Analytical Model for 2DEG Density in Graded MgZnO/ZnO Heterostructures With Cap Layer

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

“…The possible reasons for this are the simultaneous enhancement of the screening effect due to the increase in Mg composition and the suppression of optical phonon scattering due to the addition of a ZnO cap layer. At the MgZnO/ZnO interface, only the first energy sub-band is filled; the other higher sub-bands remain empty, as shown in our previous simulation work [19]. Thus, only the intra-sub-band scattering within the first subband is important in the polar optical phonon scattering mechanism.…”

“…Mobility increases from 25 cm 2 V −1 s −1 at 5 nm to 78 cm 2 V −1 s −1 at 50 nm due to the suppressed scattering of carriers with decreased density. The decrease in n s with cap layer thickness might be due to the reduction of piezoelectric polarization in the cap layer with increasing cap layer thickness [19]. A similar reduction in n s is also observed in GaN/ AlGaN/GaN material systems [18,24].…”

“…The inset of figure 2(a) shows the generic conduction energy band diagram of the bilayer and capped heterostructures, in which ϕ b is the bare surface barrier height, E F is the Fermi energy level with respect to the bottom of the conduction band at the MgZnO/ZnO interface, and ΔE C1 and ΔE are the conduction band offsets at the barrier/buffer and cap/ barrier interfaces, respectively. As the Mg composition in MgZnO increases, the ΔE C1 increases for both heterostructures, which deepens the triangular potential well that forms at the barrier/buffer interface where the 2DEG electrons are captured [19,20]. With the deepening of the triangular potential well, the number of 2D densities of states involved in the formation of 2DEG increases, enhancing the n s .…”

Impact of MgO spacer layer on microwave performance of MgZnO/ZnO HEMT

“…Further, wide bandgap materials such as GaN-based high electron mobility transistors (HEMT) are being extensively explored to devise the high-speed radio frequency devices [6]. ZnO is another promising wide bandgap material system that displays large energy bandgap (3.37 eV) [7][8][9][10], high breakdown field (∼3 MV/cm) [11], large conduction band offset for MgZnO/ZnO (MZO) heterostructures [12], high saturation velocity (≈10 7 cm s −1 ) [12][13][14]. ZnO-based heterostructures have shown higher two-dimensional electron gas (2DEG) density (∼10 13 -10 14 cm −2 ) [15,16] than that exhibited in the GaN-based heterostructures, which is one of the crucial parameters to realize high current densities and higher conductance.…”

“…Sasa et al [14] and Ye et al [19] have realized highquality epitaxially-grown MZO-based HEMT. Furthermore, there are reports in the literature of high 2DEGyielding sputtered [13,15,18,20] MZO heterostructures, implying the feasibility of large-area and hence lowcost ZnO-based HEMTs for microwave applications.…”