We have previously developed an optically modulated high sensitivity heterostructure varactor whose Cmax/Cminmiddot ratio of up to 113, and sensitivity of up to 35 are among the highest reported in the literature. These figures of merit indicate that this device is a good candidate for a number of applications including high order frequency multipliers. The device consists of a p-type delta modulation-doped heterostructure of AlGaAs/GaAs with Al0.9Ga0.1As/Al0.24Ga0.76As Distributed Bragg Reflectors (DBR) at the bottom producing a resonant cavity enhanced photodetector structure. As such the device has a dual role of being a sensitive photodetector and a Varactor. In fact, the response shows that the varactor characteristics can be optically modulated and depend on the intensity of the incident optical radiation. In this paper we present a lumped parameter model that captures the physics of the observed behavior. Validity of the model is verified by its correspondence with experimental results as well simulation of the physical structure.