磷化銦基板上之線狀量子結構

Abstract

此篇博士論文利用固態源分子束磊晶系統，在與（100）磷化銦基板晶格匹配之砷化鎵銦與砷化鋁銦基材上，探討如何成長自組化砷化銦與砷化鎵線狀量子結構。並研究這些量子線狀結構的光學與電學特性，與探索利用作為元件的特性與價值。

一開始我們利用原子力顯微鏡技術，觀察在（100）磷化銦基板晶格匹配之砷化鎵銦基材上所成長的自組化砷化銦與砷化鎵量子結構形狀，以探討各種磊晶因素對這些量子結構型態的影響。在適當的磊晶條件下，砷化銦與砷化鎵量子結構都形成沿[1-10]方向的線狀量子結構。砷化銦與砷化鎵量子結構的成長行為有些不一樣，我們將分別對砷化銦與砷化鎵量子結構成長因素分別分析探討。

利用穿透式電子顯微鏡技術，所得之樣品截面圖中，發現（100）磷化銦基板晶格匹配之砷化鎵銦與砷化鋁銦基材上，所長的砷化銦與砷化鎵量子線，有堆疊行為。在砷化鎵銦基材，砷化銦與砷化鎵量子線皆為垂直堆疊，但在砷化鋁銦基材，砷化銦量子線是交叉堆疊，頗似體心立方結構。我們亦明顯觀察到基材中的組成調變現象。基於砷化鎵銦與砷化鋁銦基材中的週期性應變分佈，所造成的組成調變行為將分別在文章中探討。之後，利用組成調變現象，探討並解釋砷化銦與砷化鎵線狀量子結構的堆疊行為機制。

良好形狀之砷化銦量子線，在偏極化光激發光實驗中，發現有明顯之光學偏極化行為。電場平行於量子線的光激發光，其亮度大於電場垂直於量子線的光激發光。我們並利用磷化銦量子線做成半導體雷射元件，其雷射光波長約在1.7 微米。為探討量子線之異向性光學行為，分別沿[110]與[1-10]方向，製作兩組不同雷射共振腔方向的樣品。從光功率電流（L-I）曲線與雷射光譜中，不同共振腔方向的雷射有極大的差異性。雷射對溫度相依的特性，也隨不同的共振腔方向而有不同，而且在共振腔垂直於量子線的雷射二極體中，出現從基態雷射狀態轉變到為激發態雷射狀態的行為。

我們亦對砷化銦量子線的電學傳輸行為做探討。砷化銦量子線包埋在砷化鎵銦與砷化鋁銦形成的異質介面附近。為了探討電子異向性傳輸行為，分別沿[110]與[1-10]方向，製作兩組霍爾槓（Hall bar)樣品。霍爾量測從10K 進行至室溫，結果顯示遷移率沿[110]與[1-10]方向，有很大的差異性，傳輸通道平行於量子線的電子遷移率大於傳輸通道垂直於量子線的電子遷移率。這個異向性電子遷移率行為是由於量子線散射源不同方向的散射截面所造成。

最後，我們對論文作總結。量子線不只提供我們研究一維系統之光學與電學行為， 並給出一些有趣的應用潛能。

This dissertation studies the self-assembled InAs/GaAs wire-like quantum structures grown in InGaAs/InAlAs matrix lattice matched to InP substrates by solid source molecular beam epitaxy. The optical and electrical properties of these wire structures and their applications were explored.

This study begins with the investigation of growth conditions of self-assembled InAs and GaAs quantum structures in InGaAs matrix on (100) InP substrates. The morphology of the grown structures was studied by the atomic force microscopic technique. In a suitable growth condition, both InAs and GaAs formed wire-like quantum structures elongated along [1-10] direction. However, the growth behaviors for the InAs wires and the GaAs wires are different. The growth parameters that influence the formation of InAs and GaAs are discussed.

By the cross-sectional transmission electron microscopic technique, the stacking behaviors of InAs/GaAs nano wires in InGaAs/InAlAs matrix on (100) InP substrates were studied. In the InGaAs matrix, InAs and GaAs wires are vertically aligned. However, the InAs wires in InAlAs matrix are arranged in a cross staggered pattern, similar to a b.c.c. structure. The composition modulation caused by the periodic strain distribution was observed. Based on the composition modulation, the mechanism of the stacking behaviors of InAs/GaAs nano wires were explained.

The polarization dependence photoluminescence of well-formed InAs quantum wires was investigated. The results show obvious anisotropy in the light polarization. The intensity of the light with its electric filed polarized parallel to the wires is stronger than that with the electric field perpendicular to the wires. The InAs quantum wires were than utilized for laser application. The lasing wavelength is about 1.7μm. In order to investigate the anisotropic optical behavior, two laser cavity directions, along [110] and [1-10], were both fabricated. From the L-I curves and the lasing spectra, lasers in two orientations have obvious different behaviors. The temperature dependence of the lasing behaviors is also found to be dependent on the cavity orientations. Transition from the ground state lasing to the excited state lasing is observed when the quantum wires are perpendicular to the laser cavity.

The electrical transport property of InAs quantum wires was also investigated. The InAs quantum wires were embedded in the InGaAs/InAlAs heterostructure. In order to measure the electron anisotropic transport behavior, two sets of Hall bar samples with orientations along [110] and [1-10] directions were fabricated. Hall measurement, from 10K to room temperature, show that the mobilities along [110] and [1-10] directions are very different. When the conduction channel is parallel to the quantum wires, the mobility is much higher than the mobility when the conduction channel is perpendicular to the wires. This mobility anisotropy is explained by the difference in the cross section of the scattering centers caused by wires.

Finally, the conclusion of this thesis research is given. The nano wires not only provide a medium for us to study the optical transition and the transport in one-dimensional systems, but also provide opportunities for interesting device applications.