Performance analysis of undoped and Mg-doped ZnO/p-Si heterojunction diodes grown by sol–gel technique

This paper reports the comprehensive analysis on the effect of Mg doping on structural, optical and electrical characteristics of Mg_xZn_1−xO/p-Si heterojunction diodes. In this work, undoped and Mg-doped ZnO thin films were directly synthesized on <100> p-Si (silicon) substrate using sol–gel spin coating method. The structural and optical properties of as-fabricated thin films are analyzed by means of XRD, AFM, SEM, ellipsometer and Photoluminescence spectroscopy. The as-grown films are having polycrystalline nature with preferred growth orientation along (002) direction. Although, no peaks due to Mg doping is exhibited in 5% Mg-doped ZnO thin films, however, due to phase segregation, the additional peaks of MgO phase at (200) and (220) direction has started visible for higher Mg-doped ZnO films. The Grain size of the films is diminished from 42.51 to 28.35 nm for Mg-doping increment from 0 to 15%, where as bandgap of the films is increased from 3.27 to 3.83 eV for same doping variation. Electrical parameters of Mg_xZn_1−xO/p-Si heterojunction diodes are studied after forming large area ohmic contacts of Al/Ti and Al on top of ZnO thin film and bottom of Si layer respectively. The significant electrical parameters of the diodes are calculated from current–voltage characteristics measured by semiconductor parameter analyzer and capacitance–voltage characteristics measured by LCR meter. With very high rectification ratio of 41741 and low reverse saturation current of 1.52 nA, Mg_0.1Zn_0.9O/Si heterojunction diode has potential to be used in future nanoelectronic devices with wider bandgap.