MSE Seminar Series: Christopher J. K. Richardson
Friday, March 30, 2012
1:00 p.m.-2:00 p.m.
Room 2110 Chemical and Nuclear Engineering Bldg.
301 405 5240
Metamorphic Molecular Beam Epitaxy
Christopher J. K. Richardson
Laboratory for Physical Sciences
University of Maryland
Molecular Beam Epitaxy is a physical vapor technique used to grow single crystal materials with physical properties that can be varied by adjusting the alloy during growth. The primary restriction on this variation is the requirement to keep the atomic spacing consistent through the structure as the constituent alloys are changed. Accordingly, it has been historically imperative to grow structures that are lattice matched to a commercially available substrate.
During this seminar I will describe the properties of single crystal films that are not lattice matched to the substrates on which they are grown. Instead of employing a randomly relaxed buffer layer, a uniform 2-dimensional edge dislocation network is employed to abruptly relax the misfit strain at the film/substrate interface. Bicrystals of numerous material pairs will be discussed. Comparisons of the experimental and theoretical strain fields of GaSb films grown on GaAs show that some of these films are approaching the theoretical limit where all of the strain is completely relaxed at the interface. A device demonstration is provided by the 70mW of total CW output power at room temperature from an AlGaInAsSb laser with a lattice constant that has a 7.8% mismatch from the GaAs substrate on which it is grown.