Awards & Honors

Biography

GaN is a direct wide bandgap semiconductor used to manufacture optoelectronic devices such as light emitting diodes (LEDs) and laser diodes (LDs). In addition, GaN has a very high breakdown field, high electron mobility, and high saturation velocity; properties which make it suitable for high voltage and high frequency power electronic devices. Due to the lack of a native substrate, the vast majority of GaN devices are grown on foreign substrates. Thus, defects and stress are introduced into devices, limiting performance. At UCSB we aim to grow high quality GaN substrates to increase the efficiency and lifetime of GaN-based optoelectronic and electronic devices. Sodium-flux method is used grow GaN from super-saturated solution. A new system for the Na-flux technique has been developed by Von Dollen et al. The system allows us to monitor the GaN growth in situ using the pressure decay of nitrogen as it is consumed by the growing GaN. Although high growth rates have been achieved with this system, the resulting GaN crystals are usually opaque with high concentrations of impurity. The transparency of GaN substrates is beneficial for light extraction from homoepitaxial optoelectronic devices.  In our research, we focus on investigating the main impurities in our flux-grown GaN crystals and their relation to the coloration of the grown GaN crystals as well as different methods to reduce the level of such impurities in our bulk GaN. In addition, we use our growth system to investigate the thermodynamics of forming GaN with a focus on controlling the growth driving force for high structure quality.

Publications:

1. A new system for sodium flux growth of bulk GaN. Part II:  in situ investigation of growth processes. Von Dollen, P., Pimputkar, S., Alreesh, M. A., Nakamura, S., Speck, J. S., (2016), Journal of crystal growth, 456, 67-72, DOI: 10.1016/j.jcrysgro.2016.08.018

2. A new system for sodium flux growth of bulk GaN. Part I: System development, Von Dollen, P., Pimputkar, S., Alreesh, M. A., Albrithen, H., Suihkonen, S., Nakamura, S., Speck, J. S., (2016), Journal of crystal growth, 456, 58-66. DOI: 10.1016/j.jcrysgro.2016.07.044

3. Investigation of oxygen and other impurities and their effect on the transparency of a Na flux grown GaN crystal.Alreesh, M. A., Abo Alreesh, M., Von Dollen, P., Malkowski, T. F., Mates, T., Albrithen, H., ... Speck, J. S. (2019). Journal of crystal growth, 508, 50-57.