| 摘要: | 薄膜成長一直都是半導體產業的核心，目前最普遍使用的技術為化學氣相沈積(CVD)。在CVD的磊晶中，需要足夠高的成長溫度才能得到一個缺陷少及結晶性好的鍺薄膜。但高溫會產生S-K模式的成長，導致鍺薄膜表面不平整。因此本實驗採用脈衝雷射沈積(PLD)系統來沈積高品質的鍺薄膜。
在PLD磊晶的過程中，原子本身就帶有足夠的動能，使其沈積在基板後能夠移動至自由能較低的位置，使沈積的薄膜有更好的結晶性，因此PLD使用一個較低的成長溫度。此外，藉由快速高溫退火可以再進一步提升薄膜的結晶程度及減少薄膜內的缺陷。最後使用實驗室所發展的微影技術，成功地將以最佳化的磊晶、退火參數成長的樣品製做成為光偵測器，完成在本實驗室第一個使用PLD磊晶的光偵測器及其特性的量測。
另一方面，鍺／矽量子點的成長為本實驗的另一個重點。基於量子侷限效應，量子點在很多光電元件的應用上有很大的潛力，這類的應用通常需要高密度、小尺寸且均勻的量子點。為此，本實驗發展了脈衝雷射退火(PLA)技術，主要是利用一道均勻的線聚焦脈衝雷射，掃過一層預先沉積在矽基板上的鍺薄膜，以此誘發量子點的形成。PLA可以藉由調整雷射通量、移動速度以及薄膜厚度來控制量子點的大小。在適當的參數設定下，PLA可以誘發大面積、小尺寸、高密度且均勻的量子點形成。在此方法下，平均直徑約25 奈米，高度約2.9奈米，密度約每平方公分 6 1010 個的量子點，可以均勻的在大於4平方毫米的面積中生成。最後基於量子點成長趨勢與脈衝雷射參數的關係，進而提出一個雷射誘發量子點形成的機制模型。
;Thin film deposition is always considered the heart of semiconductor industry. Nowadays, chemical vapor deposition (CVD) is widely used for this purpose. In CVD technique, a high growth temperature, normally at 600 °C, is required for the deposition of high quality Ge thin film with low threading dislocation density. However, the high growth temperature may lead to high surface roughness caused by S-K growth. Thus, pulsed laser deposition (PLD) system is used to deposit high-quality epitaxial Ge thin film on Si substrate in this work.
In PLD, the kinetic energy of Ge atoms is high enough for them to diffuse to a position where has the lowest free energy after striking substrate. This phenomenon results in a better crystallinity of the deposited thin film, and a lower growth temperature at which S-K growth mode won’t occur. To further improve the quality of Ge thin film, rapid thermal annealing (RTA) is introduced right after the deposition. Finally, a photodetector with optimized Ge thin film grown by PLD is fabricated and characterized, which is the first time in our lab.
On the other hand, the fabrication of Ge/Si quantum dots (QDs) is another issue in this work. Due to the quantum confinement effect, QDs exhibits a huge potential for a variety of applications in optoelectronic devices. For most of these applications, a large area with uniform high-density and small-size QDs is required. In this work, we demonstrate that this can be achieved by scanning a pre-deposited Ge thin film on Si with a line-focused pulsed laser beam. This technique is also called scanning pulsed laser annealing. Moreover, the size of Ge/Si QDs can be precisely controlled by the laser fluence, laser scan speed and Ge film thickness. With suitable settings, Ge/Si QDs with a mean height of 2.9 nm, mean diameter of 25 nm, and dots density of 6 1010 cm-2 can be formed over an area larger than 4 mm2. Based on the dependences of the formation of QDs on laser parameters, a model is proposed for the mechanism underlying the laser induced formation of the Ge/Si QDs. |
