Nanostructured graphene–Schottky junction low-bias radiation sensors

Abstract

We present a key idea of using the graphene-based Schottky junction to achieve high sensitivity and wide detection range radiation sensors. Nanostructured Schottky junction is formed at the interface between a graphene, metal electrode, and a semiconductor. The current flowing through the junction is mainly controlled by the barrier's height and width. Therefore, the detection principle is based on Schottky barrier height (SBH) modulation in response to different materials and stimuli. We have illustrated the concept for gamma (γ) radiation sensors. It’s demonstrated that the integration of graphene leads to a great enhancement in sensitivity of up to 11 times coupled with 5 times increase in the sensing range as compared to conventional Schottky junctions. Furthermore, it was demonstrated that for proposed sensors, that the change in SBH could be fairly linearized as a function in the radiation dose unlike the SBH of comparable conventional junctions. The new concept opens the door for a novel class of minitiuarized, low biased, nanoscale radiation sensors for wireless sensor networks. The devices are based on new nanostructured Schottky junctions made by growing graphene on ultrathin platinum catalytic layer grown on different silicon substrates. Graphene high uniformity film with small flakes size embedded with platinum particles was synthesized using two deposition steps. The integration of graphene layers on regular M–S junctions was only possible by using an ALD grown platinum thin film (10–40nm) and then growing graphene in PECVD at temperatures lower than platinum silicide formation temperature. The radiation sensing behaviors were investigated using two different substrate types. The first substrate type is a moderately doped n-type (n≈2×1015cm−3) silicon substrate in which a Schottky rectifier response with different threshold voltages was observed. A device that is based on Pt/n-Si conventional Schottky junction was used as a reference. The various devices were exposed to a range of γ-irradiations (2–120kGy) using Co60 source, and a change in terminal voltages before and after radiation were measured accordingly. A sensitivity of 3.259μA/kGycm2 at 1V bias over a wide detection range has been realized. The charge transport mechanisms are interpreted on the basis of testing the detectors at elevated temperatures and theoretical models, both of which both verified tunneling as the dominant charge transport in the device. Tunneling allowed the operation of the detectors at low bias voltages with good sensitivity. The detector’s realized sensitivity at low bias voltage is a significant advantage, allowing the sensor to operate on a small battery or an energy-harvesting source. This is ideal for low-cost wireless sensor networks.The obtained responses, increase in sensitivity, and increase in detection range, were explained by studying the band diagrams of the graphene–Schottky junction in comparison to that of the conventional junction. Further, the fact that graphene layer was grown on the M–S junction adds to the uniqueness of this research since exfoliated graphene will result in increased contact resistance and lower carrier mobility which might not yield the desired sensing response.