InAs/GaAs quantum-dot intermixing: comparison of various dielectric encapsulants (original) (raw)
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Quantum-Dot Intermixing Enhancement using UV Laser Irradiation
2006
We report the development of an intermixing technique in InGaAs/GaAs quantum-dot (QD) structure using the combination effects of pulsed UV laser irradiation and dielectric induced layer intermixing. Using this method, the quantum-dot intermixing rate is greatly enhanced by group-III vacancies generated by the dielectric cap during annealing. A bandgap shift as large as 180 meV has been measured from a sample exposed to 480 mJ/cm2, 150 pulses of 248 nm UV light, and annealed with a 200 nm thick SiO2 encapsulant layer. Under similar annealing conditions, the non-irradiated SiO2 and Si xNy encapsulated QDs only exhibit bandgap shifts of 18 meV and 91 meV, respectively
High-performance InAs/GaAs quantum dot laser with dot layers grown at 425 oC
Chinese Optics Letters, 2013
We investigate InAs/GaAs quantum dot (QD) lasers grown by gas source molecular beam epitaxy with different growth temperatures for InAs dot layers. The same laser structures are grown, but the growth temperatures of InAs dot layers are set as 425 and 500 • C, respectively. Ridge waveguide laser diodes are fabricated, and the characteristics of the QD lasers are systematically studied. The laser diodes with QDs grown at 425 • C show better performance, such as threshold current density, output power, internal quantum efficiency, and characteristic temperature, than those with QDs grown at 500 • C. This finding is ascribed to the higher QD density and more uniform size distribution of QDs achieved at 425 • C.
Comparison of InAs quantum dot lasers emitting at 1.55 µm under optical and electrical injection
Semiconductor Science and Technology, 2005
InAs/InGaAsP/InP(113)B quantum-dots are studied as active mediums for laser structures emitting near 1.55 µm under optical and electrical injection. In order to precisely tune the emission wavelength of QDs, the double cap growth procedure is used. Laser emission on the ground states is obtained under optical pumping at room temperature. On equivalent structures doped for electrical injection, laser emission is also observed at low temperatures up to 200 K. The difference between the optical and electrical pumping is ascribed to low carrier injection efficiency due to the presence of a 3 nm InP hole blocking barrier at each quantum dot layer which is inherent to the double cap growth procedure. Room temperature laser emission has been reached when the InP first cap layer is substituted by a quaternary GaInAsP (1.18 µm gap) layer in the double cap growth procedure. The threshold current density of the new structure with QD capped only by quaternary is as low as 840 A cm −2 at room temperature.
Opto-Electronics Review, 2010
In this paper, we present a new approach to obtain large size dots in an MBE grown InAs/GaAs multilayer quantum dot system. This is achieved by adding an InAlGaAs quaternary capping layer in addition to a high growth temperature (590° C) GaAs capping layer with the view to tune the emission wavelength of these QDs towards the 1.3 μm/0.95 eV region important for communication devices. Strain driven migration of In atoms from InAlGaAs alloy to the InAs QDs effectively increases the size of QDs. Microscopic ...
C.Y. Jin, H.Y. Liu, T.J. Badcock, K.M. Groom, M. Gutie´ rrez, R. Royce, M. Hopkinson and D.J. Mowbray, 2006
A high-growth-temperature GaAs spacer layer (HGTSL) is shown to significantly improve the performance of 1.3 mm multilayer InAs/GaAs quantum-dot (QD) lasers. The HGTSL inhibits threading dislocation formation, resulting in enhanced electrical and optical characteristics and hence improved performance of QD lasers. To further reduce the threshold current density and improve the room-temperature characteristic temperature (T0), the high- reflection (HR) coating and p-type modulation doping have been incorporated with the HGTSL technique. A very low continuous-wave room-temperature threshold current of 1.5 mA and a threshold current density of 18.8 A cm22 are achieved for a three-layer device with a 1 mm HR/HR cavity, while a very low threshold current density of 48 A/cm2 and a negative T0 are achieved in the p-doped lasers.
Applied Physics A, 2005
Room temperature 1.3 µm emitting InAs quantum dots (QDs) covered by an In 0.4 Ga 0.6 As/GaAs strain reducing layer (SRL) have been fabricated by solid source molecular beam epitaxy (SSMBE) using the Stranski-Krastanov growth mode. The sample used has been investigated by temperature and excitation power dependent photoluminescence (PL), photoluminescence excitation (PLE), and time resolved photoluminescence (TRPL) experiments. Three emission peaks are apparent in the low temperature PL spectrum. We have found, through PLE measurement, a single quantum dot ground state and the corresponding first excited state with relatively large energy spacing. This attribute has been confirmed by TRPL measurements which allow comparison of the dynamics of the ground state with that of the excited states. Optical transitions related to the InGaAs quantum well have been also identified. Over the whole temperature range, the PL intensity is found to exhibit an anomalous increase with increasing temperatures up to 100 K and then followed by a drop by three orders of magnitude. Carrier's activation energy out of the quantum dots is found to be close to the energy difference between each two subsequent transition energies.
Influence of In/Ga intermixing on the optical properties of InGaAs/GaAs quantum dots
Journal of Crystal Growth, 1998
We report on the impact of thermal annealing of buried InGaAs quantum dots (QDs) on the eigenstate energies and their inhomogeneous broadening due to size fluctuations. Application of annealing temperatures (¹) of up to 700°C for 30 min results in a blue shift of the QD ground state luminescence of 150 meV accompanied by a strong reduction of sublevel separation and inhomogeneous broadening. At the same time the wetting layer luminescence is only slightly shifted, resulting in a strongly decreased localization energy of the QDs. With increasing annealing temperature the photoluminescence peak broadening due to the QDs size distribution shows a distinct maximum and subsequently decreases below the value of as grown QDs. These observations qualitatively agree with calculations for a simple model system of spherical QDs assuming Fickian interdiffusion of dot and barrier material. Our results demonstrate that the growth temperatures (¹ %) applied after deposition of the QDs strongly affect their properties. Thus for fabrication of QD based devices in the InGaAs/GaAs system a compromise for the choice of ¹ % has to be made in order to achieve both high carrier localization energies in the QDs (low ¹ %) and high material quality of the cap layers (high ¹ %).
Toward 1550-nm GaAs-Based Lasers Using InAs/GaAs Quantum Dot Bilayers
IEEE Journal of Selected Topics in Quantum Electronics, 2000
By choice of appropriate growth conditions and optimization of the strain interactions between two closely stacked InAs/GaAs quantum dot (QD) layers, the emission wavelength of the QDs can be significantly extended, giving room-temperature emission from highly uniform QD ensembles in excess of 1500 nm. These QD bilayers are incorporated into edge-emitting laser structures and room-temperature ground-state lasing at 1420 nm and electroluminescence at 1515 nm are observed. Under high-bias conditions, asymmetric broadening of peaks in the laser gain spectra are observed, extending positive net modal gain from the devices to beyond 1500 nm, and the origin of this broadening is discussed.
Nano-engineering approaches to self-assembled InAs quantum dot laser medium
Journal of Electronic Materials, 2006
An umber of nano-engineering methods are proposed and tested to improve optical properties of alaser gain medium using the self-assembled InAs quantum dot (QD) ensemble. The laser characteristics of concerni nclude higher gain, larger modulation bandwidth, highere fficiency at elevated temperatures,h ighert hermal stability, and enhanced reliability. The focus of this paper is on the management of QD properties throughd esign and molecular beam epitaxial growth and modification of QD heterostructures.This includes digital alloysa sh igh-quality wide-bandgap barrier;u nder-and overlayers with various compositions to control thed ynamics of QD formation and evolution on the surface; shape engineering of QDs to improve electron-hole overlapa nd reduce inhomogeneous broadening; band engineering of QD heterostructures to enhance the carrierl ocalization by reduction of thermal escapef rom dots; as well as tunnel injection from quantum wells( QWs) to accelerate carriert ransfer to the lasing state. Beneficial properties of the developedQ Dm edia are demonstrated at room temperature in laser diodes with unsurpassedthermal stabilitywithacharacteristic temperatureof380 K, high waveguide modal gain . 50 cm ÿ 1 ,u nsurpassed defect toleranceo vert wo orderso fm agnitude highert han that of QWs typically used in lasers, and efficient emission from at wo-dimensional (2-D)p hotonic crystal nanocavity.