Fabrication And Properties Study Of In-based Nitride And Oxide And Cu-based Oxide Thin Films

Thin film materials is the use of special technical means, artificially preparedone-dimensional scale was significantly less than the other two scales, with specificproperties and uses. In recent years, In-based nitride and oxide and Cu-based oxidethin films have been widely studied and used in optical and electronic devices, dilutedmagnetic semiconductor, solar cell, electrode material, dielectric materials, catalysts,sensors and many other fields. InN is an important component of group III nitridesemiconductor, especially the bandgap was revised to0.7of eV in2003, has receivedmore and more attention. However, the growth of InN is the most difficult owing tothe fact that the InN decomposition temperature is low. Moreover, InN layers grownon common substrates suffer from the high density of defects due to lattice-andthermal expansion coefficient-mismatch. In₂O₃is a important transparent conductiveoxide thin films （TCO） with once widely quoted bandgap as around3.75eV. Veryrecently, cubic In₂O₃was found to have a direct bandgap of2.6eV. A promisingapproach to improve the electrical properties of In₂O₃thin films is the growth of highquality In₂O₃with extrinsic dopants such as Ti.Copper is a common element in life, rich source, non-toxic, low preparationcost and the oxide thin film materials are mainly including CuO and Cu₂O. The Cu₂Ohas bandgap of2eV matching with the solar spectrum and has higher photoelectricconversion efficiency. In order to enhance its application, the Cu₂O is usuallycombined with TCO to form heterojunction in terms of photocatalysis and solar cells.Besides, the band offsets is an important factor that affects the function of theheterojunction device. Although the photocatalytic activity of the Cu₂O/In₂O₃wasmuch higher than that of In₂O₃on the photocatalytic reduction of Cr₂O₇^2-, but there is no corresponding band offsets reports. We used x-ray photoelectron spectroscopy todetermine the valence band offset （VBO） of a Cu₂O/In₂O₃heterojunction and finallydetermine the band alignment accurately based on the VBO and conduction bandoffset （CBO）. CuAlO₂with delafossion structure is a p-type transparent conductingoxide. So far, many techniques have been used to synthesize CuAlO₂films, but thestructure and properties are very different. Up to now, the preparation of CuAlO₂withexcellent properties always is still very difficult. Fruthermore, there are two possibledoping position for CuAlO₂by transition metal to prepare diluted magneticsemiconductors（DMSs）, namely Cu¹⁺and Al³⁺. Recently, theoretical first-principlescalculations based on CuAlO₂show that the ferromagnetic states of （Cu,Co）AlO₂arehighly stable, which makes them candidates for ferromagnetic DMSs.In this thesis, we successfully synthesized InN, Ti-doped In₂O₃and Cu₂O/In₂O₃heterojunction by magnetron sputtering. Meanwhile, Co-doped CuAlO₂thin films aresynthesized by solid-state reaction from Cu₂O and Al2O3using a spin-on technique.The properties of these films have been analyzed and the main research processesachieved have been summarized as following:（1）The InN thin films were deposited on Si（111）, AlN/Si（111） andAl_0.24In_0.76N/AlN/Si（111） substrate by radio-frequency （RF） magnetron sputtering at300℃. All the InN films are investigated to hexahonal wurtzite phase regardlesssubstrate. The indium content in In-rich AlInN layer was estimated to be about0.76by Vegard’s law based on XRD spectrum. The thicknesses of the AlN buffer, In-richAlInN layer and InN film with oxygen impurity were approximately100nm,50nm,and1000nm, respectively. Note that the peak at2θ=33.11°corresponding to metallicindium clusters（In（101）） is detected for InN deposited on Si（111）, but it does notappear whenever there is a buffer between the substrate and InN film. Actually, thepoor quality of InN is also probably attributable to an amorphous layer of SiNxoriginating from unintended nitridation of the substrate surface during growth. Withthe Al_0.24In_0.76N layer, the XRD peak position of InN （002） films shift to lower angleand the full-width at half-maximum （FWHM） decreases from0.298°to0.219°, bothmuch smaller than for InN films on bare Si（111）. With buffer, the intensity of the E₂ peak at around487cm-1slightly increases in Raman spectroscopy, evidencing animprovement of crystalline quality attributed to relaxation of the residual strain in theInN films.（2） Titanium-doped indium oxide （In₂O₃） transparent conductive thin films weredeposited on glass and sapphire （0001） substrates with/without oxygen atmosphere byDC magnetron sputtering at300°C. The content of titanium is estimated to be about1.8%using energy dispersive spectroscopy. It is seen that the surface is smooth andwell covered with uniformly distributed grains. X-ray diffraction measurementsindicated that the preferential growth orientation along the （400） plane for the samplegrown without oxygen atmosphere shifts to （222） for the sample grown in the oxygenatmosphere. The higher transmittance in excess of90%is obtained by Ti-dopedIn₂O₃films deposited on the glass with oxygen atmosphere corresponding to70%forthe sample grown without oxygen. However, the average optical transmittance of85%is achieved regardless of oxygen atmosphere for Ti-doped In₂O₃films depositedon the sapphire substrate. The change of optical transmittance is mainly due to theinfluence of carrier and mobility. After introduction of oxygen flow, the carrierconcentrations of the films decrease, whereas the electron mobility is improved.（3） The Cu₂O/In₂O₃heterojunction was deposited on sapphire substrates in aradio-frequency magnetron sputtering system. We used x-ray photoelectronspectroscopy to determine the valence band offset （VBO） of a Cu₂O/In₂O₃heterojunction. Finally, the Cu₂O/In₂O₃heterojunction with a5nm Cu₂O overlayerwas grown on a500nm In₂O₃underlayer with orientation relation ofCu₂O（111）|In₂O₃（222）|sapphire（0006）. The valence band offset is found to be1.43±0.2eV eV. Given the experimental bandgaps of2.0eV and2.6eV for Cu₂O andIn₂O₃, respectively, we calculate the band alignment of a Cu₂O/In₂O₃heterojunctionwith a conduction band offset （CBO） of0.83±0.2eV. If the badgap of In₂O₃isquoted as3.75eV, the conduction band offset is calculated to be0.32±0.2eV. Theunderlayer In₂O₃in the heterojunction is thick enough to be completely relaxed. Inaddition, the overlayer Cu₂O thin film of our Cu₂O/In₂O₃sample is as thick as5nm,and so can be treated as being completely relaxed. As such, the strain-induced piezoelectric field effect can be neglected here. Another factor that may remarkablyaffect the performance of Cu₂O/In₂O₃heterojunctions is the interface defects andother properties involved in quality. The band alignment diagram of the Cu₂O/In₂O₃heterojunction has been determined based upon the measured results.（4） We synthesized thin films of CuAl1-xCo_xO₂（x=0.00-0.07） on a sapphiresubstrate using a spin-on technique assisted by proper EC and terpineol solvent at1150°C. The samples are all single-phase delafossite CuAlO₂with an averageheight of around5μm. The analysis suggests that Co is present in the+2oxidationstate in the Co-doped CuAlO₂matrix and Co ions substitute for the Al site but not theCu. The magnetic measurements of the pristine CuAlO₂sample show nearly straightlines indicating diamagnetism. Conversely, the M-H loops with Co-doped CuAlO₂have a well-defined S-shape, convincingly showing ferromagnetic ordering at roomtemperature. The observed ferromagnetism is essentially intrinsic to some extentbecause all samples are single-phase delafossite. The highest Msobserved is0.110emu/g for5%Co-doped CuAlO₂film, and the corresponding remnant magnetizations（Mr） is about0.019emu/g.In this thesis, InN, Ti-doped In₂O₃, Cu₂O/In₂O₃heterojunction and Co-dopedCuAlO₂thin films are prepared and studied. The results not only provide anexperimetnal basis for further preparation and properties study but also are greatsignificance for realization widely used of these films.