Electrical Studies of Quantum Devices
Abstract: This thesis deals with electrical measurements on quantum devices. The thesis is divided into three major areas: electrical characterization, semiconductor devices, and metal devices. The electrical characterization part present problems and advantages with the measurement techniques used in the the thesis, .i.e., Current-Voltage; Conductance, including higher order harmonics; Capacitance; Cross-capacitance compensation; and In situ measurements. The work done in semiconductor materials includes measurements of the Schottky properties for Au on InP, which were shown to improve by growing a top layer of GaInP before depositing the Au. The technique was used to fabricate a HEMT transistor. Schottky diodes with buried nm-sized metal particles were investigated for different particle densities and sizes and the theory for nanoscopic exclusions was found to agree with experimental data. Resonant tunneling diodes were fabricated in GaInP/GaAs materials. Negative differential resistance was observed with a peak-to-valley ratio of 5.9. In metals the combination of in situ measurements and the ability to move nm-sized particles with the tip of an atomic force microscope have shown quantized conductance at room temperature which could be tuned to predetermined values and it was stable for hours on individual plateaus. This technique also gave the possibility to tune the width of the tunneling gaps with Ångström control. The tuning technique was employed to fabricate Single-Electron Transistors (SETs) with a charging energy of 4.5 meV. Gate oscillations were observed for these devices up to 25 K. The theoretical charging diagram for a double dot Coulomb blockade device was experimentally verified. The technique allows for making very asymmetric SETs and the Coulomb staircase for both single and double dot SETs has been investigated. The asymmetry in a SET can be used for rectifing purposes and a so-called Coulomb blockade ratchet was shown to rectify an ac signal where the induced dc current direction could be controlled by the gate voltage.
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