Fabrication and characterization of GaN/InGaN based light emitting diodes (LEDs)

This dissertation presents high performance of InGaN/GaN Multi Quantum Well (MQW) based blue LEDs fabrication and characterization methods on c-plane sapphire substrate in two different configurations. The epitaxial material used in the production of blue light emitting LED chips were grown by Metal Organic Chemical Vapor Deposition (MOCVD) system. Two samples were prepared for fabrication and characterization studies. In the case of LED-A, Ni/Au layer was deposited as a contact on the p-GaN then subsequent annealing was performed to get NiOx ohmic form. To spread the current on the whole p-GaN surface, Indium Tin Oxide (ITO) material was deposited as current spreading layer. In the case of LED-B, it was fabricated by using flip-chip fabrication method in order to understand that the chip can be a solution to the heat and high series resistance problem. Ni/Ag was used as a reflective layer instead of the ITO. Ni/Au/ITO and Ni/Au/Ni/Ag to p-GaN specific contact resistances was obtained 2.45∙10-2 and 3.5∙10-3 ohm·cm2 respectively which is quite low for p-GaN contacts. On the other hand, Ti/Al/TiB2/Au to n-GaN specific contact resistances was obtained extrememly low for LED-A and LED-B as 1.74∙10-6 and 7.72∙10-7 ohm.cm2. When LED-A and LED-B samples were compared, it was obviously observed rapid thermal annealed (RTA) LED-B flip-chip fabrication with Ni/Au/RTA/Ni/(Ag) films could provide good electrical and optical properties to improve output power and external quantum efficiency (EQE) about 47 % and 49 % respectively at 350 mA current. Keywords: InGaN/GaN multi quantum well LED, rapid thermal annealing, reflective layer, current spreading layer, indium tin oxide.