Novel semiconductor lasers based on quantum dots

Abstract

Self-organized quantum dots have emerged as one of the more interesting approaches for new types of semiconductor photonic devices, especially lasers. In this talk we will review the status of quantum dot lasers and discuss their potential applications to MEMS.Self-organized quantum dots (QDs) represent a new type of semiconductor active material that is important for new devices, especially new types of lasers. The QDs form artificial semiconductor atoms that can provide a variety of new device characteristics that arise due to the discrete electronic levels. For lasers these include temperature insensitive thresholds, chirp-free or chirp-engineered modulation, low threshold current and current density, two-state lasing, decreased phonon sensitivity for intralevel transitions, and more. Many of these features have already been demonstrated experimentally, while others, such as the potential for higher speed modulation response, remain theoretical possibilities. The self-organized QDs also provide an important feature for very small lasers and spontaneous light sources in that they form selfburied heterostructures with the capability of laterally confining charge carriers to dimensions of a few hundred angstroms or less. Their electronic confinement features make them attractive for photonic crystal devices and very small vertical-cavity surface-emitting lasers (VCSELs). The VCSELs, in particular, are of interest for micro-electromechanical structures that may be based on tunable filters.Our devices are grown using molecular beam epitaxy of strained-layer InAs or InGaAs grown on GaAs, and can cover a range of wavelengths from -0.95 pm to beyond 1.3 pm. Figure 1 shows a schematic illustration of a QD edge-emitting laser grown and fabricated in our laboratory. This device uses fivestacks of QD layers as the laser gain region. The QDs are formed fi-om 2.5 monolayers of InAs deposited on GaAs, and covered by a thin layer of I~.~sGao.g~As. In our work we have found that closely spaced hole levels can limit the laser performance, but that this limitation can be overcome by including p-doping next to the active layers to fill the QDs with holes. Fig. 1 Schematic illustration of a five-stack QD laser containing InAs QDs designed for operation at 1.3 pm. The inset shows an expanded view of the active region. Figures 2 and 3 show the lasing characteristics. The five-stack laser operates on the ground state transition at 1.3 pm, has a low threshold current density of 166 A/cm2 at 25°C (33 Ncm2 per QD layer), and with a 5.4 mA threshold current puts out over 25 mW continuous wave at room temperature. However, the most impressive characteristic of this laser is its high temperature performance. Figures 2 and 3 show that the threshold current and slope efficiency are nearly temperature insensitive, even for temperatures above O-7803-783O-W03/$17.0002003 IEEE 1 67