The Investigation Of Cu₂O Thin Films Growth Using Pulsed Laser Deposition

Cu₂O i s regarded as one of the promising materials fo rphotovoltaic application due to its low cost, nontoxicity, and highabsorption coefficient in the visible region. Because of the fil morientation and microstructure were not well controlled in most of theprevious investigations of Cu₂O thin film growth, Cu₂O-based p-nheterojunctions have not de monstrated good photovoltaic performance.In this paper, the Cu₂O films were successfully prepared on MgOsubstrate by pulsed laser deposition （PLD） with a CuO target. Thesa mples were studied by in situ X-ray photoelectron spectroscopy（XPS）, in situ reflection high energy electron diffraction （RHEED）,X-ray diffraction （XRD）, atomic force microscopy, UV-visible-nearinfrared spectroscopy and so on. The band alignment of Cu₂O/Zn Oheterostructure was also determined by XPS. Finally we obtained thefollowing results:（1） The growth of thin films on MgO （001） substrates underdifferent temperatures without inlet oxygen was studied. We deter minedthe sample structure by in situ RHEED and non-situ XRD， which showfil ms are two-domain structure. The out-plane orientation relationshipbetween the films and the substrates is Cu₂O （011）||MgO （001）,in-plane orientation relationships are Cu₂O [100]||MgO [110] andCu₂O [100]||MgO [1-10]. Ac cording to the phase diagram, surface fr eeenergy, lattice mismatch and symmetry misma tch, we discussed themechanism of the film deposition in detail.（2） The growth of thin fil ms at500°C with different oxyge npressure of on MgO （110） substrates was studied. In-Situ RHEED fou ndthat the Metal Cu exist at the initial stage without inlet oxygen,gradually changed to Cu₂O during growth; when the O2was inlet intothe chamber, the film component is Cu₂O during all the growth process.The orientation of Cu₂O films is completely consistent with the substrates when suitable oxygen was inlet, i.e. the out-plane orientationis （110）||MgO （110）; in-plane orientation isCu₂O [1-10]||MgO [1-10].（3） Cu₂O/ZnO heterostructures were grown on c-Al₂O₃substratesby PLD, the orientation relationship is Cu₂O（110）||ZnO（0002）||Al₂O₃（0001）. The type Ⅱ band alignment was deter mined by XPS, thevalence band offset （Ev） is1.97eV and the conduction band offse t（Ec） is0.77eV. We note that the higher conduction band of the Cu₂Oin the obtained alignments shows that the heterojunctions are suitablefor solar cell application based on energy levels consideration.