Study On Dynamics Of Photo-induced Carriers In GaAs By Ultrafast Spectroscopy

Based on pump-probe technology,ultrafast spectroscopy achieves high time resolution by the relative delay of the two beams at the spatial position,and it is a relatively simple but very effective and reliable practical technique for exploring ultrafast phenomena or mechanism research.In this paper,the femtosecond pump probe technique was used to detect the variation of the time difference reflective spectroscopy of gallium arsenide(GaAs),and the dynamics of the photo-generated carriers were further analyzed by establishing a theoretical model.The main contents include:(1)In the first chapter,we outlined the development and application of ultra-short pulsed laser,ultrafast spectroscopy and the crystal structure and properties of gallium arsenide,and here listed several typical ultrafast spectroscopy techniques.Based on the crystal structure and optical properties of GaAs,the research status of GaAs in carrier dynamics was summarized.(2)In the second chapter,we summarized the dynamic mechanism of semiconductor carriers.Based on the semiconductor and photo-generated carriers,we described segmentally the semiconductor dynamic process.(3)In the third chapter,we constructed a pump-probe experimental platform.Taking into account the maximization of the use of space,and combined with femtosecond laser system,we built a pump-probe reflection system and a pump-probe transmission system in the terrific clean laboratory.According to the condition that the pump and the probe in the sample are collinear,each system is divided into two types:collinear and non-collinear.(4)In the fourth chapter,we established a model of differential reflectivity and power.We presented the concept of saturated carrier concentration(Ns).And based on the fitting experimental curves and the theoretical model,the fifth chapter calculated the saturated carrier concentration of the unintentionally doped high-purity n-type GaAs:Ns=(3.5901±0.3103)×1017cm-3(5)In the fifth chapter,we analyzed the time-resolved differential reflective spectroscopy.Varied with some optical parameters,such as center wavelength,power,the differential reflectance spectroscopy of unintentionally doped high-purity n-type GaAs were studied by femtosecond(fs)laser pump probe technique.We respectively discussed the correlations between these optical parameters and the peak differential reflectivity,the signal-to-noise ratio.Further,the dynamics of photo-induced carriers were divided into four stages:the photo-excitation process(804 ± 67 fs),the initial scattering process(134 fs-268 fs),the fast recombination process with 1 picosecond(ps)and the slow recombination process with 3 ps?6 ps.