| dc.description.abstract | 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. | en_US |