Study On Preparation And Characterization Of Inorganic Terahertz-Absorbing Materials

Terahertz (THz) band as a blank area of the research, due to its advantages inperspective, security and other aspects, has been developed greatly in recent decades.People gradually studied from the light wave and electromagnetic wave toward themiddle of the terahertz band, and THz detectors has attratced great attention. In thisthesis, we mainly focus on the THz absorption materials for uncooled THz detectors.Using electron beam evaporation method, TiO_x, Ti, and Ti/SiN_xfilms wereprepared. Such materials were prepared under different conditions, and theirmorphology, crystallinity, optical and electrical properties, and THz response werecharacterized by scanning electron microscopy (SEM), X-ray diffraction analyzer(XRD), UV-visible photometer, four-probe square resistance meter, Fourier infraredspectrometer. The main results include:(1) Coating types of substrate, deposition time, annealing conditions haveinfluences on both optical and quality of TiO_xfilms. Absorption coefficient of a150nm-thick TiO_xfilm in the THz band is in10~3. Annealed TiO_xfilms have higherdensity, and titanium has been re-oxidated to TiO_xin the annealing process. Increasedoxygen content is helpful for improve the absorption of TiO_xfilms in7.68~7.86THzband. Ti-O bonds have great impact in the absorption.(2) The thinner titanium (Ti) film, the higher degree of oxidation. When thethickness is10nm, absorption coefficient will be as high as10~5orders of magnitude,but the degree of oxidation in Ti is lower than in TiO_xfilms. The absorption coefficientof180nm-thick Ti film is10~4orders of magnitude, which is higher than that10~3magnitude of150nm-thick TiO_xfilm. Incorporation of oxygen in the Ti film isconducive to the incearse of the THz response, but if the oxygen content is too high, theTHZ absorption will be decreased.(3) Absorption coefficient of Ti/SiN_xsuperlattices is in10~4orders of magnitude.Due to not ideal thin film thickness control or less repetitive cycles, imperfect periodicstructures might be in our work. This weakenes the performance of quantum well, and leads to low absorption coefficients. But the frequency absorption peak of first Brillouinzone measured in our work is agreed well with those theoretically predicted. Theas-prepared superlattices play a role in promoting the THz absorption. With furtherimproving the key parameters, such as strict control of the uniformity of film thickness,increaseing the coating cycle and so on, new superlattice THz materials with higherTHz absorption and more suitable for application in detectors might be developed.