Origin of two-dimensional electron gas in Zn1-xMgxO/ZnO heterostructures

Although the two-dimensional electron gas (2DEG) in (001) Zn1-xMgxO/ZnO heterostructures was dis-covered about 20 years ago, the origin of the 2DEG is still inconclusive. In the present paper, the formation mechanisms of 2DEG near the interfaces of (001) Zn1-xMgxO/ZnO heterostructures were investigated via the first-principles calculations method. It is found that the polarity discontinuity near the interface can neither lead to the formation of 2DEG in devices with thick Zn1-xMgxO layers nor in devices with thin Zn1-xMgxO layers. For a heterostructure with a thick Zn1-xMgxO layer, the oxygen vacancies near the interface introduce a defect band in the band gap, and the top of the defect band overlaps with the bottom of the conduction band, leading to the formation of the 2DEG near the interface of the device. For a heterostructure with a thin Zn1-xMgxO layer, the absorption of hydrogen atoms, oxygen atoms, or OH groups on the surface of the Zn1-xMgxO film plays a key role for the formation of 2DEG in the device. Our results manifest the sources of 2DEGs in Zn1-xMgxO/ZnO heterostructures on the electronic structure level.

Automated summary

In this paper, the formation mechanisms of two-dimensional electron gas (2DEG) near the interfaces of (001) Zn1-xMgxO/ZnO heterostructures were investigated using first-principles calculations. The results showed that neither polarity discontinuity nor thick Zn1-xMgxO layers can lead to the formation of 2DEG. The presence of oxygen vacancies near the interface or the absorption of hydrogen atoms, oxygen atoms, or OH groups on the Zn1-xMgxO film surface plays a key role in the formation of 2DEG in thin Zn1-xMgxO layers. These findings provide insights into the sources of 2DEGs in Zn1-xMgxO/ZnO heterostructures at the electronic structure level.