Part of the book: Photodiodes
Part of the book: Photodiodes
In the present chapter, we describe two new photoelectric-measurement-based methods that can be used for characterization of the diffusion process of charge carriers either in mercury-cadmium-tellurium (MCT) films intended for fabrication of infrared focal plane array (IR FPA) detectors or in the absorber layers of ready MCT-based photovoltaic IR FPA detectors. First-type measurements are photocurrent measurements to be performed on special test structures involving round photodiodes provided with coaxial light-shielding cap metal contacts. Second-type measurements are spot-scan measurements of MCT photovoltaic 2D IR FPA detectors traditionally used for measuring the crosstalk value of such detectors yet implemented at low and high levels of registered diode photocurrents. Both methods permit the determination of the bulk diffusion length of minority charge carriers in MCT material. The second method, in addition, permits the determination of the local effective diffusion length of minority charge carriers in the absorber-layer region under FPA diodes. The values of the bulk diffusion length of minority carriers obtained in MCT films and in the MCT absorber material of the examined middle-wave and long-wave IR FPA detectors were found to be in good agreement with previously reported relevant data. The estimated value of the local effective diffusion length of minority carriers in the film region under back-biased FPA diodes proved to be consistent with a theoretical estimate of this length.
Part of the book: Optoelectronics
In this article, we present an overview of a focal plane array (FPA) with 640 × 512 pixels based on the AlGaAs quantum well infrared photodetector (QWIP). The physical principles of the QWIP operation and their parameters for the spectral range of 8–10 μm have been discussed. The technology of the manufacturing FPA based on the QWIP structures with the pixels 384 × 288 and 640 × 512 has been demonstrated. The parameters of the manufactured 640 × 512 FPA with a step of 20 μm have been given. At the operating temperature of 72 K, the temperature resolution of QWIP focal plane arrays is less than 35 mK. The number of defective elements in the matrix does not exceed 0.5%. The stability and uniformity of the FPA have been demonstrated.
Part of the book: Two-dimensional Materials for Photodetector
We present the results of growth of CdTe layer on (013)GaAs substrate. The sequence processes include the preparation of GaAs surface by chemical etching and annealing in ultra-high vacuum, the growth of ZnTe layer on atomically clean GaAs surface and then the growth of CdTe layer on ZnTe/GaAs. All processes were carried out without removing GaAs substrate from MBE set. The processes were controlled by RHEED and single wavelength ellipsometry. We found that the evaporation of arsenic oxides and gallium oxides from the (001)GaAs surface were observed at over 400 and 500°C, respectively. The growth of CdTe on (001)GaAs leads to appearance of mixture orientations because of large mismatch of lattice parameters. We study the growth of ZnTe on (001)GaAs and (013)GaAs substrates to prevent the growth of mixture orientations. We study the influence of cadmium and tellurium ratio in molecular fluxes and temperature on the growth mechanism of ZnTe and CdTe, crystal perfection, surface roughness and defects density. The optimal condition for growth of high quality thick CdTe on GaAs substrate were found.
Part of the book: Methods for Film Synthesis and Coating Procedures