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Title: Growth of GaAsBi pin diodes using MBE
Author: Rockett, Thomas
ISNI:       0000 0004 7964 5345
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2019
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The incorporation of bismuth into GaAs induces a large decrease in the band gap energy per unit strain. This band engineering ability makes GaAsBi a promising material for near-infrared optoelectronic devices based on GaAs substrates including LEDs and solar cells. The bismuth incorporation into GaAs and the resulting optoelectronic properties of the epilayers are dependent on the growth temperature and the fluxes of all three constituent atoms. In addition, the propensity of the bismuth atoms to segregate out of the bulk and form into droplets on the wafer surface has restricted the development of GaAsBi optoelectronic devices thus far. In this work, a systematic series of GaAsBi bulk pin diodes was grown using molecular beam epitaxy using different growth temperatures and bismuth fluxes. This series allows the influence of the growth conditions on the device properties to be independently studied. The devices grown at higher temperatures show lower bismuth contents, evidence of epilayer inhomogeneity using, brighter luminescence, and lower dark currents. The FWHM of the emitted PL is proportional to the bismuth content of the layer and independent of the growth conditions. GaAsBi multiple quantum well structures studied by other authors have had degraded performance due to strain relaxation. In this work, a series of GaAsBi multiple quantum well structures with different numbers of wells was grown and compared to a complementary set grown previously in Sheffield. The devices grown in this work had a lower strain per period of the MQW and exhibit improved electroluminescence performance for the devices with large numbers of wells. The electroluminescence of the brightest device was compared to a strain-balanced InGaAs/GaAsP device with a similar structure. The GaAsBi device has weaker electroluminscence than the InGaAs device, however, there are significant current spreading issues which obfuscate a proper comparison. The possibility of using GaAsBi based quantum well LEDs as a broadband light source for optical coherence tomography due to the large FWHM displayed by the LEDs is discussed.
Supervisor: David, John Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available