Volume 87, Issue 10, 15 May 2000
Index of content:
- DEVICE PHYSICS (PACS 85)
87(2000); http://dx.doi.org/10.1063/1.373011View Description Hide Description
We consider diodes, in which the middle p region (base) consists of a p-type quantum well current-conducting channel that is controlled by a gate potential. Hole concentrations in the channel are assumed to be such that a ballistic current flows only in the lowest quantized subband. This subband contains a negative-effective-mass (NEM) section in the dispersion relation. We carry out numerical simulation for realistic designs of this ballisticfield-effect transistor(FET) and compare them to simple analytical estimates. We show that three types of self-organized terahertz current oscillations appear in these FETs. Two of these types originate from the NEM instability, while the third arises from the two-stream instability, predicted before for conventional ballistic diodes and FETs. Frequencies of the NEM oscillations are controlled effectively by a gate potential. They are substantially higher than frequencies of two-stream oscillations. The NEM oscillation frequencies exceed 2.5 THz for large enhancing gate potentials.
87(2000); http://dx.doi.org/10.1063/1.373012View Description Hide Description
A model of a reflective bistable twisted nematicliquid crystal display was studied by detailed numerical simulation. The optimized modes of a 5 μm reflective bistable twisted nematicliquid crystal were determined by the parameter space method. We have shown that large wavelength dispersion in the reflection coefficient of such displays cause the optimal mode to have a small value of around 0.2 μm. By using a quarter-wave plate compensation film the optimized modes can have a value of around 0.4 μm. Numerical simulations show a wide viewing angle of up to ±60° for both types of reflective bistable twisted nematicliquid crystal display.
87(2000); http://dx.doi.org/10.1063/1.373013View Description Hide Description
It was recently discovered that inclusions and other types of inhomogeneities can be nondestructively detected by thermoelectricmeasurements in an entirely noncontact way by using high-sensitivity superconducting quantum interference devicemagnetometers to sense the weak thermoelectric currents around the affected region when the specimen is subjected to directional heating or cooling. In this article we present theoreticalmodels capable of predicting the magnetic field produced by thermoelectric currents around spherical and cylindrical inclusions under external thermal excitation. We investigated how the magnetic signal to be detected depends on (i) the relevant physical properties of the host and the inclusion, (ii) the size of the inclusion, (iii) the depth of the inclusion below the surface of the specimen, (iv) the polarization of the magnetometer, (v) the lift-off distance of the magnetometer from the specimen, and the (vi) direction and (vii) strength of the external heating or cooling applied to the specimen. The analytical models presented are numerically evaluated to illustrate the strength and polarization of the magnetic field for different lift-off distances and inclusion depths.