Cuprous oxide (Cu2O) was first investigated in the 1920s as a semiconductor material with Eg~2.17 eV. It is ideal for applications in solar cells, electrochromic devices, oxygen and humidity sensors because of its high optical absorption coefficient, non-toxic nature, abundant availability and low cost for production. Many groups have tried different ways to grow the cuprous oxide by, for instance, sputtering, CVD, PLD, MBE, and electro-deposition etc. Among them, the sputtering method is probably the most cost-effective and easy to operate. In this work, the cuprous oxide thin films were grown on R-Al2O3 and (110)-MgO substrates by DC reactive magnetron sputtering. Thin films grown at different temperatures under various oxygen partial pressures were studied by X-ray diffraction (XRD) to test their structural perfections. Samples with the Cu2O on Al2O3(1012) and MgO(110) were studied via measurement of cathodoluminescence(CL) spectroscopy, photoluminescence (PL) spectroscopy, transmission spectroscopy and magneto transport behaviors. The correlation of growth condition and physical properties are discussed.

Polycrystalline p-Cu2O were fabricated by reactive rf magnetron sputtering . we found that The electrical, optical, and crystallographical properties of films were strongly dependent on the deposition condition . Grant size increasing in the range from 10 to 45nm , A hole concentration increasing in the range from 1016 to 1017 cm-3 and a mobility increasing on the order of 10-1 cm2/V s were obtained in the cuprous oxide thin film prepared by controlling work pressure (Argon partial partial pressure ) . Fabricated thin-film heterojunction diodes consisting of a p-type cuprous oxide combined with and n-type Al-doped ZnO and ITO exhibited a rectifying current-voltage characteristic .

Thesis--Ph. D., University of Hong Kong, 1981. / Cover title.

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The rapid progress of n-type metal oxide thin film transistors (TFTs) has motivated research on p-type metal oxide TFTs in order to realise metal oxide-based CMOS circuits which enable low power consumption large-area electronics. Cuprous oxide (Cu2O) has previously been proposed as a suitable active layer for p-type metal oxide TFTs. The two most significant challenges for achieving good quality Cu2O TFTs are to overcome the low field-effect mobility and an unacceptably high off-state current that are a feature of devices that have been reported to date. This dissertation focuses on improving the carrier mobility, and identifying the main origins of the low field-effect mobility and high off-state current in Cu2O TFTs. This work has three major findings. The first major outcome is a demonstration that vacuum annealing can be used to improve the carrier mobility in Cu2O without phase conversion, such as oxidation (CuO) or oxide reduction (Cu). In order to allow an in-depth discussion on the main origins of the very low carrier mobility in as-deposited films and the mobility enhancement by annealing, a quantitative analysis of the relative dominance of the main conduction mechanisms (i.e. trap-limited and grain-boundary-limited conduction) is performed. This shows that the low carrier mobility of as-deposited Cu2O is due to significant grain-boundary-limited conduction. In contrast, after annealing, grain-boundary-limited conduction becomes insignificant due to a considerable reduction in the energy barrier height at grain boundaries, and therefore trap-limited conduction dominates. A further mobility improvement by an increase in annealing temperature is explained by a reduction in the effect of trap-limited conduction resulting from a decrease in tail state density. The second major outcome of this work is the observation that grain orientation ([111] or [100] direction) of sputter-deposited Cu2O can be varied by control of the incident ion-to-Cu flux ratio. Using this technique, a systematic investigation on the effect of grain orientation on carrier mobility in Cu2O thin films is presented, which shows that the [100] Cu2O grain orientation is more favourable for realising a high carrier mobility. In the third and final outcome of this thesis, the temperature dependence of the drain current as a function of gate voltage along with the C-V characteristics reveals that minority carriers (electrons) cause the high off-state current in Cu2O TFTs. In addition, it is observed that an abrupt lowering of the activation energy and pinning of the Fermi energy occur in the off-state, which is attributed to subgap states at 0.38 eV below the conduction band minimum. These findings provide readers with the understanding of the main origins of the low carrier mobility and high off-state current in Cu2O TFTs, and the future research direction for resolving these problems.

Doctor of Philosophy / Antimicrobial coatings can inhibit the spread, via surfaces, of various diseases that infect humans. Antimicrobial coatings are useful because they can continue to kill pathogens (germs) for a long time after the surface is coated. This is a big improvement over use of common disinfectants that must be applied continuously. The main goal of this dissertation research is to develop various surface coatings that are antimicrobial and can provide a rapid killing of germs. We demonstrate 6 different antimicrobial coatings that rapidly inactivate a wide variety of pathogens, such as the most recent coronavirus, drug-resistant bacteria, or fungi. The antimicrobial coatings were composed of a variety of adhesives and active antimicrobial ingredients. Traditional adhesives and recently-invented adhesives were incorporated into the coatings, and active ingredients included copper, copper oxide, or zinc oxide. In short, our coatings provide a short killing period of a few minutes to one hour. Additionally, we investigated the mechanism of action of copper oxide surface coatings, and determined that the proximity of microbial cells to an antimicrobial surface is the key to inactivation or killing of the pathogen. Also, we measured the transfer of the most recent coronavirus from solid surfaces to skin under various conditions. We found that a substantial quantity of the virus is transferred to skin. More specifically, when the virus-infected droplet is still wet, a higher percentage is transferred from the solid to skin. In addition, we composed a review of the scientific literature on antimicrobial coatings with a focus on coatings and methods that inactivate the coronavirus.

Recently, ZnO has garnered widespread attention in the semiconductor community for its large set of useful properties, which include a wide bandgap and its resulting optical transparency, a large exciton binding energy, a significant piezoelectric response, and good electrical conductivity. In many ways, it shares many properties with a widely used and technologically important semiconductor GaN, which is widely used for blue LEDs and lasers. However, ZnO cannot substitute for GaN in most optoelectronic applications, because it cannot be doped p-type. On the other hand, unlike many traditional, covalently bonded semiconductors like GaN, ZnO can be easily formed aqueous solutions at close to room temperature and pressure in the form of large crystals or a variety of nanostructures, making possible applications that are normally very difficult with traditional semiconductors. In this light, we aimed to take advantage of aqueous solution-based, ZnO growth techniques and incorporated ZnO structures novel optoelectronic and photonic structures. By controlling the morphology of ZnO, we studied the effects of nanowire-based \(ZnO/Cu_2O\) solar cells. Carrier collection was increased using a nanowire-based device architecture. The main result, however, was the time evolution of the performance of these devices due to the movement of ionized defects in the material. The effects of geometry on the ageing characteristics were studied, which showed that the carrier collection could be increased further with ageing in a nanowire \(Cu_2O\) solar cell. The aging behavior was substantially different between nanowire and planar solar cells, which implies that future design of nanostructured solar cells must long term aging effects. In addition to solar cells, we explored the possibilities of using aqueous solution growth of ZnO to fabricated whispering gallery mode optical cavities and waveguides for enhancing extraction from a single photon source. In both applications, we used templated growth of ZnO to fabricate geometrically (near) perfect rods and disks for these photonics applications. Finally, since epitaxy is important in the process of optimizing device performance and fabrication, we showed the ability to grow ZnO epitaxially on single crystalline plates of Au, expanding the options of epitaxial substrates to include a metal. / Engineering and Applied Sciences

Solar cells based on CdTe absorbers are attractive due to the optimal direct band gap energy and large absorption coefficient of CdTe, however, their performance and commercialization is hindered by the lack of reliable p-type contacts. CdTe has a low carrier concentration and a large electron affinity, which results in a requirement of non-realistic work functions for metals to be used as back contacts in the solar cell. Even noble metals such as Ag present a significantly large potential barrier for holes, thereby reducing the hole current through the semiconductor/metal interface. Several attempts to resolve this challenge have been tried, however, many drawbacks have been encountered. Two particular systems, namely Cu2Te thin films and CdTe/ZnTe strained-layer superlattices, are investigated for their potential use as ohmic contacts in CdTe solar cells. A detailed analysis of the optical, electrical, and structural properties of Cu2Te thin films deposited by magnetron sputtering is presented. It is shown that these films have an indirect band gap and highly degenerate semiconductor behavior. The large p-type carrier concentration of Cu2Te films is highly desirable for the application of Cu2Te as a p-type contact to CdTe. In-depth studies of optical transitions and miniband transport in strained-layer CdTe/ZnTe superlattices are presented as well. The band offsets between CdTe and ZnTe were determined by comparison of measured and calculated optical transitions. Superlattice structures that offer best contact performance have been identified by use of tunneling probability simulations. Characterization of CdTe solar cells with above mentioned contacts indicated that contacts based on CdTe/ZnTe superlattices are a viable Cu free option for stable and reliable p-type contacts in CdTe solar cell. The contact performance of Cu2Te thin films was comparable to that of CdTe/ZnTe superlattices and both demonstrated an advantage over contacts based on ZnTe:N thin films which were used a standard.

京都大学 / 新制・課程博士 / 博士(エネルギー科学) / 甲第23396号 / エネ博第423号 / 新制||エネ||80(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー応用科学専攻 / (主査)教授 平藤 哲司, 教授 土井 俊哉, 准教授 三宅 正男 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

V této práci byl popsán princip fotokatalýzy. Práce se soustřeďuje na kovové oxidy, které mají široké využití ve fotokatalytických aplikacích. Bylo také popsáno různé použití fotokatalytických materiálů. Tato práce se zaměřuje zejména na využití fotokatalytických materiálů pro rozklad organických vodu znečisťujících látek. Popsaný fotokatalyzátor je oxid měďný, který má velmi dobré vlastnosti pro rozklad organických látek pomocí fotokatalýzy. Schopnost rozkladu organických látek oxidu měďného byla popsána na rozkladu organického barviva methylová oranž.