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Control of etch pit formation for epitaxial growth of graphene on germanium
Graphene epitaxy on germanium by chemical vapor deposition is a promising approach to integrate graphene into microelectronics, but the synthesis is still accompanied by several challenges such as the high process temperature, the reproducibility of growth, and the formation of etch pits during the process. We show that the substrate cleaning by preannealing in molecular hydrogen, which is crucial to successful and reproducible graphene growth, requires a high temperature and dose. During both substrate cleaning and graphene growth, etch pits can develop under certain conditions and disrupt the synthesis process. We explain the mechanisms how these etch pits may form by preferential evaporation of substrate, how substrate topography is related to the state of the cleaning process, and how etch pit formation during graphene growth can be controlled by choice of a sufficiently high precursor flow. Our study explains how graphene can be grown reliably on germanium at high temperature and thereby lays the foundation for further optimization of the growth process. © 2019 Author(s)
Direct Graphene Growth on Insulator
Fabrication of graphene devices is often hindered by incompatibility between
the silicon technology and the methods of graphene growth. Exfoliation from
graphite yields excellent films but is good mainly for research. Graphene grown
on metal has a technological potential but requires mechanical transfer. Growth
by SiC decomposition requires a temperature budget exceeding the technological
limits. These issues could be circumvented by growing graphene directly on
insulator, implying Van der Waals growth. During growth, the insulator acts as
a support defining the growth plane. In the device, it insulates graphene from
the Si substrate. We demonstrate planar growth of graphene on mica surface.
This was achieved by molecular beam deposition above 600{\deg}C. High
resolution Raman scans illustrate the effect of growth parameters and substrate
topography on the film perfection. Ab initio calculations suggest a growth
model. Data analysis highlights the competition between nucleation at surface
steps and flat surface. As a proof of concept, we show the evidence of electric
field effect in a transistor with a directly grown channel.Comment: 13 pages, 6 figure
A Graphene-based Hot Electron Transistor
We experimentally demonstrate DC functionality of graphene-based hot electron
transistors, which we call Graphene Base Transistors (GBT). The fabrication
scheme is potentially compatible with silicon technology and can be carried out
at the wafer scale with standard silicon technology. The state of the GBTs can
be switched by a potential applied to the transistor base, which is made of
graphene. Transfer characteristics of the GBTs show ON/OFF current ratios
exceeding 50.000.Comment: 18 pages, 6 figure
Советская Сибирь, № 278
The Ti/HfO2 interface plays a major role for resistance switching performances. However, clear interface engineering strategies to achieve reliable and reproducible switching have been poorly investigated. For this purpose, we present a comprehensive study of the Ti/HfO2 interface by a combined experimental–theoretical approach. Based on the use of oxygen-isotope marked Hf*O2, the oxygen scavenging capability of the Ti layer is clearly proven. More importantly, in line with ab initio theory, the combined HAXPES-Tof-SIMS study of the thin films deposited by MBE clearly establishes a strong impact of the HfO2 thin film morphology on the Ti/HfO2 interface reactivity. Low-temperature deposition is thus seen as a RRAM processing compatible way to establish the critical amount of oxygen vacancies to achieve reproducible and reliable resistance switching performances
A Graphene-Based Hot Electron Transistor
We
experimentally demonstrate DC functionality of graphene-based
hot electron transistors, which we call graphene base transistors
(GBT). The fabrication scheme is potentially compatible with silicon
technology and can be carried out at the wafer scale with standard
silicon technology. The state of the GBTs can be switched by a potential
applied to the transistor base, which is made of graphene. Transfer
characteristics of the GBTs show ON/OFF current ratios exceeding 10<sup>4</sup>