A two-dimensional electron gas was observed in Zn polar

Zn Mg O ∕ Zn O

(ZnMgO on ZnO) heterostructures grown by radical source molecular beam epitaxy. The electron mobility of the

Zn Mg O ∕ Zn O

heterostructures dramatically increased with increasing Mg composition and the electron mobility

(μ \sim 250 {cm}^{2} ∕ V s)

at RT reached a value more than twice that of an undoped ZnO layer

(μ \sim 100 {cm}^{2} ∕ V s)

. The carrier concentration in turn reached values as high as

\sim 1 \times 10^{13} {cm}^{- 2}

and remained nearly constant regardless of Mg composition. Strong confinement of electrons at the

Zn Mg O ∕ Zn O

interface was confirmed by

C - V

measurements with a concentration of over

4 \times 10^{19} {cm}^{- 3}

. Temperature-dependent Hall measurements of

Zn Mg O ∕ Zn O

heterostructures also exhibited properties associated with well defined heterostructures. The Hall mobility increased monotonically with decreasing temperature, reaching a value of

2750 {cm}^{2} ∕ V s

4 K

. Zn polar “ZnMgO on ZnO” structures are easy to adapt to a top-gate device. These results open new possibilities for high electron mobility transistors based upon ZnO-based materials.

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