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为了更全面、系统地分析Si基Pinned型光电二极管(PPD,pinned photodiode)量子效率的工艺敏感特性,基于考虑表面(SRH,shockley-read-hall)复合率模型的时域有限差分数值模拟方法,对不同P+型表面层和P型外延(EPI,epitaxial)层工艺条件下PPD可见光谱量子效率的变化特征及物理机制进行了研究。结果表明,P+型表面层离子束注入剂量和注入能量的增加分别引起非平衡载流子SRH复合率升高和PPD势垒区顶部下移,均可导致低于500nm波段量子效率的衰减,而后者进一步引起的势垒区纵向宽度缩减使该影响可持续至650nm波段;P型EPI掺杂浓度增加引起PPD势垒区底部上移,导致500~750nm波段量子效率的衰减;P型EPI厚度增加引起衬底强SRH复合区光电荷比重降低,导致高于700nm波段量子效率得到提升并趋向饱和。通过分析发现,Si基材料中光子吸收深度对波长的强依赖关系是导致两种P型掺杂区工艺条件对量子效率存在波段差异性影响的根本原因。
In order to comprehensively and systematically analyze the process sensitivity of the quantum efficiency of Si-based pinned photodiode (PPD), a finite-difference time-domain numerical simulation method based on the recombination rate model of SRH (shock-read-hall) The variation characteristics and physical mechanism of visible spectral quantum efficiency of PPD under different P + type surface layers and EPI epitaxial layer process conditions were studied. The results show that the increase of ion implantation dose and implantation energy of P + type surface layer lead to the increase of SRH recombination rate of non-equilibrium carriers and the downward shift of the top of PPD barrier region respectively, which can lead to the decay of quantum efficiency below 500 nm The further reduction of the vertical barrier width caused by the barrier region makes the effect sustainable to the 650nm band; the increase of the P-type EPI doping concentration causes the bottom of the PPD barrier region to shift upward, resulting in the attenuation of the quantum efficiency in the band of 500-750nm; Which led to the decrease of the photoelectron charge in the strong SRH recombination area of the substrate. As a result, the quantum efficiency in the band higher than 700 nm is enhanced and tends to be saturated. It is found through analysis that the strong dependency of photon absorption depth on the wavelength of Si-based material is the fundamental reason for the influence of the process conditions of two P-type doped regions on the band difference of quantum efficiency.