We have fabricated and investigated InGaAs Esaki tunnel diodes, grown on GaAs or InP substrates, of varied defect densities. The tunnel diodes exhibit the same I-V characteristics in spite of the variation of defect density. Under the simple thermal annealing and forward current stress tests, the change in the valley current was not observed, indicating that defects were not increased. On the other hand, the reduction in the peak current due to the carbon diffusion was observed under both tests. The diffusion was enhanced by the stress current owing to the energy dissipation associated with the nonradiative electron-hole recombination. From the reduction rates of the peak current, we obtained the thermal and current-enhanced carbon diffusion constants in InGaAs, which are independent of defect density. Although thermal diffusion of carbon in InGaAs is comparable with that in GaAs, the current-induced enhancement of diffusion in InGaAs is extremely weaker than that in GaAs. The difference between activation energy of thermal and current-enhanced diffusion is 0.8 eV, which is independent of stress current density and close to InGaAs bandgap energy. This indicates that the current-enhanced diffusion is dominated by the energy dissipation associated with nonradiative band-to-band recombination. This enhancement mechanism well explains that the current-induced enhancement is independent of defect density and extremely weak. We also have found that the current-enhanced diffusion constant is approximately proportional to the square of current density, suggesting that the recombination in the depletion layer dominates the current-enhanced diffusion.

We propose a novel opto-electronic memory device using a single quantum dot (QD) and a logic device using coupled QDs (CQD) which performs (N)AND and (N)OR operations simultaneously. In both devices, occupation/unoccupation by a single electron in a QD is viewed as a bit 1/0 and data input/output (I/O) is performed by irradiation/absorption of photons. The (N)AND/(N)OR operations are performed by the relaxation of the electronic system to the Fock ground state which depends on the number of electrons in the CQD. When the device is constructed of semiconductor nanostructures, the main relaxation process is LA-phonon emission from an electron. Theoretical analysis of the device shows that (i) the error probability in the final state converges with the probability with which the system takes excited states at thermal equilibrium, i. e. , depends only on the dissipation energy and becomes smaller as the dissipation energy becomes larger, and (ii) the speed of operation depends on both the dissipation energy and dissipative interactions and becomes slower as the dissipation energy becomes larger if LA-phonon emission is taken into account. If the QDs are InAs cubes with sides of 10 nm and they are separated by the AlSb barrier with a width of 10 nm, the speed of operation and the error probability are estimated to be about 1 ns and about 0. 2 at 77 K, respectively. The basic idea of the device is applicable to two-dimensional (2D) pattern processing if the devices are arranged in a 2D array.