Low Temperature Epitaxial Growth of Refractory Crystals by Photo-ionization

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The final purpose of this project is to reduce epitaxial growth temperature of refractory materials utilizing high energy-state ions generated by photoionization with irradiation of vacuum ultra violet light. Fundamental approaches to realize the epitaxial growth at very low temperatures have been carried out, and the following results are obtained.1: Fundamental process of photo-ionization has been revealed in the case of aluminum atom which is an important element for compound and mixed semiconductors. A new type of experimental apparatus to get a high power and wide area light source in the vacuum ultra violet wavelength region was fabricated. The ionization rate of Al atoms increased with the photon intensity. Simple theoretical analyses of the measured dependences of the ionization rate on the Al flux density and the photon intensity revealed that the one-photon ionization process was dominant.Based on the results of photo-ionization process, low temperature epitaxial growth of Si … More has been investigated.2: The number of twins in the epitaxial layer was decreased by the irradiation of vacuum ultra violet light during deposition, which shows that the crystallinity can be improved using excitation of the substrate surface and/or Si atoms with the light.3: Under the extremely high vacuum condition, the surface cleanness of atomic level could be obtained through a relatively low temperature heat treatment around 800-900 <゛゜c> . Poly-crystalline Si was deposited on the surfaces with residual impurities such as Si <O_2> , but single-crystalline Si with a mirror surface could be epitaxially grown on the atomically clean surface at a low temperature of 650 <゛゜c> .The fundamental results of this project as mentioned above show that the refractory crystals can be epitaxially grown at low temperatures utilizing photo-excited states of constituent atoms. The increase of the ionization rate and the control of the ion energy by applying substrate bias must be needed to obtain epitaxial layers of good crystallinity reproducibly. Less