The second-order nonlinear susceptibility (SONS) in self-assembled InAs quantum dots (QDs), in the form of quantum disks, under applied electric field was studied. Using Feynman diagram, the relation of SONS for sum frequency generation was stated. Two cases were studied, which are the interband (IB) and intersubband (ISB) transitions with the consideration of the QD inhomogeneity, which is shown to be important in SONS calculations. For the ISB case, a resonance near 92 mm was predicted, which is important for infrared applications. Energy subbands and momentum matrix elements are shown as the main factors controlling SONS. It was found that adding some detuning to the pump will extend the wavelength by 45 mm which might applicable for Terahertz (THz) applications. Double resonance was shown to blue shifts the wavelength. (C) 2016 Elsevier B.V. All rights reserved.