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 report good responsivity at the wavelength of 1600nm in a Ge photodetector which had lateral p-i-n structure and butt-joint coupling structure based on conventional normal complementary metal oxide semiconductor processes. We experimentally verified the responsivity of 0.82A/W and 0.71A/W on the best and the worst polarizations, respectively. The butt joint lateral p-i-n structure is found to be polarization independent as compared with vertical ones. Although cut-off frequency was 2.3-2.4GHz at reverse bias 3V, clearly open eye diagram at 10Gbps was obtained with reverse bias over 12V. These results are promising as optical photodetectors to receive long wavelengths downstream signal wavelengths required for next-generation optical access network systems.