Fig. 1
a Capacitance–voltage–luminance (C-V-L) characteristics of D1, D2, and D3. Orange solid line shows the turn-on voltage corresponding to the maximum of the first peak in their C-V characteristics. b Current density–voltage curves of the three devices in log–log scale, additionally divided into three regions marked by purple dashed lines marked I, II, and III. The current density (J) and voltage (V) conform to the relationship of \( J\propto {aV}^m \)