Quantum Cascade Lasers (QCLs) are unipolar lasers based on intersubband transitions that have emission wavelengths in the mid- to far-infrared. Mid-infrared QCLs have recently reached a high level of technological maturity with watt level continuous wave output powers being demonstrated at room temperature. However, the performance of these conventional QCLs falls away very rapidly below -4 urn where a number of important applications exist. This thesis details the design, fabrication and characterisation of high performance 'short wavelength' QCLs that operate in the 3-4 urn region. The high conduction band offset of the InGaAs/ AIAsSb material system and its compatibility with InP based waveguides and fabrication technology has made it the most attractive solution to achieving high performance QCLs in the 3-4 urn region. This thesis covers the development of InGaAs/AIAsSb based QCLs and covers the demonstration of a number of record high output powers and maximum operating temperatures. Watt level peak powers at room temperature and operation up to at least 400 K have been achieved across the -3.3-3.7 urn range. These high performance InGaAs/ AIAsSb lasers are well suited for the realization of single-mode devices that can be used to create compact, ultra-sensitive trace-gas sensors based on absorption spectroscopy. To this effect, single-mode distributed feedback (DFB) QCLs where developed at -3.35-3.45 urn with side mode suppression ratios of up to 30 dB. The lasers employed buried third order DFB gratings and operated at room temperature. Finally, the development of strain compensated InGaAs/AlInAs QCLs grown by metal- organic vapour phase epitaxy (MOVPE) is detailed. This growth technique presents significant advantages for commercial device production when compared to the more typically employed molecular beam epitaxy growth technique. MOVPE grown InGaAs/ AlInAs QCLs with 70% indium composition in the wells operating at -4 urn are reported.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:575411 |
| Date | January 2010 |
| Creators | Commin, James Paul |
| Publisher | University of Sheffield |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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