Rectification and internal photoemission in metal/CVD diamond and metal/CVD diamond/silicon structures
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A. R. Badzian, T. Badzian, and R. Messier"' Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802 (Received 9 April 1990; accepted 6 July 1990)
Schottky diodes were formed with free-standing polycrystalline thin film diamond base as well as with polycrystalline diamond films grown on crystalline silicon. Current-voltage and internal photoemission measurements were used to characterize the Schottky diodes and the diamond film. Internal photoemission measurements yielded a barrier height of 1.15 eV. A comparison of experimental data for metal contacts to free-standing diamond films and those on silicon substrates indicates that both rectification and internal photoemission originate at the metal/diamond interface.
I. INTRODUCTION
The unique combination of electrical and physical properties of diamond makes it an attractive semiconductor material.1"3 Some of these properties include high thermal conductivity (20 times that of silicon at room temperature), low dielectric constant (er = 5.5), and radiation immunity. When Johnson's or Keyes' figures of merit are used to compare various semiconductors, diamond is the most promising candidate for several electronic applications.3 A similar conclusion has been reached using a new figure of merit developed to compare semiconductor materials for microwave power applications.4 However, until recently, experimental diamond devices were fabricated using bulk diamond where device engineering is difficult.5'6 Hence, the development of microwave plasma enhanced CVD diamond films is of particular interest for microelectronic applications. During the last few years several groups have described rectifying I-V characteristics of metal contacts to polycrystalline diamond films deposited on silicon substrates7"12 and to single crystal homoepitaxial diamond films.13"18 Internal photoemission for metal/CVD diamond/contacts has been reported as well.8'9 In principle, in the metal/diamond/silicon structure both interfaces (metal/diamond and diamond/silicon) may be electrically and optically active. It has been suggested that the diamond/silicon rather than the metal/diamond interface dominates the electrical and optical characa)Also
with Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802. b)Also with The Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, Pennsylvania 16802. J. Mater. Res., Vol. 5, No. 11, Nov 1990
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teristics of a metal/diamond//?-type silicon structure.10 Although observation of rectifying characteristics of Schottky diodes with homoepitaxial diamond base13"18 and bulk base19'20 make it improbable as a general conclusion, it is nevertheless interesting to separate electrical and optical characteristics of the two interfaces in the case of the metal/diamond/silicon structure. This is the main subject of the present work. The diamond films used in this study were prepare
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