Preparation And Nonlinear Optical Properties Of Al-doped InSe Nanofilms

The research of nonlinear optical materials promotes the development and application of nonlinear optical properties.In recent years,it has become a hot research topic for researchers to design and optimize the preparation of nonlinear optical materials with broad-band response and strong nonlinear optical properties.Pure InSe is an excellent III-VI semiconductor with high modulation rate,high nonlinearity and ultrafast response time has been widely studied.It is well known that doping is an effective way to optimize the nonlinear optical properties of materials.In this work,Al-doped InSe materials were used to improve the nonlinear response intensity in nonlinear absorption.Meanwhile,Al-doped InSe materials possess broad-band nonlinear response,ultrafast response time,large reverse saturation absorption,etc.Thus Al-doped InSe materials have good application in broad-band optical limiting.The research contents of this paper are as follows:Al-doped InSe nano films were prepared by magnetron sputtering.The surface morphology of Al-doped InSe nano films were smooth,uniform and without cracks,which characterized by AFM and SEM.The XRD results indicate that the amorphous nature of the Al-doped InSe nano films.The atomic percentage and mass percentage of Al-doped InSe nano films were obtained by EDS characterization.The characterization results of UV-Vis-NIR spectrophotometry indicate that the incorporation of Al led to the widening of the band gap of InSe,and the corresponding band gap values were 2.68 eV,2.53 eV,2.41 eV and 2.34 eV,respectively.The broad-band and different energies of Al-doped InSe nano films with different sputtering power were systematically studied by using femtosecond z-scan experiment.The experimental results show that the nonlinear absorption characteristics of Al-doped InSe nano films were enhanced with the increase of sputtering power under the same energy excitation.Meanwhile,the nonlinear absorption characteristics of Al-doped InSe nanofilm with the same sputtering power increased with the increase of laser energy.The corresponding nonlinear absorption coefficients were obtained by fitting the experimental data.The results show that there are two-photon absorption and free carrier absorption in Al-doped InSe nano films,and free carrier absorption is induced by two-photon absorption(from valence band)and one-photon absorption(from doping level).The carrier recovery process of Al-doped InSe nano films with 2.5 W sputtering power was systematically studied by femtosecond transient absorption spectroscopy.The carrier recombination processes τ1(1.85±0.35 ps),τ2(12.50±0.95 ps)and τ3(2.70±0.18ns)of Al-doped InSe nano films under the pump pulse at 350 nm and probe pulses at 532 to 1064 nm.Furthermore,we discuss the carrier recovery mechanism.Combined with the Z-scan and transient absorption spectrum experiment results,the optical limiting test of Al-doped InSe nano film with 2.5W sputtering power was carried out,and the values of optical limiting threshold in different bands were obtained.The results of this study indicate the effect of Al doping on the nonlinear optical properties of InSe materials.The incorporation of Al increases the nonlinear absorption coefficient of the material,which has certain light physical significance for the study of related materials.It is widely used in optical limiting because of its properties such as broad-band nonlinear response,ultrafast response time,high linear transmittance and low optical limiting threshold.