Design and experimental studies of multilayer coating for applications in gallium nitride light emitting devices

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dc.contributor.authorAhmed, Naser Mahmoud
dc.date.accessioned2014-11-03T02:27:12Z
dc.date.available2014-11-03T02:27:12Z
dc.date.issued2006
dc.descriptionPhDen_US
dc.description.abstractIn this work mirrors and microcavties for GaN-UV light enhancement were fabricated and studied. This work discusses methods of designing two types of mirror: first is the semiconductor distributed Bragg reflector (DBR) (Al0.4Ga0.6N/GaN) mirrors and second is the dielectric DBR (TiO2/SiO2, ZrO2/SiO2, and HfO2/SiO2) mirrors. MATLAB software and theoretical analysis based on Transfer Matrix Method (TMM) are used to investigate reflection due to depth errors that occur in films growth, number of layers, type of substrate and incidence angle. We assume that there is 10% depth error in high and low index materials. Our simulation results showed that the depth error caused the reflective band shift about 36nm for semiconductor DBR structure and 20nm for dielectric DBR structure. The optical properties of Al0.11Ga0.89N, Al0.03Ga0.97N, and GaN grown on sapphire were investigated. The ellipsometry measurement operating at wavelength 632.8nm yields  the relative amplitude change for p and s polarizations,  relative phase shift between the two polarization direction and refractive index, important parameters to develop the model for GaN on Al2O3 substrate. We demonstrated a GaN/sapphire microcavity exhibiting 1.3-1.6 fold enhancement in light extraction efficiency by using flat and dome epoxy as external medium compared with air as the external medium. Simulations results showed that by using HfO2 and MgF2 can improve the light extraction by diffracting is the internal light with a large solid angle into the escape light cone. Three types of microcavity types were fabricated using metal and dielectric DBR mirror for the enhancement and inhibition of photoluminescence in GaN. A GaN/sapphire structure as an active layer was sandwiched between two mirrors, which were silver metal reflectors. GaN layer on sapphire showed a photoluminescence (PL) peak around 364 nm. Photoluminescence measurements showed intensity enhancement of 2 and 16 fold in silver half-cavity back mirror and dielectric DBR mirror respectively. In the full cavity samples, the amplitude of the photoluminescence is enhanced 10-times when we used 50 nm silver as a front mirror. A tremendous enhancement of more than 16-fold is obtained when silver mirror of 25nm thickness was used as a front mirror. Further, a tremendous enhancement was obtained when a small hole of 4mm2 was made in the front mirror with 50nm thickness.en_US
dc.identifier.urihttp://hdl.handle.net/123456789/311
dc.language.isoenen_US
dc.subjectScience Physicen_US
dc.subjectGallium nitrideen_US
dc.titleDesign and experimental studies of multilayer coating for applications in gallium nitride light emitting devicesen_US
dc.typeThesisen_US
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