P-doping and valence band engineering of ZnO and epitaxial growth, optical properties and alloys of transition metal dichalcogenides

Abstract

ZnO is a wide band gap (~3.3 eV) semiconductor at room temperature with high excitation binding energy (~60 meV) making it extremely attractive in many optoelectronic applications, e.g., light emitting diodes (LEDs), laser diodes (LDs), transparent semiconductors, and photovoltaic [1-2]. Compared to GaN, which is already in application, ZnO is significantly cheaper and offers alternatives to overcome the cost associated with GaN technology [2]. GaN is the most important semiconductor after silicon [3]. The market of lighting industry will be amount to 120 billion by 2020 [4]. This huge lighting industry can be accessible if ZnO based technology can be realized. However, stable p-doping remains elusive in this system, thus hindering its application in bi-polar devices [5]. Extensive research is being pursued to understand the problem and overcome the difficulty. The first part of this thesis is directed towards this challenge by one of the several approaches already proposed in the literature i.e. by pushing the valence band upwards towards the vacuum level and at the same time understanding the role of native defects their role and control in this system. We have grown epitaxial forM.S. of ZnO films so that any success can be translated immediately to device fabrication stage.