MOVPE growth and characterisation of III-nitride LED structures
I started my research on nitride materials in 2003, when I came to Cambridge to do my PhD course under the supervision of Prof. Sir Colin Humphreys. My PhD project was on MOVPE growth and characterisation of near-UV emitting quantum well and LED structures on sapphire substrates. After graduation, I started working in the Cambridge Centre for Gallium Nitride as a research associate. Since then, I have been working on several EPSRC, Technology Strategy Board (TSB) and EU projects in collaboration with industrial project partners, aiming at improving the performance of LED devices by optimising the MOVPE growth process and LED structure design. My research is currently focused on the MOVPE growth of high efficiency GaN-based LED structures on large-size Si substrates.
I enjoy not only the basic science, but also the real applications related to my research. I believe that LED technology provides the ultimate light source for a bright future, which promises to enhance our quality of life.
III-nitride based LED on large-size Si substrates
Although Al2O3 (sapphire) and SiC remain the dominant substrate materials for epitaxy of nitride LEDs, the use of large size Si substrates attracts great interests because Si wafers are readily available in large diameter and low cost. In addition, such wafers are compatible with existing 6-inch processing lines commonly used in the electronics industry. However high dislocation density and wafer bowing and/or cracks due to the large lattice mismatch and thermal expansion mismatch between Si and GaN make processing difficult and impair device performance. My results show that these difficulties are manageable through the use of strain-controlling buffer layers and in-situ monitoring. And flat, crack-free GaN structures have been achieved on large-size Si substrates.
In collaborating with several industry partners, including Aixtron Ltd, RFMD UK, QinetiQ and ForgeEuropa, we have successfully demonstrated full wafer-level nitride LED processing using a conventional III-V 6-inch processing line during our previous TSB project. As one of the 26 European partners of a recent EU project on Consumerizing Solid State Lighting (https://projects.leitat.org/cssl/) led by Philips, we are focusing on improving the efficiency of the LED structures grown on large Si substrates. We are hoping to put blue LED dies processed from our LED-on-Si wafers into LED light bulbs. It will be a real test of our GaN-on-Si technology.
