Effect of the internal electric fields in Quantum Dot laser structures grown by Metal Organic Chemical Vapor Deposition

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 gm at room temperature. By comparing photoluminescence (PL), electroluminescence (EL) and photocurrent (PC) measurements in In0.5Ga0.5As QD structures emitting between 1.28 mum and 1.4 mum (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 mum 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.