Discipline: Technology and Engineering
Subcategory: Materials Science
Room: Marriott Balcony A
Paola Andrea Perez - The University of Texas at El Paso
Co-Author(s): David Kealhofer, University of California, Santa Barbara, CA; Susanne Stemmer, University of California, Santa Barbara, CA
In a capacitor whose plates are formed by metal and semiconductor films, the quantum capacitance is a contribution to the total capacitance that is a direct measure of the semiconductor’s density of states, a thermodynamic quantity fundamental to the transport characteristics of the semiconductor. Quantum capacitance is most interesting at cryogenic temperatures, where thermal broadening of features in the density of states is suppressed. In a cryostat, the quantum capacitance can be as many as six orders of magnitude smaller than the capacitance of the cables connecting the capacitor to the measurement electronics, making the design of the probe—the apparatus housing the sample platform and cabling—critical to the feasibility of the experiment. Finally, the thermal properties of the probe necessitate compromise with its electronic properties. Here we present the design and fabrication of such a capacitance probe to be used in the Quantum Design Physical Property Measurement System (PPMS) at temperatures down to 2 K. The probe’s stainless-steel tubing and cabling provide thermal anchoring to the cold isothermal region at the bottom of the cryostat without conducting a prohibitively large heat load from the top, while the configurability of the probe end allows for different experiments to be built without complete disassembly of the probe. We also present first experiments on capacitors fabricated from a Au/Ti metal top plate, Al2O3 dielectric, and Cd3As2 bottom plate. Such measurements demonstrated periodic quantum oscillations in a magnetic field. Oscillations shifted with increasing voltage bias across the capacitor due to charge modulation in the Cd3As2 layer. Additionally, the system sensitivity allowed ~5 fF changes in capacitance to be observed. Future work includes optimization of probe design and more detailed capacitance-voltage testing.
Funder Acknowledgement(s): This research was partially supported by the PREM program of the National Science Foundation under Award no. DMR 1827745 and by the MRSEC Program of the National Science Foundation under Award No. DMR- 1720256. Some of the research reported here made use of shared facilities of the UCSB MRSEC (NSF DMR 1720256), a member of the Materials Research Facilities Network (www.mrfn.org).
Faculty Advisor: Susanne Stemmer, firstname.lastname@example.org
Role: I worked on the design and fabrication of a probe that measures quantum capacitance at cryogenic temperatures. Additionally, I tested the probe on a Physical Property Measurement System machine using capacitors formed by metal and cadmium arsenide thin films.