Experimental and theoretical investigations of electron-waveguide devices
Sammanfattning: This thesis treats electron-waveguide devices bothexperimentally and theoretically. A fabrication method forelectron-waveguide devices with trench-isolated in plane gateswas developed in the In0.53Ga0.47As/InP material system. The two dimensionalelectron gas was grown by metal-organic vapor phase epitaxy.The pattern, defined by electron-beam lithography, wastransferred to the electron gas by a deep dry-etchingprocedure. For the first time, to our knowledge, indeeplyetthed In1-xGaxAs/InP, this method achieves conductancequantization demonstrating the quality of the electronwaveguides.The mechanism behind the gating for these devices wasinvestigated by measuring the current through the device as afunction of the voltage on the two side-gates and comparing theresult to a numerical self-consistent calculation. for thiscomplicated geometry. The gating was mainly mediated by theetthed surfaces, on which the potential was calculated byassurning a small leakage current. The Schottky character ofthe interface between the etthed surfacc and the electron gasesexplains the nonlinearity where a negative gate voltage affectsmore than a positive one.The same basic design was employed in a Y-branch switch(YBS), where an electric field between the gates deflects theelectrons into either of the two branthes. The entireconductance matrix was measured in a systematic way and agreedwith a criterion for coherent single-mode transport.Also, measurements on four-port cross structures of varyingsizes were done. It was found that for sufficiently smallstructures and for low source-drain volt ages, the electronsare more likely to trave1 ballistically, straight through thedevice, than to be scattered into a side arm, even at roomtemperature.The high-frequency properties of single-modeelectron-waveguide devices were studied theoretically in termsof plasma-wave propagation using a semi classical approach,which allowed the calculation of boundary conditions at discontinuities such as the junction to the reservoirs, ascattering center, and a multiport connecting a number ofwaveguides. A transmission-line analogy was developed for theplasma-wave or signal scattering, useful for the microwaveengineer. This was in turn used to calculate the high-frequencyadmittance measured between the reservoirs of an electronwaveguide.Finally, a novel operation mode of the YBS was proposed,where the switching is controlled by the potentials in thewaveguides. In this self-gated mode, the YBS was predicted tooperate at higher frequencies because of the absente of gatesand the associated high RC-constants, and on lower voltagesbecause of the more efficient gating mechanism.
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