Stability of photovoltage and trap of light-induced charges in ferroelectric WO3-doped (Pb0.97La0.03)(Zr0.52Ti0.48)O3 thin films

Abstract

The stability of photovoltage in WO3-doped (Pb0.97La0.03)(Zr0.52Ti0.48)O3 (PLWZT) ferroelectric thin films was investigated. For in-plane polarized configuration, with a greatly enhanced electrode gap, the reduction ratio of photovoltage during multicycle UV illumination was significantly smaller and stability of photovoltage was greatly improved over the sandwich capacitor configuration. The ferroelectric-metal interfacial effects including Schottky barriers and polarization screening due to the trap of photoinduced charges at interfaces were found to determine the magnitude, stability, and even the polarity of the photovoltage, particularly for the electrode-sandwiched PLWZT thin films.

Hyper-sensitive piezophotovoltaic effects in ferroelectric nanocylinders

“…41,42 It is clear that FPV effects may become very small when the average internal electric field in FNC is zero. [16][17][18][19][20][21][22][23][24] In this case, the photocurrent is only due to charge transport via diffusion.…”

“…[1][2][3][24][25][26] Both experimental and theoretical works have shown that the FPV effect is different from that in conventional p-n junctions or Schottky barriers of the semiconductors. [18][19][20][21][22][23][24][25][26][27] Although a complete understanding of the physical mechanisms involved in the FPV effect in metal-ferroelectric-metal ͑MFM͒ structures with the shortcircuit boundary conditions has not yet been accomplished, a widely accepted explanation of the photoelectric current is the separation of the photon-generated electron-hole pairs ͑excitons͒ by the internal electric field, [20][21][22][23][24] which also provides the potential difference that drives the photocurrent in the external circuit connected to the ferroelectrics. In absence of an external electric field, the internal electric field comes from the depolarization field produced by polarization screening charges in the metal electrodes and the inhomogeneous polarization distribution near interfaces.…”

“…Recent experimental and theoretical works have established that among all known perovskite ferroelectric materials, ͑Pb 0.97 La 0.03 ͒ ϫ͑Zr 0.5 Ti 0.5 O 3 ͒ ͑PLZT͒, or BFO could be the most promising candidates for photoelectric applications. [16][17][18][19][20][21][22][23][24] Photovoltaic effects occur generally in systems with asymmetric interfaces, such as semiconducting p-n junctions or metal-semiconductor interfaces with Schottky barriers. [1][2][3][24][25][26] Both experimental and theoretical works have shown that the FPV effect is different from that in conventional p-n junctions or Schottky barriers of the semiconductors.…”

“…Based on previous works by Razeghi and Rogalski 50 and Qin et al, [20][21][22][23] the carrier concentrations n and p then obey the following conservation equations:…”

“…͑2͒ was assumed to be uniform, neglecting effects due to the interface between metal electrodes and ferroelectric layer in previous works. [20][21][22][23] We consider as our thermodynamic reference a crystal of infinite extent ͑surfaceless͒ absent an applied field. Let P be the spontaneous polarization field ͑simply referred to as the polarization in the following͒.…”