Low temperature epitaxial growth of Ge on Si(100)-(2x1) with excitation laser by pulsed laser deposition

Low temperature epitaxy is important for Ge-Si device fabrication because it can lead to suppressing the introduction of defects such as dislocations and staking faults\textbf{.} The effect of laser-induced electronic excitations on the self-assembly of Ge quantum dots (QDs) on Si(100)-(2x1) grown by pulsed laser deposition is studied. The experiment was conducted under a pressure $\sim $1x10$^{-10}$ Torr. A Q-switched Nd:YAG laser ( $\lambda $ = 1064 nm, 10 Hz repetition) was split into two beams; one used to ablate a Ge target while the other to electronically excite the substrate. \textit{In-situ} reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), and \textit{ex-situ} atomic force microscopy (AFM) were used to study the morphology of the grown QDs. It was observed that excitation laser reduces the epitaxial growth temperature to 250 \r{ }C. Applying excitation laser to the substrate during the growth changes the QD morphology and island density, also enhances epitaxy, and improves the size uniformity of QDs at 390 \r{ }C and decreases the surface roughness at room temperature. A purely electronic mechanism of enhanced surface diffusion of the Ge adatoms due to a phonon kick following two hole localization could explain the results. Ongoing experiments using a femtosecond laser for excitation and \textit{in-situ} STM for detection of the early stages of island nucleation will be presented.