Fabrication of GaN-Based Light-Emitting Diodes with Decorated Metal Thin Film Structures

  • 陳 省逸

Student thesis: Master's Thesis

Abstract

In this dissertation for purposes of improving the current spreading ability and light extraction efficiency (LEE) GaN-based light-emitting diodes (LEDs) with decorated metal thin film structures were fabricated and studied The device fabrication processes and nanomaterials applications including a hybrid Al metal thin film/AZO transparent conductive layer an one-dimension (1-D) stripe Ag metal thin film hybrid ZnO nanostructure and stripe Ag metal thin film were introduced to improve wall-plug efficiency (WPE) of GaN-based LEDs Therefore enhanced performance and reliability of GaN-based LEDs could be obtained In addition optical properties and current spreading ability of the GaN-based LEDs were studied and discussed The fabrication processes of transparent contact layer (TCL) and metal thin film structures are also discussed in detail First GaN-based LEDs with a high-current spreading ability based on a hybrid Al metal thin film/AZO transparent conductive layer was fabricated and studied The use of a hybrid Al metal thin film structures improve the current crowding effect and high forward voltage problem A hybrid Al metal thin film structures substantially increases the current distribution area rather than the current crowding near the electrodes As compared with conventional GaN-based LEDs at 20 mA the studied device exhibits a 18 6% improvement in light output power In addition GaN-based LEDs with a high-current spreading ability based on a hybrid Al metal thin film/AZO transparent conductive layer could efficiently reduce specific contact resistance According to transmission line model measurement the specific contact resistance of the studied device is reduced to 8 4 x 10-4 Ω-cm2 As compared with conventional GaN-based LEDs at 20 mA the studied device can reduce 0 3 V Second an one-dimension (1-D) stripe Ag metal thin film was successfully fabricated A stripe Ag metal thin film could efficiently enhance current spreading ability and reduce the absorption of photos by semi-transparent only Ag metal thin film Although the studied device only 5% improvement in light output power the forward voltage of device substantially reduced 0 6 V In addition As DC forward current is increased from 10 to 100 mA the increased junction temperature also reduced from 53 3 to 3 3oC of the studied device The saturation point of the light output power increased from 350 to 500 mA It is attributed to an 1-D stripe Ag metal thin film could effectively abate current crowding effect and joule heating effect Due to the current distribution more uniform the performances and power consumption of GaN-based LEDs are significantly improved Finally GaN-based LEDs with a hybrid ZnO nanostructures and stripe Ag metal thin film is fabricated and studied A stripe Ag metal thin film was used to enhance current spreading ability and abate thermal effect The forward voltage was reduced from 3 54 to 3 12 V of studied devices The use of ZnO nanorods effectively reflect photons and redirect the light path rather than total internal reflection effect As compared with conventional GaN-based LEDs at 20 mA studied device exhibits 15 1% (14 9%) improvements in light output power as well as EQE Optical and electrical properties could be improved by the employment of a hybrid ZnO nanostructure and stripe Ag metal thin film Moreover due to the lattice constant approximation of AZO and ZnO ZnO nanordos could directly grow in the AZO surface by low-temperature hydrothermal It is a low cost and simple process for GaN-based LEDs In conclusion all of these specific approaches in this dissertation could effectively improve performances and power consumption of GaN-based LEDs Thus GaN-based LEDs have high potential actual applications
Date of Award2016 Jul 26
Original languageEnglish
SupervisorWen-Chau Liu (Supervisor)

Cite this

'