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Nonlinear optical rectification in symmetric coupled Al x Ga 1−x As/GaAs quantum wells with external electric field is investigated using numerical method and compact density matrix approach. Our results reveal that for the resonant peaks of optical rectification, a blue shift is exhibited for increasing electric field, while a red shift followed by a blue shift is exhibited for increasing barrier or well widths. The resonant peak values of optical rectification can reach a maximum value by an appropriate choice for the electric field, the barrier or well widths. Our studies pave the way for the design, optimization and applications of quantum-sized nonlinear optoelectronic devices. [ABSTRACT FROM AUTHOR]

• Exciton enhances refractive index changes (RICs) of Morse quantum wells (MQWs). • Exciton effect enhances optical absorption coefficient (OACs) of MQWs. • Al density and width parameter-dependent OACs and RICs of MQWs are revealed. • Hole mass-dependent OACs and RICs of MQWs are revealed. • Electric field effect on OACs and RICs of MQWs is revealed. Previously, much work on nonlinear optical effects in Morse quantum wells (MQWs) was based on electronic state transitions. However, exciton effect in MQWs is neglected and needs to be considered due to its great significance in determining nonlinear optical effects. Here, the variational method and the diagonalization method are utilized to acquire excitonic states in Al x Ga 1 − x As / GaAs MQWs. The exciton effect in MQWs induces an obvious enhancement of the linear and nonlinear optical absorption coefficients (OACs) and refractive index changes (RICs). The linear and nonlinear OACs and RICs are dynamically manipulated through tuning the electric field, and even are suppressed under a strong electric field. In addition, the linear and nonlinear OACs and RICs in MQWs are strongly affected by the hole mass, the width parameter and the aluminum concentration, which provides direction for obtaining desired nonlinear optical effects. [ABSTRACT FROM AUTHOR]