Characteristics of indium-tin-oxide Schottky contacts to ZnMgO/ZnO heterojunctions with band gap grading

Abstract

We report on electrical characteristics of indium-tin-oxide (ITO) Schottky contacts to transparent n-n isotype heterojunctions composed of a compositionally graded Zn1-xMgxO (g-ZnMgO) and ZnO films fabricated on ITO-coated glass substrates. The transparent ITO Schottky contacts to g-ZnMgO/ZnO heterostructures resulted in excellent diode characteristics with the rectification ratios as high as 10(4) at a bias voltage of +/- 3.0 V. The effective Schottky barrier heights were about 0.6 eV and could be tuned by modifying the electrical properties of g-ZnMgO layer. The formation of high barrier Schottky contacts was discussed in conjunction with a band gap grading and a highly resistive surface layer of g-ZnMgO.