Center for Semiconductor Physics in Nanostructures
 

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Research

Overview | IRG1 | IRG2 | Nuggets | Publications

IRG2: Nanoscale Interface Studies

Two-dimensional electron gases (2DEGs) have been studied in III-V heterostructures for over two decades. In 1978, the innovation of modulation doping solved the problem of ionized donor scattering. Further development of molecular beam epitaxy (MBE) technology and refinement of sample design have led to extraordinary low-temperature mobilities in GaAs, on the order of 107cm2/Vs, so that the time for an electron to scatter in such systems is 10,000 times that of an electron in a metal. This extremely low disorder enabled the Nobel Prize winning discovery of the fractional quantum Hall effect and the realization of ballistic transport devices.

Caption: Our two in situ STM/MBE systems are precisely the tools needed to examine interfaces at any stage of the growth process, looking at structure and chemical composition on the atomic level of detail. The UA system (top) is the only STM/MBE system in the United States that can grow phosphide structures. It is also one of the few that is equipped to study spin-injection in situ using ferromagnetic STM tips. Second, the focus at OU (bottom) on InSb quantum wells has made us the leading experts on their growth and electronic properties.

On the other hand, narrow gap semiconductor materials (e.g. InAs and InSb) have far better room temperature mobilities, due to their small effective electron mass. Indeed OU currently holds the world's record for room temperature mobility in semiconductor quantum wells (4´104cm2/Vs). However, these structures are far from their maximum potential. The lack of compositional abruptness and the presence of defects at interfaces limit their performance.

An understanding and control of surfaces and interfaces at the atomic level is needed as a foundation for their nanostructures at room temperature. As a bonus, the large spin-orbit coupling in these materials make them ideal candidates for magnetoelectronic (spintronic) devices. Little work has been done with these materials in this regard; hence this IRG carries out the foundational studies necessary for applications.