Properties of Electron Emitting Diode Fabricated with Single-Crystalline Diamond
- PDF / 487,715 Bytes
- 6 Pages / 390.24 x 621.9 pts Page_size
- 86 Downloads / 189 Views
below 1OV is realized. However, the latter seems to be very difficult to be overcome since it directly depends the material used for the emitter and since surface atoms are generally less stable than corresponding bulk atoms because of less numbers of the atomic bonds at the surface. On the other hand, a particular property of the hydrogenated diamond surface, or a negative electron affinity (NEA) has also been attracting many researchers[5-8]. For a NEA material, electrons excited to the conduction band near the surface can easily emit to vacuum when additional carriers are sufficiently supplied to neutralize the material. In this case, the above problems of FEEs may not arise because no high electric fields are necessary on the emitter surface nor in the vacuum. Recently, some kinds of diode-type diamond cold cathodes employing the direct NEA feature have been proposed[9-1 1]. Geis et al., for the first time, fabricated a diamond cold cathode[9], for which the cathode efficiencies attained were not more than 0.02 %. We proposed a different diode-type electron emitter of polycrystalline CVD diamond with a kind of metal-insulator-semiconductor (MIS) structure[ 11]. It should be noted that since atoms should be more stably bonded at the solid-solid interface than at the surface (solid-vacuum interface) due to differences in the number of the bonds and the space to be moved. However, in this case different problems arise that are related to efficient electron excitation to the conduction band of the NEA material and efficient carrier transportation from the injection region to the NEA surface. In order to inject electrons to the semiconducting diamond, an extremely high electric field of 10' V/cm may be necessary to be applied to the insulating (intrinsic) diamond. Fortunately, high quality diamond is still stable at such extremely high 105 Mat. Res. Soc. Symp. Proc. Vol. 558 ©2000 Materials Research Society
fields[131. This is one of reasons why diamond is suitable for this type electron emitter. The maximum emission efficiency was limited to 2 % in the case of polycrystalline diamond films, which was considered to originate from highly dense leakage current paths in the polycrystalline films[l 1, 121. When a polycrystalline diamond film was replaced by a homoepitaxial single-crystalline diamond layer, emission efficiencies more than 10% were easily realized[13,14]. We have called such a highly efficient electron emitter as an electron emitting diode (EED) although a third electrode may be used for the electron collection[15]. In the present work, we have further improved the emission efficiency of single-crystalline diamond EED by retreating EED with sufficient hydrogenation. This results in significant reduction in the density of defects acting as trapping centers of transported carriers. The measured efficiency reached 100 % at emission currents of the 10-7-A order[15]. The mechanism of the highly efficient EED is discussed. EXPERIMENTAL Diamond EED examined in this work was fabricated as follows[l131.
Details
Data Loading...
