Investigation of Free Space Optical Detection Module Operating at the Wavelength Range of 8-12 μm
The paper presents the construction and test results of a long-term radiation detector module for free space optical communication operated at the wavelength range of 8–12 μm. In the module a Polish detector manufactured in the company Vigo System S.A. was applied. High sensitivity of the detection module was achieved through a multi-layered heterostructure HgCdTe with immersion lens, which is optimized for the radiation detection at the wavelength of 10 μm. Detector noises were reduced as a result of detector cooling by means of four-stage thermoelectric cooler. The developed detection module is dedicated to design a next-generation optical data link. The link will be characterized by a greater range in difficult weather conditions in relation to the currently offered links operating at the shorter wavelengths.
Progress in MOCVD growth of HgCdTe heterostructures for uncooled infrared photodetectors
Abstract This paper describes the significant progress in the development of metalorganic chemical vapour deposition of Hg 1− x Cd x Te (HgCdTe) multilayer heterostructures on GaAs/CdTe substrates for uncooled infrared photodetectors. The paper focuses on the interdiffused multilayer process (IMP). The optimum conditions for the growth of single layers and complex multilayer heterostructures have been established. One of the crucial stages of HgCdTe epitaxy is CdTe nucleation on GaAs substrate. Successful composite substrates have been obtained with suitable substrate preparation, liner and susceptor treatment, proper control of background fluxes and appropriate nucleation conditions. Epiready (1 0 0) GaAs wafers with 2–4° disorientation towards 〈1 0 0〉 and 〈1 1 0〉 have been used. Due to the large mismatch between GaAs and CdTe, both (1 0 0) and (1 1 1) growth may occur. Generally, layers with orientation (1 0 0) show superior morphology compared to (1 1 1), but they are also characterized by hillocks. The benefits of the precursors, ethyl iodine (EI) and arsine (AsH 3 ), for controlled iodine donor doping and arsenic acceptor doping at dopant concentrations relevant for HgCdTe junction devices are summarized. In situ anneal seems to be sufficient for iodine doping at any required level. In contrast, efficient As doping with near 100% activation requires ex situ anneal at near saturated mercury vapours. Finally, the multilayer fully doped heterostructures for photovoltaic devices operated at room temperature have been fabricated. The special attention is focused on the improvement in multijunction LWIR photovoltaic detectors. The performance of photodiodes is also presented.
Organic–inorganic hybrid materials. I. Characterization and degradation of poly(imide–silica) hybrids
Poly(imide–silica) hybrid materials with covalent bonds were prepared by (3-aminopropyl)methyldiethoxysilane (APrMDEOS) terminated amic acid, water, and tetramethoxysilane (TMOS) via a sol–gel technique. Infrared (IR), 29Si and 13C CP/MAS nuclear magnetic resonance (NMR) spectroscopy, and thermogravimetric analysis (TGA) were used to study hybrids containing various proportions of TMOS and hydrolysis ratios. The microstructure and chain mobility of hybrids were investigated by proton spin–spin relaxation T2 measurements. The apparent activation energy Ea for degradation of hybrids in air was studied by the van Krevelen method. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2275–2284, 1999