Sho Nakanuma

Silicon variable capacitance diodes with high voltage sensitivity by low temperature epitaxial growth

Low temperature epitaxial vapor growth of silicon has been successfully applied to the fabrication of variable capacitance diodes which have a hyperabrupt impurity distribution profile. These diodes exhibit a strong nonlinear behavior in capacitance voltage characteristics; for example, one of the diodes has the value of n as high as 15 in the differential capacitance formula: dC/C = -n dV/(V + \Phi) . It has been found that the capacitance voltage and current voltage characteristics agree well with those calculated from the impurity profile so that the diodes with a high voltage sensitivity and with a high quality factor can be designed and fabricated reproducibly by this technique, and used in all solid-state FM modulators and automatic gain control units in a microwave relay system transmitting multiplex telephone signals. The double breakdown phenomenon in the current voltage characteristic of some diodes was observed and proved to be the saturation effect of generation recombination currents.

Some Properties of SiO2 Films Deposited by the Reaction of SiH4 with Water Vapor

SiO2 films were deposited on the n-type Si substrates by the reaction of SiH4 with water vapor in the temperature range 900°~1200°C. The refractive index and etching rate with HF solution of SiO2 films prepared at 900°C were strongly dependent on the molar ratio of water vapor to SiH4, but no shifts of the 9 micron absorption peaks by the stretching vibration of Si-O-Si bonds were observed among the films prepared at different molar ratios and at 900°C. These results indicate that Si atoms are included in these SiO4 films. A capacitance-voltage hysteresis of the metal-oxide-silicon structure was observed and attributed to a phenomenon caused by the ionization of Si atoms in the SiO4 films.