Study On GaAs Photodetector Based On Epitaxial Stripping Technology

Ultra-thin semiconductors have developed rapidly in recent years due to their excellent performance,and have become one of the most important research directions of photodetectors.In order to extend Moore's Law,researchers have made a lot of efforts in the pursuit of high performance,high photon absorption efficiency,short response time and low noise photodetectors.Among them,two-dimensional material photodetectors represented by graphene and black phosphorus have attracted widespread attention due to their ultra-thin thickness,high flexibility,and excellent photoelectric properties.However,the development of these two-dimensional detectors has been partly restricted owing to the high difficulty of preparation and the instability of the material itself.As an excellent type of direct band gap semiconductor material,GaAs has obvious advantages in material preparation and stability,so it is widely used in the development of light-emitting devices.In addition,the excellent photoelectric characteristics and negative electron affinity of the GaAs material make it useful in the development of photodetectors.Based on epitaxial lift-off technology,this research attains the quasi-two-dimensional and two-dimensional processing of the traditional material GaAs,so that the two-dimensional non-layered GaAs nanosheet detector has the inherent advantages of GaAs materials,as well as improved responsivity and shorter response time.GaAs\Al As\GaAs epitaxial structure is designed,molecular beam epitaxy is used to grow high-quality quasi-two-dimensional and two-dimensional GaAs thin film epitaxial layers.Then,chemical lift-off technology is used to transfer the epitaxial layer to Si substrate to fabricate two-dimensional GaAs thin film detector.The concrete research is conducted as follows:Based on the established model and the existing growth experience,the two-dimensional epitaxial structure is optimized and determined;the growth parameters such as the growth rate are determined and optimized.The molecular beam epitaxy is used to grow GaAs buffer layer,Al As sacrificial layer and two-dimensional GaAs thin film layer on GaAs substrate.In this way,GaAs epitaxial films with film thicknesses of 9 nm,18 nm and 36 nm were obtained.In order to clarify the thin film detection performance and determine the quality of the epitaxial film,the thin film samples before lift-off were characterized.The XRD test of the sample shows that the narrow half-width of the diffraction peak indicates that the epitaxial layer has good crystal quality;the Raman test shows that the sample before lift-off only contains GaAs and Al As peaks,and the sample has high crystal quality.Photodetectors with different thicknesses of two-dimensional non-layered GaAs nanosheets were fabricated.The material is ultra-thin,which causes a quantum size effect and a relatively high surface-to-volume ratio as well as excellent crystalline quality,contributing to a response speed of less than 1 ms,which is the fastest compared with other present two-dimensional non-layered materials.Other electrical indicators are also impressive.Specifically,The response rate reaches 293.3 A/W,and the detection rate can reach the order of 10¹⁰ cm Hz^1/2W^-1.Compared with the traditional GaAs detectors,the responsivity is greatly improved.The two-dimensional epitaxial layer was peeled off by chemical lift-off,and the thin film sample after lift-off was characterized.The Raman test shows that the Al As peak disappears completely after the lift-off,and the crystalline quality of the sample is high.AFM also shows that after lift-off,the surface of the sample is continuous and the surface morphology is good.The lifted-off two-dimensional GaAs epitaxial layer was transferred to the Si/Si O2 substrate and the corresponding detector was fabricated.The response rate of the36 nm device is still very high,reaching 135.6 A/W.Using the epitaxial lift-off technique,two-dimensional GaAs detectors with different thicknesses were fabricated for the first time in this experiment.Compared with traditional GaAs detectors and two-dimensional non-layered detectors,two-dimensional GaAs detectors effectively improve the response rate and reduce the response time,providing a new idea for the study of high-performance,large-size photodetectors.