Modelling of the field emission microtriode with emitter covered with porous silicon

Abstract

Electron field emission is obtained using high enough (≥ 1 V/nm) electric fields. Such local fields are usually obtained using sharp emitters. An alternative approach is to cover the otherwise blunt emitter (BE) with a porous silicon (PS) layer. The PS is composed of many fibrils with dimensions of several nm which act as “nano-emitters”. In this article such an emitter is considered as part of a vertical field emission microtriode (FEMT). The BE has spherical tip and conical body and protrudes through the gate circular opening, allowing the FEMT operation in the collector-assisted mode. An electric field multiplication approximation is studied using both an analytical and a numerical emitter model. The field multiplication means that the fibril increases the local electric field, which is already increased by the BE as compared with the uniform field at large distances from it. This approximation is valid as long as the fibril dimensions are much smaller than the BE ones. The fibrils mutual influence on the field is studied separately and taken into account for the FEMT case. The emission current is computed through integration of the Fowler-Nordheim J( E) current density-electric field relationship over the BE and fibrils area. Comparison is provided with the case of BE not covered with PS. The emission current is obtained as function of model parameters. FEMT modelling results include transconductance, capacitance, cut-off frequency and static gain. Reference to experimental results is provided.