Study On Germanium Alloy Semiconductor Film And Photodetector

Photodetector is a device that can convert light signals into electrical signals based on the principle of photoelectric effect or photothermal effect,and is widely used in military and civilian fields.In the past few decades,Group Ⅳ Si,Ge and other materials have been widely used in high-speed optical communications,optoelectronic integration,etc.,and they have been regarded as the preferred materials for infrared detectors by many scientific researchers due to their low cost,easy integration,and mature production process.However,Si and Ge are indirect bandgap semiconductors,and the transition of electrons requires additional phonons to participate,which reduces the performance of optoelectronic devices to a certain extent,making the cut-off wavelength of photodetectors made of them less than 1.5μm.The study found that the doping of Sn,Bi can adjust the band gap of Ge,changing Ge from an indirect band gap material to a direct band gap material,so that the Ge series thin films are expected to be used in the research of mid-infrared photodetection.This thesis mainly studies two germanium alloy semiconductor films,namely GeSn and GeBi films,and photodetector devices on the basis of the films.There have been preliminary reports on GeSn materials and the photodetector devices made by them.After preliminary explorations and experimentations,our group can use the existing molecular beam epitaxy equipment to prepare better GeSn thin films.When studying GeBi materials,we found that in addition to the influence of Bi on the band gap of Ge,it also has certain effects on its properties.For example,it can be modified into an N-type semiconductor material.This paper is focused on GeSn and GeBi materials,We have further researched and optimized the film,and based on GeSn and GeBi films,we prepared the photodetector with PIN structure.The main work and research results of this paper are as follows:（1）First,molecular beam epitaxy is used to prepare high-quality GeSn and GeBi single crystal films.The Sn content of the GeSn film is 6.46%～15.25%,the optimal surface roughness is 1.253 nm,and the carrier concentration is 10¹³ cm^-3～10¹⁶ cm^-3,the maximum carrier mobility is 1880.56 cm²/V·s;the Bi content of the GeBi film is 3.76%～19.43%,the optimal surface roughness is 1.639 nm,and the carrier concentration is about 10¹⁵ cm^-3.The maximum carrier mobility is 1110.09 cm^<sup>2/V·s.（2）A photodetector with a silicon-based PIN structure was designed and fabricated.The GeSn film was used as the intrinsic layer,the B-doped GeSn film was used as the P-type layer,and the GeBi film was used as the N-type layer.The preparation process was adjusted and optimized.We have determined the process parameters such as lithography and etching,then we used magnetron sputtering for electrode growth on the patterned film,and probe station are used for IV curve and other tests.（3）The effect of B doping time,intrinsic layer thickness and Bi content on the performance of the prepared PIN structure photodetector was studied,dark current and photocurrent were tested,and the test results were analyzed.The I-V curve shows that the PN junction has an obvious response to infrared light.The light source is periodically switched on and off,the On-Off curve shows that the device has stable light-dark current switching and fast response speed.The dark current intensity under 1 V forward bias is4.24×10^-6 A～1.25×10^-4 A,the ratio of light to dark current is between 80 and 385.