Theoretical modeling and analyzing structural characteristics of AlGaAs/GaAs negative electron affinity array cathode with optically and electrically injected variable bandgap

Abstract

In order to obtain high emission current efficiency of the AlGaAs/GaAs NEA array cathode, this array cathode has two ways to form electron emission, i.e. optical injection and electrical injection. The two-dimensional continuity equation of electronic transport in the variable bandgap emission array is solved numerically by using the finite volume method thereby obtaining the emission current and emission current efficiency. Simulation obtains the optimal parameter range for each layer of the AlGaAs/GaAs NEA array cathode under both optical injection and electrical injection. The results show that the optimal angle of incident light for the array cathode under light injection is 10°–30° for selecting an array micro-nano column with a duty cycle of 2/3. Under the condition of light injection, the P-type variable bandgap AlGaAs layer array micro-nano column height ranges from 0.3–0.6 μm. Under the condition of electrical injection, the height of the micro-nano column of the P-type variable bandgap AlGaAs layer array is 0.1–0.3 μm. The optimal thickness range of N-type variable bandgap AlGaAs layer, N-type AlGaAs layer, and P-type AlGaAs layer under light injection are 0.5–2.5 μm, 0.5–1.0 μm and 0.2–0.5 μm, respectively. The optimal thickness range of N-type variable bandgap AlGaAs layer, N-type AlGaAs layer, and P-type AlGaAs layer under electrical injection conditions are 2–3 μm, 0.8–1.2 μm and 0.1–0.3 μm, respectively. The optimal doping concentration of P-type AlGaAs layer and N-type AlGaAs layer under light injection are range from 5×10<sup>18</sup> to 1×10<sup>19</sup> cm<sup>–3</sup> and from 1×10<sup>18</sup> to 5×10<sup>18</sup> cm<sup>–3</sup>, respectively. The optimal doping concentration of the P-type AlGaAs layer and the N-type AlGaAs layer under electrical injection range from 1×10<sup>18</sup> to 5×10<sup>18</sup> cm<sup>–3</sup> and from 5×10<sup>17</sup> to 1×10<sup>18</sup> cm<sup>–3</sup>, respectively. The maximum efficiency of the emission current under the light injection is 35.04%, and the maximum emission current per unit length is 10.3 nA/μm. The maximum efficiency of the emission current under electrical injection is 31.23%, and the maximum emission current per unit length is 105.5 μA/μm. Electric injection cathode does not need expensive and complex drive laser system, and the light injection control mode is simple, so light injection or electrical injection control mode can be chosen as needed. The research of array cathode, which integrates the advantages of many advanced technologies, is of great significance for enriching the cathode array cathode emission theory and expanding its application field.