SiGe Epitaxial Growth by Ultra-high Vacuum Chemical Vapor Deposition and the Advanced Device Applications
Date Issued
2011
Date
2011
Author(s)
Lee, Cheng-Han
Abstract
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.
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.
Subjects
SiGe
QWs
QDs
GBLs
nanorings
2DEG mobility
MOSFETs
IGFETs
Si on Ge
3D to 2D growth
strain
Type
thesis
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