Search

Research was conducted to examine the time-dependent behavior of quantum cellular automata (QCA) with imperfections. A chain of quantum cells with the imperfections introduced by variations of intercellular distances, stray charges and variations of intercell tunneling strengths was investigated. Results demonstrate that the imperfections may easily impair the switching characteristics of semiconductor based QCAs.

The time evolution of the polarization of chains of quantum-dot cells called quantum cellular automata as a result of the switching of a driver cell for the particular cases of linear chains and L-shaped configurations were studied. Each cell is composed of four quantum dots on the four corners of the square and has two electrons. Dissipation processes were observed to result in satisfactory response characteristics. For the two cases investigated, there were no metastable states.

The effect of strain relaxation in a relaxed InAs quantum dot (QD) capped with InGaAs is investigated by admittance and deep-level transient spectroscopy (DLTS). Strain relaxation markedly increases the emission time in the QD region and extends carrier depletion to the bottom GaAs layer. The experimental data show the presence of relaxation traps in the QD region and the neighboring bottom GaAs layer. The electron emission from the QD region is governed by a trap located at 0.17–0.21 eV below the QD ground state. The electron-escape process is identified as thermal activation at high temperatures and direct tunneling at low temperatures from the trap. In the bottom GaAs layer near the QD, DLTS reveals a relaxation trap at 0.37–0.41 eV relative to the GaAs conduction band. The energy difference between these two traps is comparable to the QD ground-state energy relative to the GaAs conduction-band edge, suggesting that the two traps may be the same trap which is pinned to the GaAs conduction band. The considerable difference between their properties may result from different atoms surrounding the trap. [ABSTRACT FROM AUTHOR]

Examines the time-dependent behavioral pattern of quantum cellular automata (QCA) chains of quantum-dot cells. Consistency of each cell; Interactions of cells with nearby cells through Coulomb potentials; Proposal of QCA; Discussion of two different approaches concerning QCA.