Study On Low Temperature Growth Of Polycrystalline Ge Sn Films For Infrared Detectors

Photoelectric detection technology is widely used in civil and military fields,and the detection of infrared band is of great research significance.With the development of miniaturization and intelligence of various devices,most optoelectronic devices rely on silicon(Si)based large-scale integration process.From the perspective of the same material system,the group ? semiconductor materials are the most suitable candidate materials for the application of optoelectronic devices.However,germanium(Ge),which belongs to the same group ? element,is an indirect band gap semiconductor material and requires phonons to participate in the electronic transition,so its low efficiency limits its application in optical devices.In this context,GeSn alloy has aroused people's research enthusiasm due to its advantages of adjustable band gap and easy compatibility with standard silicon based CMOS process.It is found that with the continuous increase of Sn content in GeSn alloy,GeSn alloy shows the nature of direct band gap and has great application potential in optical devices.However,growing GeSn alloy with high Sn content in crystallized state has certain challenges: Sn's solid solubility in Ge is very low in thermal equilibrium state,and Sn segregation occurs at high temperature due to the lower melting point and surface free energy of Sn than that of Ge,which limits the increase of Sn content in GeSn alloy.There is a large lattice mismatch between GeSn and Si,and the film quality is difficult to improve,so the performance of the photodetector is affected.For wearable flexible applications,GeSn should be grown at a low temperature.In order to solve the difficulties in the growth of GeSn alloy and improve the performance of GeSn photodetector,the following research contents are proposed in this paper:(1)Polycrystalline GeSn films were grown by capacitive coupled plasma-assisted magnetron sputtering at room temperature.The experimental results show that this method has a certain effect on the growth of polycrystalline GeSn thin films at low temperature,and also provides a new idea for the growth of polycrystalline GeSn thin films at low temperature.(2)To solve the problem that amorphous GeSn cannot be crystallized effectively at low temperature due to the limited amount of plasma energy in the equipment used,inspired by the principle of Ge crystallization induced by Sn films,amorphous GeSn films grown by magnetron sputtering were annealed in liquid Sn to crystallize the amorphous GeSn film at low temperature,at the same time,the concentration gradient was used to inhibit the segregation of Sn,and the polycrystalline GeSn films with high Sn content were obtained.The results show that the Raman peaks of the samples annealed in the liquid tin environment move to the direction of wave number decrease compared with that of the samples annealed in the nitrogen environment,indicating that the annealed in the liquid tin environment can effectively inhibit the segregation of Sn.(3)The two studies mentioned above have their own shortcomings: due to the low amount of plasma energy provided by the current equipment,it is difficult to promote the complete crystallization of GeSn;in liquid Sn,there is still a slow cooling process in annealing and Sn segregation is still serious.In view of the problems existing in the above research content,femtosecond pulse laser was used as the post-processing method in this study.The effects of pulsed laser power and initial Sn content on the quality of GeSn films were investigated.On this basis,the GeSn photodetector was prepared and its performance was tested.The peak response wavelength of the detector can reach 1875 nm,which extends the response wavelength of Ge detector.