Fig. 3
From: Critical band-to-band-tunnelling based optoelectronic memory
Photomemory characteristics and dual NDR mechanism analysis of the critical BTBT memory. a and b Transient behaviour of the hole quasi-Fermi levels near the rising and falling edges of a signal light pulse injected into the InSe/BP heterojunction energy bands. The signal light pulse is a square wave with a duration of 0.1 ns. The times of the rising and falling edges of the pulse are ton and toff = ton + 0.1 ns, respectively. c Linear and saturation behaviour of the number density of stored holes in InSe with absorbed photogeneration density at toff + 4 ms under different gate voltages Vg from −1 to −5 V. The signal light pulse is a square wave with a 1 ns duration. The dashed curve is the boundary between the linear and saturated regions. The dashed-dotted line shows the ideal curve when all the photogenerated holes are stored. d Experimental results show dual NDR in the hysteresis curve of the gate current when the gate voltage is swept from −20 to 20 V (red curve) and back (grey). The positive direction of the hysteresis current is defined as the direction from InSe to BP. The dashed line shows the flat band condition extracted from the saturation behaviour in (c). e The outflow of excess holes due to the decreasing potential well, resulting in an NDR in the hysteresis curves. f Calculated distribution of hole flow \({\rm{d}}{Q}_{{\rm{h}}}/{\rm{d}}V\) with gate voltage Vg and the total number of holes Qh in InSe. g The tunnelling current is strongest when the energy band alignment is flat and decreases sharply when crossing over VNDR. h Calculated electron BTBT flow \({\rm{d}}{Q}_{{\rm{e}}}/{\rm{d}}V\) with gate voltage Vg and the total number of electrons Qe in InSe. Blue dots are time-dependent simulation results of the variation in Qh and Qe, with the gate voltage Vg showing hole outflow near Vhp = −1 V and electron BTBT near VBTBT = 2.2 V, respectively. Purple lines are the hole outflow current \({I}_{{\rm{h}}{\rm{p}}}=({\rm{d}}{Q}_{{\rm{h}}}/{\rm{d}}V)({\rm{d}}V/{\rm{d}}t)\) and electron BTBT current \({I}_{{\rm{B}}{\rm{T}}{\rm{B}}{\rm{T}}}=({\rm{d}}{Q}_{{\rm{e}}}/{\rm{d}}V)({\rm{d}}V/{\rm{d}}t)\). The time-dependent simulation results show that the positions of the peaks of the hole outflow current and BTBT current coincide with the two NDR peaks in (d)
