Effect of Atomic Layer Deposition Al2O3 Passivation on the Luminescence Properties of InAs/InGaAsSb Type-Ⅱ Superlattices
As an emerging mid-infrared semiconductor material,InAs/InGaAsSb superlattice possesses a wide working range covering the infrared spectrum from 2～30 μm,holding promising potential for applications in fields of infrared imaging.Compared to traditional InAs/GaSb superlattices,InAs/InGaAsSb superlattice has the advantages of high electronic effective mass,low Auger recombination efficiency,and long carrier lifetimes,making it a potential material for designing third-generation infrared photodetectors.Hence,the study on InAs/InGaAsSb superlattice has become the current research hotspot.However,the surfaces and cross-sections of InAs/InGaAsSb superlattices are easily oxidated in air,resulting in the formation of gallium oxide and arsenious oxide.These oxides act as non-radiative recombination centers,reducing minority carrier lifetimes and severely limiting the performance improvement of infrared photodetectors.Therefore,it is of great significance for surface treatment to remove surface oxides and reduce surface state density in InAs/InGaAsSb superlattice materials.Recently,research on the passivation of InAs/InGaAsSb superlattices focuses solely on surface treatment.However,the cross-sections,consisting of distinct InAs and InGaAsSb structures,respectively,exhibit heightened susceptibility to being oxidated.Consequently,it is necessary to remove the inherent oxide layers from the cross-section by etching and passivate the surfaces to prevent further oxidation.Accordingly,this paper proposes a passivation technique integrating dry etching and atomic layer deposition.Dry etching is employed to remove the inherent oxide layers from the surface and cross-section of InAs/InGaAsSb superlattices,followed by the deposition of an Al2O3 thin film through atomic layer deposition to passivate the etched surfaces.This approach aims to enhance the emission performance and long-term optical stability of InAs/InGaAsSb superlattices.In order to characterize the crystal quality of the InAs/InGaAsSb superlattice,the double-crystal X-ray diffraction(XRD)is employed.It is easy to find six orders of satellite peaks in XRD patterns,indicating excellent crystal and interface quality between InAs layers and InGaAsSb layers.Additionally,a tiny difference between the 0th-order diffraction peak and the substrate peak is observed,which is attributed to internal strain-induced effects.The surface roughness before and after treatment is analyzed by using atomic force microscopy,showing a significant reduction in surface roughness from 6.32 Å for untreated samples to 1.93 Å for the treated superlattice material.To verify the successful elimination of surface and cross-section oxides,X-ray Photoelectron Spectroscopy(XPS)is employed on the superlattice before and after treatment.For the As 3d spectrum of the untreated superlattice,the peak related to the As-O bond is observed in addition to the As 3d1/2 and As 3d3/2 peaks.However,this peak associated with the As-O bond disappears in the spectrum of the surface-treated superlattice,indicating complete removal of the surface oxide layer.The Photoluminescence(PL)characteristics of the superlattice are measured before and after treatment.The PL spectra reveal an increase in emission intensity and a decrease in full width at half maximum after passivation,which is attributed to the effective reduction of non-radiative recombination through the removal of surface oxides.Continuous PL measurement over five days showed that the emission intensity of the treated samples decreased to 89%of the original intensity,while the emission intensity of untreated samples decreased to 76%of the original intensity.These results indicate better emission stability of the superlattice after treatment.The power-dependent and temperature-dependent PL spectra are employed to analyze the mechanism of the increase in emission intensity and the improvement in emission stability.The relationship between PL intensity and excitation power is analyzed to verify the origin of the emission.The fitting coefficient α decreased from 1.17 to 1.02 after treatment,indicating an increased proportion of exciton-dominated emission.The Arrhenius formula is used to fit the relationship between emission intensity and measurement temperature,revealing that the activation energy E1 increased by 5.13～13.73 meV and E2 increased by 121.92～130.04 meV for the treated samples compared to untreated samples,which indicates a significant suppression of non-radiative recombination,especially at high temperatures.This work lays the foundation for enhancing the performance of InAs/InGaAsSb superlattices and promoting their applications in the field of optoelectronic detection.
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