"New results on III-Nitride physics and devices using MBE heterostructures"

Debdeep Jena, Professor, ECE, University of Notre Dame

February 7th (Friday), 1:15pm
Engineering Science Bldg (ESB), Room 1001

I will give an overview of four new developments of III-Nitride heterostructure work at Notre Dame.

First: Since N is the lightest group-V element, and much lighter than Ga, it dominates the electron-phonon interaction, the saturation velocity, and transistor performance. We have explored the effect of isotopes of N (N15 has one more neutron than N14) on the speed of GaN HEMTs by direct MBE growth. We see enhancement in the speed and performance of HEMTs by this form of ‘neutron engineering’.

Second: GaN has a very rich ‘k-space’ scope for innovative devices, the hot-electron transistor being investigated at UCSB being a prime example. Prof. Kroemer in ’57 had proposed the possibility of negative effective mass oscillators (NEMO). GaN may have the necessary k-space and the heterostructure band offsets to realize this dream. I will present progress on this project, in which we see negative differential resistance and directly measure the band offsets at Al(Ga)N/GaN hot-electron launchers.

Third: We have explored ultrathin pseudomorphic GaN quantum wells embedded on AlN substrates. In these structures, we have observed 2D electron gases, and some of the highest density 2D hole gases in all semiconductors. I will show preliminary n-channel and p-channel FETs using these electron and hole gases.

Fourth: By thinning the ultrathin quantum wells embedded in AlN, we end up with GaN quantum dots. Due to the large band offsets, we see remarkable quantum confinement effects, and light emission from GaN at ~5.1 eV compared to the bulk bandgap of 3.4 eV. By combining tunneling injection and polarization-induced doping, electrically pumped deep-UV LEDs emitting at ~240 nm is achieved. The possibility of such deep-UV quantum-dot lasers will be discussed.

Hosted by: Professor Umesh K Mishra