NEAGaN光电阴极第一性原理研究

采用基于密度泛函理论(DFT)框架下广义梯度近似投影缀加平面波方法,在六方结构GaN结构优化的基础上,计算了GaN(0001)A面吸附Cs后功函数变化,指出吸附系统表面形成了一个有效的GaN－Cs电偶极子层,降低了原本的GaN表面势垒,形成更加有利于电子逸出的外光电发射效应特性。接着图示吸附Cs、O后的电子结构,指出吸附原子和衬底之间的键合。六方结构GaN材料的光学性质通过Kramers-Kronig 关系得出。根据GaN的介电函数谱,得出了254nm光波长下以GaN为激活层材料的反射式光电阴极在不同少子扩散长度下的内量子效率。计算结果表明六方结构GaN(0001)A面是可见光盲光电阴极的优良发射表面,且254 nm处的量子效率可达到60%,远大于碱金属卤化物紫外光电阴极。

First principle study on NEA GaN photocathode

Using the projected augmented wave potential based upon the density functional theory within the gradual gradient approximation approach, after the optimization of wurtzite structure GaN, the affinity variation of Cs atoms adsorbed on GaN(0001)A surface was calculated, which proving that an effective GaN-Cs dipole layer was formed, and be good for electrons escaping form the substrate. The electronic structure of adsorbed Cs and O on GaN(0001)A surface was also calculated, which pointed out the bonding of Cs and GaN substrate. Furthermore, the internal quantum efficiency of reflect photocathode of GaN material on various minority carrier diffusion length were derived from dielectric functions theoretically. The calculated results demonstrate that GaN(0001)A surface is an excellent emitter for visible-blind photocathode, and the efficiency at 254nm can reach up to 60%, far more than other alkali halide UV photocathodes.