同電子性摻雜氮化物之缺陷與雜質光電特性研究

Abstract

近年來，雖然氮化物相關的成長技術進展迅速，但對於氮化物中的缺陷與雜質的特性，如同電子性摻雜對於激子複合輻射的影響、同電子性離子佈植對樣品的破壞、V型缺陷對氮化物光電特性的改變，仍非常值得深入研究探討。處此之外，由於空間解析顯微技術的快速發展，對於薄膜表面存在著約數微米到數奈米之間的微結構，例如螺旋狀丘型微結構和V型微結構等，我們已陸續發現到其對半導體光電元件的特性有顯著的影響，且微結構與塊材明顯擁有截然不同的物理特性。微結構本身具有的相關能態通常是造成一些特殊的性質來源。為了觀察到這些微結構特有的特性，我們將利用原子力顯微術的設備深入研究微結構載子捉放機制及深層能階位置等相關的電學特性，並結合我們研究群已有的顯微光學量測系統，將可以完整地觀察微結構，並對微結構整體物理特性作深入分析探討，以作為未來運用微結構獨特之性質發展新型奈米光電元件的基礎。

The progresses in nitride-based optoelectronic developments of wide-band-gap semiconductors have been very significant over the last decade, owing to the advent of the number of techniques. However, In regard to the film quality, the GaN layer contains several defects such as threading dislocations (TD), stacking faults, and inversion domain boundaries (IDBs) because of a large lattice mismatch and thermal expansion coefficient difference between GaN and sapphire. As we known, the defect density is up to ~ 1016 cm-2 that strongly affect most optical and electrical properties of GaN. While there are some progress in the device fabrications, the luminescence mechanism in GaN and AlGaN is still under intense investigation, especially how the structural and compositional inhomogeneities in the alloy affect optical properties. For example, whether defects act as nonradiative recombination centers or enhance the compositional fluctuation which induces localized exciton states to give strong emission needs to be clarified. Furthermore, these defects such as threading dislocations and point defects inside the material would penetrate from the buffer layer into the surface forming surface structures. In recent years, there has been remarkably rapid progress in the development of micro-measurement technology. Surface V-shape defect formed on the GaN is still a problem. These V defects are an open hexagonal, inverted pyramid with (101-1) side walls. Due to the difference observed between the surface structure and bulk region, much interest has focused on the micro-structure research. However, the previous studies of the origin of V defects are mainly from the AFM or STM images of InGaN/GaN MQWs and there have been very few studies on the optical and electrical properties of V-pits in AlGaN and GaN. Therefore, we attempted to investigate surface defects by the optical characterization and develop a new method to identify and show the properties of surface states.