Abstract
In this dissertation, we have demonstrated GaN-based high-speed Light-emitting diodes (LEDs). In recently, LEDs is one of the most important light sources due to its low power consumption and long lifetime. We use its natural feature to get a high modulation bandwidth. We present the high-frequency characteristics of GaN-based blue and green LEDs with different aperture diameters. In order to get higher current density, we use ring-shaped electrode to confine the current injection. Through appropriate device design, gallium-doped Zinc oxide film deposited by atomic layer deposition is used as the top contact layer with high lateral resistance to self-confine the current injection. In addition, a smaller bonding pad is used to reduce the RC time constant. The LEDs investigated have a peak emission wavelength of 450 and 500 nm. The high optical 3-dB modulation bandwidth are 225 MHz at 35 mA for the blue LEDs and 463 MHz at 50 mA for the green LEDs with an aperture diameter of 75 µm. The LED also exhibits a relatively high output power of 1.6 mW at 35 mA for the blue LEDs and 1.6 mW at 50 mW for the green LEDs. We also present the device performance of high-speed GaN-based green LEDs at different operating temperatures. Temperature dependence of the characteristics of forward voltage, reverse leakage current, electroluminescence linewidth and peak wavelength, light output power, junction temperature, and 3-dB bandwidth are investigated in details. In addition, we work with the Polymer Optical Fiber Application Center in Germany. A maximum bit rate of 4.81 Gb/s and 4.34 Gb/s was achieved over a 1-m SI-POF employing 4-pulse-amplitude (4-PAM) and None-Return-to-Zero (NRZ) modulation format, respectively. Such the LEDs can be applied to plastic optical fiber (POF) and visible light communication (VLC) in the future.