Abnormal current increases induced under high electric fields in asymmetrical graphite-intrinsic-diamond-graphite structures fabricated with high-quality homoepitaxial chemical-vapor-deposited diamond layers

Abstract

In order to investigate an abnormal current amplification phenomenon appearing in high-quality chemical-vapor-deposited (CVD) diamond under high electric fields, we have measured current-voltage and electroluminescence (EL) characteristics of an asymmetric graphite-intrinsic-diamond-graphite (G-ID-G) structure specially fabricated with a high-quality homoepitaxial CVD diamond layer. The G-ID-G structure included a flat G layer and a protrusive G layer, both of which were thin graphitic ones suitably formed on the surface layers of the CVD diamond using well-focused 30 keV Ga ions. The measured current-voltage data demonstrated that the voltages yielding the same currents were substantially lower when the protrusive G layer was positively biased. It turned out that the currents were reproduced with a sum of two components, namely, one injected from the positively biased G layer to the diamond, probably due to the Fowler–Nordheim tunneling mechanism, and the other yielding abnormal current increases in the diamond under high fields of the order of 106 V/cm. Furthermore, substantial EL was observed only in the voltage region the abnormal current increases obviously occurred. These facts and field calculations using a finite element method suggest both hole injections from the G layer to the ID layer and high-field-induced excitations of valence electrons in the ID layer to the conduction bands by the impact ionization process. An increase in the applied voltage by 15% was estimated to give a hundredfold amplification of the current. The present analysis of the measured data is discussed in detail in relation to the local structure of the high-quality diamond.