The University of Texas at Dallas

Nano & Beyond Lab

GaN/Si: Characterization of Growth Defects and Interfaces

GaN is a semiconductor that presents a high applicability in optoelectronics and in high-power, high-frequency devices. The wide band gap of GaN (3.4 eV) allows for its application as a light emitting diode, from green to ultraviolet, or a blue laser diode. Its high melting temperature and dissociation pressure are the main obstacles in obtaining a large GaN single crystal, which can serve as substrate for homoepitaxial growth. Because of the lack of a bulk substrate, this material is grown heteroepitaxially on sapphire or SiC. Due to the high cost and small size of the SiC and sapphire substrates, research efforts on growing GaN thin films on less-expensive, large Si substrates are increasing. Growth of device quality GaN on Si is hampered by the ~17% lattice mismatch and a thermal expansion coefficient (TEC) mismatch of ~56%. Defects introduce strain in GaN films, leading to adverse effects such as change in the lattice constant and band gap energy. The defect-related levels in the band gap may be the source of radiative recombination centers in devices, leading to below gap optical emission. On the other hand, defects such as dislocations act as non-radiative centers that may decrease device efficiency.

In this project, we study of growth defects in GaN grown on Si(111), its multilayer interfaces, and reliability in terms of structural degradation upon failure.


Cross-sectional TEM Bright field (Left) and Dark field (Right) diffraction contrast images of the MOCVD grown GaN on Si(111), showing growth defects.