E-Thesis 115 views 35 downloads
Novel wide bandgap semiconductor material based on ternary carbides - An investigation into Al4SiC4 / SIMON FORSTER
Swansea University Author: SIMON FORSTER
DOI (Published version): 10.23889/SUthesis.65005
Abstract
Wide bandgap semiconductor materials are able to withstand harsh environments and operate over a wide range of temperatures. These make them ideal for many applications such as sensors, high-power and radio-frequencies to name a few. However, more novel materials are required to achieve significant...
| Published: |
Swansea, Wales, UK
2020
|
|---|---|
| Institution: | Swansea University |
| Degree level: | Doctoral |
| Degree name: | Ph.D |
| Supervisor: | Kalna, Karol. and Chaussende, Didier. |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa65005 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Abstract: |
Wide bandgap semiconductor materials are able to withstand harsh environments and operate over a wide range of temperatures. These make them ideal for many applications such as sensors, high-power and radio-frequencies to name a few. However, more novel materials are required to achieve significant power efficiency of various applications or to develop new applications to complement current wide bandgap semiconductors such as GaN and SiC. In this dissertation, three different methods are used to study one of these novel materials, aluminium silicon carbide (Al4SiC4): (1) ensemble Monte Carlo simulations in order to study the electron transport properties of the novel ternary carbide, (2) experimental studies to determine its material properties, and (3) device simulations of a heterostructure device made possible by this ternary carbide. All these methods interlink with each other. Data from each of them can feed into the other to acquire new results or refine obtained results thus leading way to attractive electrical properties such as a bandgap of 2.78 eV or a peak drift velocity of 1.35£107 cm s°1. In this work, we are purely focused on the electron transport material properties. Ensemble Monte Carlo toolbox, developed in-house for simulations of Si, Ge, GaAs, AlxGa1°xAs, AlAs, and InSb semiconductors is adopted for simulations of the ternary carbide by adding a new valley transformation to account for the hexagonal structure of Al4SiC4. The Monte Carlo simulations predict a peak electron drift velocity of 1.35£ 107 cms°1 at electric field of 1400 kV cm°1 and a maximum electron mobility of 82.9 cm2V°1s°1. We have seen a diffusion constant of 2.14 cm2s°1 at a low electric field and of 0.25 cm2s°1 at a high electric field. Finally, we show that Al4SiC4 has a critical field of 1831 kV cm°1. In the experimental part, Al4SiC4 semiconductor crystals are used that had previously been grown at IMGP, one by solution grown and the other by sublimation growth. Three different experiments are performed on them: (1) ultraviolet (UV), infrared (IR) and visible (Vis) Spectroscopy, (2) X-ray Photo Spectroscopy, and (3) two-probe measurements where metal contact are grown on the crystals. Here we have found a bandgap of 2.78 ± 0.02 eV UV, IR and Vis Spectroscopy and a thick oxide layer on the samples using XPS. The two-probing DC current-voltage measurements revealed a resistivity of 2.2165£1010 ≠m and a conductivity of 4.5117£10°11 Sm°1. A commercial software Atlas by Silvaco is utilized to predict performance of heterostructure devices with gates lengths of 5 μm, 2 μm and 1 μm, made possible by the ternary carbide in a combination with SiC. The 5 μm gate length SiC/Al4SiC4 heterostructure transistor delivers a maximum drain current of 168 mA/mm, which increases to 244 mA/mm and 350 mA/mm for gate lengths of 2 μm and 1 μm, respectively. The device breakdown voltage is 59.0 V which reduces to 31.0 V and to 18.0 V for the scaled 2 μm and the 1 μm gate length transistors. The scaled down 1 μm gate length device switches faster because of the higher transconductance of 65.1 mS/mm compared to only 1.69 mS/mm for the largest device. Finally, a sub-threshold slope of the scaled devices is 197.3 mV/dec, 97.6 mV/dec, and 96.1 mV/dec for gate lengths of 5 μm, 2 μm, and 1 μm, respectively. Overall, Al4SiC4 has the potential to work in many electronic applications such as high electron mobility transistors, quantum well based semiconductor transistors, light emitting diodes, and X-ray sensors. Al4SiC4 can be used alongside current SiC technologies because of the similarities between its crystal lattice and the crystal lattice of SiC as well as chemical compatibility. However, currently due to a large effective mass, that we calculated using a dispersion relation on the minima of the conduction band, has given a limited electron drift velocity and electron mobility which could limit the usability of Al4SiC4 in this study. |
|---|---|
| Keywords: |
Wide bandgap, Semiconductor, Ternary Carbides, Al4SiC4 |
| College: |
Faculty of Science and Engineering |
| Funders: |
Swansea University/The Communauté Université Grenoble Alpes (ASD1015-100) |