鍺量子點於凹洞圖形化矽(001)基板上之成核特性與機制

Abstract

鍺量子點由於可應用於製作光偵測器，且在製程上能與矽基技術相容，因此其磊晶成核特性已被廣泛地研究。一般成長於平面矽基板上的鍺量子點，其成核位置呈現無規則的排列，且尺寸均勻度不易控制，因而限制其實際應用的可能性。本論文將詳述如何透過凹洞圖形化之矽基板來控制鍺量子點的成核特性；研究中發現經由調整矽基板上凹洞結構的直徑、間距以及深度，可使得成長於基板上的鍺量子點受到控制，因而呈現二維規則性排列，並具有極佳的尺寸均勻度。這些受到凹洞結構所控制的量子點，在空間上以<110>方向為對稱軸呈現對稱排列，形貌呈現橢圓頂狀，且其長軸平行於<100>方向。量子點的密度為4×109 /cm2，長軸、短軸以及高度尺寸分別為84 ± 7 nm、73 ± 6 nm及4 ± 1 nm。 此外，本研究發現原目的為使矽基板表面之原生氧化層產生熱脫附，以提高鍺量子點磊晶品質的磊晶前熱處理製程，將導致所製作之凹洞結構的表面形貌轉變為截頭倒金字塔型，而如此形貌之結構將影響後續所成長量子點之成核特性甚鉅。經由計算截頭倒金字塔型凹洞結構之表面化學勢，我們發現鍺量子點之成核特性的確是由這些截頭倒金字塔型凹洞結構之表面形貌所控制。本論文之研究結果有助於了解鍺量子點於凹洞圖形化矽基板上之成長特性與機制，所獲得之高密度且尺寸均勻之鍺量子點更可整合於鍺量子點光偵測器元件中，以提升元件效能。

The nucleation properties of Ge dots have been extensively researched because of its potential for photodetectors and compatibility with Si technology. In general, Ge dots grown on a blank Si substrate are randomly positioned and exhibit a broad size distribution, which limits its realistic applications. In this dissertation, we demonstrated that the nucleation properties of Ge dots can be controlled with pit-patterned Si substrate. These well-controlled Ge dots are symmetrically located with respect to <110> and exhibit an elliptical dome shape whose major axis is oriented along <100>. The dot areal density is up to 4×109 /cm2, and the means of major axis, minor axis, and height of the dots are 84 ± 7 nm, 73 ± 6 nm, and 4 ± 1 nm, respectively. Besides, we found that the pre-growth heat treatment process, a conventional process for native oxide desorption before growth, will drastically transforms the structure of the pre-patterned pits on Si(001) substrates into truncated inverted pyramids (TIPs) and crucially determines the nucleation position, shape, and spatial orientation of the subsequently grown Ge dots. The surface chemical potential of the TIP was also calculated and compared with the observed nucleation properties of Ge dots. These results raise the possibility of realizing high-performance Ge quantum dot photodetectors and provide further understanding of the growth of Ge dots on pit-patterned Si substrates.