Modifications in electrical properties of ZnO:In/PS/Si (100) heterojunction by ZnO intermediate layer

The sol-gel method has been used for the synthesis of indium doped zinc oxide (IZO) aerogel nanopowder; the obtained product was used in the target as a source for the deposition of thin IZO layers onto p-type porous silicon (PS) substrate by radio frequency magnetron sputtering. We deposited two heterostructures with (IZO/ZnO/PS/Si) and without (IZO/PS/Si) ZnO intermediate layer to study its role on the electrical properties. The obtained IZO thin films with a thickness of about 400 nm using indium concentration of 4 at%, were polycrystalline with a hexagonal wurtzite structure and preferential orientation in the (002) crystallographic direction. The effect of the intermediate ZnO layer on the electrical properties of the two heterojunctions, n-IZO/PS/p-Si and n-IZO/ZnO/PS/p-Si, was systematically investigated by current-voltage (I-V), capacitance-voltage (C-V), and capacitance-frequency (C-F) characteristics. Our measurements show that the junction properties strongly depend on temperature and the intermediate ZnO layer has significant impact on the transport properties in the n-IZO/ZnO/PS/p-Si heterostructure. The junction fabricated without intermediate ZnO layer possessed ideal rectifying behaviors (I-F/I-R = 32 at 300 K and 6 x 10(3) at 80 K for +/- 3 V). However, the rectifying behavior degrades for the n-IZO/ZnO/PS/p-Si heterojunction (I-F/I-R similar to 8 at 300 K and 7 at 80 K for +/- 3 V). The ambiguous behavior of IF/IR in the low temperature range (80-140 K) for the n-IZO/ZnO/PS/p-Si heterojunction was explained by the existence of tunnel paths active in this temperature range. The transport properties of the two diodes were explained in terms of the Anderson model and the space charge limited current model. The C-V measurements show a complex electrical behavior for the IZO/ZnO/PS/Si heterojunction, which is attributed to indium diffusion in the undoped ZnO intermediate layer during the growth process.