Electron transport in GaN/AlGaN heterostructure

Contact Hung-Tao Chou (hungtao@) for more information.

Advanced semiconductor processing now offers physicists a powerful tool to design and fabricate mesoscopic structures at the nanoscale. Using this technology, we study electron transport at the quantum regime to probe the quantum state. Almost all mesoscopic experiments up to now have been done in GaAs/AlGaAs heterostructures. Because of its clean interfaces with good lattice match and mature growth and process technologies, electrons transport in this system is usually treated as material independent and similar to electrons moving in vacuum. But when there are puzzles hard to understand such as 0.7 structure in quantum point contacts [1,2], performing experiments on another material with different properties would provide a direct comparison and offer us a more insightful understanding of the physics.

GaN has recently drawn great interests for use in power field-effect transistors and blue laser diodes. For studying mesoscopic physics, GaN has many different properties compared to GaAs. It has 3 times larger electron effective mass and 30% less dielectric constant, which would give 4 times larger electron-electron interactions at the same density. It also has 5 times larger g-factor and less spin-orbit effect, and with careful growth design, less spin-orbit effect compared with GaA. These properties make GaN a novel mesoscopic system to study electron-electron interaction and spin-related physics.

SEM picture of our split-gate quantum point contact

We have fabricated the first quantum point contact in a GaN/AlGaN heterostructure (above) and observed clear quantized conductance plateaus and 0.7 structure (below) [3]. An effective g-factor of 2.5 is also measured from the spin-split plateau at high magnetic field. We are now trying to study the 0.7 structure in GaN quantum point contacts more carefully and also fabricate more advanced mesoscopic structure such as quantum dots.

[1]  K. J. Thomas, J. T. Nicholls, M. Y. Simmons, M. Pepper, D. R. Mace, and D. A. Ritchie, Phys. Rev. Lett. 77, 135 (1996).
[2]  S. M. Cronenwett, H. J. Lynch, D. Goldhaber-Gordon, L. P. Kouwenhoven, C. M. Marcus, K. Hirose, N. S. Wingreen, and V. Umansky,  Phys. Rev. Lett. 88, 226805 (2002).
[3] H. T. Chou, S. Lüscher, D. Goldhaber-Gordon, M. J. Manfra, A. M. Sergent, K. W. West and R.J.Molnar, Appl. Phys. Lett. 86, 073108 (2005).