Rapid and Minimally Invasive Quantum Cascade Wafer Testing

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Princeton University Invention # 09-2523


Quantum Cascade (QC) wafer quality testing requires intensive processing and characterization. Conventional techniques used for wafer quality testing include photoluminescence, x-ray diffraction, Hall effect measurements, high resolution x-ray diffraction, transmission electron microscopy and secondary ion mass spectrometry, all of which are useful but are time consuming and highly invasive.


More importantly, none of these methods are complete in that they do not give the necessary QC information, such as turn-on voltage, maximum operating current density,  and the peak wavelength and full¿width at half-maximum (FWHM) value of the electroluminescence (EL) spectra. Testing QC devices under the appropriate operating bias typically entails elaborate fabrication steps, including dicing of the wafer, which destroys the integrity of the wafer and precludes further wafer scale processing.


Researchers in the Department of Electrical Engineering and the MIRTHE Research Center, Princeton University have developed a rapid and minimally invasive technique which can be applied at the wafer level and from which rapid feedback on the optical and electrical properties of a QC laser can be obtained. In this technique a single mesa, covering a total area of 0.28mm² is fabricated on a QC wafer, and its electrical and optical properties are measured. This method has been validated by comparing the results from the mesas with those of QC lasers fabricated from the same wafer. Results from the two types of QC devices show excellent agreement, differing by less than ~10 percent.


 The new technique saves time and processing cost when compared to the otherwise required full laser testing as significantly fewer processing steps are involved; e.g. 1 metallization steps instead of 2, 2 lithography steps instead of 3, no side-wall passivation and patterning steps. Overall, the number of processing steps is halved, and the processing time is shortened at least by about that amount as well.  Cost-savings result from the time savings and also from the fact that the wafer integrity is kept intact, such that the same wafer can be used for follow-on wafer-scale QC laser processing.    



MIRTHE is a National Science Foundation Engineering Research Center headquartered at Princeton University, with partners City College New York, Johns Hopkins University, Rice, Texas A&M, and the University of Maryland Baltimore County. The center encompasses a world-class team of engineers, chemists, physicists, environmental and bio-engineers, and clinicians. MIRTHE's goal is to develop Mid-Infrared (~ 3-30 µm) optical trace gas sensing systems based on new technologies such as quantum cascade lasers or quartz enhanced photo-acoustic spectroscopy, with the ability to detect minute amounts of chemicals found in the environment or atmosphere, emitted from spills, combustion, or natural sources, or exhaled.


Princeton is currently seeking commercial partners for the further development and commercialization of this opportunity. Patent protection is pending.




Bentil EN, Toor F, Hoffman AJ, Escarra MD, Gmachl C, Rapid and Minimally Invasive Quantum Testing Cascade Wafer Testing, IEEE Photonics Technology Letters, Vol 21, No.8, April 15,2009


For more information on Princeton University invention # 09-2523 please contact:


                        Laurie Tzodikov

                        Office of Technology Licensing and Intellectual Property

                        Princeton University

                        4 New South Building

                        Princeton, NJ 08544-0036

                        (609) 258-7256

                        (609) 258-1159 fax



Patent Information:
For Information, Contact:
Laurie Tzodikov
Licensing Associates
Princeton University
Claire Gmachl
Ekua Bentil