InAs-QDIP hybrid broadband infrared photodetector
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InAs-QDIP hybrid broadband infrared photodetector Chee H. Tan1, Ian C. Sandall1, Xinxin Zhou1 and Sanjay Krishna2 1 Department of Electronic and Electrical Engineering, The University of Sheffield, Sir Frederick Mappin Building, Mappin Street, Sheffield, S1 3JD, U.K. 2 Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, NM 87131-1070, USA.
ABSTRACT We demonstrated that an InAs photodiode and a Quantum Dot Infrared Photodiode can be bonded to produce a hybrid broadband infrared photodetector. When cooled to 77 K the InAs photodiode can be used to detect wavelengths from visible to a cutoff wavelength of 3 m while the Quantum Dot Infrared Photodiode detects wavelengths from 3 to 12 m. The dark current and spectral response were measured on reference devices and bonded devices. Both sets of devices show similar dark current and spectral response, suggesting that no significant degradation of the devices after the bonding process. INTRODUCTION The wavelength bands, 3-5m and 8-12 m, commonly referred to as the Midwave infrared (MWIR) and Longwave Infrared (LWIR) respectively, are important for a variety of infrared applications including infrared spectroscopy, radiation thermometry and thermal imaging. This is because the atmospheric attenuation is low and many chemicals of interest have unique infrared absorption spectrum in the MWIR and LWIR bands. Previous generations of infrared detectors have focused on the development of focal plane arrays and achieving high operating temperature. While these will continue to be important, development of future generation infrared detectors could add additional capabilities such as multispectral, polarization, internal gain and enhanced dynamic range. One detector technology that is of interest to multispectral sensing is the Quantum Dot Infrared Photodiodes (QDIPs). QDIPs have peak responses that can be modified by applied bias [1]. When combined with a post processing algorithm, multispectral capability can be realized without using external wavelength selecting optical components (such as grating or filter) [2,3]. The absence of these optical components could reduce the cost and size of the infrared instruments, making QDIPs an attractive option. In addition to multispectral sensing QDIPs can also offer a broad spectral response by varying the composition of the quantum dots. However, they are not suitable for detection of wavelengths below 3 m, which is also of interest to gas sensing and spectroscopy measurements. With a bandgap of 0.35 eV at room temperature, InAs is an obvious detector option to extend the lower detection wavelength if it can be integrated with QDIPs. Besides having good detection efficiency at shorter infrared wavelengths, InAs has also been shown to have excellent impact ionization properties where high gain can be achieved with a gain independent excess noise factor below 2 [4]. In addition the gain-bandwidth product in InAs avalanche photodiodes is not limited [5] since only electrons can initiate impact ioniza
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