No abstract

A sharp step-like structure, which is seen in the current-voltage characteristic of a laterally confined AlGaAs/GaAs resonant tunnelling structure, is a novel manifestation of a quantum effect arising when one-dimensional wires feed electrons into a zero-dimensional quantum box. The authors can analyse the data to deduce a tunnelling time, an inelastic scattering time and the transmission probability for electrons in this system. The height of the current steps, Delta I, gives the electron tunnelling time, taue, via Delta I=e/2 taue, while the differential conductance gives the peak transmission probability, T0, via G approximately (e2/h)T0. The authors must invoke inelastic scattering to explain the low value of T0 approximately 9% obtained from the data, and so they find that tunnelling in their structure is sequential.

We report magnetotunneling through a quantum dot realized in a 200-nm-diameter Al"Gal As-GaAs double-barrier diode. Steplike current-voltage characteristics are observed at low temperatures in the low-bias regime and are assigned to tunneling though zero-dimensional states. With increasing magnetic field parallel to the current direction, the first six resonances shift to higher bias by the same amount. The data are discussed in terms of a simple model of electrostatic quantum confinement in a magnetic field, allowing for Coulomb-charging effects. W'e conclude that a more detailed theory is needed to obtain a clear explanation of the mechanism leading to the current steps.

A swept frequency absorbance plasma diagnostic technique for measurement of self-resonance frequency, intrinsic plasma-tool distributed capacitance, radiative energy loss, and effective plasma capacitance is described. The ex situ probe measures the plasma properties independently of all contributions from the plasma-tool and transmission line connection to the rf supply. The technique employs a swept frequency source and a balanced equal ratio arm bridge to measure the frequency response of the plasma tool after the plasma has been extinguished under plasma conjugate matching conditions. The resonant frequency of the combination of capacitances due to plasma-tool geometry ͑intrinsic capacitance, C i ) and the matching network (C m ) exhibits a shift from the excitation frequency ͑13.56 MHz͒ that is dependent on the effective plasma capacitance. Resonance frequency shift data are given for He, Ne, Ar, O 2 , N 2 , and N 2 O as a function of both pressure ͑0.02-0.8 mbar͒ and incident power ͑50 and 100 W͒. This technique allows the differentiation between dissociation and ionization processes within the plasma through a simple noninvasive rf measurement.

Resonant tunneling is studied in an ultrasmall asymmetric GaAs-AI, Gal -"Asdouble-barrier diode