The Manfra Group utilizes several labs across the Purdue campus to complete our research. We have two MBE systems, one for GaN and one for GaAs, in the Birck Nanotechnology Center. At Birck, we also have access to several spectroscopy techniques such as x-ray diffraction, atomic force microscopy, scanning electron microscopy, and transmission electron microscopy. Low temperature mobility studies are completed in the basement of the Physics building on Purdue's main campus. The photoluminescence equipment is part of a collaboration with Prof. Malis and also resides in the Physics building.
Low Temperature Measurement Lab
The Manfra low temperature lab performs electrical characterization of two-dimensional electron gases in GaAs/AlGaAs heterostructures. The primary focus is on research related to the fractional quantum Hall effect (FQHE). Quick characterization of material and devices is performed with a home-made 4K dipper probe equipped with a 2 Tesla magnet while more complete measurements can be made at 300 mK in a Janis He3 cryostat equipped with a 9 Tesla superconducting magnet. Our Oxford Kelvinox He3/He4 dilution refrigerator, with a 15 Tesla magnet, allows for lower (T < 50 mK) temperature examination of FQHE states and measurement of their energy gaps.
Gallium Nitride Lab
The gallium nitride (GaN) MBE machine in the Birck laboratory is a Riber 3200 machine brought to Purdue by Professor Manfra from Bell Labs. The machine includes a load lock, a sample heating chamber, and a main growth chamber. In the main growth chamber the system is configured with two gallium sources, one aluminum source, a nitrogen plasma source, as well as sources for silicon, carbon and indium. It is equipped with a reflection high-energy electron diffraction (RHEED) gun for measuring sample layer growth rates as well as a Stanford Labs residual gas analyzer (RGA) for analyzing gaseous contaminant levels in the MBE chambers. Finally, attached to the machine are two CT8 cryopumps and one CT10 cryopump, two ion pumps and a titanium sublimation pump.
Project include the growth and characterization of AlGaN/GaN and AlInN/GaN heterostructures both on polar and non-polar GaN substrate for intersubband device applications.
Gallium Arsenide Lab
The Manfra GaAs MBE lab focuses on growth and characterization of ultra-high mobility two-dimensional electron systems (2DESs) and two-dimensional hole systems (2DHSs) in GaAs/AlGaAs heterostructures and quantum wells. The extremely low impurity levels in these devices allow for sensitive experiments in a wide range of many-body quantum mechanical systems. Beyond fundamental physics research, these devices are also theorized to be useful for future applications such as fault-tolerant quantum computing implementations.
The primary tool in the lab is a dedicated high mobility Veeco Gen II MBE customized to improve overall vacuum quality and resulting crystal purity. Routine electrical transport characterizations are performed at 4K in liquid helium and at 300mK in a He3 cryostat which allows for rapid feedback on crystal quality.