Jonathan E Spanier

We have previously developed an optically modulated high sensitivity heterostructure varactor whose C max /C min middot 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 Al 0.9 Ga 0.1 As/Al 0.24 Ga 0.76 As 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.

We have previously demonstrated the improved time response performance of the heterostructure metal-semiconductor-metal (HMSM) photodetector, due to the presence of a two-dimensional electron gas (2DEG). However, the time response presents a long tail due to the slow moving holes, which would still be an impediment for high frequency operation. In order to overcome this limitation, we have developed a new photodetector based on a two-dimensional hole gas (2DHG) in which the electric field in the GaAs absorption layer attracts the photogenerated holes to a reservoir of holes thus reducing their transit time. We present the designed structure, fabrication sequence, current-voltage, capacitance- voltage characterizations carried out in the dark and under light. Time response data verifies a distinctive reduction in tail of response as expected.