Distinct band UV–Visible photo sensing property of ZnO-Porous silicon (PS):p-Si hybrid MSM heterostructure

Abstract

Present article deals with fabrication of UV–Visible radiation sensing photodetector (PD) by architecting planar and sandwiched (PD1 and PD2) electrode configurations on ZnO-PS:p-Si heterostructure. PS:p-Si structure is prepared by electrochemical anodization method. Thin ZnO layer of ~162 nm is deposited on PS:p-Si substrate using pulsed DC magnetron sputtering technique. Gold (Au) is combined with Aluminium (Al) to provide rectifying Schottky contacts to the devices. Prior to device testing it is tested for various conventional characterizations. FESEM studies confirm uniform deposition of nanocrystalline ZnO thin film with mean particle size of ~ 35 nm, whereas its cross section shows uniform interface between ZnO and PS with combined thickness of ~700 nm. Cross sectional EDX analysis confirms diffusion of ZnO particles into PS layer. UV–vis absorption spectrum gives bandgap of ZnO as ~3.3 eV. Reflectance measurement of the heterostructure shows decrease in reflectivity compared to bulk c-Si with ZnO-PS:p-Si showing multiple interference pattern compared to bare ZnO coated on glass within the spectral range 200 nm-800 nm. The pattern is remarkably increased compared to that of PS:p-Si. Photoluminescence study reveals various luminescence bands peaked at ~378 nm, 388 nm, 398 nm, 410 nm, 420 nm, 433 nm, 450 nm, 467 nm, 482 nm 492 nm and 597 nm. Current- Voltage (I–V) measurement for dark current (Id) gives low leakage current of the devices PD1 and PD2 respectively as 6.6×10−8A and 7.5×10−7A at -5V, which is however an order of magnitude more than the ZnO coated one on glass. Both the devices PD1 and PD2 show UV–Visible photoresponse, whereas the ZnO device on glass shows response to UV (375 nm) only. Both the devices show response time ~1 s in visible range which is nearly half the value in UV range.