Two-dimensional electron gases in MgZnO/ZnO and ZnO/MgZnO/ZnO heterostructures grown by dual ion beam sputtering

Abstract

This work reports on the formation of high-density (~1013–1014 cm−2) two-dimensional electron gas (2DEG) in ZnO-based heterostructures, grown by a dual ion beam sputtering system. We probe 2DEG in bilayer MgZnO/ZnO and capped ZnO/MgZnO/ZnO heterostructures utilizing MgZnO barrier layers with varying thickness and Mg content. The effect of the ZnO cap layer thickness on the ZnO/MgZnO/ZnO heterostructure is also studied. Hall measurements demonstrate that the addition of a 5 nm ZnO cap layer results in an enhancement of the 2DEG density by about 1.5 times compared to 1.11 1014 cm−2 for the uncapped bilayer heterostructure with the same 30 nm barrier thickness and 30 at.% Mg composition in the barrier layer. From the low-temperature Hall measurement, the sheet carrier concentration and mobility are both found to be independent of the temperature. The capacitance–voltage measurement suggests a carrier density of ~1020 cm−3, confined in 2DEG at the MgZnO/ZnO heterointerface. The results presented are significant for the optimization of 2DEG for the eventual realization of cost-effective and large-area MgZnO/ZnO-based high-electron-mobility transistors.

Analytical study of MgZnO/ZnO heterostructure field effect transistor for power switching

“…ZnO is another promising wide bandgap material system that displays large energy bandgap (3.37 eV), 6 high breakdown field (~3 MV/cm), 7 and large saturation drift velocity (≈10 7 cm/s) 6 and this material system has not been explored extensively for power HFET applications. ZnO‐based heterostructures have shown higher two‐dimensional electron gas (2DEG) density (~10 13 –10 14 cm −2 ) 6,8,9 than that exhibited in the GaN‐based heterostructures, which is one of the crucial parameters to realize high current densities in power HFETs. In addition, ZnO, as a material, provides unique advantages of high‐quality material production at lower temperatures (100–300°C) using even a cost‐effective polycrystalline growth system along with the accessibility to large‐area ZnO substrates at relatively low cost 6,10,11 .…”

Analytical Study of ZnO-based HEMT for Power Switching

“…As Si and GaAs-based power devices have reached their theoretical limits of power density [3,5], wide bandgap materials, such as GaN-based high electron mobility transistors (HEMT) are being extensively explored to further push the efficiency and power density limits of power devices [4]. ZnO is another promising wide bandgap material system that displays large energy bandgap (3.37 eV) [6], high breakdown field (∼ 3M V /cm) [7], and large saturation drift velocity (≈ 10 7 cm/s) [6] and this material system has not been explored extensively for power HEMT applications. ZnO-based heterostructures have shown higher two-dimensional electron gas (2DEG) density (∼ 10 13 − 10 14 cm −2 ) [6,8,9] than that exhibited in the GaN-based heterostructures, which is one of the crucial parameters to realize high current densities in power HEMTs.…”

“…ZnO is another promising wide bandgap material system that displays large energy bandgap (3.37 eV) [6], high breakdown field (∼ 3M V /cm) [7], and large saturation drift velocity (≈ 10 7 cm/s) [6] and this material system has not been explored extensively for power HEMT applications. ZnO-based heterostructures have shown higher two-dimensional electron gas (2DEG) density (∼ 10 13 − 10 14 cm −2 ) [6,8,9] than that exhibited in the GaN-based heterostructures, which is one of the crucial parameters to realize high current densities in power HEMTs. In addition, ZnO, as a material, provides unique advantages of high-quality material production at lower temperatures (100 to 300 ℃) using even a cost-effective polycrystalline growth system along with the accessibility to large-area ZnO substrates at relatively low cost [6,10,11].…”

“…ZnO-based heterostructures have shown higher two-dimensional electron gas (2DEG) density (∼ 10 13 − 10 14 cm −2 ) [6,8,9] than that exhibited in the GaN-based heterostructures, which is one of the crucial parameters to realize high current densities in power HEMTs. In addition, ZnO, as a material, provides unique advantages of high-quality material production at lower temperatures (100 to 300 ℃) using even a cost-effective polycrystalline growth system along with the accessibility to large-area ZnO substrates at relatively low cost [6,10,11]. Sasa et al [12], Koike et al [13], and Ye et al [14] have realized high-quality epitaxially-grown MgZnO/ZnO (MZO) based HEMT.…”

“…Sasa et al [12], Koike et al [13], and Ye et al [14] have realized high-quality epitaxially-grown MgZnO/ZnO (MZO) based HEMT. Moreover, reports of realizing high 2DEG yielding sputtered [6,9,15,16] MZO heterostructures are available in the literature, suggesting the possibility of achieving large-area and therefore, low-cost ZnO-based power HEMTs.…”