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ABSTRACT: We have studied the possibility to utilize semiconductor quantum dots (QDs) as an optical phase shifter within a vertical geometry for ultrafast information processing. From theoretical analyses, an optical phase nonlinearity in QD structures has been predicted which can be enhanced through the use of an vertical optical cavity. Asymmetric cavity structures with 16/30 periods of GaAs/AlGaAs layers for the front/back mirrors have been fabricated to demonstrate a practical device with significant nonlinear characteristics for optical switching. A phase shift of 18° has been initially observed with a tilted pump scheme. This observation paves the way toward a Mach–Zehnder optical switch using QDs inside a vertical cavity.
Applied Physics Letters 06/2011; 98(23):231101-231101-3. · 3.84 Impact Factor
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ABSTRACT: We have investigated the carrier tunneling process in a quantum-dot (QD) tunnel injection structure, which employs a GaAs1−xNx quantum well (QW) as a carrier injector. The influence of the barrier thickness between the GaAs1−xNx well and InAs dot layer has been studied by temperature-dependent photoluminescence. Although the 2.5 nm barrier sample exhibits the best tunneling efficiency, a 3.0 nm thickness for the barrier is optimum to retain good optical properties. The carrier capture time from the GaAs1−xNx QW to QD ground states has been evaluated by time-resolved photoluminescence. The result indicates that efficient carrier tunneling occurs at temperatures above 150 K due to the temperature dependent nature of phonon-assisted processes.
Applied Physics Letters 04/2010; 96(15):151104-151104-3. · 3.84 Impact Factor
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ABSTRACT: Self-assembled InAs/GaAs quantum dots (QDs) incorporated in an asymmetric GaAs/Al0.8Ga0.2As vertical cavity have been employed as an optical nonlinear medium for reflection-type all-optical switches. Switching time down to 23 ps together with wavelength tuning range over 30 nm have been achieved in this structure. An angle-dependent behavior of the switching time has been observed, which suggests there is a coupling mechanism between the ground and excited states in QDs with different sizes.
Applied Physics Letters 07/2009; 95(2):021109-021109-3. · 3.84 Impact Factor
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ABSTRACT: We have developed a simple theoretical model to account for the effects of different p -doping levels on the temperature-dependent performance of InAs/GaAs self-assembled quantum dot (QD) lasers. An assumption of equal occupation probabilities among QDs has been applied for operating conditions near the lasing threshold. Theoretical results indicate that there is an optimum p -doping region, which can provide the lowest temperature dependence of lasing threshold at room temperature.
Applied Physics Letters 11/2008; · 3.84 Impact Factor
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ABSTRACT: The authors report the creation of low reflectivity angled facets by focused-ion-beam postfabrication etching. A method to directly measure the effective facet reflectivity of such facets, utilizing gain saturation effects in the quantum dots is described. The reflectivities of the angled facets are shown to decrease by increasing the facet angle from 0° to 15°. With a reflectivity of ≪1×10<sup>-6</sup> obtained for a facet with a 15° angle, allowing quantum dot superluminescent light-emitting diodes to be fabricated. The use of different angled facets to control the emission wavelength of both quantum dot lasers and superluminescent light-emitting diodes is outlined.
Applied Physics Letters 09/2007; · 3.84 Impact Factor
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ABSTRACT: The excitation power dependence of the ground and excited state transitions in type-II InAs-GaAs0.78Sb0.22 quantum dot structure has been studied. Both transitions exhibit a strong blueshift with increasing excitation power but their separation remains constant. This behavior indicates a carrier-induced electric field oriented predominantly along the growth axis, which requires the holes to be localized in the GaAsSb above quantum dots. An accelerated blueshift of the ground state emission is observed once the excited state in the dots starts to populate. This behavior can be explained by a smaller spontaneous recombination coefficient for the excited state transition.
Applied Physics Letters 07/2007; 91(2):021102-021102-3. · 3.84 Impact Factor
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ABSTRACT: An InGaAs strain-reducing capping layer with a stepped composition is shown to significantly reduce the temperature sensitivity of the lasing wavelength in a 1.3 mum InAs/GaAs quantum-dot laser. With this technique, the sensitivity is reduced from 0.48 nm/K for a laser with standard capping layer to 0.11 nm/K for the new design over the temperature range 20-130degC
Electronics Letters 02/2007; · 0.96 Impact Factor
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ABSTRACT: A room-temperature negative characteristic temperature (T<sub>0 </sub>) and ultralow threshold current density (J<sub>th</sub>) of 48 Amiddotcm<sup>-2</sup> are demonstrated for a 1.3-mum InAs quantum dot laser. These characteristics are obtained by combining a high-growth-temperature GaAs spacer layer with p-type modulation doping of the quantum dots in multiple layer dot-in-a-well structures. Through a comparison of p-doped and undoped devices, a photon coupling mechanism is proposed to account for the different temperature dependences of Jth for the two devices. Numerical simulations based on a rate equation model, which includes photon coupling between ground and excited quantum dot states, are performed. The simulations are able to account for the very different temperature-dependent Jth behavior of the doped and undoped device
IEEE Journal of Quantum Electronics 01/2007; · 1.88 Impact Factor
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ABSTRACT: A high-growth-temperature GaAs spacer layer (HGTSL) is shown to significantly improve the performance of 1.3 mum 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 (T<sub>0</sub>), 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 cm<sup>-2 </sup> are achieved for a three-layer device with a 1 mm HR/HR cavity, while a very low threshold current density of 48 A cm<sup>-2</sup> and a negative T<sub>0</sub> are achieved in the p-doped lasers
IEE Proceedings - Optoelectronics 01/2007; · 0.71 Impact Factor
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H. Y. Liu,
S. L. Liew,
T. Badcock,
D. J. Mowbray,
M. S. Skolnick,
S. K. Ray,
T. L. Choi,
K. M. Groom,
B. Stevens,
F. Hasbullah, C. Y. Jin,
M. Hopkinson,
R. A. Hogg
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ABSTRACT: A modification of the thickness of the low-growth-temperature component of the GaAs spacer layers in multilayer 1.3 μm InAs/GaAs quantum-dot (QD) lasers has been used to significantly improve device performance. For a p-doped seven-layer device, a reduction in the thickness of this component from 15 to 2 nm results in a reduced reverse bias leakage current and an increase in the intensity of the spontaneous emission. In addition, a significant reduction of the threshold current density and an increase of the external differential efficiency at room temperature are obtained. These improvements indicate a reduced defect density, most probably a combination of the selective elimination of a very low density of dislocated dots and a smaller number of defects in the thinner low-growth-temperature component of the GaAs spacer layer.
Applied Physics Letters 08/2006; 89(7):073113-073113-3. · 3.84 Impact Factor
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ABSTRACT: We have investigated the effects of growth temperature on the properties of 1.6 μm GaInNAs/GaAs multilayer quantum wells (MQWs). Strong room-temperature optical efficiency is obtained at 1.58 μm for the sample grown at 375 °C. However, the photoluminescence intensities with emission at similar wavelength are dramatically degraded for the samples grown at 350 and 400 °C. Structural investigations show that compositional modulation and defects occurred in the sample grown at 400 °C and possible point defects within the MQWs grown at 350 °C. Based on these observations, the mechanism of effects of growth temperature on near-1.55-μm GaInNAs/GaAs MQWs is discussed.
Applied Physics Letters 05/2006; 88(19):191907-191907-3. · 3.84 Impact Factor
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Electronics Letters 02/2006; 42(16):923- 924. · 0.96 Impact Factor
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Electronics Letters 02/2006; · 0.96 Impact Factor
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IEE Proceedings - Optoelectronics 01/2004; · 0.71 Impact Factor
