Conformal core-shell nanostructured photodetectors with enhanced photoresponsivity by high pressure sputter deposition

ABSTRACTWorking gas pressure during sputter deposition can significantly affect the conformality of a thin film when it is grown on a nanostructured surface. In this study, we fabricated core-shell nanostructured photodetectors, where n-type In2S3 nanorod arrays (core) were coated with p-type CuInS2 (CIS) films (shell) at relatively low and high Ar gas pressures. In2S3 nanorods were prepared by glancing angle deposition (GLAD) technique using a thermal evaporator unit. CIS films were deposited by RF sputtering at Ar pressures of 2.7x10-2 mbar (high pressure sputtering, HIPS) and 7.3x10-3 mbar (low pressure sputtering, LPS). The morphological characterization was carried out by means of SEM. The photocurrent measurement was conducted under 1.5 AM Sun under no bias. Nanostructured photodetectors of HIPS-CIS/GLAD-In2S3 (i.e. HIPS-GLAD) were shown to demonstrate enhanced photoresponse with a photocurrent value of 98 μA, which is about ∼230% higher than that of LPS-GLAD devices. The enhancement originates from the improved core-shell structure achieved by more conformal coating of the CIS shell. In addition, the results were compared to their counterpart thin-film devices incorporating an In2S3 film coated either with HIPS or LPS CIS layer. Nanorod devices with high and low pressure CIS films showed photocurrent values ∼20 times and ∼ 19 times higher compared to those of high and low pressure film devices, respectively. This finding can be explained by the higher light absorption property of nanorods, and the reduced inter-electrode distance as a result of core-shell structure, which allows the effective capture of the photo-generated carriers. Therefore, the results of this work can pave way to the development of high photoresponse core-shell semiconductor devices fabricated by physical vapor deposition techniques.