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Title: A1InGaN based materials and devices for optoelectronics
Author: Ranalli, Fabio
ISNI:       0000 0004 2719 8862
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2011
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In this work the optimisation of metal contacts to Ill-nitrides will be analysed together with the optical and optoelectronic properties of AlIllGaN /GaN epistructures and devices. The activation of p-Ca : was optimized by varying the annealing temperature, time and the mixture of flowing gases. Around 850°C the sheet resistance reached the lowest value and the dissociation energy of the Mg-H complex was calculated to be 3.65 eV. Surface treatment for the removal of native oxide and impurities from the surface of p-GaN was considered. When treated with HF and, prior to metal deposition, HCI the lowest value for the specific contact resistivity and the contact resistance were found. 4.45 x 10-4 Ώcm2 and 142Ώ. respectively. From this data the concentration of free carriers was estimated to 1017cm-3. The technique commonly used to characterize ohmic contacts to semiconductors, based on the Circular Transmission Lino Model, has been analysed. When applied to semiconductors with large sheet resistance the technique proved to be not sensitive enough to provide reliable data for low specific resistivity contacts. The growth of InGaN/GaN mqw epilayers has been optimized to generate a strong luminescence at about 420 run. Laser structures were grown. The processing of blue/violet LDs has been analysed. Etching of the ridge and the mesa can affect the conductivity of the p-region and the quality of the contacts. Exposure of the conductivity to plasma was found to introduce significant damage and to lower the quality of the contacts. Superlurniuescent devices w« re processed which showed no lasing. Samples from the same material and processed elsewhere were characterized. Lasing was recorded from these devices with a threshold current density of 16 kAcm-2 at 424mm The growth of AllllGaN/AlInGaN \IQ\V epilayers was optimized. Growth temperature and pressure were found to affect both the incorporation of Al and In and the crystal quality. Strain relaxation in MQW was found to degrade the optical per- formance with respect to SQV· UV-LEDs were processed, emitting at 350 nm, which produced bright luminescence.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available