The Refractive Index and Other Properties of Doped ZnO films
- PDF / 747,309 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 94 Downloads / 187 Views
C3.21.1
The Refractive Index and Other Properties of Doped ZnO films A. L. Cai, J. F. Muth* Department of Electrical and Computer Engineering North Carolina State University, Raleigh, NC 27695 H. L. Porter, A. Kvit, J. Narayan Department of Materials Science and Engineering North Carolina State University, Raleigh, NC 27695 ABSTRACT Ordinary and extraordinary indices of refraction, film thickness and waveguide mode information of zinc oxide, zinc oxide doped with nitrogen and zinc oxide doped with tellurium were measured by using a prism coupling waveguide technique. The films were grown on c-axis sapphire substrates by pulsed laser deposition (PLD). High accuracy waveguide measurements show that the ordinary and extraordinary indices of refraction of ZnO samples change with the introduction of nitrogen or tellurium. The densification of films with annealing could also be tracked with precision refractive index measurement. The crystal structure and the optical properties of the films were also characterized by using x-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and cathodoluminescence (CL). INTRODUCTION Recently there have been reports of p-type ZnO thin films1 and p-type ZnO substrates have been sold commercially2. This development suggests that ZnO is a promising material for optoelectronic devices 3. It has a large excitonic binding energy of ~60 meV, which results in extremely efficient emission at room temperature (RT) by optically pumping4. The band gap engineering of ZnO films has been studied by alloying ZnO with Mg and Cd5. Previously we have investigated the absorption edge and refractive index of MgZnO alloys6. In this paper we explore the effects of doping ZnO with nitrogen and alloying with tellurium on the refractive index of ZnO. ZnO has the wurtzite structure and is a uniaxial crystal. The ordinary and extraordinary indices can be obtained by performing the experiment for the transverse electronic (TE) and transverse magnetic (TM) polarization, respectively. Refractive index dispersion of ZnO films has been measured in a variety of ways such as transmission interference spectroscopy7, reflection interference spectroscopy, ellipsometry8 and prism coupling6. The first three methods listed require prior knowledge of the film thickness. Of the methods listed prism coupling is the most accurate for measuring refractive index below the optical absorption edge. When more than one mode is present the thickness and refractive index can be measured to the 4th decimal place 9. In this study we investigate the changes in refractive index that result from the incorporation of nitrogen and tellurium into ZnO. Both of those elements have been proposed as p-type dopants. We also observe changes in refractive index depending on how the ZnO films are grown, with or without an ion gun sputtering the surface, and upon annealing. The films were *
Electronic Mail: [email protected]
Downloaded from https://www.cambridge.org/core. The Librarian-Seeley Historical Library
Data Loading...
