Simulation of New Solid State Cold Cathode Emitters Using Current Carrying Thin Films

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9632511 Cahay We analyze two new types of cold cathode emitters which consist of a thin wide bandgap semiconductor material sandwiched between a heavily doped semiconductor (or metallic material) and a low work function semimetallic thin film. First, we develop an Ensemble Monte Carlo (EMC) simulator to study electron transport in a Aluminum Gallium Nitride (AlGaN) / Gallium Nitride (GaN)/ Lanthanum Hexaboride (LaB6) cold cathode emitter recently proposed by Akinwande and coworkers. Our simulations focus on the calculation of the energy spectrum of electrons emitted into vacuum and the quantum efficiency of the new cold cathode. Then, using an analytical treatment, we show that under forward bias operation the electrons captured in the low work function material of a typical cold cathode are responsible for an effective reduction of the semimetallic film work function, leading to a substantial increase of the cathode emitted current. Since the investigation of this Dynamic Work Function Shift would be quite cumbersome using EMC simulations, we investigate it here using a semi-analytical treatment. Even though the dynamic work function shift could be observed in Akinwande's cold cathode emitter, we illustrate it here for a new type of cold cathode emitter using Cadmium Sulfide (CdS) as a wide bandgap semiconductor and Lanthanum Sulfide (LaS) as the semimetallic thin film. We will analyze the importance of current crowding in the proposed cold cathodes and will determine the range of dc bias over which cold cathodes of different width must be operated to minimize current crowding and self-heating effects. We will also study the possibility of current self-quenching in the new cold cathode as a function of the applied gate bias. This self-quenching will be examined in terms of the dynamics of the spacecharge effects in the region between the gate and the anode. These space-charge effects are expected to lead to the onset of current mscillations in the anode current. The period of these current oscillations will be calculated as a function of the applied gate bias. The simulation tools to be developed in this program can be easily modified to model a wide variety of other devices including: efficient blue and ultraviolet light-emitting devices, high-energy photodetection systems, flat panel displays, and microwave vacuum transistors, among others. ***