Charge-imaging field-effect transistors for scanned probe microscopy

This thesis presents experiments on integrating a charge-imaging field-effect transistor onto a scanned probe microscopy cantilever to make a moveable charge-imager. Such an imager would be used for imaging the spatial distribution of electric charge in semiconductor heterostructures and devices. Learning about the spatial distribution of charge yields knowledge about electrical transport at the microscopic level. The information gained from measuring the spatial distribution of charge increases with improvements in the spatial resolution and charge sensitivity of the charge-imaging probes. So, the goal is to devise a charge-imager with sub-micron spatial resolution and single-electron charge sensitivity.; To achieve high spatial resolution and excellent charge sensitivity, the charge-imaging field-effect transistors are made with a quantum point contact geometry. The charge response is confined to a disc with full width half-maximum comparable to its channel width, and the charge noise spectrum reaches values «1 e/Hz½ at 30 kHz. Their low power dissipation (<10 μW) makes them suitable for operation at He dilution refrigerator temperatures.; A strain-sensing field-effect transistor integrated on the base of the same cantilever (c.f. Beck 1998a) allows for simultaneous topography-mapping. The strain-sensing field-effect transistor measures the strain caused by vertical deflections of the cantilever to map the sample topography. The strain-sensing field-effect transistors have a white noise value for the deflection noise of 0.5 nm/Hz½ at 10 kHz.; This thesis describes the fabrication and characterization of charge-imaging field-effect transistors and scanned microscopy cantilevers with integrated strain-sensing transistors. The transistors and cantilevers were fabricated in a GaAs/AlGaAs heterostructure using electron-beam lithography and were characterized at liquid Helium temperatures. Possible future experiments include demonstrating the charge-imaging FET's sensitivity to single electrons, creating a charge- and topography-imaging cantilever, and directly measuring the electron distributions in nanostructures.