ECE Distinguished Lecture with Professor Charles W. Tu

Starts:
4:00 pm on Wednesday, March 28, 2012
Location:
Photonics Building, 8 Saint Mary's Street, Room 211
URL:
http://www.bu.edu/ece/files/2011/12/Tu-flyer.pdf

Bandgap Engineering and Device Applications of Dilute Nitrides

With Professor Charles W. Tu, Distinguished Professor of the Department of Electrical and Computer Engineering, University of California, San Diego

Faculty Host: Theodore Moustakas

Refreshments will be served outside Room 339 at 3:45 p.m.

Abstract: In the last decade there has been much interest in dilute nitride III-V compound semiconductors, because only a small amount of nitrogen incorporation (~ 1%) in conventional GaAs- and InP-based III-V compounds results in very large bandgap bowing, large change of band lineups, and even change in band structures. These three properties produce interesting electronic and optoelectronic device applications.

The large bandgap bowing is due to lowering of the conduction band, which is the result of the interaction of the nitrogen energy level and the conduction band of the host material. This has stimulated an intense interest in using GaInNAs/GaAs heterostructures on GaAs substrates for 1.3 and 1.55 micron vertical-cavity surface-emitting lasers and in using GaInNAs for the base of heterojunction bipolar transistors with a low turn-on voltage. Furthermore, recently the highest solar cell efficiency has been reported for a tandem cell with GaInNAsSb as one of the multiple junctions.

Incorporating only 0.5% of nitrogen in GaP results in a change in the band structure: from indirect to direct, with strong PL emission in the yellow-amber or the red. Tu and his research team have fabricated red-to-amber light-emitting diodes (LEDs) from Ga(In)NP/GaP heterostructures and quantum wells grown with one-step epitaxy, which is simpler than the commercial process of GaAs substrate removal and wafer bonding to a transparent GaP substrate for high-brightness AlInGaP LEDs.

Finally, preliminary work on using dilute nitrides for intermediate-band solar cells and nanowire solar cells will be presented.

About the Speaker: In the last decade there has been much interest in dilute nitride III-V compound semiconductors, because only a small amount of nitrogen incorporation (~ 1%) in conventional GaAs- and InP-based III-V compounds results in very large bandgap bowing, large change of band lineups, and even change in band structures. These three properties produce interesting electronic and optoelectronic device applications.
The large bandgap bowing is due to lowering of the conduction band, which is the result of the interaction of the nitrogen energy level and the conduction band of the host material. This has stimulated an intense interest in using GaInNAs/GaAs heterostructures on GaAs substrates for 1.3 and 1.55 micron vertical-cavity surface-emitting lasers and in using GaInNAs for the base of heterojunction bipolar transistors with a low turn-on voltage. Furthermore, recently the highest solar cell efficiency has been reported for a tandem cell with GaInNAsSb as one of the multiple junctions.
Incorporating only 0.5% of nitrogen in GaP results in a change in the band structure: from indirect to direct, with strong PL emission in the yellow-amber or the red. Tu and his research team have fabricated red-to-amber light-emitting diodes (LEDs) from Ga(In)NP/GaP heterostructures and quantum wells grown with one-step epitaxy, which is simpler than the commercial process of GaAs substrate removal and wafer bonding to a transparent GaP substrate for high-brightness AlInGaP LEDs.

Finally, preliminary work on using dilute nitrides for intermediate-band solar cells and nanowire solar cells will be presented.