Ferroelectric-semiconductor Sn2P2S6 Research Articles

Ultrafast spectroscopy of shift-current in ferroelectric semiconductor Sn2P2S6

We report sub-picosecond photocarrier dynamics observed via emitted terahertz waves in a ferroelectric semiconductor Sn2P2S6. Excitation photon energy, intensity and polarization dependences of the photocarrier dynamics testify that the ultrafast photocurrent originates from the shift-current under interband excitation. The photocurrent excitation spectrum shows a quantitative agreement with that derived from first-principles calculations with the Berry connection integrated, showing the shift-current to be a sensitive feature in ferroelectrics. The terahertz emission spectroscopy is a powerful tool to identify the intricate carrier dynamics under pulsed photoexcitation.

The temperature dependence of the photoinduced soft mode in Sn2P2S6 crystal

In this paper, we present the results of the temperature dependence studies of the photoinduced phonon mode which appears in a ferroelectric-semiconductor Sn2P2S6 (SPS) crystal under the influence of femtosecond laser pulses. We show that its behavior reminds the soft mode one near the phase transition. However, the observed decrease in the oscillation frequency in the vicinity of Curie temperature Tc is much weaker than previously reported. This can be explained by the shadowing of the pure soft mode by its interaction with other photoinduced modes.

Optical second harmonic generation and its photoinduced dynamics in ferroelectric semiconductor Sn2P2S6

By means of optical pump–probe technique, the ultrafast dynamics of nonlinear optical response of the ferroelectric semiconductor Sn2P2S6 crystal excited with a femtosecond laser pulse has been investigated. It has been shown that, under the action of femtosecond pulses, change in optical second harmonic generation occurs in the sample, which can be due to screening of existing electric polarization.

Photoinduced dynamics and femtosecond excitation of phonon modes in ferroelectric semiconductor Sn2P2S6

The ultrafast dynamics of electrons and phonons excited by femtosecond light pulses in ferroelectric semiconductor Sn2P2S6 is investigated using the optical pump–probe technique. It is demonstrated that a soft mode can be excited in this ferroelectric in the vicinity of the phase transition initiated by laser radiation.

Effect of Polarization State on Photovoltaic Properties of Ferroelectric Semiconductor Sn2P2S6 Films

In this work, the experimental results of pyroelectric and photovoltaic responses of semiconductor-ferroelectric Sn2P2S6 films are presented for both preliminary polarized samples and films under external electric field. The measurements were carried out in short-circuit conditions under illumination of the Al/Sn2P2S6/Al structure by modulated laser light with λ = 6328 Å. It is shown that varying the intensity of monochromatic laser irradiation by focusing enables to separate the pyroelectric and photovoltaic responses of ferroelectric semiconductors.

Photorefractive waveguides in He^+ implanted pure and Te-doped Sn_2P_2S_6

We have demonstrated for the first time, to the best of our knowledge, photorefractive two-wave mixing in He+ implanted waveguides in one of the most promising materials for infrared photorefractive applications, the ferroelectric semiconductor Sn2P2S6. The high optical nonlinearity is preserved after implantation and at the telecommunication wavelength λ=1.55 μm, a maximal two-wave mixing gain of 2.5 cm−1 has been measured in Te-doped waveguides. In the nominally pure material an increase of the effective number of traps after implantation has been observed, resulting in an increase of the two-beam coupling gain by a factor of almost 2 in the 633-1064 nm spectral range. In 1% Te-doped Sn2P2S6 the effect of ion implantation to the photorefractive response is completely different than in pure materials. While the dominant contribution by holes is not considerably affected, a strong, thermally induced charge compensation is observed in the He+ implanted Te-doped waveguides.

High-speed photorefraction at telecommunication wavelength 155 μm in Sn_2P_2S_6:Te

We demonstrated for what is the first time to our knowledge photorefractive two-wave mixing in a bulk ferroelectric crystal using cw light at the telecommunication wavelength 1.55 microm. In the Te-doped ferroelectric semiconductor Sn2P2S6 with absorption constant <0.1 cm(-1) at 1.55 microm, grating recording times of 10 ms and a two-beam coupling gain of 2.8 cm(-1) have been measured at 350 mW power (intensity 440 W/cm(2)) without a necessity to apply an external electric field. With a moving grating technique, a maximal gain of 6.0 cm(-1) has been obtained.

Transient short-circuit photocurrent in ferroelectric semiconductor Sn2P2S6 films

Transient short-circuit photocurrents in films of the ferroelectric semiconductor Sn2P2S6 are studied in a temperature range that includes the phase transition point. The influence of an external electric field and white-light illumination on the photoelectric response of samples is discussed.

Elastic and electromechanical properties of new ferroelectric-semiconductor materials of Sn2P2S6 family

The crystals of ferroelectric-semiconductor Sn2P2S6 exhibit a strong piezoelectric effect. We present measurements of ultrasonic and piezoelectric properties of other crystals of the Sn2P2S6 family: i.e., Sn2P2Se6 and CuInP2S6. The acoustoelectric method was applied to measure electromechanical coupling parameters in the ferroelectric phase of Sn2P2Se6 single crystals. The electromechanical coupling coefficients in lamellar CuInP2S6 crystalline plates were measured by the resonance method. The CuInP2S6 plate was employed as a piezoelectric transducer. The signal detected by this transducer was measured as a function of temperature and it was shown that the piezoelectric coupling disappears in the paraelectric phase. Anomalies at the phase transition have been observed at ultrasonic investigations of CuInP2S6 crystals.

Investigation of acoustoelectric phenomena in Sn2P2S6 single crystals

The ultrasonic measurements of electronic attenuation have been performed in the crystals of ferroelectric semiconductor Sn2P2S6, which exhibit strong piezoelectric effect. From the dependence of electronic attenuation of ultrasound on conductivity the electromechanical coupling parameters have been calculated. The temperature dependence of acoustoelectric voltage has been measured and it was shown that it mainly follows the variation of electromechanical coupling constant. The influence of the long time crystal exposure in paraelectric phase near the phase transition temperature together with illumination of the Sn2P2S6 sample on ultrasonic velocity and attenuation has been also studied. It was shown, that relaxation of electronic subsystem significantly changes the critical ultrasonic behaviour. In this case the temperature anomalies of ultrasonic velocity and attenuation become very similar to that of feroelectric with incommensurate phase.

Polarization distribution in ferroelectric-semiconductor Sn2P2S6 in the phase transition region

Polarization distribution Sn2P2S6 single crystals has been characterized experimentally. It is shown that the polarization is distributed nonuniformly near the surface both in the ferroelectric and paraelectric phase. The observations may be connected to the surface effects and not necessarily related to the domain structure.

Surface layers of TGS class ferroelectrics and Sn2P2S6ferroelectric-semiconductor in the phase transition region

Abstract The results of a study of pyroelectric properties of surface layers in ferroelectric-semiconductor Sn2P2S6 with the aid of pyrocurrent frequency dependence measurements are presented. On this basis estimates of the surface layer thickness are obtained.

Effect of illumination on the polarization reversal processes in ferroelectric-semiconductor Sn2P2S6

A study has been made of the switching processes in ferroelectric-semiconductor Sn2P2S6 single crystals as affected by illumination. The investigation has been performed with the aid of Barkhausen effect method. It is shown that the processes of establishing the equilibrium polarization values are accelerated by illumination such that the effect is the greater the higher is the rate of polarization changes.

Photoferroelectric Phenomena in Sn2P2S6 Single Crystals and Thin Films

ABSTRACTTne present paper is devoted to the experimental study and the analysis of photoferroelectric phenomena in ferroelectric-semiconductor Sn2P2S6 crystals and films. These photoactive light-induced phenomena observed in polarized Sn2P2S6 samples are described by the model of screening the depoling field of remanent polarisation by free charge carriers fixed at the deep energy levels.

Film structures based on the ferroelectric-semiconductor Sn2P2S6

Abstract Polycrystalline films of the ferroelectric-semiconductor Sn2P2S6 with the crystallite orientation of different types have been prepared by the method of thermal vacuum evaporation in quasiclosed volume. The films exhibit, upon volume excitation, high piezomodulus. Distinctive features of the temperature and frequency dependence of the capacitance of the structures metal-ferroelectric film-metal indicate that the capacitance of such structures is, in low-frequency measuring fields, determined by surface layers of the film. The structures metal-ferroelectric film-semiconductor have been studied by the method of C-V characteristics. The character of the hysteresis of C-V loops points to the presence of an intrinsic field effect which continues during ten minutes.

Influence of magnetic field on the ferroelectric properties of Sn2P2S6 crystals

The influence of the permanent magnetic field on the dielectric properties of ferroelectric-semiconductor Sn2P2S6 single crystals has been investigated near the ferroelectric phase transition. It is found that the value of Curie temperature shift ΔTc depends on the orientation Ps[101] respectively to the magnetic field. Maximum ΔTc for the annealed sample is 0.2° for H = 23 kG. Accordingly to results of dielectric measurements the phase transition in Sn2P2S6 is referred to the first order. The shift of Tc is connected with the interaction of the moving phase boundary with the magnetic field.