Predicted electrical properties of modulation-doped ZnO-based transparent conducting oxides

Abstract

A one-dimensional Poisson/Schrödinger program has been used to predict the effect of layer thicknesses, donor concentration, and band-gap offset on the electrical properties of transparent conducting modulation-doped ZnO∕ZnMgO multilayer structures. Mobilities as high as 145cm2∕Vs were predicted for a structure with an average carrier density of 3.8×1018cm−3 and a resistivity of 1×10−2Ωcm; for a comparable resistivity in monolithic ZnO, the mobility would be lower ∼30cm2∕Vs and the carrier density would be higher, leading to higher optical absorption. However, it was found that the maximum sheet electron density that could be transferred from the doped to the undoped layers was ∼1013cm−2, limiting the lowest calculated resistivity to ∼1.5×10−3Ωcm. The optimal thicknesses to simultaneously achieve high mobility and low resistivity were 2–5nm for both the pure ZnO and ZnMgO:Al layers. For ZnO thicknesses above this range the resistivity steadily increased, and below 2nm the mobility decreased. For ZnMgO:Al thicknesses increased above this range, the mobility rapidly decreased, whereas decreasing below 2nm increased the resistivity. The effect of the pure ZnMgO set-back layer thickness on mobility is discussed and a spacer layer of ∼1.5nm is proposed for ZnO∕ZnMgO multilayers. The effect of ZnO layer thickness on possible intersubband scattering is also discussed.

Enhanced Electron Mobility Due to Dopant‐Defect Pairing in Conductive ZnMgO

“…Accordingly, Mg‐substituted ZnO (Zn 1‐ x Mg x O) is a candidate band‐gap‐energy tunable and band‐edge‐energy tunable transparent conducting oxide (TCO). This tunability is of great use in optimizing the performance of many optoelectonic devices . However, a substantial and usually undesired decrease in the maximum obtainable conductivity is observed with increasing Mg content .…”

Steady-State Electron Transport and Low-Field Mobility of Wurtzite Bulk ZnO and Zn1−x Mg x O

“…Therefore the conduction-band offset value (0.25 eV) is selected as the alloy potential, as provided in Ref. 16.…”

Growth and structural characterization of intrinsic, acceptor, and donor doped (Mg,Zn)O epilayers via metalorganic vapor phase epitaxy on (1 0 1¯ 0) ZnO substrates

“…In spite of the sustained interests in the development of the hexagonal wurtzite material zinc oxide (ZnO) and related alloy (Mg,Zn)O because of its attractive optical [1][2][3] and electronic [4][5][6][7] properties, the historic limitations due to poor hole injection [8,9] and polycrystalline and/or three dimensional [10][11][12][13] deposition on c-plane substrates remain notable challenges. Astute deposition schemes [14] have been used to achieve contiguous epilayers on c-plane ZnO by MOVPE; the realization of Frank-van der Merwe growth mode has often been limited to physical deposition techniques such as pulsed laser deposition [15,16] and molecular beam epitaxy [17][18][19][20] or solution growth [21][22][23].…”