Influence of rapid thermal annealing on self-assembled quantum-dot superluminescent diodes
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V5.1.1/FF5.1.1
Influence of rapid thermal annealing on self-assembled quantum-dot superluminescent diodes
Z.Y. Zhanga), Y.Y. Tsuia), R. Fedosejevsa), Z.G. Wangb) a)
Department of Electrical & Computer Engineering, University of Alberta, Edmonton, AB, TG6 2V4, Canada
b)
Key laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of
Sciences, P.O.Box 912, Beijing 100083, People’s Republic of China
Superluminescent diodes (SLD) have great potential for application as light sources including optical gyroscopes and sensors, optical time domain reflectometers (OTDR) and wavelength-division multiplexing (WDM) system testing. High output power and large spectral bandwidth are key features for SLD. High output power has been attempted by antireflection coating of the facet1 and utilizing the tapered active region2, 3. In addition, as the spectral width broadened, the coherence length is reduced. The short coherence length can reduce the Rayleigh backscattering in fiber gyroscope systems and can improve the spatial resolution in OTDR application. Therefore, broadening spectral width of SLD offers an advantage for obtaining the ultimate sensitivity in these applications. In recent years, quasizero dimensional system, especially SAQD grown by Stranski-Krastanow mode has been investigated from both fundamental studies and potential device applications such as laser diodes4. But in current SAQD technology, the size of inhomogeneity is common and the typical nonuniformity is not less than 10%5. In general, such inhomogeneous size distribution of SAQD in the active region is disadvantageous for achieving lasing of QD laser. However, the coherence length Lcoh of SLD is given by Lcoh=λ2/∆λ, where ∆λ is the emission spectral width of the SLD and λ is its central wavelength, so for the designed quantum-dot SLD, it becomes an effective, intrinsic advantage for broadening spectrum. Moreover, there also have two other advantages when making the SAQD as the active region of SLD: One is the efficiency of luminescence of QD materials is higher than that of quantum well and other low dimensional materials due to the atomic-like density of state in QD system; the other is the changing of energy of SAQD is continuous, the flat spectrum can be realized and it will be good for wavelength-division multiplexing (WDM) and other applications of SLD6. In this work, two kinds of SAQD-SLDs have been fabricated. Both of them were with tilted-stripe active region. The detailed descriptions of the fabrications were as follows:
V5.1.2/FF5.1.2
the SAQD-SLDs structures were grown by molecular beam epitaxy on n+- doped GaAs (100) substrate. Two graded index separate confinement heterostructures (GRINSCH) is formed in connection with the multiple stacked QD active layers. The active medium in the superluminescent diodes consists of five InAs SAQD layers. The waveguide layers and the active region were claded by p and n Al0.5Ga0.5As layers of 1µm thickness. The epilayer was followed by a SiO2 layer on which a stripe
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