Hybrid Si nanowire/amorphous silicon FETs for large-area image sensor arrays

Silicon nanowire (SiNW) field-effect transistors (FETs) were fabricated from nanowire mats mechanically transferred from a donor growth wafer. Top- and bottom-gate FET structures were fabricated using a doped a-Si:H thin film as the source/drain (s/d) contact. With a graded doping profile for the a-Si:H s/d contacts, the off-current for the hybrid nanowire/thin-film devices was found to decrease by 3 orders of magnitude. Devices with the graded contacts had on/off ratios of ∼10(5), field-effect mobility of ∼50 cm(2)/(V s), and subthreshold swing of 2.5 V/decade. A 2 in. diagonal 160 × 180 pixel image sensor array was fabricated by integrating the SiNW backplane with an a-Si:H p-i-n photodiode.