Helicity dependent temporal profile of the semiconductor thin film photoresponse

Abstract

We demonstrate that the transverse photovoltage pulses generated in the thin CuSe/Se semiconductor nanocomposite film irradiated by circularly and linearly polarized femtosecond laser beams have different durations indicating the dependence of the relaxation time of the photogenerated carriers on their spin. For the linearly polarized excitation beam, the photovoltage is a unipolar pulse that reverses polarity when the polarization azimuth changes sign, while its duration is polarization independent. For the left-and right-circularly polarized excitation beams, the photovoltage pulses are also unipolar having the same amplitude and duration but the opposite polarities. However, the temporal profile of the photoresponse changes drastically when the excitation beam is elliptically polarized. Specifically, it can be either a unipolar or bipolar pulse depending on the degree of the circular polarization of the excitation beam. We show that the observed helicity-sensitive temporal profile of the photoresponse originates from the interference of photocurrents generated in the subsurface layer of the film due to the linear and circular surface photogalvanic effects.The growing interest in the effects of chirality in the light-matter interaction has attracted attention to the photogalvanic effect that manifests itself as the generation of the polarization-sensitive dc current in noncentrosymmetric crystals. 1 In chiral media, the amplitude and direction of this photocurrent can be controlled by the degree of the circular polarization (helicity) of the excitation beam. 2 Such a "circular" photocurrent flows in opposite directions for the leftand right-circularly polarized excitation beams and may originate from the excitation and transport of the spin-polarized electrons. It is usually accompanied by the so-called linear photocurrent, which does not depend on the helicity of the excitation beam and is associated with spin-independent electron transport. Both circular and linear photocurrents can be observed in two-dimensional structures, in which the inversion symmetry is lifted by the interface. 3 The circular photocurrent has been extensively studied in gyrotropic bulk crystals [4][5][6][7][8] , quantum wells, two-dimensional materials, and thin films. [9][10][11][12][13][14][15][16][17][18][19][20] Generation of the circular and linear photocurrents in the vicinity of the interface can occur due to the surface photogalvanic effect (SPGE), which is associated with diffuse scattering of the

Incident Angle Dependence of the Waveform of the Polarization-Sensitive Photoresponse in CuSe/Se Thin Film

“…It is known that the transverse photocurrent j y for elliptical excitation beam polarization consists of a CPC (j y,cir ) and an LPC (j y,lin ), i.e., j y = j y,cir + j y,lin . According to [48] and taking into account [29], for positive angles of incidence, the transverse photocurrent amplitude in the CuSe/Se film structure for elliptical beam polarization can be represented as follows:…”

“…With the simultaneous occurrence of longitudinal PDE and SPGE, due to their interplay, it is possible to generate bipolar PSPC pulses consisting of front and tail parts of opposite polarity, which change their polarities when the sign of the angle of incidence changes [40]. It was shown in our most recent work [48] that, at a given angle of incidence, the interference of the CPC and LPC generated due to the SPGE in a CuSe/Se nanocomposite film also leads to the generation of bipolar photocurrent pulses. The temporal profiles of those pulses strongly depend on the polarization ellipse of the incident femtosecond laser beam.…”

“…The PDE and SPGE photocurrent pulses excited by pulsed laser pumping are usually unipolar (see, for example, [14,[43][44][45][46]). The dependence of CPC and LPC excited in film and 2D structures due to the PDE and SPGE on the beam incidence angle α is described by an odd function [36,37,39,[46][47][48]. Therefore, under pulsed laser pumping, the LPC and CPC unipolar pulses change their polarity when the sign of the incidence angle changes.…”

Phase transformations in composite films of the system Se-Cu, obtained using explosive crystallization and thermal annealing

“…It is very interesting to study the circular photoinduced current, which depends on rotation direction of the electric field vector of incident radiation observed in the mentioned thin-film structures [17,18,20]. By varying the phase composition of synthesized films, efficiency of circular photoinduced current generation can be controlled and mechanisms of its occurrence can be studied.…”

Управляемый синтез текстурированной пленки CuSe(006) вакуумно-термической обработкой пленочной структуры Se/Cu

“…В работах [13,14] нами было установлено, что при облучении фемтосекундным лазером стехиометрических пленок CuSe и нанокомпозитных пленок CuSe/Se в них генерируются фототоки, зависящие от направления вращения вектора электрического поля лазерной накачки. Пленочные структуры на основе CuSe могут быть использованы для разработки и создания быстродействующих анализаторов знака циркулярной поляризации света [15].…”