Nano-Engineering Approaches to Self-Assembled InAs Quantum Dot Laser Medium S. OKTYABRSKY, 1,2 V. TOKRANOV, 1 G. AGNELLO, 1 J. VAN EISDEN, 1 and M. YAKIMOV 1 1.—College of Nanoscale Science and Engineering, University at Albany–SUNY, Albany, NY 12203. 2.—E-mail: soktyabrsky@uamail.albany.edu A number of nano-engineering methods are proposed and tested to improve optical properties of a laser gain medium using the self-assembled InAs quan- tum dot (QD) ensemble. The laser characteristics of concern include higher gain, larger modulation bandwidth, higher efficiency at elevated tempera- tures, higher thermal stability, and enhanced reliability. The focus of this paper is on the management of QD properties through design and molecular beam epitaxial growth and modification of QD heterostructures. This includes digital alloys as high-quality wide-bandgap barrier; under- and overlayers with various compositions to control the dynamics of QD formation and evo- lution on the surface; shape engineering of QDs to improve electron-hole overlap and reduce inhomogeneous broadening; band engineering of QD het- erostructures to enhance the carrier localization by reduction of thermal escape from dots; as well as tunnel injection from quantum wells (QWs) to accelerate carrier transfer to the lasing state. Beneficial properties of the developed QD media are demonstrated at room temperature in laser diodes with unsurpassed thermal stability with a characteristic temperature of 380 K, high waveguide modal gain .50 cm ÿ1 , unsurpassed defect tolerance over two orders of magnitude higher than that of QWs typically used in lasers, and efficient emission from a two-dimensional (2-D) photonic crystal nanocavity. Key words: InAs, quantum dots (QDs), molecular beam epitaxy (MBE) INTRODUCTION In recent years, numerous technologies to manip- ulate materials at nanometer scale have been devel- oped. One of the most productive and, in fact, the most mature areas of nanoscale science and tech- nology involves quantum-confined semiconductor heteroepitaxial structures, which have given rise to numerous applications. Over two decades of research in this area have resulted in significant advances in various electronic devices including microwave and power transistors, laser diodes, and photodetectors, just to name a few. An ultimate three-dimensional (3-D) quantum confinement is achieved in quantum dots (QDs), where the corresponding energy states are discrete, giving rise to fundamentally different electronic properties that make them desirable for these types of applications. The ensemble of semi- conductor epitaxial QDs (such as InAs QDs in AlGaAs matrix) is even more attractive than quan- tum wells (QWs) for electronic and, in particular, for photonic devices. A good example is the projected performance of QD-based laser diodes. According to theoretical predictions, heterojunction lasers with QD active media will have superior characteri- stics as compared to the conventional QW lasers. 1,2 The major reason for this superiority is the discrete atom-like electronic spectrum of QDs without ther- mal spreading of carriers. These characteristics include larger modulation bandwidth, higher effi- ciency at elevated temperatures, higher thermal stability, and enhanced reliability. However, these exciting benefits of the QD active media for lasers have not evolved into devices so far due to inhomo- geneous broadening of the QD electronic spectrum resulting from the size dispersion of QDs, relatively slow relaxation of carriers to the ground level in the QDs, relatively low gain of the QD medium, (Received October 12, 2005; accepted November 11, 2006) Journal of ELECTRONIC MATERIALS, Vol. 35, No. 5, 2006 Special Issue Paper 822