Molecular Beam Epitaxy

The Molecular Beam Epitaxy (MBE) laboratory at the Laboratory for Physical Sciences exists in a class 10 clean room on the University of Maryland Campus.  We use our four deposition chambers to focus on advancing both the state-of-the-art in materials growth and device structure for electronic, optoelectronic, and MEMS applications.  Research in the MBE lab is cross-disciplinary that encompasses many areas of expertise.  We operate and maintain a large array of laboratory equipment that allows us to conduct research across the entire process of creating and using new semiconductor materials. The MBE staff conducts independent and collaborative research with scientists representing academic, industrial, and government organizations.  To learn more about collaborating with or joining our staff please contact us.
Our research areas encompass the entire III-V compound semiconductor landscape in addition to material heterotructures in the Si-Ge-C system.  The figure illustrates the range of elements that are used for our research.

An concept that we consider of central importance to our success is to consider the entire material system.  Our collaborations lead us to consider the mechanical, electrical, optical, and structure properties of the individual materials and the heterotructures that are grown from them.  Our work in the antimonide system relies on the type-II band alignment (see below) of GaSb and InAs to create multiple quantum well unit cells that can efficiently confine both electrons and holes.  The work that we are pursuing in SiGe photodetectors uses a similar concept to produce an optic al transition that is smaller than any of the constituent alloys.  In some of our collaborations using MEMs structures it is the piezoelectric and mechanical properties of the heterotructures that are of key importance.

The nature of the band alignment is of critical importance when designing a device heterostructure of dissimilar materials.  As shown in the blue-purple diagram, type-I band alignment indicates that the band edge discontinuities of the conduction and valence band have opposite signs.  Materials that are lattice matched to GaAs and InP exhibit Type-I alignment.  Type-I alignment is an important design feature because it allows a quantum well to be defined in the valence and conduction bands with a single thin layer of a smaller bandgap material.

Material heterotructures like those in the yellow-green figure that exhibit a type-II alignment have band edge discontinuities that are in the same direction. Material heterojunctions between GaSb and InAs create a type-II alignment.  To create a heterostructure that confines both the electrons and holes must be created with a more complex unit cell than a single thin layer of a smaller bandgap material because a quantum well can not be made in any single layer that confines both the electrons in the conduction band