Carrier dynamics in quantum well and quantum dot lasers.
Klotzkin, David J.
1998
Abstract
This dissertation concerns the high speed characteristics of semiconductor lasers. From analysis of the frequency dependence of optical modulation characteristics and small signal impedance, it has been possible to extract information about the carrier dynamics and particularly, the carrier capture time. Study of quantum dot high speed characteristics as a function of temperature have led to good understanding of their dynamics. Analysis of the room temperature impedance in quantum dot laser has shown typical capture times of about 30-40ps. The capture times agree reasonably well with values calculated values based on electron-hole scattering being the important capture mechanism. Measured modulation bandwidths of 20GHz at 80K are consistent with pump-probe measurements of capture time of about 10ps. Theoretical calculations show that the capture time is expected to reduce at low temperatures. The onset of severe capture time limitations was at about 150K which resulted in an extracted spacing between the ground and excited electron state of 60 meV, in good agreement with theoretical calculations of 56 meV. Hence, both the magnitude and temperature dependence of the modulation response are consistent with the mechanism for carrier capture being electron-hole scattering. In contrast, maximum modulation bandwidth of very high speed quantum well lasers has shown an increase of less than a factor of two between room temperature and cryogenic temperature. Extremely high speed $\rm 1.55\mu m$ tunneling injection lasers increased from 20 GHz bandwidth at room temperature to an extrapolated 35 GHz at cryogenic temperature, while the differential gain increased by a factor of fifty. The K-factor and hence the damping limit was almost independent of temperature. This suggest that the gain compression factor is proportional to differential gain. The general result is that for devices which are damping limited, no great improvement in bandwidth is expected from operating at lower temperature. A comparative study was made between a tunneling injection laser (TIL) and three different confinement heterostructure (SCH) 1.55 $\rm \mu m$ devices with similar gain regions. The TIL showed more than twice the room temperature modulation bandwidth of the best of the SCH devices, double the differential gain, and the same K-factor. The TIL was limited much less by heating and somewhat less by capture time than the SCH devices. These differences between both their dynamic and DC characteristics are consistent with the tunneling injection mechanism resulting in a cold carrier distribution. Measurements of large-signal modulation characteristics are compared to full numerical rate equantion simulations and show reasonable agreement. An expression is determined for temporal photon density as a function of small signal parameters, and comparison of this expression with full numerical simulation shows that it is valid for output switching ratios up to about 2. The determined maximum digital transmission speed is approximately 23/K (ns) or 1.4/(capture time)(ns) in Gb/sec. This analysis indicates that large signal pulse widths are typically limited to K-factor in quantum well lasers, and are limited by both K-factor and capture time in quantum dot lasers. (Abstract shortened by UMI.)Subjects
Carrier Dynamics Quantum Dot Quantum Well Semiconductor Lasers
Types
Thesis
Metadata
Show full item recordCollections
Remediation of Harmful Language
The University of Michigan Library aims to describe library materials in a way that respects the people and communities who create, use, and are represented in our collections. Report harmful or offensive language in catalog records, finding aids, or elsewhere in our collections anonymously through our metadata feedback form. More information at Remediation of Harmful Language.
Accessibility
If you are unable to use this file in its current format, please select the Contact Us link and we can modify it to make it more accessible to you.