High performance quantum dot lasers on gallium arsenide and silicon.

Abstract

The performance of conventional quantum dot lasers has been limited by some unique characteristics of self-organized quantum dots, such as thermally broadened hole distributions, hot-carrier related effects, and large inhomogeneous broadening. In this study, with the development of special epitaxial growth techniques and the incorporation of p-doping and tunnel injection in device active regions, significantly improved performance has been realized in quantum dot lasers grown on GaAs, InP, and Si substrates. Self-organized InAs/GaAs quantum dot bilayers with nearly perfect size distribution have been grown and characterized. A record small photoluminescence linewidth of 17.5 meV is measured at 300 K, which is almost identical to that measured in the emission from a <italic>single</italic> dot, indicating that the linewidth is determined by homogeneous broadening. Special techniques of p-doping and tunnel injection have proved to be effective, and essential, to improving the performance of quantum dot lasers. Utilizing these techniques, high performance 1.3 mum InAs/GaAs pseudomorphic quantum dot lasers, 1.5 mum InAs/GaAs metamorphic quantum dot lasers, and 1.65 mum InAs/InP quantum dash lasers have been demonstrated. These novel devices exhibit nearly ideal characteristics, such as ultra-low threshold current (<italic>J_th</italic> = 63 A/cm<super>2</super>), temperature invariant operation (<italic>T₀</italic> &ap; infinity), large frequency response (<italic>f_-3dB</italic> = 12GHz), and near-zero chirp and alpha-parameter. This is the first demonstration that a semiconductor laser can exhibit characteristics of an atomic laser. The DC and dynamic characteristics of these unique devices are analyzed, and the role of p-doping and tunnel, injection in enhancing the performance of quantum dot lasers is examined. Additionally, the first room temperature operational quantum dot laser grown directly on Si has also been demonstrated. A novel dislocation reduction technique, with the use of multiple layers of self organized InAs quantum dots as an effective dislocation filter, is developed. Utilizing this technique, quantum dot lasers monolithically grown on Si exhibit, for the first time, relatively low threshold current (<italic>J_th</italic> = 900 A/cm<super> 2</super>), high output power (&ge; 150 mW), and large characteristic temperature (<italic>T₀</italic> = 244 K) and constant output slope efficiency (&ge; 0.3 W/A) in the temperature range of 5 to 95&deg;C.