Photoluminescence characterization of quantum dot laser epitaxy Y. Li * , Y. C. Xin, H. Su and L. F. Lester Center for High Technology Materials, University of New Mexico 1313 Goddard SE, Albuquerque, NM 87106 A. L. Gray, S. Luong, K. Sun, Z. Zou, and J. Zilko Zia Laser, Inc., Albuquerque, NM 87106 ABSTRACT The correlations between the photoluminescence (PL) wavelength, integrated intensity, peak intensity, and FWHM with laser diode performance such as the maximum gain, injection efficiency, and transparency current density are studied in this work. The primary outcome is that the variation in PL intensity within a wafer originates primarily from differences in the radiative and non-radiative recombination rates and not from dot density variation. PL generated from 980 nm wavelength pumping appears to give more consistent data in assessing the optical quality of quantum dots that emit in the 1300 nm from the ground state. 1. INTRODUCTION Quantum dot (QD) materials have been studied extensively in recent years 1-6 . Due to their delta-like density of states of QDs, lasers fabricated from these novel materials provide many superior characteristics such as ultralow threshold current 2,3 , low temperature dependence of the threshold current 4 , low linewidth enhancement factor 5 . One shortcoming of the QD technology, though, is the small modal gain of optical active regions formed from dots. In reaction to this challenge, much effort has been expended to improve the maximum optical gain of InAs QD semiconductor lasers on GaAs substrates. Either increasing the dot density or adding more layer of dots have been attempted. In some cases, it appears that the optical gain does not always scale with an overall increase in dot density per layer. The reasons for this behavior are unclear at this time, but materials characterization data is a logical starting point to gain insight. However, the materials characterization of quantum dot layers is still in its infancy. The purpose of this work is to explore correlations between photoluminescence (PL) wavelength, integrated intensity, peak intensity, and FWHM with laser diode performance such as maximum gain, injection efficiency, and transparency current density. As expected, it is observed that the PL peak intensity scales with QD layer number for values between 1 and 6. In this instance, one expects a direct correlation between the maximum available gain and the PL strength. However, within a wafer it is not clear what PL peak intensity variation indicates. The challenge is to separate the influence on the PL strength from dot density variation, non-radiative dots (dark dots), and changing recombination processes across the wafer. For one of the wafers under study, two areas where the PL intensity differs by as much as 8 times are identified. Lasers fabricated from these different regions and PL data indicate that the density of activated QDs are similar since the maximum gains, PL and lasing wavelengths, and PL FWHMís are nearly identical. However, the transparency current densities vary by a factor of 3. These results indicate that the source of the PL variation on this wafer originates from differing recombination rates and not dark dots or dot density changes. 2. PL MAPPING DATA AND WAFER DESCRIPTION Generally speaking, the PL intensity and maximum gain in QD material increases when more layers of dots are added. Figure 1 shows the PL peak intensity as a function of QD layer number for 1, 3, and 6 stacks. One can see that the PL peak intensity almost linearly increases with quantum dot layer number, which also confirms that the optical pumping in uniform across the QD active layer. * yanli@chtm.unm.edu; phone 1 505 272-7933; fax 1 505 272-7801 Quantum Dots, Nanoparticles, and Nanoclusters II, edited by Diana L. Huffaker, Pallab K. Bhattacharya, Proceedings of SPIE Vol. 5734 (SPIE, Bellingham, WA, 2005) 0277-786X/05/$15 · doi: 10.1117/12.597089 138