台灣留學生出席國際會議補助

2008年7月29日 星期二

Over 1.5 μm photoluminescence from InAs quantum dots on patterned GaAs substrates by MOCVD

論文發表人:翁秉秀(新墨西哥大學光電所博士班)

 

http://iprm2008.org/

 

在這篇論文中,我們報告了以區域選擇性之奈米磊晶生長定址砷化銦量子點,並得到1.5微米以上之常溫光激發螢光頻譜的技術。我們首先探討了砷化銦量子點在砷化鎵金字塔結構奈米晶面上之選擇性結晶成核。此種方式成長出之量子點,其形狀和大小均較Stranski-Krastanow成長模式易於控制。砷化鎵金字塔結構是以金屬有機化學氣相沉積術在由二氧化矽定址之(001)砷化鎵基板上生長。圓形的定址區域是由干涉式微影術在二氧化矽上形成。砷化鎵金字塔結構由包含了{11n}{10n}(001)等三個晶面族的平衡晶體形狀組成。接下來的定址量子點結晶成核高度偏好(11n)平面,這是由於該平面提供較佳之能量最小化。在(11n)平面上形成之量子點的形狀十分容易預測,也十分均勻。這些砷化鎵平衡晶體形狀及高度晶面化之量子點均由高解析度之掃描式電子顯微鏡來分析。

我們並且展示了常溫下之光激發螢光頻譜,峰值最長可達1.65微米。低溫的螢光頻譜也證實了三維量子限制的存在。經由分析證實此長波長砷化銦量子點螢光頻譜是由於增大的量子點尺寸,以及減小的量子點內之應力兩者共同促成。量子點的大小可以在不影響密度的狀況下,以單一的生長條件(生長時間)來控制。而應力減小則可能是來自於在量子點生長平面邊緣的部份應力降低、生長平面傾斜、以及量子點尖端的應力釋放。

 

In this paper, we report room-temperature (RT) photoluminescence (PL) emission above 1.5 μm from InAs patterned quantum dots (PQDs) by selective area nano-epitaxy.  The selective InAs QD nucleation on nano-faceted GaAs pyramidal facets is explored.  This technique of QD growth enables better control of QD shape and size, than is possible with the Stranski-Krastanow growth mode.  The GaAs pyramids are formed by metal-organic chemical vapor deposition (MOCVD) in patterned SiO2 mask on a (001) GaAs substrate, where the circular openings are formed by interferometric lithography.  The GaAs pyramids are characterized by well-defined equilibrium crystal shapes (ECS) defined by three crystal plane families including {11n}, {10n} and (001).  Subsequent PQD nucleation on the GaAs pyramidal facets is highly preferential towards the (11n) planes due to superior energy minimization and the shape of the QDs on the (11n) planes is also highly predictable and uniform.  The GaAs ECS pyramid and highly faceted PQDs are examined using high-resolution scanning electron microscopy (HRSEM). 

We also demonstrate strong RT PL emissiom from these InAs PQDs up to 1.65 μm.  The low temperature PL confirms the existence of three dimensional quantum confinements.  Analyses show that the long wavelength emission from InAs QDs is contributed by both the enlarged QD size and reduced residual strain inside the QD.  The size of QDs can be controlled with a single parameter, the growth time, without affecting the density of QDs.  The strain relaxation is likely due to the possible partial strain relaxation of the PQD at the edges of the GaAs pyramid facets where it nucleates, tilt of the growth plane, and the fully relaxed InAs matrix near the tip of the large PQDs