Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492128
Title: Stacked self-assembled InAs/GaAs quantum dot lasers
Author: Ng, Jen Teik
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2008
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Abstract:
Stacked self-assembled binary InAs/GaAs quantum dot (00) lasers without strain reduction layers were grown using molecular beam epitaxy, operating near 1.3 I-lm under almost room temperature conditions. In order to fabricate the most efficient 00 laser, this work was divided into two major sections: the first part investigated the material properties of ODs, more specifically in stacked structures, and the second part was characterisation of the laser diode based on the optimised stack structure. Material characterisation investigations revealed that ODs grown from the self-assembly of nominally 2.73 monolayer thick InAs were suitable for near 1.3 I-lm emission. Due to the large size of the dots fabricated using this method, a high density of defects was observed in the stacked structure, reducing the quantum efficiency of the material. Optimisation work revealed that for a GaAs spacer layer thickness of 25 nm and 50 nm, the maximum number of stacking periods permissible before the onset of defect formation are three and eight periods respectively. Additionally, different growth conditions were investigated to understand their effects on the size and density of the nano-islands. Based on the results obtained from materials characterisation, two laser diodes were grown: a four- and three-stack structure with a GaAs spacer thickness of 25 nm, and 50 nm respectively. The use of such thick spacer layers was to decouple the strain between the adjacent dots and improve the crystallinity of the stacked structure. For the 25 nm case, the presence of defects in the structure, coupled with a high series resistance, lead to devices that were unable to demonstrate stimulated emission. By contrast, for the case of 50 nm, laser oscillation was observed under pulsed mode conditions up to 280 K, with a very high characteristic temperature (To) of 415 K from 100-200 K operation. Above that temperature To decreased rapidly to 45 K, indicating high losses in the cavity caused by defect processes. The results are very promising as there are many techniques not yet included that could enable the device to operate under continuous wave at room temperature.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.492128  DOI: Not available
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