Theoretical modeling and simulation-based assessment of graded-bandgap AlGaAs/GaAs electron-injection cathode

The electron emission model of a negative electron affinity graded-bandgap AlGaAs/GaAs electron-injection cathode was developed from two-dimensional continuity equations. The emission current was obtained from a simulation of the model, and the emission current efficiency and emission current per unit length were calculated. Based on the simulation results and preparation conditions, the range of optimum parameters for the cathode structure were determined. The ranges of optimum thickness for the p-AlGaAs and the graded-bandgap p-AlGaAs layers were 0.05-0.15 μm and 0.1-0.3 μm, respectively. The optimum width of the base electrode ranged from 1 to 4 μm, and the optimum molar ratios of Al in the p-AlGaAs and the n-AlGaAs layers were 0.2-0.3 and 0.4-0.5, respectively. This abrupt PN heterojunction inhibited the hole current and increased the emission current efficiency, with a maximum value of 25.3%. According to the emission current per unit length, the optimum range of width of emission unit surface was 6 to 10 μm, and the peak emission current per unit length reached 43.2 μA/μm.