phys. stat. sol. (c) 0, No. 4, 1173– 1176 (2003) / DOI 10.1002/pssc.200303032 © 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1610-1634/03/00007-1173 $ 17.50+.50/0 Optical properties of hexagonal and cubic GaN self-assembled quantum dots Yong-Hoon Cho *, 1 , B. J. Kwon 1 , J. Barjon 2 , J. Brault 2 , B. Daudin 2 , H. Mariette 2 , and Le Si Dang 2 1 Department of Physics, Chungbuk National University, Cheongju 361-763, Korea 2 Nanophysics and Semiconductors, CEA-CNRS-UJF group CEA Grenoble, DRFMC/SP2M/PSC, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France and Laboratoire de Spectrometrie Physique (CNRS UMR 5588), Université J. Fourier-Grenoble, BP 87, 38402 Saint Martin d’Heres Cedex, France Received 30 September 2002, accepted 2 December 2002 Published online 23 June 2003 PACS 78.47.+p, 78.55.Cr, 78.60.Hk, 78.67.Hc, 81.07.Ta Optical characteristics of hexagonal GaN (h-GaN) and cubic GaN (c-GaN) self-assembled quantum dots (QDs) were investigated by means of photoluminescence (PL), PL excitation, cathodoluminescence (CL), and time-resolved PL experiments. We observed a Stokes-like shift between PL excitation absorption ed- ge and PL emission from the h-GaN QDs as well as Al(Ga)N base layer. With increasing temperature, the PL intensity of Al(Ga)N base layer or GaN quantum wells was dramatically decreased while that of GaN QDs was not changed much. We also observed wavelength-resolved CL images reflecting strong carrier localization in the QD confinement. From the time-resolved PL experiments, we found that the measured lifetime of the h-GaN QDs emission increased with decreasing emission energy (i.e., increasing QD size), while that of the c-GaN QDs kept almost constant. Therefore, we conclude that the h-GaN QD emissions are strongly influenced by built-in interal electric field as well as carrier localization in the QDs. 1 Introduction Wide-bandgap nitride semiconductors and their quantum structures have attracted much attention, especially for their optical device applications in the visible and ultraviolet energy range. It has been discussed that the carrier localization formed in the plane of the layers enhances the quantum efficiency by suppressing lateral carrier diffusion, thereby reducing the probability for carriers to be trapped by nonradiative recombination centers [1, 2]. In the wurtzite nitrides system, it has been reported that the built-in macroscopic polarization, which consists of the spontaneous polarization due to interface charge accumulations between two constituent materials and the piezoelectric polarization due to lattice- mismatch-induced strain, plays a significant role in carrier recombination [3, 4]. Recently, there has been considerable interest in GaN-based quantum dot (QD) structures for their zero-dimensional carrier con- finement. Detailed studies on the optical properties related to both the built-in internal field and carrier localization present in the GaN self-assembled QDs are essential not only for the physical interest in atomic-like confined system but in designing practical visible and ultraviolet light emitting applications with better performance and quantum efficiency. In this paper, we have systematically studied the optical properties of hexagonal GaN (h-GaN) self-assembled QDs by means of photoluminescence (PL), PL * Corresponding author: e-mail: yonghcho@chungbuk.ac.kr, Phone: +82 43 261 3342, Fax: +82 43 261 3342