Role of Surface States and Interface Charges in 2DEG in Sputtered ZnO Heterostructures

In this paper, we report on the influence of surface (donor and acceptor) states and interface charges on the formation of 2-D electron gas (2DEG) in MgZnO/ZnO heterostructure grown by sputtering. Donor and acceptor states alone cannot yield an order of magnitude higher value of 2DEG as observed by sputtering growth as compared to epitaxial techniques. While surface donor states are reported to govern the formation of 2DEG in epitaxially grown heterostructures, our simulations suggest a non-negligible contribution of surface acceptor states in the 2DEG density. In addition, the existence of interface charges due to high defect density along with appropriate values of donor and acceptor states is essential to accurately predict an order of magnitude higher 2DEG density grown by sputtering. This paper analyzes the distinct roles of donor and acceptor states along with interface charges in 2DEG formation and achieved values.