QDev Seminar: Mohana Rajpalke  

Postdoctoral Fellow
Norwegian University of Science and Technology, Trondheim

MBE growth and properties of group III-V semiconductors

III-V semiconductors such as III-nitrides, III-antimonides and III-arsenides are well suited for application on optoelectronic devices including light emitting diodes, photodetectors, and solar cells. In the present talk, the first topic of interest will be the importance of III-nitride heterostructures in alternative orientations, which have reduced polarization (semipolar) or no polarization (nonpolar) in the growth direction. MBE growth and characterization of polar and nonpolar III-nitride heterostructures were carried out. The fabrication of Au/GaN and InN/GaN Schottky junction will also be discussed. The second part is focused on MBE growth and optical studies of GaSb alloyed with Bi atoms. This alloying enables the band gap to be tuned for different optoelectronic applications while producing only small changes to the lattice parameter. The interaction of the Bi states with the band structure of GaSb is investigated using optical spectroscopy and k.p band structure modelling. Finally, the recent investigation of MBE grown III-AsN and InAs quantum dots for intermediate band solar cells will be discussed. This type of solar cells have recently drawn a lot of interest due to its reported theoretical efficiency limit of 63.2%, much higher than the Shockley–Queisser limit. In particular, InAs/(Al)GaAs(N) quantum dots are promising intermediate band material candidates because of gain in photocurrent through sub-bandgap energy absorption. Introducing Al in the barriers allows for decoupling of the Quasi-Fermi levels of the intermediate band and the conduction band, facilitating voltage recovery at room temperature.