Dependence of the emission wavelength on the internal electric field in quantum-dot laser structures grown by metal-organic chemical-vapor deposition

We show that the combination of different electric fields in In0.5Ga0.5As/GaAs quantum-dot electroluminescent devices dramatically blueshifts the emission wavelength even though the photoluminescence occurs at the expected value of 1.3 mum at room temperature. Systematic photoluminescence (PL), electroluminescence (EL), and photocurrent measurements demonstrate that the electric field associated with the built-in dipole in the dots, directed from the base of the dots to their apex, and the device junction 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 (whereas the photoluminescence comes from the ground level). 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. This effect expands the possibilities for the achievement of efficient lasing in the spectral region of interest for optical transmission. The electric field associated to the dipole moment is estimated to be around 150 kV/cm. (C) 2001 American Institute of Physics.