Raman Spectra And Second Harmonic Properties Of InP Nanosheets With Different Crystal Structures

Ⅲ-Ⅴ nano-semiconductor arrays have been widely used in optical,electrical and photoelectronic applications.Bottom-up epitaxy of nanostructures is an effective approach to modify their crystal structures and realize the epitaxy of stable zinc blende（ZB）and metastable wurtzite（WZ）Ⅲ-Ⅴ semiconductor.Metastable phase fabricated by selective area epitaxy（SAE）is regarded as one of effective methods of modulating semiconductor band structure and their optical and thermal properties.Therefore,to develop semiconductor information devices,it has significant research value to reveal optical and thermal properties of semiconductors with different crystal structures.Indium Phosphide（In P）either with ZB or WZ structures is a direct band gap semiconductor material with high carrier mobility and low surface recombination speed,which has potential application among near-infrared（near-IR）optics and photoelectric information,such as solar cells,light-emitting devices,photodetectors,and higher speed electron lasers.In this paper,the Raman spectra and second harmonic properties of Ⅲ-Ⅴ compound semiconductors represented by In P are studied.The results achieved are as follows:（1）Here,we take WZ InP nanosheet arrays as an example and perform detailed optical and Raman scattering studies.The opposite trends of A₁（TO）and E_2hmodes are shown in polarization-dependent Raman scattering.It is shown in temperature-dependent Raman scattering that Al₂O₃provides good protection for nanosheets under the environment with temperature below 873 K,with no observable deterioration in optical properties or phase transition.The first-order temperature coefficient and thermal expansion coefficient of WZ and ZB In P could also be obtained from temperature-dependent Raman experiments which are quite close to each other.Furthermore,by applying density functional theory and density functional perturbation theory,the Grüneisen parameter and the thermal expansion coefficient of WZ In P lattice are calculated,showing good agreement with the experimental Raman data.The difference between WZ and ZB In P phase is negligible in thermodynamic property.The revealed thermal properties of the In P nanosheets provide valuable information for those devices that operate at high temperatures.（2）Aiming at the application of ZB and WZ InP nanostructures in nonlinear optics,the properties of SHG are studied in this paper.Firstly,the refractive index and second-order nonlinear coefficients of ZB and WZ In P are obtained by first-principles calculation.On this basis,the relationship between SHG polarization effect and In P crystal structure and morphology was explored with COMSOL simulation software.The results show that the SHG conversion efficiency can be maximized by shape engineering,crystal structure and polarization excitation to regulate the SHG response.At the same time,the regulation of SHG radiation direction by different morphology and crystal structure was explored,and it was proved that forward radiation of SHG could be realized by controlling the morphology and crystal structure of In P nanosheets,and the collection efficiency of SHG was greatly enhanced.The research results lay a theoretical foundation for the application of WZ In P nanostructure arrays with epitaxial growth in SHG based polarization detectors,high efficiency devices and optical communication devices.