The measured dependence of the lateral ambipolar diffusion length on carrier injection-level in Stranski-Krastanov quantum dot devices

Naidu, D.; Smowton, P. M.; Summers, H. D.

doi:doi:10.1063/1.3471812

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Using the segmented contact method we separate and numerically evaluate the components making up the threshold current density dependence of quantum dot ridge waveguide lasers. An increasing internal optical mode loss and an increasing lateral out-diffusion current are the significant processes in ridges of widths between 4 and 10 μm, with no significant contribution from a deteriorating gain-mode overlap. By fitting a diffusion length model to the lateral out-diffusion process, we extract the ambipolar diffusion length, L_d, as a function of intrinsic carrier injection-level which covers carrier densities appropriate for functioning light-emitting diode and laser devices. The measured dependence fits a diffusion mechanism involving the thermal redistribution of carriers via the wetting-layer and most significantly leads to two regimes where L_d can be reduced in self-assembled quantum-dot systems. Only one of these is shown to be beneficial to the overall efficiency of the device, while the other is at the expense of undesired high-order nonradiative recombination processes at high injection-levels. Covering a peak modal gain range of approximately 5 to 11 cm⁻¹ over injection-levels of 65 to 122 meV at 350 K, this dependence caused L_d to change from 0.75 to 1.50 μm, with the maximum occurring at 84 meV where the peak modal gain is 6 cm⁻¹. Decreasing the temperature to 300 K reduced L_d to <0.75 μm over approximately the same injection-level range.

Article Outline

INTRODUCTION
EXPERIMENTAL
EXPERIMENTAL RESULTS AND DISCUSSION
AMBIPOLAR DIFFUSION LENGTH ANALYSIS
1. Lateral out-diffusion modeling
2. L_d dependence on injection-level
3. Temperature dependence
DISCUSSION
CONCLUSIONS

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KEYWORDS and PACS

Keywords

carrier lifetime, current density, optical losses, quantum dot lasers, ridge waveguides, self-assembly, waveguide lasers, wetting

PACS

42.55.Px

Semiconductor lasers; laser diodes
42.60.By

Design of specific laser systems
42.79.Gn

Optical waveguides and couplers

ARTICLE DATA

Digital Object Identifier

http://dx.doi.org/10.1063/1.3471812

PUBLICATION DATA

ISSN

0021-8979 (print)

1089-7550 (online)

Publisher

$abstract.society.value is a Member of CrossRef

American Institute of Physics

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