Effect of the internal electric fields in Quantum Dot laser structures grown by Metal Organic Chemical Vapor Deposition
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Effect of the internal electric fields in Quantum Dot laser structures grown by Metal Organic Chemical Vapor Deposition A. Passaseo, G. Maruccio, M. De Vittorio, S. De Rinaldis, T. Todaro and R. Cingolani National Nanotechnology Laboratory-INFM, c/o Dipartimento di Ingegneria dell’Innovazione, Università di Lecce, Via Arnesano, 73100 Lecce (Italy)
ABSTRACT By means of a systematic study carried out on In0.5Ga0.5As/GaAs quantum dot electroluminescent devices grown by Metal Organic Chemical Vapor Deposition, we show that the combination of internal electric fields in such structures dramatically blue shifts the emission wavelength with respect the photoluminescence emission that occurs at the expected value of 1.3 µm at room temperature. By comparing photoluminescence (PL), electroluminescence (EL) and photocurrent (PC) measurements in In0.5Ga0.5As QD structures emitting between 1.28 µm and 1.4 µm (at 300 K), we demonstrate that the electric field associated to the built-in dipole in the dots, directed from the base of the dots to their apex, and the device junction field (when parallel to the dipole field) lead to the depletion of the ground state. As a consequence, structures grown on n-type GaAs substrates exhibit electroluminescence only from the excited states. Instead, by growing the same device structure on p-type GaAs substrates, i.e. by reversing the direction of the built-in electric field of the device, the effect of the permanent dipole is strongly reduced, thus allowing us to obtain EL emission at the designed wavelength of 1.3 µm at 300 K, coincident to the PL. The consequence on the achievement of efficient lasing in the spectral region of interest for optical transmission. are illustrate.
INTRODUCTION In the last years great effort has been dedicated to the study and fabrication of optoelectronic devices containing InGaAs quantum dot (QD) structures as active layers, for 1.3 micron operation. The fabrication of long wavelength InGaAs/GaAs quantum dot (QD) lasers was shown to be a promising way to extend the optical emission range of the GaAsbased optoelectronic down to 1.3 µm for application to short-range telecommunications. Due to the modification of density of states, laser structures containing QDs as active material are expected to exhibit high differential gain, low threshold current and high characteristic temperature [1,2]. This would allow the replacement of InP-based devices by the less expensive GaAs devices. However, even if room temperature lasers emitting in the 1.3 µm region have been recently fabricated by Molecular Beam Epitaxy (MBE) [3,4], longwavelength lasing in QD laser structures grown by metalorganic chemical vapor deposition (MOCVD) has not been reported so far, and very few works have shown emission wavelength at 1.3 µm in QDs fabricated by MOCVD [5,6]. In the present work we carried out systematic studies in In0.5Ga0.5As QD structures emitting between 1.28 µm and 1.4 µm (at 300 K) by using photoluminescence (PL), electroluminescence (EL) and photocurrent (PC) spectroscopy. O
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