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. Installation of an Oxford Kelvinox He3/He4 dilution refrigerator with a 15 Tesla magnet is also underway which will allow lower (T < 50 mK) temperature examination of FQHE states and measurement of their energy gaps.
Author Archive for: admin
This author has yet to write their bio.Meanwhile lets just say that we are proud admin contributed a whooping 79 entries.
Entries by admin
The gallium nitride (GaN) MBE system is a Riber 32. The machine includes a load lock, a sample outgassing chamber, and a main growth chamber. In the main growth chamber the system is configured with 2 gallium sources, 2 aluminum sources, a nitrogen plasma source, an indium source as well as a source for silicon. It is equipped with in-situ diagnostics including a reflection high-energy electron diffraction (RHEED) gun for measuring sample surface evolution as well as a residual gas analyzer. Projects include the growth of AlGaN/GaN and AlInN/GaN heterostructures both on polar and non-polar GaN substrates for intersubband device applications. In addition this system has been used to produce the highest 2DEG mobility ever reported in an AlGaN/GaN heterostructure.
Our GaAs MBE is a Veeco Gen II system highly customized to improve overall vacuum quality and resulting crystal purity. Meticulous vacuum hygiene results in base pressure ~1x10-12 torr and all the effusion cells in our system are custom designed by our group in an effort to reduce the thermal load during growth. The lab also houses 2 ancillary vacuum chambers used for cleaning and characterization of components before loading into the MBE. One vacuum chamber has been specifically designed for gallium purification and mates with the MBE so that components can be transferred between chambers without exposure to air. This MBE system has recently produced 2DEGs with low temperature mobility in excess of 30x106cm2/Vs as well as 2DEGs exhibiting the highest excitation gap at ν=5/2 ever measured.
December 16, 2014 Prof. Manfra profiled in COS Insights Magazine. [COS Insights Magazine]
November 30, 2014 Baby girl Michelle born to Jiayi. Congratulations to Jiayi and her family.
November 5, 2014 GaAs 2DEG mobility exceeds 30 million! Congrats to GaAs team.
October 15, 2014 New Oxford Triton 200 top-loading dilution refrigerator is delivered. This new capability will be shared with the Csathy group.
September 1, 2014 Major renovations to GaAs MBE complete. Newly designed sample manipulator and Arsenic cell added. System loaded with specially treated gallium source material.
August 1, 2014 Manfra group teams with Microsoft Station Q to explore materials for topological quantum computing.
May 15, 2014 Prof. Manfra discusses topological quantum computing in Quanta Magazine. [Quanta Magazine]
Birck Nanotechnology Center
1205 W State Street
West Lafayette, IN 47907-2057
Department of Physics and Astronomy
525 Northwestern Avenue
West Lafayette, IN 47907-2036