Dependence of the E 2 and Ai (LO) modes on InN fraction in InGaN epilayers
- PDF / 90,057 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 81 Downloads / 194 Views
E3.22.1
Dependence of the E2 and A1 (LO) modes on InN fraction in InGaN epilayers S. Hern´andez,1 R. Cusc´o,2 L. Art´us,2 K.P. O’Donnell,1 R.W. Martin,1 I.M. Watson,3 Y. Nanishi,4 M. Kurouchi,4 and W. Van der Stricht5 1 Department of Physics and Applied Physics, University of Strathclyde, Glasgow, G4 0NG, Scotland, United Kingdom. 2 Institut Jaume Almera (CSIC), C. Llu´ıs Sol´ e i Sabar´ıs s.n., 08028 Barcelona, Spain. 3 Institute of Photonics, University of Strathclyde, Glasgow G4 0NW, United Kingdom. 4 Dept. of Photonics, Ritsumeikan Univ., 1-1-1 Noji-higashi, Kusatsu 525-8577 Japan. 5 University of Ghent, Ghent, Belgium. ABSTRACT The behavior of the E2 and A1 (LO) optical phonons in Inx Ga1−x N has been analyzed by Raman scattering over the whole composition range. The frequencies of the E 2 and A1 (LO) modes decrease with increasing InN fraction. These modes display a significant broadening for an InN fraction of ≈ 60% and their linewidth decreases towards both ends of the composition range as a consequence of reduced cation disorder. Our results show a one-mode behavior for both E2 and A1 (LO) modes of InGaN. INTRODUCTION Group III-nitrides have attracted much interest in the last few years because of their wide range of possible applications as light-emitting and detector devices [1]. In particular, the InGaN alloys can be used to cover the emission energy range from the ultraviolet to near infrared by varying the InN fraction. However, their fundamental optical properties are not well established yet. For instance, there is still controversy about the band gap energy of InN, with substantially different values of 1.9 eV [2, 3], 1.4 eV [4, 5] and 0.8 eV [6, 7] reported by different groups. With regard to their vibrational properties, these are affected by the modification of the inter-atomic distances resulting from the cation distribution. As the composition is changed, the optical-mode frequencies evolve from those of one end-member binary compound to those of the opposite end. In a mixed crystal Ax B1−x C the phonon behavior can be classified in two categories, one-mode or amalgamation type and two-mode or persistent type. In the first case, the frequency of the modes varies with the composition x continously from one end-member (BC) to the other (AC). For the two-mode type, there are two bands of frequencies which vary continuously from the mode frequencies of each binary to the impurity mode in the other binary. The behavior of long-wavelength optical phonons in III-V alloys with zincblende structure has been well established both experimentally and theoretically [8, 9, 10]. Most of these alloys exhibit a two-mode behavior (Ga1−x Alx As, Ga1−x Alx Sb, InAsx P1−x , Inx Al1−x As). For nitrides with the wurtzite structure, theoretical calculations based on a modified random element isodisplacement model (MREI) predict different behaviors of the optical phonons for different alloys (Alx Ga1−x N, Alx In1−x N and Inx Ga1−x N) [11]. Experimental results on Alx Ga1−x N alloys show a good agreement with the theor
Data Loading...
