n 型及p 型 ZnSe 薄膜之激子特性研究

Abstract

n型和p型ZnSe之激子特性研究 摘要 利用分子束磊晶法（MBE）成長p型ZnSe（ZnSe:N）薄膜及n型ZnSe（ZnSe:Cl）薄膜，並藉由PL光譜來分析討論。ZnSe基質晶體，在PL量測中透過激子躍遷輻射的發光特性，可以驗證到其會因不同的雜質摻入而造成其結晶體內部，產生許多不同複合結構的雜質層，如：ZnSe:N薄膜中，施子型複合結構 NSe-Zn-VSe或NSe-NZn，及深層受子型複合結構 (NSe)n-Zn；而ZnSe:Cl薄膜中，則有ClSe-Zn和ClSe-VZn兩種。觀察ZnSe:N的PL光譜，我們發現到因ZnSe摻雜氮的濃度過高，導致施子-受子對復合放射會有非常明顯的紅移現象產生，且隨著量測溫度逐漸增加的同時，發覺其峰值會有繼續往低能量變化的傾向，也因此了解到晶格結構內部聲子對激子的交互作用影響；對於ZnSe:Cl的PL光譜，在實驗的結果中，可看到一個強度很強的峰值，推測其應該是當Cl原子取代ZnSe中的Se原子時，如同在晶格構造上形成一個帶負電的等電子中心，它能夠藉由與電洞的吸引而構成一個束縛激子，以產生束縛激子復合發光，因為束縛在等電子中心的激子是被侷限在很小的範圍內，所以具有較大的復合機率，從而具有較高的強度。且再利用迅速熱退火處理過程，使材料結構重新排列以減少其內部缺位的存在，用意在提高束縛激子復合能量及消弭深層放射的出現。

Abstract The p-type ZnSe (ZnSe:N) and n-type ZnSe (ZnSe:Cl) films are grown by molecular-beam epitaxy (MBE).The photoluminescence (PL) spectroscopy is used to characterize the optical properties of these films with various concentration of dopants N and Cl and therefore describe the results specifically. The characteristics of the recombination emission between different impurity levels are studied by PL measurements. The impurity levels are ascribed to the complex defects due to various dopant concentrations, for instance, the donor-type complexes such as NSe-Zn-VSe and NZn-NSe of the N-doped ZnSe (ZnSe:N). The (NSe)n-Zn may play the role of a deep acceptor. And in the Cl-doped ZnSe film there are two complex defects, by ClSe-Zn and ClSe-VZn respective. The high N concentration of N-doped ZnSe causes the prominent red-shift of the donor-acceptor pair (DAP) recombination emission. The DAP peak becomes broaden and shifts to lower energy as the temperature is increased. Consequently, our result explores that the interact ion of the phonons and the exciton within the crystal. The ZnSe:Cl PL spectra shows exhibits a very strong peak. Let is ascribed that the incorporated Cl atoms are located at the substitutional lattice sites of Se atoms, and thus behaves like a negative isoelectric center which may form a bound-exciton by binding a free hole. The spectra are the result of the recombine emission of these electron-hole pair. The excitons trapping at isoelectric center are located in a smaller region so that they have larger probability to recombine. And thus causes a peak with stronger intensity. Using the annealing technique, we make the material structure rearrange to reduce the inner vacancies. This result may raise the bound-exciton recombine energy and mediate the deep-level emission.