低禁带热光伏电池制备中锌扩散传质机理及电池结构优化设计研究

Reducing the combustion temperature can improve the stability and portability of thermophotovoltaic (TPV) power generation system, the low bandgap TPV cells should be used in order to ensure the power output density, the quarternary GaInAsSb has attracted more and more attention due to its tunable bandgap of 0.49~0.55eV. Compared to the GaInAsSb cells fabricated using the epitaxial method, the cells fabricated through Zn diffusion has a strong Zn concentration gradient and would form the surface built-in electric field; the minority carrier recombination rate would be reduced and the open circuit voltage would be enhanced due to this surface electric field; thus the investigation of Zn diffusion is important. Under the constant Zn vapor concentration diffusion conditions, the Zn diffusion profiles in GaInAsSb would not follow the complementary error function distribution and a distorted profile with double humps would be formed. The Zn diffusion experiments using multi species diffusion sources will be processed in this proposal, we anticipate to obtain the double hump Zn profiles with good regularity and investigate the formation mechanism, the single hump Zn profiles are anticipated to obtain for the first time; the Zn diffusion model will be established considering the self-diffusion of matrix atoms, the intrinsic relationship between the single and double hump Zn profiles will be revealed; the model of cell with Zn gradient will be established using PC1D, the optimal Zn profile fits for fabrication of cells will be investigated, which render useful guidance and new ideas to develop high-performance GaInAsSb cells.

热光伏系统中燃烧温度的降低可提高其稳定和便携性，为保证电能输出密度需采用低禁带热光伏电池，四元半导体GaInAsSb具有0.50-0.55eV的可调禁带受到了越来越多的关注。相比于外延法，Zn扩散法制备的GaInAsSb电池其发射区为梯度型掺杂，可有效提高电池开路电压，因此研究Zn在其内的扩散机理对电池制备有重要指导作用。在恒定表面Zn浓度扩散条件下，Zn在GaInAsSb中扩散曲线不遵循余误差函数分布，而呈扭曲的双驼峰型，使扩散过程难以预测。本项目中将以多种类扩散源进行Zn扩散实验，研究双驼峰Zn曲线生成机理，并预期通过改变扩散源成分的方法首次获得最适合制备电池的单驼峰型Zn曲线。建立计及基质原子自扩散的Zn扩散模型，揭示单-双驼峰曲线的内在联系。采用电池模拟软件PC1D建立梯度型掺杂电池模型，研究制备电池的最优Zn扩散曲线，为制备高性能GaInAsSb电池提供科学依据和设计思路。

热光伏发电是通过燃料燃烧或同位素衰变等方式加热辐射器，使其发射出近红外波段光子照射到低禁带光伏电池上产生电能的过程，此类发电技术具有单位面积输出电能密度高、静音等优点。本项目以低禁带GaInAsSb热光伏电池中Zn扩散传质过程制备PN结为出发点，主要研究了Zn在GaInAsSb中非规则扩散现象以及新型Zn扩散法制备GaInAsSb热光伏电池。研究发现，Zn在GaInAsSb中的扩散曲线形貌类型与基质原子Ga的自扩散过程紧密相关。Zn在GaInAsSb 中双驼峰曲线的形成是由于扩散过程中晶片内部处于晶格位置的 Ga 原子自扩散向外溢出造成的；Zn 原子首先通过占据 Ga 空位，直到 Ga 空位低于其热平衡值时才通过踢出晶格中 Ga 或 In 原子的方式进行扩散；两种不同的扩散机制造成了双驼峰类型 Zn 扩散曲线的产生；在扩散源中加入Ⅲ族原子Ga 和In，能够遏制第一个高浓度驼峰扩散区域的产生，直接生成仅具有低浓度扩散曲线的单驼峰Zn曲线。. 传统Zn扩散法制备GaInAsSb热光伏电池时，通常在扩散源中加入As、Sb 等五族原子，得出的为双驼峰类型 Zn曲线，需要采用精确腐蚀法将第一个高浓度驼峰扩散区域去除，才能够制备出量子效率高的电池。此高浓度驼峰区域深度约为200-300nm，较难对此百纳米级的高浓度层进行精确腐蚀，每批电池的腐蚀深度不可能完全一致，将导致不同批次电池的电学输出性能有差别。采用本研究中的遏制高浓度驼峰扩散区域产生的方法，可省略电池表面的精确腐蚀过程，扩散后晶片可直接进行电极、减反射层等其它工艺，可保证不同批次的电池电学性能输出的稳定性。