In this thesis, different approaches are studied in order to enhance the performance of LED systems in terms of cost-effeteness and efficiency.

In chapter 2, a reflective Ni/Ag/Ni/Au (1/150/30/100 nm) p-GaN contact is studied and optimized for flip-chip and vertical LEDs application. For samples annealed under ambient O₂ at 500°C for 3 minutes, 2.98V of forward voltage is achieved under 20mA current injection, which is improved by 12.8% when it is compared with a traditional Ni/Au (5/5 nm) p-GaN contact with mirror. A maximum reflectance of 91.6% at 700 nm, 84.2% at 450 nm and 83.8% at 400 nm is successfully demonstrated.

An integrated LED system-on-a-chip (SoC) is introduced in chapter 3. A possible solution of optimizing the cost and the material use by integrating the pa...[ Read more ]

In this thesis, different approaches are studied in order to enhance the performance of LED systems in terms of cost-effeteness and efficiency.

In chapter 2, a reflective Ni/Ag/Ni/Au (1/150/30/100 nm) p-GaN contact is studied and optimized for flip-chip and vertical LEDs application. For samples annealed under ambient O₂ at 500°C for 3 minutes, 2.98V of forward voltage is achieved under 20mA current injection, which is improved by 12.8% when it is compared with a traditional Ni/Au (5/5 nm) p-GaN contact with mirror. A maximum reflectance of 91.6% at 700 nm, 84.2% at 450 nm and 83.8% at 400 nm is successfully demonstrated.

An integrated LED system-on-a-chip (SoC) is introduced in chapter 3. A possible solution of optimizing the cost and the material use by integrating the passive components, LED driver, and LED into a single platform is studied. The first prototype successfully demonstrates the feasibility of the LED Soc technology. The prototype can be directly powered by a standard 110 V AC line and the power factor measured by a Voltech PM100 Single Phase Power Analyzer is 0.95 and the overall efficiency for the LED driver is approximately 73%.

In the last chapter, both a vertical LED (VLED) and inverted planer structure LED (IPS-LED) are studied. The VLED shows a maximum light output power (LOP) improvement from 1 mW to 11.2 mw and the wall-plug efficiency is also improved from 1.4% to 6.4%. However, the forward voltage degradation seriously affects the performance of the VLED. Hence an IPS-LED is developed so as to tackle the forward voltage degradation problem. The result shows an improvement from 0.58 mW to 3.9 mW of LOP and an improvement from 0.7% to 5.1% in wall-plug efficiency.