结合第一性原理的近红外InGaAs光电阴极光电发射机理研究

The longest response wavelength of the traditional low-light image intensifier is 0.9 µm. It has low utilization with the night airglow. The spectrum response of the negative electron affinity (NEA ) InGaAs photocathode extends to the infrared region, covering night airglow and the sensitivity will be improved substantially, following the change of the In component. The spectral response and the electron escape probability of our domestic InGaAs photocathode in the range of 1-3µm are not satisfying. The photoelectric emission mechanism and the structure design of the InGaAs photocathode just can be studied from the spectral response and the light current because of the limit of the observation methods in experiments. The cycle of experiments is long and the experiments cost a lot. Therefore, the photoelectric emission mechanism will be studied from the experiments combined the first principles in our project. The three aspects which are related closely with the photoelectrons emission will be mainly studied. The three aspects are the first the photoelectrons emission and transmission in the bulk of emission layer, then the influence of the interfaces to the light absorption and photoelectrons emission and the last the photoelectrons escape from the surface effectivity. The photoelectric emission mechanism will be revealed theoretically based on the first principles and the experiments, which will guide the design of InGaAs photocathode structure. The electron escape probability and the spectrum response will be improved during the range 1-3µm.

传统微光像增强器响应波长最长到0.9µm，对夜天光的能量利用率低；负电子亲和势（NEA）InGaAs光电阴极通过改变In组分的大小可以有效提升光电阴极在近红外的长波灵敏度和截止波长位置，能覆盖夜天光的全部光谱范围，能量利用率高。国内InGaAs光电阴极的研究在1-3μm间的光谱响应和电子逸出几率均不理想。由于观察手段的限制，只能从光谱响应和电子逸出情况来研究光电发射机理，判断光电阴极结构是否合理，实验周期长，成本高。为此，本项目拟采用第一性原理与实验相结合的方法对InGaAs光电阴极光电发射机理进行研究，着重研究与光电发射密切相关的三个方面：发射层的体发射和体输运性质、界面对光吸收和光发射的影响和光生电子在发射层表面的有效逸出。从理论上揭示InGaAs光电阴极光电发射机理，指导InGaAs光电阴极结构设计，提高InGaAs光电阴极在1-3μm间的电子逸出几率和光谱响应。

InGaAs是一种重要的三元III-V族半导体材料，对InGaAs表面进行合适的敏化可以生成负电子亲和势。负电子亲和势InGaAs光电阴极在1~3 μm的近红外区域具有较好的光谱响应，对于制备新型的近红外微光夜视器件和系统，研究高性能的近红外微光像增强器有比较重要的意义。本项目结合基于密度泛函理论的第一性原理计算方法，对InGaAs光电阴极的界面性质、发射层体性质和表面敏化进行了研究，在理论和模拟层面为InGaAs光电阴极的研制提供了指导。.InGaAs光电阴极的InP衬底与InGaAs发射层之间存在晶格失配问题，当InGaAs发射层直接生长在InP衬底上时，界面在1000-2000nm范围内反射率与吸收率均最低，有利于InGaAs在该光谱范围内光的吸收与光电子的产生；界面处的电荷转移形成的由界面处向外逐渐减弱的由InGaAs指向InP的内建电场；促进界面附近的光电子向表面进行输运。本项目研究了掺杂和空位对体材料性能的影响。指出在替位掺杂时，替换In还是Ga原子对材料的影响一致，可以不考虑区分，都能形成合适的p型掺杂InGaAs材料。同时，项目研究指出As空位缺陷与Zn掺杂原子共同作用后，InGaAs体内会产生受主能级，有利于光电子的输运；而Ga、In空位会产生间接带隙，应该尽量避免。.InGaAs材料的表面敏化是产生负电子亲和势的关键，本项目着重研究了其表面敏化机理。InGaAs材料表面存在弛豫与重构，分析表明Zn4掺杂位是最合适的掺杂位，为表面敏化提供了较好的基础，并指出表面激活时， Cs覆盖度的临界值为0.5 ML。超过这个值时，需要对表面进行Cs与O的交替激活，从而在表面形成InGaAs(Zn)-Cs与Cs-O双重偶极子。进一步研究了残气吸附在表面对表面敏化的影响，以及去除方法，以期更好的达到降低表面功函数，实现InGaAs光电阴极表面敏化的目的。