Bandgap Engineering and Device Applications of Dilute Nitrides

Bandgap engineering of semiconductor heterostructures has three key parameters: bandgap, band alignment, and quantum confinement, and they have pronounced effects on electrical, optoelectronic, and photovoltaic devices.We use dilute nitrides to illustrate these points.Incorporating ~1% nitrogen into GaAs, InP, and GaP results in a large bandgap bowing and a large change of conduction band lineup, both of which can be explained by the band anti-crossing model. In the case of GaP, the band structure changes from indirect to direct bandgap. (1) Because of the smaller bandgap of GaInNAs than GaAs and InGaAs, when GaInNAs is used as the base of a GaAs heterojunction bipolar transistor (HBT), the turn-on voltage is lower than that of GaAs-base and GaInAs-base HBT.(2) Because GaInNAs can be lattice-matched to GaAs, it can improve the conversion efficiency of a multijunction GaAs-based solar cell, and GaAs-based long-wavelength vertical-cavity surface-emitting lasers (VCSELs) have gained renewed interest. (3) Incorporating 0.5% of N into GaP results in a direct band gap material.Thus, GaNP solar cells achieve 3 times the conversion efficiency at one quarter of the thickness when compared to GaP solar cells.(4) Because of the larger conduction-band offset, the light output of a GaNP/GaP light-emitting diode (LED) is larger than that of an AlGaInP/GaAs LED at the same wavelength.

​Speaker’s bio:​

Charles Tu is a Yushan Fellow and Research Professor in the Department of Electrical Engineering, National Chung Hsing University in Taichung, Taiwan, and he is also a Distinguished Professor Emeritus in the Department of Electrical and Computer Engineering (ECE) at University of California, San Diego (UCSD).

He was a faculty member at UCSD faculty from 1988 to 2018, the ECE Department Chair from 1999 to 2003, and an Associate Dean of the Jacobs School of Engineering from 2004 to 2013. Tu's research interests include molecular beam epitaxy (MBE) of novel compound semiconductor heterostructures and nanostructures for electronic, optoelectronic and photovoltaic applications. He was a Distinguished Member of Technical Staff at AT&T Bell Laboratories, Murray Hill, New Jersey from 1980 to 1988.

He earned his Ph.D. in Engineering and Applied Science from Yale and his B.Sc. (Hon.) in Physics from McGill University in Montreal. Tu is a Fellow of the IEEE, American Physical Society, and AVS Science and Technology Society. He received Taiwan's Pan Wen-Yuan Foundation Outstanding Research Award in 2009, the North American MBE Innovator Award in 2011, an honorary doctorate from Linköping University, Sweden in 2013, the IEEE Region 6 (Western U.S.) Educator of the Year Award in 2014, and the Al Cho MBE Award from the International Conference on MBE in 2020.