Design

Materials

Process

Surface Kinetics in Pulsed Laser Deposition of Homoepitaxial Germanium (001)

J.P. Leonard, B. Shin, M.J. Aziz December 2002
Division of Engineering and Applied Science, Harvard University, Cambridge MA 02138

Figure 1. Morphology map for molecular beam homoepitaxy of germanium. In the low temperature regime, layer by layer growth breaks down as growth proceeds. Kinetic processes may play a role in the onset of roughening, but are currently not well understood.

Evolution of surface morphology during epitaxial growth can provide important insight into surface kinetics. In the molecular beam epitaxy (MBE) community, epitaxy of silicon, germanium and silicon-germanium systems has been intensively investigated over the last two decades. This has resulted in well-developed experimental techniques and equipment, as well as detailed theoretical models of atomic surface diffusive processes, surface reconstructions, step-adatatom interactions, as well as larger scale morphological evolution. Germanium homoepitaxy is chosen both as an analogue to Silicon, as well as for the ongoing interest of Si-Ge systems and nanostructures. An extensive survey of the literature suggests the following process/morphology map, although much remains unknown due to complications associated with carbon contamination-induced step pinning.

Extension of this understanding into new kinetic regimes attainable by pulsed laser deposition (PLD) is the goal of this work. Pulsed laser deposition is unique in that deposition occurs in pulses, in which large numbers of adatoms can be introduced onto a surface in a very short time, typically microseconds. The dynamics of island formation, step flow, and adatom concentrations are highly transient in this case, in contrast to the steady-state conditions existing in traditional MBE. Experimentally, pulsed laser deposition has been demonstrated to produce morphologies different than observed in MBE, while recent Kinetic Monte Carlo simulations suggest an anomalous behavior, yet unexplained, in roughening transition temperatures. Moreover, extension of diffusional rate equation models into the transient regime encountered in PLD are of current interest.

Figure 2. Schematic of UHV system incorporating MBE and PLD sources.

Our experiments take advantage of existing MBE technology and analysis tools, but to this add a PLD system. A schematic of the chamber is shown in Figure 2. The system is unique in that both MBE (using a solid-source effusion cell) and PLD can be carried out under identical conditions, with a base pressure below 9x10^-11 Torr

Publications relating to this project

B. Shin, J.P. Leonard, J.W. McCamy, M.J. Aziz, “On the phase shift of reflection high energy electron diffraction intensity oscillations during Ge(001) homoepitaxy by molecular beam epitaxy”, Journal of Vacuum Science and Technology A 25, 221 (2007).
B. Shin, J.P. Leonard, J.W. McCamy and M.J. Aziz, "Comparison of morphology evolution of Ge(001) homoepitaxial films grown by pulsed laser deposition and molecular-beam epitaxy", Appl. Phys. Lett. 87, 181916 (2005).
J.P. Leonard, B. Shin, J.W. McCamy, M.J. Aziz, "Comparison of Growth Morphology in Ge (001) Homoepitaxy Using Pulsed Laser Deposition and MBE ", Mat. Res. Soc. Symp. Proc. 749, (2003).