Refractive Indices of A-plane GaN Thin Films on R-plane Sapphire
- PDF / 1,545,062 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 27 Downloads / 188 Views
0892-FF23-10.1
Refractive Indices of A-plane GaN Thin Films on R-plane Sapphire A. L. Cai, I. P. Wellenius, M. Gerhold, J. F. Muth Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695-7911 A. Osinsky, J. Q. Xie, J. W. Dong. SVT Associates, 7620 Executive Dr., Eden Prairie, MN 55344
Abstract A-plane GaN grown on r-plane sapphire is a promising material for optoelectronic applications such as laser diodes and LEDs. The absence of a built-in electrostatic field in the nonpolar a-plane GaN-based quantum wells can limit the piezoelectric polarization effect and result in higher emission efficiency. The knowledge of the planar anisotropic nature of nonpolar a-plane GaN is important to understand the growth mechanism of a-plane GaN is fundamental for optoelectronic device design. Two a-plane GaN samples were grown on r-plane sapphire, one being grown on intentionally miscut 4 degrees from r-plane sapphire. The films exhibited different surface morphologies and were characterized using imaging cathodoluminescence and SEM. The ordinary and extraordinary indices of a-plane GaN thin film were obtained using a prism-coupling technique. It was found that one sample the c-axis lay in the plane of the thin film as expected, and in the sample grown on miscut sapphire the c-axis was out of the plane of the film.
Introduction Recently, there has been great interest in the growth of a-plane GaN on r-plane sapphire. The absence of a built-in electrostatic field in nonpolar a-plane GaN-based quantum wells can limit the piezoelectric polarization effect. The electron and hole wave functions in the quantum wells overlap completely resulting in higher emission efficiency.1, 2 This feature is promising for optoelectronic applications such as laser diodes and LEDs. The knowledge of the planar anisotropic nature of nonpolar a-plane GaN is important to understand the growth mechanism of a-plane GaN, and fundamental for optoelectronic devices design.
(a)
(b) Figure 1 (a) Diagram showing crystallographic planes of GaN (b) Orientation of the a-plane GaN and r-plane sapphire with the incident angle for prism couple light indicated.
0892-FF23-10.2
Experimental details A Metricon 2010 prism coupling system was used to measure the refractive indices of two a-plane GaN samples. The two samples were distinct in that one was much thicker than the other, and the thinner sample was grown on an intentionally miscut r-plane sapphire substrate. The misorientation of the miscut substrate for the thin sample was 4 degrees. A rutile (TiO2) prism was used to couple light into the air/a-plane GaN /r-sapphire waveguide. In order to make this rotation, the sample mount was modified so that the sample could be rotated azimuthally about a vector normal to the surface of the a-plane GaN/r-plane sapphire. Thus the angle between the incident light and the c-axis could be varied. The contact spot between the film and the prism during the rotation is kept stationary in order to avoid errors due to thickn
Data Loading...
