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22 March 2007 Maximising the gain: optimising the carrier distribution in InGaAs quantum dot lasers
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The performance of lasers with self assembled quantum dot active regions is significantly affected by the presence of the two dimensional wetting layer and the other states necessary for carrier injection due to the manner in which carriers are distributed amongst the various states. In this work we describe three approaches to overcome the low value of maximum saturated gain, which has been observed by many groups worldwide, and explain the approaches in terms of the impact on the distribution of carriers within the available states. We present results of direct measurements of the modal gain and measurements that indicate the form of the carrier distribution within the samples to justify our argument. The structures examined include the use of a high growth temperature to smooth the matrix layer, the use of p-type modulation doping and the use of InAlAs capping layers and all have been grown by solid source molecular beam epitaxy. We demonstrate CW operation at 1.3&mgr;m for 1mm long devices with uncoated facets and very low threshold current density (< 40Acm-2) in longer devices. We also demonstrate that the negative T0 (reducing threshold current density with increasing temperature) obtained around room temperature in our p-doped devices is due to the temperature dependence of the gain.
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Peter M. Smowton, Ian C. Sandall, David J. Mowbray, Hui-Yun Liu, and Mark Hopkinson "Maximising the gain: optimising the carrier distribution in InGaAs quantum dot lasers", Proc. SPIE 6468, Physics and Simulation of Optoelectronic Devices XV, 646817 (22 March 2007);


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