Investigations of evaporated silicon p-n junctions and their application to junction field-effect transistors

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Abstract
p‐n junctions formed by vacuum evaporation of silicon on crystalline silicon have been investigated. The junctions were formed by ion implantation of 49BF+2 in the evaporated silicon films. Subsequently, an isochronal heat treatment in the range of 600–850 °C was performed and its influence on the doping distributions and corresponding diode behavior was studied. Secondary‐ion mass spectrometry was used to investigate the resulting boron distributions. A sharp decrease in the boron concentration was found at the interface for the sample annealed at 850 °C.The fabricated p‐n junctions were evaluated by measuring the current‐voltage characteristics. Comparisons were made to ordinary diffused p‐n junctions in bulk silicon. Using the current‐voltage measurements, the leakage current and the ideality factor of the diodes were extracted. The reverse currents were also measured and show a nonsaturating behavior. The resistivity of the films were investigated as a function of anneal temperature, and it was found that the boron in the films is effectively activated for heat treatments >700 °C. An estimation of the hole mobility in the films was made from the measured resistivity and doping distributions. The annealed structure was investigated with transmission electron microscopy. The heat treated films were found to be polycrystalline with very small grains (<250 Å). To demonstrate the usefulness of this technology, a junction field‐effect transistor with evaporated gate diode was fabricated. The performance of this transistor is also demonstrated.