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  • 2015luphd

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Mid-infrared antimonide based type II quantum dot lasers for use in gas sensing

Research output: ThesisDoctoral Thesis

Publication date2015
Number of pages152
Awarding Institution
  • Lancaster University
<mark>Original language</mark>English


Type II InSb/InAs quantum dots (QDs) emitting in the 3-4 µm range are promising candidate as the gain medium for semiconductor laser diodes. The molecular beam epitaxy (MBE) growth of the QDs on GaAs and InP substrates can largely cut down the costs for future devices and massively broaden its application possibilities using the more mature material platforms. Different metamorphic growth techniques including inter-facial misfit (IMF) arrays were experimented for the integration of the InSb QDs on GaAs substrates. The density of threading dislocations and the quality of the QDs were investigated using cross-sectional transmission electron microscopy (TEM) images, high resolution X-ray diffraction (XRD) and photo-luminescence (PL). The 4 K PL intensity and linewidth of InSb QDs grown onto a 3 μm thick InAs buffer layer directly deposited onto GaAs proved to be superior to that from QDs grown on 0.5 μm thick InAs buffer layers using either AlSb or GaSb interlayers with IMF technique. Even though the dislocation densities are still high in all the 3 samples (~109 cm-2), they all achieved comparable PL intensity as the QDs grown on InAs substrates. Electro-luminescence (EL) from the QDs on GaAs substrates were obtained up to 180 K, which was the first step towards making mid-infrared InSb QD light sources on GaAs. From the study of PL temperature quenching, thermal excitation of holes out of the QDs was identified as one of the major reasons for weaker PL/EL signals at higher temperature range. To compensate the thermal leakage problem, the QDs integrated on InP substrates were grown between InGaAs barriers, which can provide a larger valence band offset compared with InAs. The QD PL peak moved to shorter wavelength (~2.7 μm) partly due to the stronger confinement, and the PL quenching was significantly slower for T > 100 K. From microscopy images, PL characteristics and calculations, the size and composition of the QDs were estimated.The InSb QD laser structures on InAs substrates emitting at around 3.1 µm were improved by using liquid phase epitaxy (LPE) grown InAsSbP p-cladding layers and two step InAs n-cladding layers. The maximum working temperature was increased from 60 K to 120 K. The gain was determined to be 2.9 cm-1 per QD layer and the waveguide loss was around 15 cm-1 at 4 K. The emission wavelength of these lasers showed first a blue shift followed by a red shift with increasing temperature, identical with the PL characteristics. Multimodal spectra were measured using Fourier transform infrared spectroscopy (FTIR). Spontaneous emission measurements below threshold revealed a blue shift of the peak wavelength with increasing current, which was caused by the charging effect in the QDs. The characteristic temperature, T0 = 101K below 50 K, but decreased to 48K at higher temperatures. Current leakage from the active region into the cladding layers was possibly the main reason for the increase of threshold current and decay of T0 with rising temperature.