Band profiles of ZnMgO/ZnO heterostructures confirmed by Kelvin probe force microscopy

Abstract

The band profiles of ZnMgO/ZnO heterostructures were confirmed through surface potential measurements by Kelvin probe force microscopy. A simple model for the band profile was proposed and the various band parameters were evaluated experimentally and theoretically based on the band model. The band profile was calculated and validated with experimental results using the Schrödinger–Poisson equation. The energy level of the ZnMgO surface donor state, which serves as the source of the two-dimensional electron gas in ZnMgO/ZnO heterostructures, was estimated from the band parameters; nearly identical energy levels around 0.8 eV were obtained for Zn1−xMgxO layers with Mg compositions x ranging from 0.12 to 0.42 and the corresponding charge densities were estimated to be 8×1012 cm−2.

From 20.9 to 22.3% Cu(In,Ga)(S,Se)2solar cell: Reduced recombination rate at the heterojunction and the depletion region due to K-treatment

“…For the ZMO layer, we assume there is no defects with the following material properties: E g of 3.37 eV, dielectric constant of 7.7, electron affinity of 4.15 eV and a donor concentration at the order of 10 15 cm −3 . Due to the low electron affinity of the ZMO layer, 31) a positive CBO was induced [ Fig. 4(c)].…”

Polarization discontinuity induced two-dimensional electron gas at ZnO/Zn(Mg)O interfaces: A first-principles study

“…30,31 The presence of the 2DEG is normally confirmed by Hall effect and capacitance measurements. 24,27,28 The observation of the quantum Hall effect 25 and the fractional quantum Hall effect 29 in these heterostructures testifies to the high quality of these interfaces. Charge concentrations on the order of 10 13 cm −2…”

“…26,28,29 Recently, a spin-polarized 2DEG at ZnO/Zn(Mg)O interfaces has been reported. 31,32 The ferromagnetism was presumed to be carrier mediated and originating from the formation of Zn vacancies.…”

“…23 Recently, a different type of system supporting a 2DEG, wurtzite ZnO/Zn(Mg)O heterostructures, has been investigated experimentally. [24][25][26][27][28][29][30][31][32] These heterostructures are usually grown using molecular beam epitaxy; 24,25 however, a 2DEG was also demonstrated in samples grown with metal-organic vapor deposition which is suitable for mass production. 30,31 The presence of the 2DEG is normally confirmed by Hall effect and capacitance measurements.…”

Electron confinement at diffuse ZnMgO/ZnO interfaces

“…For a non-zero polarization gradient, however, it is possible for carriers to be confined in the interface region where the bandgap is not at its minimum value. This is schematically illustrated in Figure 1 1,[6][7][8][9][10] The "bulk" Mg concentration at z > ζ is 40%. The carrier concentration in both the ZnMgO and ZnO far from the interface region is taken to be 10 18 cm 3 .…”