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  • Heterojunction Diode Manufactured With SRC Light

    Peter Dowben, Keith Perkins, and his students, Seong-don Hwang and Dongjin Byun, recently succeeded in a first time ever fabrication of a heterojunction diode via Chemical Vapor Deposition (CVD) on silicon using synchrotron radiation. The intense X-ray beam from the SRC Focused White Light beamline was used to induce the decomposition of a metalorganic molecule, creating a Boron Carbide/Si(III) junction. Part of this work has been published in: D. Byun et al., Appl. Phys. Lett. 64, 1968 (1994).

    The use of synchrotron radiation to initiate the selective area deposition of thin film materials from vapor phase chemical precursors has only recently been explored, with much of the preliminary work being done at SRC. In a major step forward in the field, Professor Dowben’s research team from the University of Nebraska has shown (see accompanying figure) that a heterojunction can be fabricated by this technique. The rectifying behavior of the current versus voltage curves for a diode grown with the use of synchrotron radiation assisted decomposition can be seen identified by the solid line, and the curves for the plasma enhanced CVD grown diodes, the more conventional fabrication technique, are identified by the broken lines.

    This work is an extension of Dowben’s past research in direct-write patterning of boron using synchrotron assisted processing, in combination with unusual molecular precursor compounds. The importance of the experiment lies in the potential for combining the high spatial resolution possible with X-ray lithography, with a process for directly fabricating junctions, and ultimately, transistor devices.

    In order to succeed with synchrotron radiation patterning, a suitable molecular precursor needed to be found, which could be decomposed by the short wavelengths used in X-ray lithography. After examining the decomposition of other compounds, Dowben and his colleagues from U. Nebraska and the Naval Research Laboratory discovered that orthocarborane (C2B10H12) has unique properties that make it suitable for fabricating semiconductor junctions. Using Auger spectroscopy, they find that the film composition is close to B5C following the initiation of film growth. This is similar to the composition found for diodes fabricated using plasma-enhanced CVD, and the diode performance using the two methods is similar.

    This experiment was part of a project in which Dowben and his group are studying ways to produce electronics able to withstand harsh environments. The process they have discovered may have uses in other applications as well. For example, recent refinements of the method have shown that transistor fabrication is possible, which is one more step along the quest for direct-write microelectronic components.

    Aladdin -- Editor Brian Tonner