A polaron approach to photorefractivity in Fe : LiNbO₃

Abstract

The thermally activated, incoherent hopping of small electron polarons generated by continuous illumination in iron-doped lithium niobate is simulated by a Marcus-Holstein model for which all the input parameters are known from literature. The results of the calculations are compared with a comprehensive set of data obtained from photorefractive, photogalvanic and photoconductive measurements under green light excitation on samples with different doping levels and stoichiometries in the temperature range between 150 K and room temperature. We show that the temperature and composition dependence of the photorefractive observables can be interpreted by a change in the abundance of the different hop types that a polaron performs before being captured by a deep Fe trap. Moreover, by a comparison between experimental and numerical data we obtain new insights on the initial photo-excitation part of the photorefractive process. In particular all results are consistent if a single value of the photogalvanic length L 1.44 0.05 PG =  ( )Åis assumed for all the samples and all the temperatures. The photo-generation efficiency f under green light excitation (somewhere denoted as quantum efficiency) is also estimated. It appears to decrease from 10%-15% at room temperature to about 5% at 150 K. This behavior is qualitatively interpreted in terms of a temperature-dependent retrapping probability of the light-emitted particles from the initial Fe donor center.

Enhancement of Photorefraction in Vanadium-Doped Lithium Niobate through Iron and Zirconium Co-Doping

“…Also, it is reported that, in LN:Fe, the charge transportation through polaron hopping of electron/holes is slow and is processed on Li-sites due to the presence of Nb Li defects. It was suggested that in the absence of the antisites Nb, the hopping transport is shifted to the Nb sites and is much faster than chaotic Li-sites [42,43,44]. Therefore, doping V and Zr with Fe ions changes the hopping transport to Nb sites by reducing the Nb Li sites and does not disturb the usual lithium site occupation of Fe and instead helps in eliminating the undesired intrinsic traps as shown in Figure 5b.…”

Trifurcated Splitting of Water Droplets on Engineered Lithium Niobate Surfaces

“…The main contribution to the photovoltaic current arises along the z axis of the material and is almost independent of light polarization since β zxx = β zyy and β zzz are nearly the same size (4 × 10 –8 V –1 ); in contrast, the in-plane contributions to the photovoltaic current along the y axis are practically reduced to one-tenth, since the elements β yxx = β yyy are smaller by almost 1 order of magnitude (2 × 10 –9 V –1 ) . Therefore, photoexcited electrons easily accumulate on the + z face of the Fe:LiNbO 3 crystal, leading to a surface charge density σ c = ϵ zz r ϵ 0 L p v Λ , where ϵ zz r = 28 is the relative dielectric constant along the z axis, ϵ 0 the dielectric constant in vacuum, and L pv and Λ are the mean photovoltaic transport length and the drift coefficient, ,, respectively. According to the values of L pv and Λ reported in the literature, in the sample used in this study, surface charge densities of up to 720 μC/m 2 are expected to be photoinduced, leading to a photovoltaic field inside the crystal of approximately 3 × 10 6 V/m.…”

Влияние примеси железа на электрическую проводимость кристаллов LiNbO-=SUB=-3-=/SUB=-

“…Подобный механизм ранее уже обсуждался в рамках модели транспорта фотоиндуцированного электрона по двум типам ловушек в процессе возникновения фоторефракции [1]. Отметим, что в последнее время достаточно активно обсуждается роль ПМР в фоторефрактивном эффекте [27][28][29].…”