超高真空化學氣相沉積矽鍺磊晶成長暨先進元件應用

Abstract

於本論文中，超高真空化學氣相沉積矽鍺磊晶技術被詳細的探討。我們成長矽鍺量子點與奈米環狀結構以供光偵測器元件等先進光學元件應用開發，而矽鍺量子井以及矽鍺漸進層結構則被設計來提供金氧半場效電晶體元件以及絕緣層閘極場校電晶體元件等先進電子元件的開發。 於本論文的第一部份，矽鍺量子井與矽鍺量子點這兩種已經歷史悠久的矽鍺奈米微結構的生長機制將被再次討論，特別是載流氣體對矽鍺量子井與量子點結構的生長影響。氫原子表面覆蓋現象在矽鍺量子井與量子點結構的生長中扮演很重要的角色，特別是會影響到矽鍺奈米結構中的鍺濃度以及應變分布。除此之外，這兩種奈米結構在元件上的應用也被充份的討論。利用在Si(100)，Si(110)與Si(111)三種基板上製作的金氧半場效電晶體在本次論文中亦被開發。等效質量的差異導致了在這三種基板上製作之元件的載子遷移率不同。另一方面，利用多層量子點結構製作的紅外光偵測器特性也在此部份被討論。 在矽鍺量子井與矽鍺量子點之生長與元件應用介紹後，我們利用類似的概念開發出矽鍺奈米環狀結構。兩種生長機制：矽原子表面擴散與鍺原子外擴散現象分別被建構在於六百度生長與於五百度生長的矽鍺奈米環狀結構上。利用鍺原子外擴散現象所製作的矽鍺奈米環狀結構，由於對環狀結構的深度以及邊緣的鍺濃度具有較好的控制性，被我們認為是比較適合於開發未來新型光偵測器等先進元件應用。而除了開發出此結構外，我們亦同時開發出在Si(100)，Si(110)與Si(111)三種基板上的矽鍺奈米環狀結構。利用改變底部基板，我們可以控制矽鍺奈米環狀結構的基底形狀，藉以得到更多光學元件的應用。 在本論文的第三部份，我們開發出了具有目前世界紀錄二維電子氣載子遷移率的高速元件，並進一步的將此紀錄往前推進。此項高速元件在載子濃度於1.5×1011 /cm2時，具有約1.6×106 cm2/Vs的二維電子氣載子遷移率。另一方面，我們更進一步的將此概念開發成可同時具有二維電子氣以及二維電洞氣載子遷移率的互補元件。P型通道場效電晶體的特性以及反用換流器也同時被開發成功。除此之外，我們也討論了對於二維電子氣密度以及二維電子氣載子遷移率的限制性。各種在矽鍺奈米結構內的散射現象，包括雜質、背景雜質、介面粗糙度、還有線差排密度等，都可以很直接的降低我們的二維電子氣載子遷移率。而藉由這部份的發現，我們也成功將我們二維電子氣載子遷移率的紀錄推進到2×106 cm2/Vs，並在可預期的未來，我們還有更多進步空間。 最後一個部份裡，我們討論了在鍺基板上成長矽的生長機制。一個與一般在矽基板上生長鍺狀況不同，從三維生長回歸到二維生長的機制，被第一次在鍺基板上成長矽的情形中發現。這一連串的生長分成三個階段，首先，矽量子點會先出現在鍺基板表面。在持續的矽沉積後，一種奈米環狀結構將會取代原本的矽量子點。而最後，整個矽表面將會變平，回歸到二維的生長當中。這種生長機制，推測是來自於拉伸應變可以增強矽原子在表面的表面擴散效應，並增進側向的成長，從而形成從三維生長回歸到二維生長的機制。這種平坦狀的矽磊晶層，對於先進的光電以及奈米電子元件開發，具有非常大的助益。

SiGe epitaxial growth by ultra-high vacuum chemical vapor deposition has been investigated in this dissertation. The SiGe quantum dots (QDs) and nanorings were fabricated for the applications of the photodetectors, while the SiGe quantum wells (QWs) and the SiGe graded buffer layers (GBLs) were fabricated for the applications of the metal-oxide-semiconductor field effect transistors (MOSFETs) and the insulator-gate field effect transistors (IGFETs). In the first part of this thesis, the growth mechanisms of the SiGe QWs and SiGe QDs have been discussed. The carrier gas effects on the growth of the QWs and QDs are also discussed. The hydrogen passivation, which can influence the Ge concentration and the strain in the SiGe nanostructures, plays a crucial role in the SiGe QWs and SiGe QDs growth. Moreover, the device applications are also introduced. The MOSFETs fabricated from the SiGe QWs grown on Si(100), Si(110), and Si(111) have been discussed. The higher mobility in the <110> direction of Si and SiGe is due to the smaller conductive effective mass. The quantum dot infrared photodetectors (QDIPs) made by the multi-layer SiGe QDs substrate have also been demonstrated. After the discussion on the growth of the SiGe QWs and QDs, the SiGe nanorings have also been investigated. The Si surface diffusion mechanism and the Ge out-diffusion mechanism were proposed for nanorings formation at 600oC and 500oC, respectively. The SiGe nanorings created by Ge out-diffusion show controllable depth and well-defined Ge content at edges. The novel nanoring structures can be used in new optoelectronic devices. Moreover, the surface orientation effects on SiGe QDs and nanorings formation are investigated. The base shapes of SiGe QDs and nanorings can be controlled by different surface orientation. In the third part of this thesis, the two dimensional electron gas (2DEG) devices with the world record high 2DEG mobility have been investigated. The 2DEG in a Si QW on SiGe GBLs with the world record high mobility of 1.6×106 cm2/Vs at carrier densities n~1.5×1011 /cm2. On the other hand, the complementary devices on an undoped Si/SiGe substrate where both 2D electrons and holes have also been investigated. A p-channel FET is characterized and the operation of an inverter is demonstrated. Moreover, the limitations of the two dimensional electron densities and 2DEG mobility have been discussed. The scattering from remote dopants, background impurities, interface roughness, and threading dislocations can all degrade the mobility in SiGe heterostructures. Based on the knowledge above, we have successfully improved the 2DEG mobility to 2×106 cm2/Vs by changing the substrate structures. Finally, the growth mechanism of the Si on Ge growth was investigated. The transition from 3-dimensional (3D) to 2-dimensional (2D) growth for Si on Ge, which is different from the Ge on Si case, was observed for the first time. The Si quantum dots can be observed in the initial Si growth on Ge. With the increasing Si deposition, the ring-like structures appeared. Finally, the flat surface without any nanostructures above can be observed. The tensile strain to enhance surface mobility of Si atoms favors proposedly the lateral growth, and leads to the three to two dimensional growth. The flatter Si layer growth directly on Ge can be used for the application of novel nanoelectronics and optoelectronics devices.