The C-V characteristics of the discussed junction measured at RT with different ac voltage frequency together with the equivalent circuit (see the inset). Observed capacitance drop is approximately ΔC 0 = 1 nF within the tested range of reverse bias.
The I-V characteristics of the discussed junction measured at RT, presented in linear (a) and semi-logarithmic (b) scale. The series resistance appears to be about 250 Ω. The inset in Fig. 2(a) shows the narrow range of applied bias (±0.5 V) in which the structure reveals pure rectifying behavior.
The Mott-Schottky analysis of the ZnO/GaN heterostructure producing the donor concentration in ZnO and diode's built-in voltage (see the dotted linear fit). Low frequency (f = 10 kHz) measurements are required (the black solid line) as the high frequency regime (f = 1 MHz) yields the strong and meaningless C− 2(V) dependence (shown by the black dashed line).
The admittance spectroscopy data (capacitance (C) and loss (L)) of the ZnO/GaN heterostructure obtained between 140 K (thick blue dashed curves) and 300 K (thick red solid curves)—as indicated.
Admittance spectrum of the capacitance (C) and loss (L) of ZnO/GaN heterostructure as a function of applied ac bias in the range of −0.48 V (green curves, dashed one for C and solid one for L) up to +0.2 V (red curves, dashed one for C and solid one for L). The results were obtained at RT.
Capacitance transients measured between 230 K and room temperature (as indicated). To determine the capacitance relaxation time τ either single or double exponential decay formula—see Eq. (3) —was fitted. This yielded the trap energy of about 0.57 eV. The applied bias was: V fill = 0 V and V empty = −2 V.
The Arrhenius plot of the ZnO/GaN heterojunction with the linear fits estimating the donors' activation (trap) energies E T. The applied bias was: V fill = 0 V and V empty = −2 V. The C–t measurements were performed within 300 s using 10 kHz signal of the ac voltage.
The estimated capacitance relaxation times τ(s) and emission rates e n (s−1) at indicated temperatures for ZnO/GaN heterostructure tested for 300 s using bias conditions of V fill = 0 V and V empty = −2 V. Only the transient obtained at T = 230 K was collected for a longer time (400 s). In case of fitting with the double-exponential formula only the meaningful value of τ was considered—see description in the text. Basing on these data, a defect level with the energy of E T1 ≈ (0.57 ± 0.03) eV was found.
Calculated activation energy, trap density and capture cross-section for defect levels found in the examined ZnO/GaN heterostructure.
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