Influence of carrier statistics on InGaN quantum dot device performance D.S. Sizov*, V.S.Sizov, E.E, Zavarin, V.V. Lundin, A.V. Fomin, A.F. Tsatsulnikov, N.N. Ledentsov A. F. Ioffe Physicao-Technical Institute, Russian Academy of Sciences, 26 Politekhnicheskaya st., St.Petersburg 194021, Russia ABSTRACT In this work InGaN quantum dots (QDs) in GaN matrix formed during strain induced phase separation were investigated. We show that although electron – photon interaction rate in residual quantum well (QW) InGaN is high, carrier capture to QD levels and carrier escape from QD levels to the QW is slowed presumably due to large energy distance between the QD levels and between the QD levels and the QW band. This leads to deviation of quasiequilibrium of carrier distribution in QDs even at temperature higher than 300K. We also modify rate equation model taking into account this deviation. In this model we consider the QW as a quasiequilibrium reservoir, but carrier statistics in the QDs is calculated in term of nonequilibrium statistics of Sah-Noyce-Shokkley-Read centers with strongly inhomogeneous localization depth. This model describes lasing line broadening in terms of carrier burning and formation of multimode emission. Keywords: quantum dots, InGaN, carrier statistics, localization, semiconductor laser 1. INTRODUCTION Heterostructures with quantum dots (QD) attract more and more attention of investigators due to their unique properties 1 such as complete spatial carrier confinement and discrete electronic spectra, both not pertaining to other kinds of heterostructures. As distinct from another quantum confining system where infinite carrier motion at least during one direction and so quasicontinous electronic spectra exists, in QDs energy distance between the ground state and the first excited state can excide the thermalization energy T k B ( B k - is Boltzmann constant T - temperature) 2 . Without any carrier pumping carrier distribution in QD levels obeys the Fermi rule. When the pumping is applied two cases can be distinguished 3 . In case of high probability of intraband transitions as compared with recombination rate, the carrier distribution is quasiequilibrium. It means that within one band (for example conductivity band (CB)) carrier redistribution rate is much higher than rate of carrier leaving from and coming by means of recombination and pumping. Hence, carrier relaxation within this statistical subsystem is so high as compared with processes of exchange with other subsystems that local equilibrium must be established in this band 4,5 . Analogous reasoning can be made for the valence band (VB). Thus, differing chemical potentials (quasi Fermi levels) can be found for each band. In other case, when carrier redistribution within band is not quick enough this approach is not valid. In the opposite case, when recombination rate is much higher than carrier redistribution, another approaches are suggested 3,6 . In quantum wells redistribution times are known to be fast. These processes are usually assisted by electron – phonon interaction, and in case of quasicontinous electron spectra probability of these processes is high because there is no exact requirement for phonon energy. At the same time in QDs the interband transitions are limited by low probability of absorbtion or emission of a phonon (in case of large energy distance even a few phonons 2,7,8 ) with corresponding energy. It can also lead to the so called bottleneck effect 9 and nonequelibrium carrier distribution that was observed in some QD systems at corresponding conditions 10,8 . The carrier relaxation can also be assisted by Auger processes 11,2 but this effect is significant only in narrow bandgap semiconductors and falls quickly with increase of the bandgap. Furthemore, the Auger processes are also typical for high excitation densities 7 , however the measurements in present work were made under low pumping density (except lasing measurements). * dsizov@pop.ioffe.rssi.ru, phone +7 -921-2473182, fax +7-921-2473178