基于第一性原理研究杂质补偿对硅光电性能的影响

First-principles study of effect of impurity compensation on optical properties of Si

通过磷(P)和硼(B)共掺杂在硅禁带中构建了P^(+)/B^(-)局域态能级,形成了具有杂质补偿结构的硅.采用基于密度泛函理论框架下的第一性原理研究了杂质补偿硅(n/p-Sic)的电子态密度、介电函数和折射率等光电性能.态密度研究表明,相同浓度P和B掺杂(12.5%)的n-Si和p-Si被完全杂质补偿后,费米能级位于两相邻态密度峰构成的谷底,且态密度不为零.在介电函数和折射率研究中,发现n-Sic在掺杂比例C_(B)/C_(P0)=0.25时,在低能区具有最大的介电函数和最大折射率.此外,对比本征硅及其掺杂物的介电常数实部(Re),发现如下规律:在E> 4 eV的高能区,本征Si,n/p-Si和p-Sic的Re为负值;而在0.64 <E <1.50 eV的低能区,n-Sic在掺杂比例C_(B)/C_(P0)=0.25时的Re为负值;这表明在此掺杂比例下n-Sic能在更低的能量下就能获得较好的金属性,从而揭示了其价带电子更易被低能量的长波长光激发.理论研究表明,n-Sic在掺杂比例C_(B)/C_(P0)=0.25时具有较好的光电性能,可能与n-Si被B杂质补偿后部分Si—Si键变成Si—B键的同时产生的Si悬挂键以及在Si禁带中形成的局域态能级有关.

Presently,impurity-compensated silicon(Si)has no clear potential applications due to high resistance and few carriers.Thus,it has received little attention from researchers.In this study,we find that impurity compensation can make localized state energy levels form in Si bandgap,which can improve the light absorption of Si in the near infrared region.In this work,in order to comprehensively and deeply understand the photoelectric properties of impurity-compensated Si,the localized state energy levels composed of P+/B-ions are constructed in Si bandgap through the co-doping of phosphorus(P)and boron(B),thereby forming impurity-compensated Si.The first-principles based on a density functional theory framework is used to study the photoelectric properties of the impurity-compensated Si(n/p-Sic)such as the density of states(DOS),dielectric function and refractive index.The DOS study reveals the following results:after the n-and p-Si with the same concentration of P and B(12.5%)are fully compensated for by impurities,the Fermi energy levels of their compensated counterparts are at the valley bottom formed by the two adjacent DOS peaks,and the DOS is not zero at the valley bottom.In the study of dielectric function and refractive index,it is found that when the doping ratio is CB/CP0=0.25,n-Sic has the largest dielectric function and refractive index in the low energy region.In addition,comparing intrinsic Si with its doped counterparts in the real part(Re)of their dielectric constant,the following regularity is found:in the high energy region of E>4 eV,the Re values of the intrinsic Si,n/p-Si and p-Sic are negative.In the low energy region of 0.64 eV<E<1.50 eV,the Re value of n-Sic is negative for the doping ratio of CB/CP0=0.25.The above comparison indicates that the n-Sic with CB/CP0=0.25 can achieve good metallicity in the low energy region,indicating that the electrons in valence band are easily excited by low-energy long-wavelength light.Theoretical studies show that the good photoelectric properties of n-Sic with CB/CP0=0.25 may be related to Si dangling bonds and localized state energy levels in Si bandgap.The Si dangling bonds are caused by the impurity compensation of B dopant for n-Si,leading part of Si-Si bonds to change into Si-B bonds.This study provides theoretical guidance for the application of impurity-compensated Si in the field of photodetectors such as CMOS image sensors and infrared photodetectors.