Investigation of mercury cadmium telluride heterostructures grown by molecular beam epitaxy

Richard Sewell

    Research output: ThesisDoctoral Thesis

    325 Downloads (Pure)

    Abstract

    [Truncated abstract] Infrared radiation detectors find application in a wide range of military and civilian applications: for example, target identification, astronomy, atmospheric sensing and medical imaging. The greatest sensitivity, response speed, and wavelength range is offered by infrared detectors based on HgCdTe semiconductor material, the growth and characterisation of which is the subject of this thesis. Molecular Beam Epitaxy (MBE) is a versatile method of depositing layers of semiconductor material on a suitable crystalline substrate. In particular, MBE facilitates the growth of multilayer structures, thus allowing bandgap engineered devices to be realised. By modulating the bandgap within the device structure it is possible to improve the sensitivity or increase the operating temperature of photodetectors when compared to devices fabricated on single layer material. Furthermore, dual-band detectors may be fabricated using multi-layered HgCdTe material. The bulk of this thesis is concerned with the development of the MBE process for multilayer growth, from modelling of the growth process to characterisation of the material produced, and measurement of photoconductive devices fabricated on these wafers. In this thesis a previously published model of HgCdTe growth by MBE is reviewed in detail, and is applied to the growth of double layer heterostructures in order to determine the optimum method of changing the mole fraction between layers. The model has been used to predict the change in the temperature of the phase limit when the mole fraction and growth rate change suddenly as is the case during growth of an abrupt heterostructure. Two options for growth of an abrupt heterostructure were examined (a) modulating the CdTe flux and (b) modulating the Te flux. The change in the phase limit temperature between the layers was calculated as being 4:1±C for option (a) and 5:2±C for option (b) when growing a Hg(0:7)Cd(0:3)Te/Hg(0:56)Cd(0:44)Te heterostructure
    Original languageEnglish
    QualificationDoctor of Philosophy
    Publication statusUnpublished - 2005

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