Effect of Threading Dislocations on Local Contacts in Epitaxial ZnO Films

Abstract

Local conductance of a ZnO epifilm with a columnar-grain structure was studied by conductive-mode atomic force microscopy. The probe-ZnO junction at the grain boundary with high density edge threading dislocations ͑TDs͒ behaves as a Schottky contact while the junction at the epitaxial core behaves as an ohmic contact, resulting in the nonuniformity of conductance throughout the film. The calculated Schottky barrier is 0.4 Ϯ 0.025 eV. The point defects of doubly charged Zn vacancies accumulated at the edge TDs induce local band bending of ZnO, thus contributing to the Schottky nature at the grain boundary.

Edge dislocation effect on optical properties in wurtzite ZnO

“…It should be noted that the deep-level emission energy associated with dislocations here depends on the strength of electrostatic potential. It can be also related with the electrical activities of point defects accumulated at dislocations, as suggested before [20]. Fig.…”

“…By applying a direct electric field, the movement of GL from anode to cathode indicates that GL is due to complex defects involving zinc interstitials [39]. These point defects can be localized at dislocations due to the strain field, causing the negatively charged dislocations and introducing electronic states within the band gap [20,21,23,34]. Lin et al [20] proposes that doubly charged Zn vacancies accumulated around dislocations contribute to conduction band bending, consistent with Read's model [25].…”

“…In heteroepitaxial ZnO films, due to the large lattice mismatch with substrates, a high dislocation density between n dis ¼10 8 À 10 10 cm À 2 has been commonly observed [20][21][22]. Among three types of threading dislocations (i.e.…”

“…These point defects can be localized at dislocations due to the strain field, causing the negatively charged dislocations and introducing electronic states within the band gap [20,21,23,34]. Lin et al [20] proposes that doubly charged Zn vacancies accumulated around dislocations contribute to conduction band bending, consistent with Read's model [25]. In addition to GL, red luminescence (RL) [27,36,40] at $1.75 eV, and violet luminescence (VL) [36,41,42] at $ 3.1 eV have also been observed.…”

The Role of Edge Dislocations on the Red Luminescence of ZnO Films Deposited by RF‐Sputtering

“…Nowadays ZnO is among other semiconductors, one of the most studied materials, due to the potentialities offered by its wide direct band gap (3.37 eV) at room temperature and high (∼60 meV) free exciton binding energy [1,2]. These characteristics together with the easiness of depositing thin ZnO films by different techniques with a considerable quality make this material a suitable semiconductor for a broad range of applications in optical and electrical devices (light emitting diodes, transparent thin film transistors, and surface acoustic wave systems [2][3][4][5][6]). Despite the increasing interest in this material, a deeper understanding of the role of the structural defects in the oxide host is still necessary, for example, to overcome the difficulties in obtaining p-type conductivity, among others.…”