The influence of growth interruption on quantum dot laser

Growth interruption was introduced during the growth of GaAs capping layer of self-organized quantum dots. The comparison of two QD lasers with and without growth interruption in their active regions shows that growth interruption leads to lower threshold current, higher characteristic temperature, and weaker temperature dependence of lasing energy.

X-ray diffraction and optical characterization of interdiffusion in self-assembled InAs/GaAs quantum-dot superlattices

We report on the characterization of thermally induced interdiffusion in InAs/GaAs quantum-dot superlattices with high-resolution x-ray diffraction and photoluminescence techniques. The dynamical theory is employed to simulate the measured x-ray diffraction rocking curves of the InAs/GaAs quantum-dot superlattices annealed at different temperatures. Excellent agreement between the experimental curves and the simulations is achieved when the composition, thickness, and stress variations caused by interdiffusion are taken in account. It is found that the significant In-Ga intermixing occurs even in the as-grown InAs/GaAs quantum dots. The diffusion coefficients at different temperatures are estimated. (C) 2000 American Institute of Physics. [S0003-6951(00)02440-2].

Self-assembled InAs/GaAs quantum dots and quantum dot laser

Systematic study of molecular beam epitaxy-grown self-assembled In(Ga)As/GaAs, In-AlAs/AlGaAs/GaAs, and InAs/InAlAs/InP quantum dots (QDs) is demonstrated. By adjusting growth conditions, surprising alignment, preferential elongation, and pronounced sequential coalescence of dots under the specific condition are realized. Room-temperature (RT) continuous-wave (CW) lasing at the wavelength of 960 nm with output power of 1 W is achieved from vertical coupled InAs/GaAs QDs ensemble. The RT threshold current density is 218 A/cm(2). An RT CW output power of 0.53 W ensures at least 3 000 h lasing (only drops 0.83 db). This is one of the best results ever reported.

Tuning of conduction intersublevel absorption wavelengths in (In, Ga)As/GaAs quantum-dot nanostructures

We demonstrate that by increasing the amount of (In, Ga)As deposit in a quantum dot layer, the intersublevel absorption wavelength for (In, Ga)As/GaAs quantum-dot infrared photodetectors can be blue-shifted from 15 to 10 mu m while the photoluminescence peak is red-shifted. We directly compare the measured energy spacing between intersublevels obtained from infrared absorption spectroscopy with those obtained from photoluminescence spectroscopy. We find that the intersublevel energy spacing determined from absorption measurements is much larger than that obtained from the photoluminescence measurements. (C) 2000 American Institute of Physics. [S0003-6951(00)04524-1].

Photoluminescence study of multilayer In0.55Al0.45As/Al0.5Ga0.5As quantum dot at various temperature

The photoluminescence of self-assembled multilayer In0.55Al0.45As/Al0.5Ga0.5As quantum dot (QD) was measured at various temperatures. Strong photoluminescence of wetting layer (WL) and quantum dots were observed at the same time. Furthermore, direct excitons thermal transfer process between the wetting layer and quantum dots was observed. In the study of temperature dependence of PL intensity it was found that the PL peak of wetting layer contains two quenching processes: at low temperature, excitons are thermally activated from localized states to extended two-dimensional states and then trapped by QDs; at high temperature excitons quench through the X valley of barriers. Using rate equation excitons thermal transfer and quenching processes were analyzed quantitatively.

Quantum-confinement-effect-driven type-I-type-II transition in inhomogeneous quantum dot structures

We investigate the electronic structures of the inhomogeneous quantum dots within the framework of the effective mass theory. The results show that the energies of electron and hole states depend sensitively on the relative magnitude 77 of the core radius to the capped quantum dot radius. The spatial distribution of the electrons and holes vary significantly when the ratio eta changes. A quantum-confinement-driven type-II-type-I transition is found in GaAs/AlxGa1-xAs-capped quantum dot structures. The phase diagram is obtained for different capped quantum dot radii. The ground-state exciton binding energy shows a highly nonlinear dependence on the innner structures of inhomogeneous quantum dots, which originates from the redistribution of the electron and hole wave functions.

Quantum-dot superluminescent diode: A proposal for an ultra-wide output spectrum

We propose a novel superluminescent diode (SLD) with a quantum dot (QD) active layer, which should give a wider output spectrum than a conventional quantum well SLD. The device makes use of inhomogeneous broadness of gain spectrum resulting from size inhomogeneity of self-assembled quantum dots grown by Stranski-Krastanow mode. Taking a design made out in the InxGa1-xAs/GaAs system for example, the spectrum characteristics of the device are simulated realistically, 100-200 nm full width of half maximum of output spectrum can be obtained. The dependence of the output spectrum on In composition, size distribution and injection current of the dots active region is also elaborated.

Electron transport through a double-quantum-dot structure with intradot and interdot Coulomb interactions

Electron transport through a double-quantum-dot structure with intradot and interdot Coulomb interactions is studied by a Green's function (GF) approach. The conductance is calculated by a Landauer-Buttiker formula for the interacting systems derived using the nonequilibrium Keldysh formalism and the GF's are solved by the equation-of-motion method. It is shown that the interdot-coupling dependence of the conductance peak splitting matches the recent experimental observations. Also, the breaking of the electron-hole symmetry is numerically demonstrated by the presence of the interdot repulsion. [S0163-1829(99)01640-9].

Spectral properties of a double-quantum-dot structure: A causal Green's function approach

Spectral properties of a double quantum dot (QD) structure are studied by a causal Green's function (GF) approach. The double QD system is modeled by an Anderson-type Hamiltonian in which both the intra- and interdot Coulomb interactions are taken into account. The GF's are derived by an equation-of-motion method and the real-space renormalization-group technique. The numerical results show that the average occupation number of electrons in the QD exhibits staircase features and the local density of states depends appreciably on the electron occupation of the dot.

Ground-state properties of an artificial molecule: a simple model calculation for the double quantum dot

The ground state of a double quantum-dot structure is studied by a simplified Anderson-type model. Numerical calculations reveal that the ground-state level of this artificial molecule increases with the increasing single particle level of the dot, and also increases with the decreasing transfer integrals. We show the staircase feature of the electron occupation and the properties of the ground-state eigenvector by varying the;single particle level of the dot.

Morphology and photoluminescence of GeSi self-assembled quantum dot on Si(113)

Morphology of self-assembled GeSi quantum dot grown on Si(113) by Si molecular beam epitaxy has been studied by transmission electron microscopy and atomic force microscopy. Photoluminescence from the as-grown sample and annealed sample was studied. The results were analyzed and explained.

Intraband absorption in the 8-12 mu m band from Si-doped vertically aligned InGaAs/GaAs quantum-dot superlattice

Normal-incident infrared absorption in the 8-12-mu m-atmospheric spectral window in the InGaAs/GaAs quantum-dot superlattice is observed. Using cross-sectional transmission electron microscopy, we find that the InGaAs quantum dots are perfectly vertically aligned in the growth direction (100). Under the normal incident radiation, a distinct absorption peaked at 9.9 mu m is observed. This work indicates the potential of this quantum-dot superlattice structure for use as normal-incident infrared imaging focal arrays application without fabricating grating structures. (C) 1998 American Institute of Physics. [S0003-6951(98)01151-6].

Normally incident infrared absorption in vertically aligned InGaAs/GaAs quantum dot superlattice

30-period InGaAs/GaAs quantum dot superlattice was fabricated by MBE. Using cross sectional transmission electron microscopy, the InGaAs quantum dots were found to be perfectly vertically aligned in the growth direction (100). Under normally incident radiation, a distinct absorption in the 8.5 similar to 10.4 mu m range peaked at 9.9 mu m was observed. The normally incident infrared absorption in vertically aligned quantum dot superlattice in the 8 similar to 12 mu m range was realized for the first time. This result indicates the potential application of the quantum dot superlattice structure without grating as normally incident infrared detector focal plane arrays.

Electronic structures of cubic lattice quantum dots

In this article, we give the electronic structure and optical transition matrix elements of coupled quantum dots (QDs) arranged as different cubic lattices: simple cubic (sc), body-centered cubic (bcc), and face-centered cubic (fcc) superlattices. The results indicate that electron and hole energies of bcc, sc, and fcc superlattices are the lowest, the highest, and the middle, respectively, for the same subband under the same QD density or under the same superlattice constant. For a fixed QD density, the confinement effects in sc, fcc, and bcc superlattices are the strongest, the middle, and the weakest, respectively. There are only one, two, and four confined energy bands, with energies lower than the potential barrier for sc, bcc, and fcc QD superlattices, respectively. The results have great significance for researching and making semiconductor quantum dot devices. (C) 1998 American Institute of Physics. [S0021-8979(98)02119-7]

Normal-incidence intersubband (In, Ga)As/GaAs quantum dot infrared photodetectors

We report the device performance of normal-incidence (In, Ga)As/GaAs quantum dot intersubband infrared photodetectors. A primary intersubband transition peak is observed at the wavelength of 13 mu m (E-0 --> E-1) and a secondary peak at 11 mu m (E-0 --> E-2). The measured energy spacing in the conduction band of the quantum dots is in good agreement with low temperature photoluminescence measurement and calculations. A peak detectivity of 1 x 10(10) cm Hz(1/2)/W at 13 mu m was achieved at 40 K for these devices. (C) 1998 American Institute of Physics. [S0003-6951(98)01440-5].