We have prepared hemispherical Si nanocrystals as quantum dots (QDs) on thermally-grown SiO2 layers in a self-assembled manner by controlling the early stages of LPCVD using SiH4, and also formed Si-QDs with a Ge core by controlling the selective growth conditions in SiH4- and GeH4-LPCVD. From the change in the surface potential at each of QDs caused by electron injection or emission through ultrathin SiO2 as measured with an AMF/Kelvin probe technique, we have quantified how many electrons or holes can be retained stably in the single dot covered with ultrathin SiO2 at room temperature without any external biases. We have found that, for Si-QDs with a Ge core, electrons are retained stably in Si clad while holes in Ge core. MOS capacitors and FETs with the Si dots as a floating gate have also been designed and fabricated. Multiple-step electron charging (or discharging) characteristics of the Si-dot floating gate are observable presumably because columbic force arising from charged dots efficiently suppresses the electron charging of neighboring neutral dots. From the temperature dependence of temporal change in the drain current at a fixed positive gate bias after complete discharging of the Si-QDs floating gate, we were found that the multiple step charging proceeds with an thermal activation energy being almost equal to the energy separation in the sum of quantized and charging energies between the charged states.
Light propagation loss of the micron size optical waveguides is found to be improved from 1.8 to 0.6 dB/cm by capping waveguides by Al film. Al micromirrors for changing the light propagation direction in the vertical and horizontal planes were fabricated. Various shapes of Al corner mirrors to change the light direction in the horizontal plane were investigated. The straight simple mirror at an angle of 45 degree(s) against the incident light has the largest reflectivity of 50%. Branched waveguides were also fabricated by using Al corner mirrors and resulted in the almost equal distribution of the light for three branches. Light emitting diodes (LEDs), micromirrors, waveguides and photodetectors have been integrated on a single chip and the signal transfer from the LED to the photodetector has been verified.
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