銻化物基材之量子結構及元件

Abstract

近年來，半導體奈米結構及量子元件儼然已成為一個主要的研究課題，分子束磊晶 系統中已經可已成長出各式各樣化的自組式奈米結構，基於其完美之磊晶界面，可使得 物理研究及元件應用上得到良好的成果，然而過去這些元件大部分是使用砷及磷的三五 族化合物半導體結構，此種結構皆屬於第一類異質界面結構，也就是電子及電洞都被侷 限於量子結構中。但是另一種五族元素—銻，因為其晶格常數較一般常見之砷化鎵及磷 化銦基板來的大，所以過去較少被使用於三五族化合物半導體中。 銻化合物半導體具有較大的能隙變化範圍，因此使得它在長波長的光電元件應用中 具有重要的地位，其中銻化銦則具有目前已知之化合物半導體中最大的電子遷移率。此 種元素除了具有較大之能隙變化範圍外，它與其他化合物半導體（如：砷化鎵、磷化銦） 的異質界面，則屬於第二類或是第三類異質界面結構，此種特殊之異質界面可以變化出 很多有趣的物理研究及元件應用，且此種特性僅見於銻元素的化合物半導體中。 在我們的計畫中，我們計畫成長銻化鎵及銻化銦奈米結構於砷化鎵基板上，並研究 其光學及電子遷移特性。在此種第二類異質界面結構之量子點中，電洞是被侷限於價帶 之量子結構中，而電子則是因為電洞之庫倫作用力而分佈於此奈米結構周圍。我們近期 的研究中發現，在此種小尺寸的量子結構中，其依然具有良好的光響應強度，如此我們 便可以將此奈米結構應用於元件中。另外，我們實驗室也架設了一套低溫強磁場的量測 設備，如此可使我們更深入的瞭解此奈米結構的特性。 此外，銻元素也是一種良好的界面活性劑，可以使得我們磊晶的結構表面維持平 坦，且維持良好之磊晶品質，我們將利用此特性成長高應力的砷化銦鎵磊晶層，使得發 光波長可以達到2um。 多年來，本實驗室對於奈米結構及量子元件的研究有著深厚的基礎，且對於分子束 磊晶中銻材料的使用大約有一年之久，對於銻化合物磊晶技術的掌握也已成熟，並對於 此種第二類異質界面結構的特性也有諸多的瞭解，因此可以掌握此材料的特性並設計新 的元件結構。若能得到此計畫的支持，我們將可以對於銻化合物的奈米結構及量子元件 有更深入的研究。

Semiconductor nanostructures and quantum devices are subjects of intensive research in recent years. Self-assembled nanostructures with various geometries can be easily grown with modern epitaxial growth techniques. The perfect interfaces make these structures free from defects and therefore suitable for many interesting physics studies and device applications. These nanostructures, however, are mostly based on heterostructures made from arsenide and phosphide compounds. The band alignment of these heterostructures is typically type I, with both electrons and holes confined in the nanostructures. Anther group V compounds, antimides (Sb), however, are rarely used because of the relatively large lattice miss match between the antimides and the commonly used substrates such as GaAs and InP. The antimides, by themselves, are very interesting semicoductors. The wide bandgap range makes possible for optoelectrnic devices with long wavelength responses. InSb also possesses the highest electron mobility in all semiconductors. The band alignment between the antimides and other group V compounds can vary from type I to type II or even type III. The combination of these heterostructures and their nanostructures makes it possible for many interesting physics studies that are not available in other material systems. In this program, we propose to grow Ga(In)Sb quantum structures in Ga(In)As host materials and to study their novel optical and transport properties. One example is the GaSb quantum dots in GaAs. Because of the type II band alignment, holes are trapped in the GaSb well while the electrons stay in the GaAs region surrounding GaSb. So by nature, we have a quantum ring structure for the electrons. The confinement for the electrons is purely due to the Coulomb potential between the spatially separated electrons and holes. We recently found that the light emission from the spatially indirect transitions is surprising strong at low temperatures for structures with small dimensions. This gives us an opportunity to explore many novel applications involving these type II nanostructures. We have recently set up a low temperature magneto-optical measurement system, which will be used to characterize these structures. Sb is known to be a good surface surfactant, capable to smooth out the epilayer during growth and improve the layer quality. We will explore the possibility of using this property to improve the highly stained InGaAs layer and extent the wavelength range of this material to beyond 2 um. Our laboratory has a long experience in nanostructure growth and quantum device fabrication. Our new Sb MBE system has been up and running for about a year. We are now able to grow most of the antimonide compounds with excellent material quality. We have recently started the growth of Sb based quantum structures. Many interesting phenomena have been observed and have provided us insight for possible new device applications. With the help of this program, we will be able to do a thorough study on this material system, its nanostructues, and their device applications.