A Luminescence Study of Electron-Irradiated ZnO Crystals
- PDF / 307,606 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 104 Downloads / 210 Views
1201-H05-09
A Luminescence Study of Electron-Irradiated ZnO Crystals M.Avella1, O.Martínez1, J. Jiménez1, B.Wang2, P. Drevinsky3, and D. Bliss3 1
GdS Optronlab. Univ. de Valladolid, Paseo de Belén 1, 47011 Valladolid, Spain
2
Solid State Scientific Corp. 27-2 Wright Rd., Hollis, NH 03049
3
Air Force Research Laboratory, Sensors Directorate, Hanscom AFB, MA 01731
ABSTRACT ZnO crystals were irradiated with high energy electrons (1MeV). The main defects created were analyzed by cathodoluminescence (CL) spectroscopy. The main effects of irradiation on the CL spectrum were the partial quenching of the emission, the shift of the visible luminescence to the yellow, and the observation of an additional band and its phonon replicas at ≈3.32 eV. Zinc vacancy related defects are postulated as responsible for the changes induced in the spectrum. INTRODUCTION The understanding of point defects is essential for the management of the electronic and optoelectronic applications of semiconductors. ZnO is a very promising semiconductor for UV optoelectronics, because of its large bandgap (3.3 eV), and its large free exciton binding energy (60 meV). On the other hand, ZnO substrates are available to produce homoepitaxial layers suitable for devices. However, reliable p-type material is not yet available, which prevents the application of ZnO for advanced devices. To achieve successful p-type doping, one needs to improve the knowledge about the native defects, which can complex with impurities and also form compensating levels precluding effective p-type conversion [1]. The role of the native point defects in ZnO is still controversial. High energy e-irradiation is an efficient method to create vacancies and interstitial defects, while luminescence techniques are very useful to study the signature of the defects [2]. However, the luminescence spectrum of e-irradiated ZnO has not reported dramatic spectral changes, which is consistent with the strong radiation hardness of ZnO. Positron annihilation studies have revealed the presence of Zn vacancies under high energy electron irradiation, as the main defects generated by the irradiation [3,4]. Zinc vacancies are acceptors which can compensate the n-type nature of as grown ZnO. We present herein a cathodoluminescence (CL) analysis of ZnO crystals irradiated with high energy electrons. The eirradiation seems mainly generating Zn sublattice primary defects, which interact with the previously existing defects and impurities in the crystal; therefore, the final defects shall depend on the growth conditions and the history of the samples. EXPERIMENTAL DETAILS ZnO wafers from different vendors were irradiated at room temperature with high energy electrons (1 MeV) at fluences of 1017 cm-2. The wafers from vendor 1 (labelled as M) were annealed at 650ºC in 1.4 Torr O2 atmosphere during 0.5 h. Then they were irradiated. Samples from vendor 2 (labelled as TD) were irradiated without previous annealing.
The CL measurements were carried out at 80 K with a XiClone System from Gatan (Gatan UK)
Data Loading...
