Thierry Weil

Equivalence between resonant tunneling and sequential tunneling in double‐barrier diodes

Resonant tunneling is known to lead to negative differential resistance in double‐barrier diodes. Sequential tunneling has been proposed by S. Luryi [Appl. Phys. Lett. 47, 490 (1985)] as an alternative mechanism for the negative differential resistance observed. We show that the two interpretations lead to the same predictions for the dc current.

Elastic scattering centers in resonant tunneling diodes

The effect of impurities placed in the wells of double‐barrier resonant tunneling diodes on the current‐voltage characteristics was experimentally determined. Four different double‐barrier structures were grown by molecular beam epitaxy with n‐type, p‐type, undoped, and highly compensated doping in the center of the well. Resonant tunneling devices of various sizes were fabricated, and measured at 77 K. Systematic shifts in the peak position and peak to valley ratios were observed for the different dopant profiles. The shifts in peak position are correctly predicted by a ballistic model which includes the effects of band bending due to ionized impurities in the well. The doped devices showed a systematic decrease in the peak to valley ratio which is not predicted by the ballistic model. By scaling our results, it is apparent that in most cases unintentional background impurities are not sufficient to significantly degrade the current‐voltage characteristics of resonant tunneling diodes.

Analysis of critical architectural and programming parameters in a hierarchical

Scalable shared-memory multiprocessors are the subject of much current research. but little is known about the performance behavior of these machines. This paper studies the performance effects of two machine characteristics and two program characteristics that seem to be major factors in determining the performance of a hierarchical shared-memory machine. We develop an analytical model of the traffic in a machine loosely based on Stanford’s DASH multiprocessor and use program parameters extracted from multiprocessor traces to study its performance. It is shown that both locality in the data reference stream and the amount of data sharing in a program have an important impact on performance. Although less obvious, the bandwidth within each cluster in the hierarchy also has a significant performance effect. Optimizations that improve the intracluster cache coherence protocol or increase the bandwidth within a cluster can be quite effective.

The Effect Of Elastic Scattering Centers On The Current Voltage Characteristics Of Double Barrier Resonant Tunneling Diodes

The effect of impurities placed in double barrier resonant tunneling diodes, on the current voltage characteristics of the devices was experimentally determined. Four different double barrier structures were grown by Molecular Beam Epitaxy with n-type, p-type, undoped and highly compensated doping in the center of the well. Two additional samples were grown with and without n-type doping in the barriers. Resonant tunneling devices of various sizes were fabricated, and measured at 77 K. Systematic shifts in the peak current voltage and peak to valley ratio were observed for the devices with different dopant profiles. The shifts in peak current position for the devices with varied well doping are correctly predicted by a modified ballistic model which includes the effects of band bending due to ionized impurities in the well. The doped devices showed a systematic decrease in the peak to valley ratio which is not predicted by the ballistic model. A scattering assisted tunneling mechanism which increases the valley current is proposed. The magnitude of the calculated increase in valley current due to elastic scattering by impurities which were intentionally placed in the well, is consistent with the observed lowering of the peak to valley ratio.