Paper TF-ThM4
Effects of Pulsed Laser Deposition Conditions on the Growth of Ge Quantum Dot on Si(100)-(2x1)

Thursday, October 23, 2008, 9:00 am, Room 302

The growth of Ge quantum dots (QD) by pulsed laser deposition of Ge on Si(100)-(2x1) is studied. The samples were first cleaned by using modified Shiraki and IMEC methods and then transferred into the deposition chamber. The vacuum system was then pumped down, baked for at least 12 hours, and the sample was then flashed to 1100 °C in order for the 2´1 reconstruction to form. The experiment was conducted under a pressure ~1x10-9 torr. A Q-switched Nd:YAG laser (wavelength l = 1064 nm) with 10 Hz repetition rate was used to ablate a Ge target. Different substrate temperatures and ablation laser energy densities were used and were shown to affect the quantum dot morphology. In-situ RHEED and ex-situ STM and AFM were used to study the morphology of the grown QD. During deposition, the RHEED patterns changed from elongated streaks to spots. As we increased the ablation laser energy density or the substrate temperature, formation of RHEED spots occurred at less coverage. AFM scans show that the number of clusters and coverage ratio increases with the ablation laser energy density, while the average area of clusters decreases. As we increased the substrate temperature from 400±20 to 500±20 oC, the Ge QD morphology changed from the asymmetric hut shape to the symmetric dome shape. Also, a decrease in the number of clusters and coverage ratio was observed.