The Nanoscale World
Metrology Spotlights | AFM Research Spotlights | MBE Research Spotlights | Share Your Research
Send As Chief Experimental Officer within the Physics Department of the University of Nottingham, Dr. Richard Campion’s main role is the MBE growth of Arsenide and Nitride III-V semiconductors. An important aspect of this effort is the incorporation of Mn and other transition elements into materials such as the ferromagnetic semiconductor Gallium Manganese Arsenide (GaMnAs). Much of this work is undertaken at very low growth temperatures (for MBE), requiring precise control of temperature and growth stoichiometry. Hence, Dr. Campion and his colleagues had to revisit and investigate some of the fundamentals of MBE. This work takes place on a Veeco GEN III™ MBE System utilizing a Veeco Mark V Arsenic Valved Cracker with precise control of substrate temperature achievable through a system integrated band-edge temperature measurement system.
This most recent work, as presented jointly with Veeco at the 2009 North American Molecular Beam Epitxy (NAMBE) Conference, arose from earlier studies by Dr. Campion and his colleagues during the growth of high quality GaMnAs with high Curie temperatures after suitable annealing. [1,2] At which time, a key issue became obvious—avoid Mn surface segregation, meaning growing films at temperatures as low as or lower than 200°C.
When growing high quality films at low temperatures, it is also essential to avoid incorporation of arsenic anti-site defects. This requires film growth to take place very close to but just above stoichiometry, i.e. with the minimum amount of arsenic needed to grow the particular structure. It also means that it is better to use the arsenic dimer (As2) as opposed to the tetramer (As4) , which is known from an earlier study to have a much shorter lifetime on the surface at low temperatures and is thus less likely to result in the incorporation of anti-site defects.
With notable requirements, the need to study the precise nature of the species coming from the Veeco Arsenic Valved Cracker as a function of the operating conditions (the temperature of the cracking zone, the arsenic flux and the absence or presence of catalytic baffles) was evident. To achieve this, a novel modulated beam mass spectrometer (MBMS) system was constructed with the unique ability to report upon the flux emitting from an MBE source.[3] Using this technique, it is possible to distinguish the real signal coming from the source due to gases in the vacuum system.
Figure showing MBMS system schematic—when used, the baffles are inserted into the front end of the cracking zone.
The MBMS system has been used to study the arsenic species from both the Veeco Mark IV and Mark V Arsenic Valved Cracker designs as a function of the operating conditions, which in turn will enable us to produce even better films in the future.
Graph showing the modulated signal for the As2 (red) and As4 (black) flux components produced by a Veeco Mark V Arsenic Valved Cracker with standard baffles fitted. The cracker temperature is varied in steps from 950°C (far left) to 650°C (far right), giving rise to the step like changes.
REFERENCES
[1] M. Wang, R.P. Campion, A.W. Rushforth, K.W. Edmonds, C.T. Foxon, B.L. Gallagher, "Achieving high Curie temperature in (Ga, Mn) As", Appl. Phys. Lett 93, 132103 (2008).
[2] R.P. Campion, K.W. Edmonds, L.X. Zhao, K.Y. Wang, C.T. Foxon, B.L. Gallagher, C.R. Staddon, "The growth of GaMnAs films by molecular beam epitaxy using arsenic dimers", J. Cryst. Growth, Vol. 251, No. 1 (2003): pp. 311-316.
[3] R.P. Campion, C.T. Foxon, and R.C. Bresnahan, "Modulated beam mass spectrometer studies of a Mark V Veeco cracker", J. Vac. Sci. Technol. B 28(3), May/Jun 2010.
Comment
Send
Subscribe
Dr. Richard Campion
Chief Experimental Officer
Physics Department
University of Nottingham
Dr. Richard Campion is widely recognized for his work on the growth of spintronic materials by MBE. He began his professional life in industry, coming as a mature student to Nottingham University in 1991. His undergraduate B.Sc. Degree, with first class honors, is in pure and applied physics, being awarded the prestigious “Bill More Prize for Applied Physics” in his final year. He than obtained a Ph.D. in experimental physics in 1997, at Nottingham, on the growth and properties of high temperature superconductors. Upon receiving his degree, Dr. Campion joined Nottingham’s Nitride MBE Group led by Professor Foxon, where he designed and commissioned a novel plasma-assisted CBE/low-pressure MOVPE reactor that was used for detailed mass spectrometry studies of the growth of group III nitrides from metal-organics. Since 2001, he has been responsible for the growth of III-V materials and devices by MBE for spintronic applications, which includes providing GaMnAs samples with world record Curie temperatures after suitable annealing. Devices including Al, Ga, In, As and P as well as Mn and Fe have been the principle focus of this work, although group III nitrides and dilute nitrides have also been featured. He has also grown single crystal metal (e.g. epitaxial Fe and Al) on semiconductor devices as well as quantum dot and resonant tunnelling structures incorporating magnetic impurities. He routinely provides high quality conventional GaAs devices for ultra-fast time-resolved phonon and optical studies and other fundamental investigations. Most recent work involves the growth of InGaN solar cell devices by MBE and studies of novel materials and MBE sources using a newly constructed modulated beam mass spectrometer system. Richard has published more than 130 papers, on MBE growth and characterization of III-V materials, many of which are highly cited.
For more information, click here.