| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
Q7, Lateral Confinement of Electrons and Quasi-1D Channels Based Devices |
| Author(s) |
Digbijoy N Nath, Pil Sung Park, Michele Esposto, David Brown, Stacia Keller, Umesh K Mishra, Siddharth Rajan |
| On-Site Speaker (Planned) |
Digbijoy N Nath |
| Abstract Scope |
Devices based on 1D transport such as carbon nanotubes, Si nanowire FETs, etc. are being increasingly investigated as performance of conventional planar MOSFETs and HEMTs are pushed to limits due to aggressive scaling of device dimensions. Fabricating an array of aligned nanowires for useful device applications however presents significant lithographic challenges. In this work, we demonstrate the first non-lithographically defined quasi 1D channels using polarization engineering. Vertical confinement provided by heterostructure engineering and lateral confinement provided by electrostatic polarization engineering lead to 1D confinement of the electrons in these structures. We also propose a simple theory to compare device performance for 1D and 2D regimes and compare the device performance of the fabricated channels to the theoretical prediction. Devices fabricated on MOCVD grown N-polar AlGaN/GaN HEMT structures on vicinal sapphire substrate (40 miscut towards a-plane) were found to exhibit anisotropy in current and channel pinch-off voltages. Channels parallel to the miscut direction pinched off at lower gate biases and hence carried more 2DEG charge than the perpendicular direction as measured by direction-dependent C-V profiling. An electrostatic model, which predicts a saw-tooth energy band profile in the lateral direction, has been proposed to explain the charge anisotropy. Each atomic terrace, characteristic of the surface morphology of vicinal GaN, with its corresponding saw-tooth energy profile is proposed to exhibit quasi 1D confinement. Extending the above idea, we obtained pure anisotropy without a gate, using controlled recess etching of the GaN channel. The intrinsic 2DEG density was gradually reduced in both directions by etching the channels in small steps of channel-recess. At a critical etch depth, drain current ID (up to 150 mA/mm) is found to flow in the parallel direction, while no current flows perpendicular to the steps. This indicates the formation of quasi-1D channels along the steps. Using C-V, we investigated the charge-dependent current properties of the channels. We found that for the same charge density, quasi-1D channels carried more current than 2D channels. We believe this may be attributed to the fundamental transport properties of 1D channels. To verify, we developed a simple theory based on optical phonon scattering that anticipates our experimental results. We will discuss the consequences of these differences in electron transport between 1D and 2D channels for device performance. |
| Proceedings Inclusion? |
Undecided |