Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10141407 | Applied Surface Science | 2019 | 29 Pages |
Abstract
Al2O3 and Al2O3/HfO2 bilayer gate stacks were directly deposited on the surface of 2D materials via low temperature ALD/CVD of Al2O3 and high temperature ALD of HfO2 without any surface functionalization. The process is self-nucleating even on inert surfaces because a chemical vapor deposition (CVD) component was intentionally produced in the Al2O3 deposition by controlling the purge time between TMA and H2O precursor pulses at 50â¯Â°C. The CVD growth component induces formation of sub-1â¯nm AlOx particles (nanofog) on the surface, providing uniform nucleation centers. The ALD process is consistent with the generation of sub-1â¯nm gas phase particles which stick to all surfaces and is thus denoted as nanofog ALD. To prove the ALD/CVD Al2O3 nucleation layer has the conformality of a self-limiting process, the nanofog was deposited on a high aspect ratio Si3N4/SiO2/Si pattern surface; conformality of >90% was observed for a sub 2â¯nm film consistent with a self-limiting process. MoS2 and HOPG (highly oriented pyrolytic graphite) metal oxide semiconductor capacitors (MOSCAPs) were fabricated with single layer Al2O3 ALD at 50â¯Â°C and with the bilayer Al2O3/HfO2 stacks having Cmax of â¼1.1â¯ÂµF/cm2 and 2.2â¯ÂµF/cm2 respectively. In addition, Pd/Ti/TiN gates were used to increase Cmax by scavenging oxygen from the oxide layer which demonstrated Cmax of â¼2.7â¯ÂµF/cm2. This is the highest reported Cmax and Cmax/Leakage of any top gated 2D semiconductor MOSCAP or MOSFET. The gate oxide prepared on a MoS2 substrate results in more than an 80% reduction in Dit compared to a Si0.7Ge0.3(0â¯0â¯1) substrate. This is attributed to a Van der Waals interaction between the oxide layer and MoS2 surface instead of a covalent bonding allowing gate oxide deposition without the generation of dangling bonds.
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Physical Sciences and Engineering
Chemistry
Physical and Theoretical Chemistry
Authors
Iljo Kwak, Mahmut Kavrik, Jun Hong Park, Larry Grissom, Bernd Fruhberger, Keith T. Wong, Sean Kang, Andrew C. Kummel,