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In-line and Compact QWIP Reference Detector at 4.6μm: Design and Applications

This paper presents the design and development of an in-line and compact quantum well infrared photodetector (QWIP) specifically tailored for detection at 4.6µm. The authors, Ekua Bentil, Germano Penello, and Claire Gmachl, from Princeton University and the Federal University of Rio de Janeiro, discuss the potential applications of this detector in advanced laser systems, including signal detection and beam splitting technologies. This work was presented at the 2010 MIRTHE Quantum Cascade Laser Workshop.

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In-line and Compact QWIP Reference Detector at 4.6μm: Design and Applications

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  1. In-line and Compact QWIP Reference Detector at 4.6µm

    Ekua Bentil1, Germano Penello1,2 and Claire Gmachl1 1Princeton University 2Federal University of Rio de Janeiro 2010 MIRTHE Quantum Cascade Laser Workshop – November 12
  2. Motivation Beam splitter or ZnSe Laser Signal detector Reference detector New approach to obtain a reference signal needed in gas spectroscopy To study laser fluctuation To obtain reference intensity in direct absorption equation: Beer-Lambert’s Law Current methods include: Beam splitter or ZnSe window Lack of control over Reflection/Transmission Unnecessary split for a reference signal Complex algorithms to fit reference signal Introduction of error into data Time consumming
  3. Desired parameters Our solution Laser Signal detector Minimally absorbing QWIP In-line reflection or transmission setup Reference QWIP detector Laser Reference QWIP detector Signal detector Absorb small percentage of the original beam Reflect or transmit > 70% Leave majority of the beam untouched or improved if possible Room temperature use Easy to implement in a sensor system
  4. QWIP design E InAlAs InAlAs InGaAs z Energy levels in a QW Comparison between two codes Comparing two independent codes in order to obtain the best QW thickness
  5. QWIP Structure Etching z Contact layer 50 x QWIPS Contact layer InP Substrate Metalization z 3D view Bonding
  6. Possible solutions Reflect or transmit > 70% Leave majority of the beam untouched or improved if possible Reflection Transmission Several angles of incidence Arbitrary polarity (must have TM!) Less disturbance on original beam Fixed angle of incidence (Brewster) Fixed polarity (TM) Easy to implement
  7. Reflection – Fresnel Equation θB θB Brewster angle
  8. Transmission – Fresnel Equation θB θB Brewster angle
  9. Difficulties High reflectance only at high incidence angles.
  10. Spot size Size of the detector L Projected beam on the surface L/L0 L0 Typical detector size around 1002 to 10002 µm2 [1] Problem in large area detectors: Increase dark current; Carrier recombination [1] Quantum Well Infrared Photodetectors – Physics and Applications,Schneider, H.; Liu, H. – Springer 2007
  11. Solution Reflection in a mirror polished substrate Beam size over the sample; Size of each detector; Metallization on the top of the sample; TE and TM polarities instead of only TM, as it would be in transmission ; Different angles instead of a fixed angle, as it would be in transmission; One point of concern?
  12. InP Substrate Properties Absorption in a substrate Courtesy of Xue Huang
  13. Results Wavelength absorption on QWIPs Absorption peak at 5,2 µm. Growth uncertainty of 1 monolayer (~3 A) explains this behavior
  14. Results Processed QWIPs for reflection Samples size (µm): a a b 180 285 243 385 306 485 b 369 585
  15. Results Processed QWIPs for transmission 200 µm 200 µm 200 µm 3 mm 3 mm 3 mm 3 mm
  16. Results for R-QWIPs Fresnel equations Fixed angle of incidence (80º and 72º) Varying polarization (TM to TE) Polarizer Sample Polarizer ZnSe lens MCT MCT Sample ZnSe lens
  17. Results for R-QWIPs Incidence angle = 80o Incidence angle = 72o TM TE TM TE Experimental results for shallow incidence agree well with theoretical simulation
  18. Future Work Finishing setup for actual R-QWIPs characterization Fabrication and characterization of T-QWIPs Design, fabrication, characterization at differente wavelengths for both types of QWIPS Implementing in an actual gas sensor
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