Optical And Electrical Properties Of Quantum Well Infrared Detectors And Infrared Materials Research

The study on the GaAs/AlGaAs quantum well infrared photodetector (QWIP) is a hotspot in the field of the research on infrared materials and infrared apparatus. By selecting the different structure parameters such as the width of the well and the barrier layers, and the barrier Al mole fraction, the energy band structure of the material can be changed to satisfied the need of the detector.In this thesis, the photo-electric properties of GaAs/AlGaAs quantum well infrared detectors are studied and the optical properties of the GaAs/AlGaAs quantum well materials and a new ferroelectric crystal — Ca_0.28Ba_0.72Nb₂O₆ (CBN-28) crystal are investigated. The main contents includes:(1) The relations between the structure parameters of GaAs/AlGaAs quantum well material and the performance of the infrared detector is investigated, by using the K-P model and the interference model of the electron waves. The result shows that there is a conversion from the superlattice material to the multi-quantum wells material along with the width of the barrier increasing. The peak wavelength are decreased with the width of the well and the barrier Al content increasing.(2) The optical properties of the Cr doped semi-insulating GaAs and the GaAs/AlGaAs quantum well material are studied using the spectroscopic ellipsometry. The optical constants of these two materials such as the refractive index, the extinction coefficient and the dielectric constant, as a function of the photon energy are obtained. As a result, there is no remarkable difference in the optical constants between the intrinsic and the Cr doped GaAs. The refractive index and the dielectric constant become small after doping. As to the quantum well material, intersubband transition resulting from the transition between the heavy hole state and the electric state is observed, which can show the quantum limited effect. Compared to the 'bulk' material, the refractive index and the extinction coefficients are decreased.(3) According to the need of the quantum well infrared photodetectors, Then the suitable structure parameters such as the well width and the barrier width, the barrier Alcontent and the doping density in well etc. are selected. And according to our design, the GaAs/AlGaAs quantum well materials are grown. The photocurrent and the infrared absorption spectrum of the samples are measured respectively. The measured results are in good agreement with theoretical calculated data. This provides the optimum method of designing the structure of materials.(4) Furthermore, we compare the performance of the quantum well photodetectors with the HgCdTe photodetector's. The mechanisms of detection in quantum well infrared detectors and the HgCdTe photodetector are analysised and the advantages and limitations of two types of detector technologies for LWIR FPA applications are clarified.(5) Optical properties of the novel single Cao^gBao.72Nb206(CBN-28) crystal in the room temperature are investigated. The transmission and refractive index of Cao78Bao.72Nb206 as a function of wavelength are measured by the double beam spectrophotometer and the spectroscopic ellipsometry respectively. The normal dispersions were observed. And the ordinary refractive index no is larger than the extraordinary index ne, which indicates that this crystal is a minus uniaxial crystal. The dispersion curves display that the birefringence is up to about 0.12 in the short wavelength range. The transmission spectrum demonstrates that this crystal is transparent from 400nm to 900nm. According to the transmittance, the absorption coefficient and its square root were calculated. The direct and indirect energy gap and phonon energy for this crystal have been estimated respectively. As a result, the band gap is 3.33eV, and the indirect band gap energy is 2.94eV with the phonon energy 0.17eV. By changing the directions of vibrations of the polarizer in the optical system, the transmission spectra of the ordinary light and the extraordinary light are obtained. And the absorption coefficients of these two lights are calculated.