

Single-particle relaxation times in In0.7Ga0.3As/In0.52Al0.48As quantum well high electron mobility transistor (QW-HEMT) structures for two subbands (i=0 and 1) are studied by fast Fourier transform analysis of Shubnikoov-de Haas (SdH) oscillations measured at 4 K in order to investigate remote impurity (RI) scattering in the QW-HEMT structure with effectively atomically flat interfaces over a wafer-size area ((4 1 1)A super-flat interfaces) grown on a (4 1 1)A InP substrate by molecular beam epitaxy. The (4 1 1)A QW-HEMT structure with thin spacer thickness of 3 nm shows two times longer single-particle relaxation times (τs(0)=0.71×10−13 s and τs(1)=1.08×10−13 s) compared to those (τs(0)=0.37×10−13 s and τs(1)=0.49×10−13 s) for the corresponding QW-HEMT structure with conventional (1 0 0) interfaces, indicating that RI scattering is much reduced in the (4 1 1)A sample. Calculations of τs(0) limited by RI scattering assuming random distribution of sheet-doped impurities show that the enhancement of τs(0) for the (4 1 1)A QW-HEMT structure cannot be explained by laterally uniform spacer thickness resulting from the (4 1 1)A super-flat interfaces. Much reduced RI scattering in the (4 1 1)A QW-HEMT structure is considered to be mainly caused by extremely uniform distribution of sheet-doped impurities. [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]

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]

The surface migration length of As4 molecules on (4 1 1)A surfaces during molecular beam epitaxy has been determined from lateral profiles of As content (x) in GaAsxP1−x layers grown on (4 1 1)A GaAs substrates with a (1 0 0) side-slope using As4 and P2 molecular beams. The migration length of As4 molecules on (4 1 1)A surfaces at a substrate temperature of 535°C was found to steeply increase from 4 to 10 μm and saturate to 10 μm with increasing V/III flux ratio. This V/III ratio dependence of migration length of As4 is understood by a proposed model where an As4 molecule is dissociated and incorporated into the crystal phase when an As4 molecule encounters a Ga adatom on the (4 1 1)A surface. Quantitative analysis is made using rate equations based on the model and the experimental results are reproduced with reasonable fitting parameter. [Copyright &y& Elsevier]