Measurement method of in-depth profiles of recombination lifetime in epitaxial Si layer with test element pattern

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For the high quality Si Photodetector, the high resistivity epitaxial wafer using the low resistivity substrate were studied. The butter layer was introduced in the interface, and it was very effective on the crystal quality of the epitaxial layer (epilayer). Recombination lifetime of a epilayer is automatically measured by using the conductivity modulation technique. A lateral p^+-n^--n^+ diode test structure on the surface of the epilayer is formed to evaluate the minority carrier lifetime. Depth profiles of the recombination lifetime are obtained from current-voltage curves of a lateral p^+-n^--n^+ diode and a vertical n^+-n^--n^+ structure between the substrate and the top surface. We measure the lifetime in epilayers with and without a buffer-layer. In addition, photo-response of photodiodes with and without the buffer-layer is measured. Profiles of the recombination lifetime depend on the thickness of the epilayer but not on the thickness of the buffer-layer. Recombination lifetime in the epilayer became very uniform and long even in the interface region which was confirmed by measuring the lifetime depth profiles. Then Si Photodiode was fabricated on the above high quality epitaxial wafer and its epitaxial wafer and its optoelectric characteristics was evaluated. The observation of oxygen atoms from the substrate into the epilayer during thermal oxidation. The oxygen in the epilayer was diffused from the substrate.