Singlemode Monolithically Quantum-Dot Vertical-Cavity Surface-Emitting Laser in 1.3 μm with Side-mode Suppression ratio > 30dB H. C. Kuo* 1 , Gray Lin 2 , W. K. Tsai 1 , Y. H. Chang 1 , P. C. Peng 1 , FangI Lai 1 , H. C. Yu 2 , H. P. Yang 2 , K. F. Lin 2 , Jim Y. Chi 2 1. Department of Photonics and Institute of Electro-optical Engineering, National Chiao-Tung University, Hsin-Tsu 300, Taiwan, R.O.C. 2. Opto-Electronics and System Laboratory, Industrial Technology Research Institute Hsin-Tsu 310, Taiwan, R.O.C. ABSTRACT — We present monolithically quantum-dot vertical-cavity surface-emitting laser (QD VCSELs) operating in the 1.3 μm optical communication wavelength. The QD VCSELs have adapted fully doped structure on GaAs substrate. The output power is ~ 330 μW with slope efficiency of 0.18 W/A at room temperature. Single mode operation was obtained with side-mode suppression ratio of > 30 dB. Modulation bandwidth was also presented for the first time. Index Terms — quantum dots, surface emitting laser, single mode, bandwidth. I. INTRODUCTION Vertical-cavity surface-emitting lasers (VCSELs) at around 1.3 μm fabricated on GaAs substrates have been expected to realize high- performance and low-cost light sources for fibre-optic communication systems. The large conduction band offset improves the temperature performance over that of conventional InP-based materials. The GaAs system provides high-performance AlGaAs/GaAs DBR mirrors and permits the use of the well-established oxide- confined GaAs-based VCSEL manufacturing infrastructure. So far, the most promising materials at 1.3 μm on GaAs substrate were GaInAsN quantum wells (QWs) [1-3] and quantum dots (QDs) [4-6]. However, GaInAsN is a very challenging material system from a growth perspective and the reliability is still an issue [7]. Self-organized quantum dots (QDs) [8] are particularly advantageous for VCSELs, as nonequilibrium carriers are localized in the QDs and thus spreading of nonequilibrium carriers out of the injection region can be suppressed. This may results in ultralow threshold currents (< 70 μA) at ultrasmall apertures [8, 9]. In the 1.3 μm range, N. Ledentsov et al. previously illustrated QD VCSEL by using intracavity structure. In this paper, we demonstrated monolithically single-mode QD VCSELs grown by MBE with high side-mode suppression ratio (> 30 dB). Modulation bandwidth was also presented for the first time. II. EXPERIMENTAL All structures were grown on GaAs (100) substrates by molecular beam epitaxy (MBE). The epitaxial structure was as follows (from bottom to top) - n + -GaAs buffer, 33.5-pair n + -Al 0.9 Ga 0.1 As/n + -GaAs (Si- doped) distributed Bragg reflector (DBR), undoped active region, p-Al 0.98 Ga 0.02 As oxidation layer, 22-pair p + -Al 0.9 Ga 0.1 As/p + -GaAs DBR (carbon-doped) and p + - GaAs (carbon-doped) contact layer. The graded-index separate confinement heterostructure (GRINSCH) active region consisted mainly of three stack of QDs active region, with PL emission at 1.266 µm, embedded between two linear-graded Al x Ga 1-x As (x = 0 to 0.9 and x = 0.9 to 0) confinement layers. The thickness of the cavity active region was 1λ. Carbon was used as the p- type dopant in the DBR to increase the carrier concentration (2-3×10 18 cm -3 ). The interfaces of both the p-type and n-type Al 0.9 Ga 0.1 As/GaAs DBR layers are linearly graded to reduce the series resistance. The optical characteristics of QDs were optimized through PL measurement and structural analysis. The details of the process were fully described in our previous works [10]. The mesa diameter of the fabricated device is 26