MBE GROWTH AND CHARACTERIZATION OF COMPOSITE InAlAs/In(Ga)As VERTICALLY ALIGNED QUANTUM DOTS A. R. KOVSH, A. E. ZHUKOV, A.YU. EGOROV, N. N..MALEEV, S. S. MIKHRIN, V. M. USTINOV, V. A. ODNOBLYUDOV, YU. G. MUSIKHIN, D. A. LIVSHITS, A. F. TSATSUL'NIKOV, M. V. MAXIMOV, YU. M. SHERNYAKOV, B. V. VOLOVIK, D. A. BEDAREV, N. N. LEDENTSOV, P. S. KOP'EV, ZH. I. ALFEROV, A. A. SUVOROVA*, P. WERNER*, AND D. BIMBERG** loffe Physico-Technical institute Russian Academy of Sciences, 26 Politekhnicheskaya, St. Petersburg, 194021, Russia, kovsh@beam.ioffe.rssi.ru *Max-Planck-Institut ftir Mikrostrukturphysik, Weinberg 2, D-06120 Halle, Germany *Institut fur Festk6rperphysik, Technische Universitat Berlin, Hardenbergstr. 36, D-10623 Berlin, Germany ABSTRACT In the present work we study the effect of vertical alignment in the quantum dot array formed by successive deposition of several rows of InAlAs and InGaAs quantum dots separated by thin AIGaAs spacer layers. Transmission electron microscopy and photoluminescence studies revealed that the InAlAs QDs characterized by high areal density force InGaAs to be transformed into the denser array as compared to the case of spontaneous transformation. Using denser array of composite quantum dots in the active region of a diode laser leads to the increase in modal gain, decrease in internal loss, and decrease in the threshold current density for short cavity diodes. Room temperature continuous wave output power as high as 3.3 W at 0.87 ýim is achieved. INTRODUCTION Self-organized quantum dots (QDs) formed at the initial stage of epitaxy of lattice mismatched layers are considered as a promising candidate for application in the active region of diode lasers [1]. In this case there is a possibility to control the number of active states which is directly proportional to the number of QDs as opposite to the quantum well case when the density of states is set by fundamental material properties [2]. Moreover, deltalike density of states should provide temperature insensitivity of laser characteristics [3]. Significant progress has been achieved in this field. Quantum dot (QD) lasers have already proved a possibility to exhibit low threshold and high characteristic temperature (TO) operation [4] as well as to extend the optical emission range for the GaAs based heterostructures [5]. However, the usually observed rapid gain saturation with drive current leads to steep increase in Jth when cavity length is reduced. The maximum gain characteristic for a real QD ensemble is much less than the theoretically possible value due to inhomogeneous broadening in optical gain caused by the QD size distribution. In addition, a possibility to achieve a high output power in QD laser diodes has not been studied in detail. One of the dominant mechanisms limiting the power of a semiconductor laser is spectral hole burning, associated with the finite capture time of charge carriers on the active states. The capture time in InGaAs 109 Mat. Res. Soc. Symp. Proc. Vol. 571 © 2000 Materials Research Society