同電子性磷離子佈值氮化鎵薄膜之光性研究

Abstract

在本論文中，我們以冷激光光譜(Photoluminescence, PL)、冷激光激發光譜(Photoluminescence excitation, PLE)、拉曼光譜(Raman)等方法，研究成長在藍寶石(Al2O3, Sapphire)基板上之磷佈植氮化鎵薄膜的光學特性。佈植濃度由1014 變化到1016 cm-2 。藉由快速熱退火(RTA)在11000C的處理來復原佈植造成的缺陷。磷摻雜樣品的冷激光光譜，顯示出主導的發光頻譜在430奈米，這是束縛在磷同電子性電洞陷阱(P-hole isoelectronic trap)的激子復合效應。其伴隨的振盪頻譜是干涉效應。由冷激光光譜強度與溫度的關係，我們由其阿瑞尼士圖推算出電洞束縛在磷同電子性電洞陷阱的束縛能為180±18 meV、激子的侷限能為28±5 meV。而佈植後未退火的樣品，其冷激光光譜顯示了467奈米寬頻譜與黃光頻譜(YL)。根據first-principles total energy 理論的計算，氮間隙缺陷(NI)是一個深層受子能偕、其位置約在價帶上方1eV處。因此，佈植可能引發了氮間隙缺陷或是與磷相關的缺陷。比較I2 (D0,X)頻譜與偵測黃光的冷激光激發光譜，我們發現冷激光激發光譜的吸收邊緣與I2 頻譜相當吻合。顯示出黃光的來源與能帶間的躍遷及淺層施子能偕有關。Guénaud等人也提出自由激子(free exciton)的吸收有助於I2與黃光的放射，而自由電子電洞對(free electron-hole pairs)則較有助於黃光的放射。快速熱退火的處理確能有效修補佈植造成的缺陷與幫助磷取代氮的位置。磷的植入阻斷了自由電子電洞對能偕躍遷到深層能偕的管道，同時也引發了一些侷限性能偕，這些能偕與佈植後的黃光輻射有相當大的關聯。我們推測在氮化鎵塊材中，部份I2 放射的光子可能會被吸收而放出黃光。

We have studied photoluminescence (PL), photoluminescence excitation (PLE), Raman spectra of epitaxial GaN layers grown by MOCVD which are implanted by isoelectronic impurities of phosphorus (P) with different doses from ~1014 to ~1016 cm-2. The P- implanted samples were treated by rapid thermal annealing (RTA) at temperature of 1100℃ under flowing N2 with different duration using proximity cap method to recover implantation-induced damages. The PL spectra of GaN：P shows strong emission peaked around 430 nm with oscillations due to the microcavity effect. This band is due to the recombination of bound exciton to P-hole isoelectronic traps (P-BE). We have also measured the temperature dependent PL intensity and obtained from the thermal quenching of the Arrhenius plot two activation energies; one for the hole binding energy localized at the P-isoelectronic trap is found to be 180±18 meV and the other for the exciton localization energy 28±5 meV. The low temperature PL spectra of as-implanted samples showed the dominant YL and another broadband located at 467 nm. According to the two different first-principles total-energy calculations, the implantation likely induces NI and P-related defects. NI is a single, deep acceptor at approximately EV+1.0eV. By comparing the emission of I2 (D0, X) with the PLE profile probed at YL band, we found that the absorption edge of the PLE profile almost coincides with the I2 emission. This indicates that the absorption by band-to-band and shallow donors enhances the YL. Guénaud et al., suggested that the free exciton absorption contributes to both I2 and YL emissions while the free electron-hole pairs preferentially promotes YL than I2 [6]. RTA can recover the damage and help the substitution of P at Nitrogen site. The incorporation of P has induced localized states that not only increase the YL but also suppress the transition from the free electron-hole pairs to the deep-levels associated to the YL. We believe that part of I2 emission can be reabsorbed in the bulk to promote the YL.