Effects of Femtosecond Laser Ablation on Optoelectronic Properties of Gallium Arsenide in Different Environments(Invited)
Objective In the current rapid development of optoelectronics technology,gallium arsenide as a semiconductor material plays a crucial role in optoelectronic devices such as lasers and photodetectors in the field of communication.As a typical representative of compound semiconductor materials of Ⅲ‒Ⅴ groups,gallium arsenide has a direct bandgap of dual-energy valleys and high mobility,and its excellent optoelectronic and thermal properties are highly favored.However,increasing the absorptivity and resistivity of the material should be considered to enhance its key properties such as responsivity and thus expand the application fields of GaAs more comprehensively and further optimize the GaAs performance,especially in the detection field.In the study of GaAs,laser ablation technology has great potential.We focus on the enhancement of photovoltaic properties by laser ablation technique.The high energy density and ultrafast time scale of femtosecond laser pulses can form plasma on the surface of semiconductor materials and produce micron-scale micro-nano-structures,thus enhancing light absorption.Our goal is to understand the effects of different environments on the surface properties of GaAs by systematic experiments and in-depth theoretical analysis,and finally provide more comprehensive references for the future practical applications of this material.Methods We employ intrinsic GaAs material and conduct laser ablation experiments by adjusting various processing parameters including laser power,scanning speed,spot size,and scanning spacing.After determining the optimal processing parameters,a confined gas cavity is introduced and laser ablation experiments are carried out under four different environments,including air,vacuum,nitrogen,and sulfur hexafluoride.Additionally,the surface morphology of the material is observed and analyzed in detail using scanning electron microscopy(SEM),with the mechanism of surface structure formation studied in depth.To analyze the changes in the properties of the material surface,we perform X-ray photoelectron spectrometer(XPS)tests.Meanwhile,infrared spectroscopy tests performed on each sample show that the absorbance of the samples processed under different environments is significantly increased.Additionally,by analyzing and discussing the Ⅰ‒Ⅴ curves of the samples,the pressure resistance changes of the samples after laser ablation in different environments are observed to reveal a systematic improvement in the optoelectronic properties of the materials.Results and Discussions Under different environments,femtosecond laser ablation leads to the formation of different structural morphologies on the GaAs surface.In air and nitrogen,the surface structure is relatively regular.In the vacuum,the splashing of GaAs can form raised impurities due to surface thermal adsorption.In addition,in sulfur hexafluoride,irregular ellipsoidal structures appear(Fig.3).In the high-energy laser field,sulfur hexafluoride molecules may dissociate and react to produce reactive species such as fluorine,which may affect the material surface during laser processing.The presence of elemental fluorine in samples processed only in sulfur hexafluoride is confirmed by XPS tests,and the oxygen content of samples processed in air is significantly higher than that in other environments according to the test results.Fourier transform infrared spectroscopy(FTIR)analysis of the sample surfaces indicates that the transmittance of the samples is significantly reduced after laser ablation.The transmittance of the samples processed in the vacuum is decreased to about 1%(Fig.6).When laser light is directed at the surface structure of a material,this may result in multiple reflections,scattering,or localization of the incident light in the material,increasing the propagation path of the light through the material.This enhances the interaction between the light and the material,thus increasing the probability of the material absorbing the light(Fig.7).To better analyze the conductivity properties of the materials,we measure Ⅰ‒Ⅴcurves for each sample.The samples processed in sulfur hexafluoride exhibit higher resistivity in both dark and light conditions(Fig.9).According to the specific needs,processing in different gas environments can be chosen to achieve the most suitable properties.Conclusions We investigate the optoelectronic property changes of the GaAs surface by femtosecond laser ablation in different environments.SEM tests show that the changes in the processing parameters have an effect on the surface micro-nanostructures,and different environments also change the structural morphology.Meanwhile,the material is further tested and analyzed by XPS tests and we find the changes in the surface properties of the material.The processed material exhibits a significant increase in absorptivity compared to the original sheet,and a resistivity increase in light conditions.In particular,the samples processed in vacuum conditions show the highest light absorption,while the samples processed in sulfur hexafluoride gas present better pressure resistance in dark and light conditions.According to specific needs,processing in different gas environments can be selected to yield the most suitable performance.As a result,GaAs materials with surface micro-nano-structures exhibit higher responsiveness in detection applications and can be adopted for optimizing detector performance.This provides new ideas and solutions for developing more efficient optoelectronic devices.Finally,we expect to provide valuable technical methods and experimental data for the development and application of new optoelectronic materials and thus promote the progress and innovation of optoelectronic technology.
ultrafast opticsoptoelectronicsfemtosecond laserlaser ablationphotoconductive material
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