"Cross-Section Scanning Tunneling Microscopy of InAs/GaSb Superlattice Interfaces"

Speaker:Dr. Cecile Uzan-Saguy
Affiliation:Solid State Institute, Technion
Organizer:Materials Engineering
Abstract:InAs/GaSb-based type II superlattices are considered as one of the leading candidates for the next generation infrared detectors, able to operate at room temperature.
The unique properties of short period superlattices are based on the capabilities to grow very thin layers within 0.5 to 1 ML precision with abrupt interfaces. The molecular beam epitaxy (MBE) technique, which allows precise control of the growth rate, is used to grow the InAs/GaSb heterostructures. However, two main difficulties are encountered during the growth process. (1) Since InAs and GaSb have different anion and cation, the interfaces can be GaAs or InSb like yielding Sb monolayer islands at the interfaces. (2) Reducing the thickness of each layer may result in an increase of species mixing due to composition fluctuations and segregation. Such disorder at the interface will have an obvious influence on the optical and electronic properties by deteriorating transport and scattering of carriers across interfaces.
An important issue for optimizing the InAs/GaSb heterojunction based devices is therefore to get a fast feedback on the interface quality after each growth and to relate it with the growth conditions. Cross section STM has emerged to be the technique of choice for the characterization of III-V heterostructure interfaces.
Here we present results of cross sectional scanning tunneling microscopy (XSTM) experiments developed at the Technion, at an atomic resolution level, aimed to investigate the chemistry and roughness of the InAs/GaSb interface. In particular, the combination of images obtained at negative and positive bias a well as the use of image contrast caused by the difference in bond length allow identifying the interfacial bonding type and the intermixing species occurring during the MBE growth.