 | Effects of carrier relaxation processes on quantum dot laser properties
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| | A. Tohyama1), R. Lang1), K. Misawa1), H. Saito2) and K. Nishi2) |
| 1) Applied Physics Department, Tokyo University of Agriculture and Technology
2) Photonic and Wireless Devices Research Labs., NEC Corporation |
| | The lasing properties of the quantum dot (QD) lasers are critically dependent on the carrier relaxation processes that redistribute carriers among different confined states and dots. For example, they are essential in reducing the spectral and spatial hole-burnings which would otherwise cause multi-mode lasing [1]. In turn, lasing characteristics are sensitive indicators of the various relaxation rates in QDs. Much attention is being focused on the direct modulation properties of QD lasers. In this report, effects of the inter-confined levels relaxation and Pauli blocking on modulation properties are analyzed. The down- and up-ward relaxation flows between the ground confined (denoted as 1) and the first excited (2) levels can be expressed as γ21p2(1-p1) and γ12p1(1-p2), respectively, where p1 and p2 are the occupation probabilities of the relevant states. It has been pointed out that the inter-confined level relaxation may be affected by so called phonon bottleneck. Experimental and theoretical values reported for γ21 vary widely around from 1012 to 1010s-1, which very likely results from the dependence of the coefficient on device parameters such as the level separations determined by the dot size and carrier densities in QDs and confining layers. |
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