MATERIALS I RESEARCH
The AC field method is being used successfully for a variety of applications. For example, the technique is used in measurements of photovoltaic and thermoelectric materials for alternative energy applications, including amorphous silicon (a:Si), copper indium galliumselenide (CIGS), and other solar cell materials which typically have mobilities between 10-3 and 10 cm2/(V s)
The AC field method is being used successfully for a variety of applications. For example, the technique is used in measurements of photovoltaic and thermoelectric materials for alternative energy applications, including amorphous silicon (a:Si), CIGS and other solar cell materials which typically have mobilities between 10-3 and 10 cm2/(V s).
The method is also useful for new display technologies that use transparent conducting oxide (TCO) semiconductors like zinc oxide (ZnO),indium gallium zinc oxide (IGZO), and other TCO materials with mobilities between16 and 300 cm2/(V s). While the higher end is well handled by DC measurements, the low end would benefit greatly by using the higher precision AC measurement.
Another class of materials that researchers can better understand by using AC Hall measurements is organic electronic materials, whichare being investigated for use in electronic devices and have very small mobilities ranging from below 10-3 to 1 cm2/(V s).These materials, including organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and organic thin-film transistors (OTFTs), are lighter, more flexible and cheaper tomanufacture than inorganic materials and are showing much promisein advancing the electronics market.
One example of AC Hall effect instrumentation that researchers can now use to examine the electronic and magneto-transport properties of electronic materials is the 8400 Series Hall effect
Image 3: In low mobility and moderate resistivity (< 1 GΩ) materials, the misalignment voltage – mainly a result of asymmetry in sample contacting – is frequently the predominant contributor to error in DC Hall measurement, limiting resolution of mobility measurement. AC field techniques eliminate this form of error, allowing for significantly lower mobility measurements
measurement
system.This fully automated and integrated measurement system was developed by Lake Shore Cryotronics, in collaboration with Toyo Corporation of Japan, a company with years of experience in AC field technology. The 8400 Series HMS features optional AC field measurement capability that enables measurement of Hall mobilities down to 10-3 cm2/(V s). It is also capable of measuring resistances ranging from 200 gigaohms to as low as 10 micro-ohms over a range of temperatures extending from as low as 15K to as high as 1273K. With the capability to measure low mobility materials, the AC Hall effect method provides solutions to researchers working with novel materials that will be used for next generation devices and technology.
Image 2: Mobility ranges for the AC and DC field Hall References
[1]Hall measurements on low-mobility materials and high resistivity materials, Jeffrey Lindemuth and Shin-Ichiro Mizuta, Proc. SPIE 8110, 81100I (2011), DOI:10.1117/12.893100.
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www.solar-international.net I Issue II 2012
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