A늌W  ݷ֕   The Electro-Optics Association  The Photonics Society of Chinese-Americans Northern California Chapter

 A늌W

2014 Seminar

20140531 (Stanford, CA)

Substrate techniques for III-N materials and devices

Abstract:

GaN is the cornerstone of all III-N based devices, including nitride based LED. However, GaN is mostly heteroepitaxially grown on non-native substrates, such as sapphire, Si, and SiC. The large thermal mismatch and lattice mismatch between GaN and foreign substrates usually induce a large residual stress and defects in GaN films. Homoepitaxy is very essential to improve the crystal quality and accommodate device applications. However, the high cost of homogeneous substrate and complexity of heterogeneous substrate patterning process limit the development of low cost LED.

This presentation will first introduce rapid synthesizing techniques of bulk GaN crystals in existence and then propose two novel GaN substrate techniques for both polar and non-polar substrates to facilitate different device applications. Nonpolar GaN-based LEDs are expected to exhibit higher external quantum efficiency (EQE) at high current densities, as well as emitting polarized light.

 

Bio: 

 

        Dr. Xiaoqing Xu received her Ph.D. in Materials Science from Institute of Semiconductors, Chinese Academy of Science where she developed two novel GaN substrate techniques: self-patterned GaN/InGaN epitaxial lateral overgrowth (ELO) technique and GaN thick film technique using combined MOCVD-HVPE equipment. With first method, nearly stress-free single-crystalline c-GaN film with single polarity and high quality non-polar a-GaN with mirror like morphology were achieved. This template technique liberates us from the complicated processes of traditional ELO and highly reduces the cost. With the second method, a 22-m thick GaN film with smooth surface was obtained, providing a promising technique for free standing GaN substrate.

        She joined Stanford University as a postdoc of electrical engineering in 2011, where she works on MOCVD growth of III-V thin films, heterostructures, selective-area and VLS growth of nanowires; Design and fabrication of biosensor and nano-antennas. Currently she is a research associate in Stanford Nanofabrication Facility.