晶格常數不匹配將產生應力(strain)，應力造成偏極化場(polarization field)或內部電 場(internal electric field)，此乃壓電效應(piezoelectric effect)。對光電裝置而言，此偏極化 場或內部電場會引起元件內電子與電洞之波函數在空間上分離，因而很可能降低光效 率，此現象將被本計劃研究，並尋求解決方法。 當應力作用下，壓電晶體造成偏極化場或內部電場。偏極化電場是一個向量場，因 而具有反對稱性之晶體，將不會因為應力作用而電偏極化，也就是說，不會有壓電現象。 zincblende 與wurtzite 半導體是缺乏反對稱性之晶體，將因應力作用而會有壓電現象。 本計劃，亦將由極性鍵觀點(鍵對稱性、鍵極性大小、鍵長度、鍵角度)去分析此壓電場。 閃鋅(Zincblende)與伍采(wurtzite)半導體之極性鍵，存在永久的內建電耦極動量，其 對鄰近能隙之電光性質的影響，在此計劃中將被探討。當外界電場﹝光或電偏壓﹞作用 在閃鋅與伍采材質裝置，此永久性電耦極造成能帶在Gamma 點附近的非等向性 (anisotropy)現象，結果造成臨近能隙之光性質的非等向性，其影響將在此計畫中被計算。 Lattice-mismatch-induced strains generate polarization fields (or internal electric field) by the piezoelectric effect. For optoelectronic devices, the internal electric field is generally deleterious as it causes a spatial separation of electron and hole wave function in the quantum wells, which, in turn, likely decreases efficiency, which will be explored by this project and also find the solutions to this polarization field. Piezoelectrically active crystals are a class of crystals which produce a polarization field when stressed. Because electric polarization is vector, crystals which have a center of inversion symmetry cannot be polarized by a stress and therefore cannot be piezoelectric. Zincblende and wurtzite semiconductors lack inversion symmetry and are known to be piezoelectrically active. In this project, we will explore the piezoelectric field from the viewpoint of polar bonds (bond symmetry, bond polarity, bond length, and bond angle). The built-in permanent dipole moment of polar bonds existing in zincblende and wurtzite semiconductors, which influences their electro-optic properties, will exploited theoretically in this project. When an external field is applied to the zincblende- or wurtzite-based devices, the permanent dipoles cause the anisotropy of the band structure in the vicinity of the Γ point and, consequently, the anisotropy of optical properties near the band edge, whose influences will be estimated in this project.
