Structural Phase Transition And Optical Properties Of GaAs Nanowires Under High Pressure

After several decades of development,III-V semiconductor materials have always played an important role in the application of optoelectronic devices,while Ga As nanowires have excellent mechanical,electronic and optical properties,which is a potential candidate for making nano photoelectric devices.However,due to the small size effect and high surface energy of Ga As nanowire,the photoluminescence is low at room temperature,and the application in optoelectronic devices is also hindered.The high-pressure technology can change the material structure and internal electron distribution by adjusting the distance between atoms,and can provide new ideas and methods for modifying the performance of optoelectronic devices based on Ga As nanowires.We used diamond anvil cell(DAC)and in-situ high pressure spectroscopic method to study the structure evolution and optical properties of Ga As nanowires under high pressure.The main research results are as follows:1 We studied the high-pressure phase transition and electronic properties of GaAs nanowires(~ 40 nm diameter)of zinc-blende structure by synchrotron X-ray diffraction and infrared reflectance spectroscopy methods at room temperature,with the pressure up to 26.2 GPa.The phase transition of zinc-blende to the orthorhombic phase was observed at around 20.0 GPa.Pressure-induced metallization of Ga As nanowires was confirmed by infrared reflectance spectroscopy in the same pressure range,and metallization was derived from the phase transition of zinc-blende to the orthorhombic phase.Decompression results indicate that the phase transitions and pressure-induced metallization are reversible.Due to the size effects and high surface energy,Ga As nanowires show larger bulk modulus and enhanced transition pressure comparing to bulk materials.2 Combined with high-pressure photoluminescence spectroscopy and Raman spectroscopy methods,we investigated the optical properties of Ga As nanowires under high pressure up to 5 GPa.We observed that the pressure can modify the band gap of the Ga As nanowires,and induce direct-indirect band gap transition of the nanowires.In the experiment with using 4:1 methyl-ethanol as the pressure transfer medium,a significant increase of PL intensity was observed under high pressure,which is about 9 times higher than that under atmospheric pressure.In the experiment with no pressure transfer medium,no pressure-induced PL enhancement was observed under high pressure.The laser with a shorter wavelength will have a thermal effect on the surface of the Ga As nanowire,thereby suppressing the luminous.However,under the irradiation of incident laser light of different wavelengths,the photoluminescence of Ga As nanowires will be subjected to pressure regulation to exhibit a first-enhanced and then weakened.We believe that the methyl alcohol molecule adsorbs on the surface of Ga As nanowires,and there is charge transfer on the surface.Within a certain pressure range,the charge transfer effect is increase,thus photoluminescence intensity is significantly enhanced.