Research On Lattice Mismatch And Biaxial Stress In ZnO Thin Films And Related Devices

Zinc oxide (ZnO) is a dirct wide band gap (3.37 eV) semiconductor and has a binding energy of exciton as high as 60meV at room temperature (RT), which has attracted much attention as a strong candidate for ultraviolet light emitting diode and lasing diode. However, there are still some unsolved problems limiting its further application in optoelectric field. The problems are as follows:(1)High quality ZnO thin film is very important for realizing high-efficient UV emission of LED. However, the lack of good lattice-matched and thermal-matched substrates influences the crystal quality of ZnO thin film and limits its further application in optoelectron field.(2)High quality heterostructure, which can efficiently confine carriers and photons in well layer, is necessary for obtaining LED or LD with high performance. However, the quality of the interface between barrier and well layers is still problem due to lattice-mismatch.(3)Reproducialbe, High quality and low resitivity p-type ZnO thin film is expected to realize UV LED. However, the poor quality of p-type ZnO thin film hampered the realization of UV emission in ZnO-based material.According to the present research difficulties on ZnO, we pay much attention to the lattice-mismatch, biaxial stress,p-type MgZnO films and ZnO-based heterostructure LED in this thesis. The details are as follows:(1)Characteristics of biaxial stress in ZnO thin film is investigated by side-inclination x-ray diffraction method and Raman spectroscopy. The origin of biaxial stress in ZnO film grown on quartz substrate is clarified. The effect of biaxial stress on optical properties of ZnO film is also studied by combining experiment with first-priciple. The influence of biaxial stress on electronic structure is discussed in detail.(2)MgZnO and Nitrogen-doped MgZnO alloy thin films are fabricated by P-MBE. Electron concentration of MgZnO alloy film decreases with the increase of Mg content due to shift of conduction band minimum to high energy. Nitrogen p-type MgZnO alloy thin films are obtained.(3)ZnO/MgZnO-based heterostructure UV LED and photodiode are fabricated on n-GaN, Si and sapphire substrates by P-MBE. The influence of lattice-mismatch on the performance of ZnO-based heterostructure optoelectinc devices has been investigated in detail.