氮化物薄膜之攙雜與離子佈值效應之特性分析與研究

Abstract

在本論文中，我們利用拉曼光譜、冷激光光譜、冷激光激發光譜、時域解析冷激光光譜、掃描式電子顯微鏡、原子力顯微鏡、X射線繞射及霍爾量測來研究氮化鎵之不同元素攙雜，包括n型矽攙雜、p型鎂攙雜、等電子價位銦、砷攙雜與磷離子佈值之結構與光學特性相關研究。 在n型矽攙雜之氮化鎵方面，在薄膜沒有龜裂和微小空洞的條件下，電子濃度可達1.3X10^19 cm^-3。且經由計算，可得到0.055的高固態-氣態融入率。由冷激光光譜量測，我們也發現其能隙之變化正比於電子濃度的1/3次方(n^1/3)。 鎂攙雜的氮化鎵薄膜之X繞射光譜與拉曼頻譜出現藍位移，顯示出鎂原子可能取代了鎵原子的位置。我們也研究冷激光光譜隨雷射激發強度變化的影響，同時觀察到發光強度隨時間遞減的亞穩態現象，並進而對430 nm之發光機制作探討，經由數據分析我們得到69 meV之光學位能障。 我們發現氮化鎵薄膜的電性、光性與結構，可藉由攙雜適當的等價位銦提升品質；且薄膜表面之平整度與表面缺陷均有所改善，有利元件之製作。在低溫15 K的冷激光光譜，發現施子束縛激子之半高寬僅達10 meV。由時域解析冷激光光譜，發現銦攙雜之氮化鎵薄膜之激子生命期只有30 ps，且不隨攙雜濃度與量測溫度而變化，我們認為這是由於銦攙雜產生了本質性弛豫的通道。 在磷離子佈值氮化鎵薄膜方面之研究，我們探討了黃光螢光之機制，以及磷離子對黃光螢光的影響。我們也檢測快速熱退火對樣品的影響，快速熱退火後，薄膜之霍爾濃度與電子機動率都回覆到原始狀態，甚更略優。由變溫冷激光光譜，我們也得到磷相關缺陷之束縛能與其激子之游離能。 在等價位砷元素攙雜薄膜方面，砷原子的加入有助於延伸磊晶溫度的範圍，到達900 ℃，其霍爾濃度則從3X10^18 cm^-3 降到5X10^17 cm^-3；我們相信適當的砷攙雜也有助於薄膜品質的改進。另一點與銦攙雜所不同的是，其激子之生命期會隨量測溫度變化而增加或減少，此乃氮化鎵本質性之雜質與砷原子所形成之類受子淺能階形成互相角逐的現象。

The structural and optical properties of impurity doped and P-implanted GaN films were studied by using Raman scattering, photoluminescence, photoluminescence excitation, time-resolved photoluminescence, scanning electronic microscopy, atomic force microscopy, X-ray diffraction, and Hall measurements. The electron concentration reached as high as 1.3x10^19 cm^-3 without cracks or nanopits by using the Si dopant. The solid-vapor ratio was also high about 0.055. The band gap shrinkage of GaN:Si was observed that is proportional to n^{1/3}. In GaN:Mg, we observed the blue-shifts in both X-ray and Raman peaks indicating that Mg dopants possibly replace Ga atoms. The excitation power dependence of photoluminescence were examined. The blue-violet band intensity slowly decreases under continuous wave pumping reflecting the metastable behavior, that may account for the mechanism of the 430 nm peak, and an optical potential barrier of 69 meV was obtained. The isoelectronic In-doping with an adequate TMIn flow rate was found to improve the electrical, crystalline and optical qualities of GaN films. They also show improved surface smoothness with greatly reduced nanopits. More importantly, isoelectronic doping has caused the PL linewidth of the donor-bound exciton emission of GaN to decrease sharply to 10 meV or less at 15 K. The recombination dynamics of GaN:In were also studied by time-resolved photoluminescence. The recombination lifetime decreases sharply to 30 ps, regardless of the measured temperature and the TMIn flow rate that could be related to the intrinsic relaxation channel of the isoelectronic In doping. The P-implantation effects on GaN and the mechanism of yellow luminescence were studied. We also examined the rapid thermal annealing (RTA) effects. The localized states in GaN:P were observed that are different from the step absorption in as-grown GaN. After the RTA processes, the Hall concentration and mobility recovered to the initial values of the as-grown GaN and even slightly better than that. From the Arrhenius plot, the binding energy of the P-iso trap and ionization energy were obatined. For As-doping, we observed that the growth temperature window can be extended to about 900 ℃. The Hall concentration decreased from 3x10^18 to 5x10^17 cm^-3 and the mobility is about 150 cm/V.s. We believed that the proper As-doping indeed helps the electrical properties and crystalline structures. The exciton recombination dynamics were also studied and compared to that of In-doped GaN. The decay time was measured to be temperature dependent and interpreted by the competition between the intrinsic impurity levels and As-induced shallow-acceptor-like levels.