CuCl is a I-VII semiconductor material with a direct band gap of ∼3.4 eV. It exhibits a zincblende structure (γ -phase) at low temperatures, up to ∼680 K. Unlike GaN, ZnO and related materials, CuCl has a relatively low lattice mismatch with Si (<0.4%) and a large excitonic binding energy (∼190 meV). This suggests the possibility of the fabrication of excitonic-based blue/UV optoelectronic devices on Si with relatively low threading dislocation densities. In this study, CuCl has been deposited and examined as a candidate material for the fabrication of these devices. X-ray diffraction (XRD) measurements confirmed that the deposited films were preferentially oriented in the (1 1 1) plane. Room temperature photoluminescence measurements reveal a strong Z 3 free exciton peak (3.232 eV). Both steady state dc and ac impedance spectroscopy experiments suggested that the deposited CuCl is a mixed ionic-electronic semiconductor material. An electronic conductivity of the order of 2.3 × 10 −7 S cm −1 was deduced to be in coexistence with Cu + ionic conductivity using irreversible electrodes (Au), while a total conductivity of the order of 6.5 × 10 −7 S cm −1 was obtained using reversible electrodes (Cu) at room temperature. Further to this, we have identified some of the challenges in fabricating an optoelectronic device based on a CuCl/Si hybrid platform and propose some possible solutions.
Optoelectronic technology frequently demands optically transparent materials. In this paper we present an overview of the development of ultrathin chromium films of above 80% optical transparency and 10 2 -10 3 mV cm resistivity using bipolar pulsed dc magnetron sputtering. The surface morphology and film resistivity are investigated using atomic force microscopy (AFM) and four point probe, respectively. The variation of the electrical properties of the film with thickness, pulse duty cycle and target power are examined. An optimal experimental condition is suggested for developing transparent metal contacts, which can be used for the realisation of optoelectronic devices including organic light-emitting diodes on flexible, low cost polymeric substrates. This process does not require high temperature and post-deposition annealing unlike other transparent conducting oxides.
g-CuCl semiconductor material has been identified as a candidate material for the fabrication of blue-UV optoelectronic devices on Si substrates due to its outstanding electronic, lattice and optical properties. However, CuCl thin films oxidise completely into oxyhalides of Cu II within a few days of exposure to air. Conventional encapsulation of thin g-CuCl by sealed glass at a deposition/curing temperature greater than 250 1C cannot be used because CuCl interacts chemically with Si substrates when heated above that temperature. In this study we have investigated the behaviour of three candidate dielectric materials for use as protective layers for the heteroepitaxial growth of g-CuCl on Si substrates: SiO 2 deposited by plasma-enhanced chemical vapour deposition (PECVD), organic polysilsesquioxane-based spin on glass material (PSSQ) and cyclo olefin copolymer (COC) thermoplastic-based material. The optical properties (UV/Vis and IR) of the capped luminescent CuCl films were studied as a function of time, up to 28 days and compared with bare uncapped films. The results clearly show the efficiency of the protective layers. Both COC and the PSSQ layer prevented CuCl film from oxidising while SiO 2 delayed the effect of oxidation. The dielectric constant of the three protective layers was evaluated at 1 MHz to be 2.3, 3.6 and 6.9 for C0C, SiO 2 and PSSQ, respectively.
γ-CuBr is a I-VII wide bandgap mixed ionic-electronic semiconducting material with light emitting properties suitable for novel UV/blue light applications. Its structural and physical properties allow for vacuum deposition on a variety of substrates and herein we report on the deposition of γ-CuBr on Si and Indium Tin Oxide (ITO) coated glass substrates via vacuum evaporation with controllable film thickness from 100 nm to 500 nm. Temperature dependent Photoluminescence (PL) characteristics of these γ-CuBr films on Si (100) reveals familiar Z f and I 1 excitonic features. A Thin Film Electroluminescent Device (TFELD) using a γ-CuBr active layer was fabricated and the room temperature Electroluminescence (EL) was obtained for γ-CuBr for the first time. CuBr features relating to known excitonic (Z f , 3.1 eV) emissions were observed as well as a number of previously unknown emissions at 3.81 eV, 3.02 eV, 2.9 eV, 2.75 eV, and 2.1 eV. We speculate on the origins of these peaks and attribute them to the presence of monovalent Cu+ generated during a.c. excitation.
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