Superconductor/semiconductor heterojunction is expected to exhibit various photoresponse characteristics when forming Schottky or pn junctions. Additionally, the formation of ohmic contacts plays a crucial role in injecting carriers into the semiconductor, which is particularly important when forming a pn junction directly on the superconductor. In either case, it is advantageous from the perspective of device design flexibility to be able to deposit both p-type and n-type semiconductor thin films on the same type of superconductor, and to perform thin film deposition and microfabrication using methods that are environmentally friendly and simple. Regarding superconducting thin films, we have successfully prepared Bi2Sr2CaCu2O8+δ (BSCCO) using the metal-organic decomposition (MOD) method [1,2] and have also succeeded in forming bridges with a minimum width of 75μm using citric acid etching [3]. For semiconductor thin films, we have been prepared them by the MOD method and evaluating their band gaps and transmittance. Based on these insights, we are currently attempting to prepare superconductor/semiconductor heterojunctions using the MOD method. In this report, we present (1) that the BSCCO/CuxO junction, as a BSCCO/p-type semiconductor heterojunction, forms a good ohmic contact, and (2) our attempts to prepare BSCCO/n-type semiconductor heterojunctions. In this study, ZnO and NbOx were used as n-type semiconductors.
For the deposition of BSCCO, CuxO, ZnO, and NbOx thin films, we used solutions from High Purity Chemical Laboratory Co., Ltd.: BSCCO solution (SK-BSCCO008), Cu-O solution (Cu-03A), Zn-O solution (Zn-05), and Nb-O solution (Nb-05), respectively. MgO (100) or SrTiO3 (100) substrates with dimensions of 10×10×0.5 mm were used. A typical preparation process is as follows:
1. Use a spin coater to apply the first layer solution over the entire substrate.
2. Heat-treat the substrate with the first layer solution in a muffle furnace.
3. Using wrap film or mending tape for masking, partially apply the second layer solution to approximately half of the substrate area using the spin coater.
4. Heat-treat the substrate with the second layer solution in the muffle furnace.
5. Attach terminals.
The spin coating was performed using the spin coater (ASC-300) from Able Co., Ltd., and the heat treatment was conducted using the muffle furnace (KDF-P70) from Denken Co., Ltd. For the prepared semiconductor thin films, transmittance was measured and the band gap was evaluated using a Tauc plot. The transmittance measurement was performed using a UV-Vis spectrophotometer (UVmini-1240) from Shimadzu Corporation. Details will be discussed in the presentation.
[1] Y. Yamada, T. Kato, T. Ishibashi, T. Okamoto, and N. Mori, AIP Advances 8, 015101 (2018)
[2] Y. Yamada, N. Mori, T. Atsumi, T. Kato, T. Ishibashi, Physics Procedia 65, 165 (2015)
[3] Y. Yamada, T. Okamoto, Journal of Physics: Conference Series 1590, 012046 (2020)
Keywords: BSCCO, metal-organic decomposition method, MOD, semiconductor, heterojunction