SiC-graphene heterojunction ultraviolet detector

In our study, we report a ultraviolet photodetector based on SiC-graphene heterojunction with P-doped graphene and N-doped 4H-SiC. The device combines the advantages of the two materials, both the low dark current owing to the P-N heterojunctions and the befitting magnitude of responsivity of the conventional PIN UV photodetectors are obtained. The device consists of positive electrode, single layer P-doped graphene, N⁻-doped SiC layer, N-doped buffer layer, N⁺-doped substrate and back electrode, from top to bottom. Initially, a 0.5um N⁻-doped SiC epitaxial layer was grown (Nd=1×10¹⁶cm⁻³) on a 2um N+-doped buffer layer on a N+-doped 4H-SiC substrate. SiC mesas were etched 1um into the interior with a litho-graphically patterned Ni mask and SF6/O2-based inductively coupled plasma (ICP) etch. Then the back ohmic contact electrode was formed with Ni by high temperature annealing. Single layer P-doped graphene was then transformed onto the devcice surface with the graphene mesa etched by O2-based reactive ion etching(RIE) etch. Ti/Au was used as the ohmic contact for graphene regions. After the device fabrication is finished, the diode current — voltage (I-V) characteristics were tested under reverse biased voltage from 0V to 6 V at room temperature. The dark current of the device is at the magnitude of 10⁻¹⁴A∼10⁻¹²A. The responsivity from the illumimation of different wavelengths of lights under reverse bias of 1V was measured. The responsivity peak lies near the 270nm wavelength, and the maximum response is 0.032A/W. Since the doping concentration of the N⁻-doped SiC layer is 1×10¹⁶cm⁻³, it is too large to completely depleted under 1V reverse bias voltage. These data do not reflect the best performance of the device. We then test the device under 5 V reverse bias from the illumimation of 270nm wavelength UV irradiation, the current reached 1 × 10⁻⁸A magnitude, this means that the responsivity is raised by an order of magnitude, which beyond the level of traditional PIN ultraviolet photodetectors.