Electron confinement at diffuse ZnMgO/ZnO interfaces

Abstract

Abrupt interfaces between ZnMgO and ZnO are strained due to lattice mismatch. This strain is relaxed if there is a gradual incorporation of Mg during growth, resulting in a diffuse interface. This strain relaxation is however accompanied by reduced confinement and enhanced Mg-ion scattering of the confined electrons at the interface. Here we experimentally study the electronic transport properties of the diffuse heteroepitaxial interface between single-crystal ZnO and ZnMgO films grown by molecular-beam epitaxy. The spatial extent of the interface region is controlled during growth by varying the zinc flux. We show that, as the spatial extent of the graded interface is reduced, the enhancement of electron mobility due to electron confinement more than compensates for any suppression of mobility due to increased strain. Furthermore, we determine the extent to which scattering of impurities in the ZnO substrate limits the electron mobility in diffuse ZnMgO–ZnO interfaces.

Rapid Thermal Annealing for Surface Optimisation of ZnO Substrates for MBE-Grown Oxide Two-Dimensional Electron Gases

“…The resistance initially increases before gradually decreasing and reaching a level lower than that of the untreated substrate. The reduction in resistance after many annealing cycles is promising as it suggests these substrates will result in higher 2DEG mobilities [22], but the non-monotonic behaviour warrants explanation.…”

“…The treated sample (green) shows clear Shubnikov de Haas (SdH) oscillations at fields above 5 T, while no such oscillations are observed in the untreated sample (magenta). The SdH oscillations were used to determine the mobility and carrier concentrations of the 2DEG following [22]. The insert in Figure 3d shows the fit used to determine these properties.…”

Rapid Thermal Annealing for Surface Optimisation of ZnO Substrates for MBE-Grown Oxide Two-Dimensional Electron Gases

“…The resistance initially increases before gradually decreasing and reaching a level lower than that of the untreated substrate. The reduction in resistance after many annealing cycles is promising as it suggests these substrates will result in higher 2DEG mobilities [20], but the non-monotonic behaviour warrants explanation.…”

“…The treated sample (green) shows clear Shubnikov de Haas (SdH) oscillations at fields above 5 T, while no such oscillations are observed in the untreated sample (magenta). The SdH oscillations were used to determine the mobility and carrier concentrations of the 2DEG following [20]. The insert in 3d shows the fit used to determine these properties.…”