氫表面鈍化矽奈米晶體之電子結構與光學特性

Abstract

我們透過理論模型研究量子侷限效應對奈米晶體電子結構與吸收光譜的影響，因為半導體奈米晶體的電子結構與吸收光譜對發展成本更低且具有高效率的太陽能電池是相當大的誘因。在研究中我們以 sp3d5s*第一近鄰緊束縛模型考慮電子自旋計算氫原子鈍化表面的矽奈米晶體，並大範圍改變奈米晶體的直徑，大約0.5 nm至7.6 nm。在研究結果發現要正確的計算出直徑3 nm以下的矽奈米晶體能隙，氫原子表面鈍化是必要的。我們發現矽奈米晶體導電帶基態由塊材矽在倒空間中六個X點上的電子基態所演變，而價電帶基態由塊材矽在倒空間Γ點上的電洞基態演變。此外量子侷限效應使得光吸收 振子能量峰值隨奈米晶體直徑變大而紅移，但矽奈米晶體光吸收振子強度卻隨著直徑變大而快速下降並由偶極矩陣元素中原子偶極矩項所主導。

Abstract We report on theoretical investigations of the electronic structure of the quantum confinement effect and size-controlled optical spectrum which make semiconductor nanocrystals (NCs) to attract a great attention for cheap and highly efficient solar cells. The electronic structure and optical spectra of various Si NCs (with hydrogenated passivation ) for a wide range of sizes (0.57.6nm) are studied by using nearest-neighbor sp3d5s* tight-binding model including the spin-orbit interaction. Our results show that the inclusion of hydrogenated passivation into Si nanocrystal is necessary for a proper description of the energy gap for dot sizes below 3 nm.The ground state of conduction band of nanocrystals evolve from the ground state of electron of bulk silicon in six X-point,and the ground state of valence band of nanocrystals evolve from the ground state of hole of bulk silicon inΓ-point. In addition , quantum confinement effect bring about red shift of oscillator strength of absor -ption when diameter of nanocrystal vary from 0.5nm to 7.6nm , and oscillator strength of absorption decrease quickly. Finally,We find that the atomic dipole moment domainate oscillator strength of absorption.