Kouichi YAMAGUCHI (山口 浩一)

Abstract

InAs/InAsSb ultrahigh-density quantum dots (UHD QDs) with a density of were fabricated using MBE, and their photoluminescence (PL) properties were characterized. Through temperature dependences of PL energy, intensity and decay time of UHD QDs, it was found that in-plane strong coupling between adjacent QDs of excited and ground states due to homogeneous broadening of QD levels progressed above 60 K and above 100 K, respectively. The findings regarding the strong coupling at ground states were consistent with the temperature dependence of PL minimum energy outlined in appendix. In addition, abnormal phenomenon in PL full width at half maximum was attributed to the in-plane miniband formation resulting from strong coupling.

Abstract

Resonant tunneling diodes containing closely double-stacked InAs quantum dots (QDs) were grown on GaAs substrates by molecular beam epitaxy. After growing a thin GaAs capping layer on the double-stacked InAs QDs, nanoholes were selectively formed just above the larger second QDs by thermal annealing. The Au thin film was deposited directly on top surface of the larger second QDs through the nanoholes. The second QDs contacted with Au film served as conducting dots, which can locally inject electrons into the underlying first QDs. In current versus voltage (I-V) measurements, (dI/dV) peaks were clearly observed in the forward bias voltage region. It was due to the tunneling current through a non-doped GaAs thin layer between double-stacked QDs and n-GaAs conduction band. The (dI/dV) peaks shifted toward the lower forward voltage region with increasing temperature. It was explained by the temperature dependence of the electron energy distribution in the GaAs conduction band.

InAs nanowires (NWs) were grown on SiOx pinholes formed on Si(111) substrates by molecular beam epitaxy. Influences of electron-beam (EB) irradiation on the SiOx layer on the pinhole formation and the subsequent InAs NW growth were studied. As the EB irradiation dose increased, the pinhole density in the SiOx layer decreased. From atomic force microscopy, transmission electron microscopy, and x-ray photoelectron spectroscopy results, it was found that the pinhole etching of the SiOx layer by Ga droplets was suppressed by carbon adsorption due to the EB irradiation. By forming high-density pinholes on the SiOx layer without the EB irradiation, high-density InAs NWs with 1–2 × 1010 cm−2 were grown successfully, and the uniformity in the NW diameter improved. The standard deviation of the NW diameter was 1.8 nm (8.8%) for high-density NWs. In addition, the NW diameter decreased with decreasing EB dose, and the NW diameter was controlled by adjusting the diameter of Ga droplets forming the pinholes. As the NW diameter decreased, photoluminescence spectra of the NWs shifted to higher energies than the bandgap energy of the wurtzite InAs bulk. From these results, we successfully fabricated high-density and high-uniformity InAs NWs with quantum size effects on EB-unirradiated SiOx/Si(111).