QUANTIZED CONDUCTANCE AND ELECTRON FOCUSING SPECTRA OF GAAS ALGAAS POINT CONTACTS FABRICATED BY OPTICAL LITHOGRAPHY/

Split gate quantum point contacts on a two-dimensional electron gas (2 DEG) of GaAs/AlGaAs heterostructures are fabricated using conventional optical lithography. The typical opening of the split gates ranges fr om 0.25 to 0.5 mum. Applying negative voltages to the gate introduces horn-shaped constrictions. In a double point contact device, the point contact conductances are measured as a function of gate voltage, and transverse electron focusing is studied using one point contact to inj ect electrons ballistically into the 2DEG and the other to collect the electrons. Clear quantized conductance steps in units of 2e2/h are fo und at temperatures between 0.1 and 2 K. Also, electron focusing spect ra are obtained for various point contact widths and some features are characterized by the geometry of the split gate.