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Title: Characerisation of Ingan gan quantum well light emitting diodes
Author: Pope, Iestyn A.
ISNI:       0000 0004 2745 992X
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2004
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By focussing on the properties of InGaN/GaN quantum well (QW) LEDs the key physical processes relevant to all InGaN/GaN light emitters are studied. These include the strength of the piezoelectric field, the important current pathways and the effect doping densities and anneal temperatures have on device performance. Photocurrent absorption spectra, of 35A Ino.1Gao.9N QW LEDs, were measured for a range of reverse bias. A bias of 8.5 V was necessary to counteract the affect of the internal piezoelectric field. Using this value and an appropriate approximation for the depletion width of a p-z'-n junction the calculated piezoelectric field was (1.9 0.15) MVcm"1, in good agreement with 1.8 MVcm"1 calculated using piezoelectric constants interpolated from the binaries. The absorption spectra of 26A wide Ino.i6Gao.84N QW LEDs exhibit a band tail extending to low photon energies whereas emission occurs from the low energy side of this band tail, suggesting emission occurs from localised potential minima. Light-current (LI) characteristics, measured as a function of temperature, are sublinear and exhibit a distinctive temperature dependence. These characteristics are explained in terms of drift leakage which is exacerbated due to the large acceptor activation energy in Mg doped GaN. The data was simulated using a drift diffusion model and good agreement between experimental and simulated results is obtained providing the model includes the band tailing. Emission and absorption spectra and LI characteristics were measured for 25A Ino.1Gao.9N/GaN QW LEDs subject to four different anneal temperatures of 700, 750, 850 and 900°C. Using a drift diffusion model, incorporating different acceptor concentrations to simulate the effect of different anneal temperatures, good agreement was achieved between the trends seen in the experimental results and those produced by the simulations. This confirms the important roles drift leakage and thermal annealing have on these devices.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available