Subcategory: Physics (not Nanoscience)
Nicholas P. Calvano - Delaware State University
Co-Author(s): Andrew Voshell, Keesean Braithwaite, and Mukti Rana, Delaware State University, DE
Uncooled infrared (IR) detectors are employed in numerous radiometric systems and recording devices because of their cost, compact size and performance. Pyroelectric infrared (PIR) is a type of uncooled IR detector and has a spontaneous polarization change with change in temperature. PIR operates on the basis of Plancks law which states – any entity at a given temperature (>0K) at thermal equilibrium produces a spectral radiance of electromagnetic radiation. IR radiation from matters travels to PIR detector and the absorbed radiation causes the temperature of the sensing layer to change. Then it generates a spontaneous polarization that causes a voltage output in the PIR detector. Aluminum Nitride (AlxN1-x) is a wide bandgap semiconductor which has low electrical and high thermal conductivity with a high decomposition temperature. This work describes the deposition and characterization of AlxN1-x thin films for using them as pyroelectric detector’s sensing materials. Characterization of AlxN1-x thin films was conducted after fabricating capacitors of various sizes, the diameter and distance between the electrodes were 1100 m. A 100 nm thick AlxN1-x thin film was deposited at room temperature by radio frequency (RF) sputtering from an Al target in Ar: N2 environment on a 3-inch silicon wafer. Then the samples were annealed at 700 0C in N2 environment for 10 minutes. Next, a 100 nm thick Au film was sputtered and lifted-off using conventional photo-lithography to form the electrodes of the capacitors. X-ray diffraction was performed and revealed poly-crystalline peaks in the (100), (002) and (101) directions. For the thin film, when the temperature increased between 303 K to 353 K on a probe station, the pyroelectric coefficient increased from 8.60 × 〖10〗^(-9)C/m2K to 3.76 × 〖10〗^(-8)C/m2K. The loss tangent remained almost constant at (~1.5 × 10-5) when the temperature was varied within the same range. Between the wavelengths of 600 nm to 3000 nm the non-annealed films were were found to be transparent. Variations of optical transmission, reflection and index of refraction between the same wavelength range were also measured. The refraction coefficient varied between 2.0 and 2.2, while the extinction coefficient was found to be zero. The optical bandgap was determined using Tauc’s equation to be 1.65 eV. Future work will include prepertion of thin films with varying temperatures, gas mixtures and chamber pressure during reactive sputtering and annealing temperature and time after deposition. References: T.P. Drusedau, J. Blasing, “Optical and structural properties of highly c-axis oriented aluminum nitride prepared by sputter-deposition in pure nitrogen”, Thin Solid Films 377–378 (2000) 27–31. Choudhary R., Mishra P., Biswas A., and Bidaye A., “Structural and Optical Properties of Aluminum Nitride Thin Films Deposited by Pulsed DC Magnetron Sputtering”, Hindawi Publishing Corporation, ISRN Materials Science, Volume 2013, Article ID 759462, 2013.ERN AlN 2018 abstact V3.docx
Funder Acknowledgement(s): This work is partially supported by US Department of Navy Grant # N0014-15-1-2812, National Science Foundation Grant # MRI-1427089 and National Aeronautics and Space Administration Grant # NNX15AP84A.
Faculty Advisor: Mukti Rana, firstname.lastname@example.org
Role: The majority of it with assistant from undergrads and professors.