Ferromagnetic properties of Cu-doped ZnO thin films according to the substrate temperature

Abstract

ABSTRACT

Ferromagnetic properties of Cu-doped ZnO thin films according to the substrate temperature

Lee, Yong Su Dept. of Physic The Graduate School Hanyang University Diluted magnetic semiconductors are semiconductors with magnetic properties in which transition-metal (TM) cations are substituted into the host semiconductor materials. Recently TM-doped ZnO has been intensively studied as a promising candidate material with a view to stable room-temperature operational spintronics. ZnO is one of II-VI compound semiconductors for such applications. It has wide bandgap (~ 3.37 eV at room temperature) and a high exciton binding energy (60 meV), assuring more efficient excitonic emission at high temperatures. Despite many researchers have tried to figure out the nature of room-temperature ferromagnetism (RTFM), there is no definite evidence of RTFM until now. To understand the origin of RTFM of ZnO, I investigated the physical properties of Cu-doped ZnO and compare them with previously studied systems such as ZnCoO and ZnMnO. By using various growth parameters such as background gas pressure and substrate temperature, I fabricated Cu-doped ZnO film on an Al2O3 (111) and Si (100) substrates in a ultrahigh-vacuum sputtering system, and their structural and magnetic properties were measured. All the Cu-doped ZnO thin films with a thickness of about 200 nm were prepared by co-sputtering method by using Cu chips (radius ~ 1 mm), which is embedded at the center of ZnO target. The Cu composition of films was analyzed by secondary ion mass spectrometry, turning out to be about 2% (3 Cu chips used). The structural properties were checked by x-ray diffraction (XRD). To investigate the magnetic properties, a superconducting quantum interference device magnetometer was employed. The XRD results of samples show excellent crystalline and preferentially well-grown along the c-axis. As the substrate temperature increases, the intensity of (101) peak tends to decrease, but there is abrupt increases at 300℃. At the same time, the positions of (002) and (101) peaks shift to higher angles. The magnetic hysteresis loops of films were measured at room temperature. All the films show evident RTFM, and the film deposited at 100℃ exhibits the best result. The magnetic moment tends to decrease and the coercivity increases at elevated substrate temperatures. It was found that the magnetic properties and the structures of films are very sensitive to the substrate temperature during the deposition, the correlations between magnetic properties and crystalline structures are elucidated.