Abstract
A novel small signal equivalent circuit model is proposed in the inversion regime of metal/(ZnO, ZnMnO, and ZnCoO) semiconductor/Si3N4 insulator/p-Si semiconductor (MSIS) structures to describe the distinctive nonlinear frequency dependent capacitance (C-F) and conductance (G-F) behaviour in the frequency range from 50 Hz to 1 MHz. We modelled the fully depleted ZnO thin films to extract the static dielectric constant (εr) of ZnO, ZnMnO, and ZnCoO. The extracted enhancement of static dielectric constant in magnetic n-type conducting ZnCoO (εr ≥ 13.0) and ZnMnO (εr ≥ 25.8) in comparison to unmagnetic ZnO (εr = 8.3–9.3) is related to the electrical polarizability of donor-type bound magnetic polarons (BMP) in the several hundred GHz range (120 GHz for CdMnTe). The formation of donor-BMP is enabled in n-type conducting, magnetic ZnO by the s-d exchange interaction between the electron spin of positively charged oxygen vacancies {V}_{o}^{+} in the BMP center and the electron spins of substitutional Mn2+ and Co2+ ions in ZnMnO and ZnCoO, respectively. The BMP radius scales with the Bohr radius which is proportional to the static dielectric constant. Here we show how BMP overlap can be realized in magnetic n-ZnO by increasing its static dielectric constant and guide researchers in the field of transparent spintronics towards ferromagnetism in magnetic, n-ZnO.
Highlights
A novel small signal equivalent circuit model is proposed in the inversion regime of metal/(ZnO, ZnMnO, and ZnCoO) semiconductor/Si3N4 insulator/p-Si semiconductor (MSIS) structures to describe the distinctive nonlinear frequency dependent capacitance (C-F) and conductance (G-F) behaviour in the frequency range from 50 Hz to 1 MHz
The ZnO, ZnCoO, and ZnMnO thin films have been grown by pulsed laser deposition (PLD) on insulator-semiconductor (Si3N4/p-Si) MIS structures for investigating the static dielectric constant of the magnetic ZnO thin films (Fig. 1)
The static dielectric constant εr (Table 1) calculated for ZnO, ZnCoO, and ZnMnO grown at 6.50 × 10−3 mbar (LP), 3.91 × 10−2 mbar (HP) oxygen partial pressure is plotted in Fig. 2(a) for contact area A1 and in Fig. 2(c) for contact area A2 (A1 = 5.026 × 10−7 m2 and A2 = 2.827 × 10−7 m2)
Summary
A novel small signal equivalent circuit model is proposed in the inversion regime of metal/(ZnO, ZnMnO, and ZnCoO) semiconductor/Si3N4 insulator/p-Si semiconductor (MSIS) structures to describe the distinctive nonlinear frequency dependent capacitance (C-F) and conductance (G-F) behaviour in the frequency range from 50 Hz to 1 MHz. The formation of donor-BMP is enabled in n-type conducting, magnetic ZnO by the s-d exchange interaction between the electron spin of positively charged oxygen vacancies Vo+ in the BMP center and the electron spins of substitutional Mn2+ and Co2+ ions in ZnMnO and ZnCoO, respectively. BMPs are formed by the s-d exchange interactions between the electron spin of a singly charged oxygen vacancy Vo+ in the center of the BMP and the electron spins of substitutional 3d transition metal ions in a sphere with Bohr radius rB9–11. Investigations of dielectric constant of ZnCoO powders modelled from measured shift in bandgap showed that it is not possible to achieve significant increase in dielectric constant This may be due to the absence of singly ionised oxygen www.nature.com/scientificreports vacancies (Vo+) in ZnCoO powders enabling s-d exchange interaction and bound magnetic polaron formation which would enhance the static dielectric constant of ZnCoO powders. We chose a MSIS heterostructure in order to extract the static dielectric constant of magnetic, n-type conducting ZnO layers
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