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Title: Study of the III-nitride based nanostructures
Author: Tang, Hao
ISNI:       0000 0004 5358 4740
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2014
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The III-nitrides has wide application in opto-electronic devices, including green/blue light-emitting diodes (LEDs), laser diodes and solar cells. This thesis addresses the fundamental issues of these devices from a concern of efficiencies. InGaN-based LEDs present efficiency losses (droop) at higher injection intensities. By relieving the quantum-confined-stark effect (QCSE), the nanorod structure reduces the electron-longitudinal-optical phonon coupling strength by 40% on average, as measured by the Huang-Rhys Factor. Consequently, a weaker indirect Auger recombination could potentially curb the droop. Besides, surface plasmon polariton–exciton coupling leads to 5.5 times enhancement of the internal quantum efficiency (IQE) and is found to be motivated by the carrier delocalization effect. Both SP and nanorods contribute to high LED efficiencies. The whispering gallery mode ring cavities are studied in the Finite Difference Time Domain (FDTD) approach in order to design high efficiency nitride laser diodes. For InGaN based rings with a radius of 1000-1500nm, the ideal Q-factor reaches 106 at the resonance wavelength around 500nm. The mode splitting effect with separation of bonding and anti-bonding modes is observed as a result of the interference between rings. A 2-3 times enhancement of the Q-factor can be realized when two rings is 25-50nm apart. Q-factors reduce when two rings have a deviation in size. InGaN based quantum dot (QD) solar cell taking advantages of both the intermediate band solar cell (IBSC) structure and prominent piezoelectric fields in III-nitrides is theoretically researched. The IB provided by QDs increases the short circuit current density, and the piezoelectric field enhances the open circuit voltage. The optimized structure reaches a highest conversion efficiency of 55.4%. The InGaN QD structures are viable for high performance nitride solar cells.
Supervisor: Wang, Tao Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available