Interband and intraband photocurrent of self-assembled InAs/InAlAs/InP nanostructures

The interband and intraband photocurrent properties of InAs/InAlAs/InP nanostructures have been studied. The doping effect on the photoluminescence properties of the quantum dots and the anisotropy of the quantum wire interband photocurrent properties are presented and discussed. With the help of interband excitation, an intraband photocurrent signal of the InAs nanostructures is observed. With the increase of the interband excitation power, the intraband photocurrent signal first increases and then decreases, which can be explained by the variance of the ground state occupation of the InAs nanostructures and the change of the mobility and lifetime of the electrons. The temperature dependence of the intraband photocurrent signal of the InAs nanostructures is also investigated.

InAs/GaAs quantum-dot superluminescent diodes with 110 nm bandwidth

Broadband superluminescent diodes are fabricated by using InAs/GaAs self-assembled quantum dots as an active region. The devices exhibited properties of 110 run bandwidth with the centre of 1.1 mu m and above 30 mW output under pulse injection at room temperature.

Silicon doping induced increment of quantum dot density

Low-indium-content self-assembled InGaAs/GaAs quantum dots (SAQD) were grown using solid-source molecular beam epitaxy (MBE) and investigated by atomic force microscopy and photoluminescence (PL) spectroscopy. Silicon, which was doped at different quantum dot (QD) growth stages, markedly increased the density of QD. We obtained high density In0.35Ga0.65As/GaAs(001) quantum dots of 10(11)/cm(2) at a growth temperature of 520degreesC. PL spectra and distribution statistics show the high quality and uniformity of our silicon-doped samples. The density increment can be explained using the lattice-hardening mechanism due to silicon doping.

Photoluminescence of self-assembled InAs/GaAs quantum dots covered by InAlAs and InGaAs combination strain-reducing layer

Self-assembled InAs/GaAs quantum dots covered by the 1-nm InxAl(1-x)As (x = 0.2,0.3) and 3-nm In0.2Ga0.8As combination strain-reducing layer are fabricated, whose height can take up to 30-46 nm. The luminescence emission at a long-wavelength of 1.33 mum and the energy separation between the ground and the first-excited state of 86 meV are observed at room temperature. Furthermore, comparative study proves that the energy separation can increase to 91 meV by multiple stacking.

Role of different cap layers tuning the wavelength of self-assembled InAs/GaAs quantum dots

We have investigated the effect of different cap layers on the photoluminescence (PL) of self-assembled InAs/GaAs quantum dots (QDs). Based upon different cap layers, the wavelength of InAs QDs can be tuned to the range from 1.3 to 1.5 mum. An InAlAs and InGaAs combination layer can enlarge the energy separation between the ground and first excited radiative transition. GaAs/InAs short period superlattices (SLs) make the emission wavelength shift to 1.53 mum. The PL intensity of InAs QDs capped with GaAs/InAs SLs shows an anomalous increase with increasing temperature. We attribute this to the transfer of carriers between different QDs.

Optical properties of InGaAs self-assembled quantum dots with InAlAs wetting layer

A new self-assembled quantum dots system where InGaAs dots are formed on InAlAs wetting layer and embedded in GaAs matrix has been fabricated. The photoluminescence linewidth increases with increasing temperature, which is very different from normal In(Ga)As/GaAs quantum dots. The results are attributed to a higher energy of the wetting layer which breaks the carrier transfer channel between dots and keeps the dots more isolated from each other.

Proof of InAs/GaAs self-organized quantum dot lasing and the experimental determination of local Strain effect on the band structures

Confirmation of quantum dot lasing have been given by photoluminescence and electro-luminescence spectra. Energy levels of QD laser are distinctively resolved due to band filling effect, and the lasing energy of quantum dot laser is much lower than quantum well laser. The energy barrier at InAs/GaAs interface due to the built-in strain in self-organized system has been determined experimentally by deep level transient spectroscopy (DLTS). Such barrier has been predicted by previous theories and can be explained by the apexes appeared in the interface between InAs and GaAs caused by strain.

Effect of InAlAs/InGaAs cap layer on optical properties of self-assembled InAs/GaAs quantum dots

We have investigated the effect of InAlAs/InGaAs cap layer on the optical properties of self-assembled InAs/GaAs quantum dots (QDs). We find that the photoluminescence emission energy, linewidth and the energy separation between the ground and first excited states of InAs QDs depend on the In composition and the thickness of thin InAlAs cap layer. Furthermore, the large energy separation of 103 meV was obtained from InAs/GaAs QDs with emission at 1.35 pm at room temperature. (C) 2002 Elsevier Science B.V. All rights reserved.

Structure and optical properties of self-assembled InAs/GaAs quantum dots with In0.15Ga0.85As underlying layer

A high density of 1.02 x 10(11) cm(-2) of InAs islands with In(0.15)Gao(0.85)As underlying layer has been achieved on GaAs (10 0) substrate by solid source molecular beam epitaxy. Atomic force microscopy and PL spectra show the size evolution of InAs islands. A 1.3 mum photoluminescence (PL) from InAs islands with In(0.15)Gao(0.85)As underlying layer and InGaAs strain-reduced layer has been obtained. Our results provide important information for optimizing the epitaxial structures of 1.3 mum wavelength quantum dots devices. (C) 2002 Elsevier Science B.V. All rights reserved.

Modification of emission wavelength of self-assembled In(Ga)As/GaAs quantum dots covered by InxGa1-xAs(0 <= x <= 0.3) layer

Red shifts of emission wavelength of self-organized In(Cla)As/GaAs quantum dots (QDs) covered by 3 nm thick InxGa1-xAs layer with three different In mole fractions (x = 0.1, 0.2 and 0.3, respectively) have been observed. Transmission electron microscopy images demonstrate that the stress along growth direction in the InAs dots was reduced due to introducing the InxGa1-xAs (x = 0.1, 0.2 and 0.3) covering layer instead of GaAs layer. Atomic force microscopy pictures show a smoother surface of InAs islands covered by an In0.2Ga0.8As layer. It is explained by the calculations that the redshifts of the photoluminescence (PL) spectra from the QDs covered by the InxGa1-xAs (x greater than or equal to 0.1) layers were mainly due to the reducing of the strain other than the InAs/GaAs intermixing in the InAs QDs. The temperature dependent PL spectra further confirm that the InGaAs covering layer can effectively suppress the temperature sensitivity of PL emissions. 1.3 mum emission wavelength with a very narrow linewidth of 19.2 mcV at room temperature has been obtained successfully from In,In0.5Ga0.5As/GaAs self-assembled QDs covered by a 3-nm In0.2Ga0.2As strain reducing layer. (C) 2001 Elsevier Science B.V. All rights reserved.

Influence of growth conditions on self-assembled InAs nanostructures grown on (001)InP substrate by molecular beam epitaxy

Self-assembled InAs nanostructures on (0 0 1) InP substrate have been grown by molecular beam epitaxy (MBE) and evaluated by transmission electron microscopy (TEM) and photoluminescence (PL). It is found that the morphologies and PL properties of InAs nanostructures depend strongly on the growth condition. For the same buffer layer, elongated InAs quantum wires (QWRs) and no isotropic InAs quantum dots (QDs) can be obtained using different growth conditions. At the same time, for InAs quantum dots, PL spectra also show several emission peaks related to different islands size. Theoretical calculation indicated that there are size quantization effects in InAs islands. (C) 2001 Elsevier Science B.V. All rights reserved.

Photoluminescence properties of self-organized InGaAs/GaAs quantum dot structures

Optical properties of InGaAs/GaAs self-organized quantum dots (QDs) structures covered by InxGa1-x As capping layers with different In contents chi ranging from 0. 0 (i.e., GaAs) to 0. 3 were investigated systematically by photoluminescence (PL) measurements. Red-shift of the PL peak energies of the InAs QDs covered by InxGa1-xAs layers with narrower linewidth and less shifts of the PL emissions via variations of the measurement temperatures were observed compared with that covered by GaAs layers. Calculation and structural measurements confirm that the red-shift of the PL peaks are mainly due to strain reduction and suppression of the In/Ga intermixing due to the InxGa1-xAs cover layer, leading to better size uniformity and thus narrowing the PL linewidth of the QDs. 1. 3 mum wavelength emission with very narrow linewidth of only 19. 2 meV at room temperature was successfully obtained from the In0.5Ga0.5As/GaAs QDs covered by the In0.2Ga0.8As layer.

Photoluminescence studies of type-II self-assembled InAlAs/AlGaAs QDs grown on (311)A GaAs substrate

The photoluminescence (PL) spectra of self-assembled In0.55Al0.45As/Al0.45Ga0.5As quantum dots (QD) grown on (311)A GaAs substrate were measured. The type- I character of PL related to the X valley was verified by excitation power dependence of peak position and the PL spectra under different pressure , which was attributed to the type- II transition from X valley in Al0.5Ga0.5As to heavy holes in In0.55Al0.45As The high energy Gamma -related transition was also observed above 70K and assigned as the transition between Gamma valley and heavy holes in In-0.55 Al0.45As. The X-valley split was discussed to interpret the observed second X-related peak under pressure.

Influence of InxGa1-xAs (0 <= x <= 0.3) cap layer on structural and optical properties of self-assembled InAs/GaAs quantum dots

Optical and structural properties of self-organized InAs/GaAs quantum dots (QDs) with InxGa1-xAs or GaAs cover layers grown by molecular beam epitaxy (MBE) have been characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM) and photoluminescence (PL) measurements. The TEM and AFM images show that the surface stress of the InAs QDs was suppressed by overgrowth of a InxGa1-xAs covering layer on the top of the QDs and the uniformity of the QDs preserved. PL measurements reveal that red shifts of the PL emission due to the reduction of the surface strain of the InAs islands was observed and the temperature sensitivity of the PL emission energy was suppressed by overgrowth of InxGa1-xAs layers compared to that by overgrowth of GaAs layers.

Structural and optical properties of self-assembled InAs/GaAs quantum dots covered by InxGa1-xAs (0 <= x <= 0.3)

Optical and structural investigations of InAs quantum dots (QDs) covered by InxGa1-xAs (0 less than or equal to x less than or equal to 0.3) overgrowth layer have been systematically reported. The decrease of strain in the growth direction of InAs quantum dots covered by InGaAs layer instead of GaAs is demonstrated by transmission electron microscopy experiments. In addition, the atomic force microscopy measurement shows that the surface of InAs islands with 3-nm-thick In0.2Ga0.8As becomes flatter. However, the InGaAs islands nucleate on the top of quantum dots during the process of InAs islands covered with In0.3Ga0.7As. The significant redshift of the photoluminescence peak energy and reduction of photoluminescence linewidth of InAs quantum dots covered by InGaAs are observed. The energy gap change of InAs QDs covered by InGaAs could be explained in terms of reducing strain, suppressing compositional mixing, and increasing island height. (C) 2000 American Institute of Physics. [S0021-8979(00)04018-4].