Study Of Preferred Orientations Controlled Growth And Band Alignment For ZnO-based Materials And Heteroiunctions

ZnO has a hexagonal wurtzite structure and grows preferentially along the [0001] direction, which leads to strong spontaneous and piezoelectric polarization fields along the c-axis and as a result, reduces the internal quantum efficiency of devices. It is suggested that the growth of nonpolar and semipolar films can eliminate/suppress the polarization effects. On the other hand, there are still many problems remained for p-type ZnO. In recent years, group-I elements such as Li, Na have been proposed as dopant instead of N. Alternatively, as the p-type GaN or NiO is chosed for ZnO-based heterojunctions, the measurements of the valence band offsets (VBOs) and the determination of band alignment at interface will be of crucial important.In this thesis, we produced two kinds of NiO/ZnO p-n junctions on nonpolar r-plane sapphire and quartz substrates by pulsed laser deposition (PLD). Their VBOs are measured and the band alignments are determined. The revealed ZnO-orientation dependent band offsets are analyzed. Additionally, nonpolar p-type Zn(Mn, Na)O films are prepared on R-plane sapphire. Semipolar ZnO films are also obtained on various amorphous substrates through (Co, Ga) or Mn-Li cododing. The main work included:1. Nonpolor a-plane and polar c-plane ZnO thin films were prepared on r-plane sapphire and quartz substrates, respectively. We have determined the VBOs for the NiO(111)/ZnO (1120) and NiO(111)/ZnO(0002) systems. Type-Ⅱ band alignments are formed at the interfaces for both the samples with VBOs of1.54±0.1eV (and CBO of1.98±0.1eV) and1.32±0.1eV (and CBO of1.73±0.1eV), respectively. The variations in VBOs between the two heteroj unctions are attributed to ZnO-orientation dependant spontaneous polarization effect.2. Non-polar Zn(Mn, Na)O thin films were deposited on r-plane sapphire substrates with various Na doping concentration by pulsed laser deposition (PLD). The results indicate that high growth pressure was harmful for the nonpolar growth of ZnO-based films and meanwhile, the conduction polarity changed from n-type to p-type with the increasing of growth pressure. It was found that the films with2%Na concentration showed the best quality.3. Co-Ga codoped semipolar ZnO thin films were prepared on quartz substrates by PLD. Contradictory to that on crystal substrates, the increasing of growth pressure can promote the tendency of change in PO from c-axis to semipolar axes. The substrates are found have great influence on the growth orientation of the films. After that, semipolar Zn(Mn, Li)O thin films were fabricated and pure semipolar ZnO were prepared using the Zn(Mn, Li)O films as a buffer layer. The processing-texture relationship, doping effect and the growth mechanism are well elucidated.