The research related to THz radiation science has several applications in different domains such as the agriculture field, high resolution imaging, security and defence etc. The research in the development of THz radiation sources at specific emission frequency is being explored in the scientific community, In order to fabricate THz sources at specific emission frequencies, the THz quantum cascade laser are best devices where emission frequencies can be tuned by varying thickness of quantum well and height of barrier. In the current study, numerical simulations of a hybrid active region design are reviewed to evaluate the optical gain spectra and the corresponding electric field strengths. The simulation considers approximately three periods of the QCL structure to analyze the electron distribution.