Application Of Internal Photoemission Mechanism In Short Wave Infrared Photodetectors

Optical communication,using photons as the information carrier,has become one of the most significant inventions in modern society by virtue of the excellent performance of speed transmission and information capacity.Furthermore,the Si-based photonic devices,including various active and passive ones,are becoming the most promising technology in short-range communications due to their compatibility with the mature complementary metal-oxide-semiconductor(CMOS).Among the photonic devices,the photodetector(PD)that detects the optical signal by interacting with the matter is a critical part of the photoelectric conversion devices.Although the Si-based PDs have been widely used in the visible spectrum(0.4-0.7?m)so far,they are still suffering from poor performance in the communication wavelengths of 1.31?m and 1.55?m because of little light absorption in silicon for infrared photons with energy smaller than 1.12 eV.Therefore,the development of Si PDs working in the range of near-infrared band(above 1.1?m)is still a challenge of the monolithic optoelectronic integration technology development.Recently,Si-based Schottky photodetector(SPD)has attracted much attention due to their unique thermionic emission mechanism allowing sub-band energy detection at room temperature by adjusting the barrier height.Such PDs with a simple manufacturing process,high switching ratio,high transconductance gain and rapid response could be a promising strategy for realizing Si-based near-infrared detection.Therefore,the goal of this dissertation is to improve the Si-based SPD performance in near infrared band.In this dissertation,the Si-based SPD with ultra-low dark current operating in 1.1?m-1.55?m was obtained using an innovative structure based on the principle of the SPD.The main work can be divided into the following two parts:1.Dark current suppression of Si-based near infrared SPDs.It is difficult for traditional metal-Si SPDs to achieve considerable responsivity due to the strong reflection from metal.Although transparent conductive glass(ITO)is a promising alternative to metal for improving the responsivity,one of the challenges for the ITO/Si PD is that the high dark current from a low Schottky barrier(SB)will severely drag down the sensitivity of it.Fortunately,Au with a high work function of5.1 eV can form a high SB with Si,which will suppress the dark current in principle.Accordingly,the 100 nm ITO/n-Si SPD with a 6 nm Au insertion layer for near-infrared detection is prepared.It turns out that the implementation of a thin Au insertion layer into an ITO/n-Si SPD can profoundly affect the barrier height,thus significantly suppressing the dark current.The dark current density at-1 V is about3.7×10^-7 A/cm²,7000 times lower than that without Au insertion,in addition to a high rectification ratio of 1.5×10⁸ at±1 V.This silicon-based PD exhibits a considerable response at 1.3?m wavelength with a record dark current density,which is one-sixth of that in other researches.2.Responsivity improvement of Si-based near-infrared SPDs.The responsivity is another essential parameter in addition to the dark current of detectors.Although the dark current has been effectively suppressed,the low transmittance in the near-infrared band of the electrode with Au film(6 nm)and ITO(100 nm)will severely damage the responsivity of the device.Since that Au is the most malleable metal with excellent film-forming ability,the responsivity of the SPD is further improved without dark current performance recession by reducing the thickness of the insertion Au layer while keeping the high SB between Au and Si.The transmittance is a nearly double improvement,while the dark current density of 100nm ITO/2 nm Au/n-Si SPD is kept in the order of 10^-7 A/cm²,resulting in a substantial increase of responsivity.As a result,the silicon-based near-infrared detector with ultra-low dark current,high response,high rectification ratio,and sub-GHz response frequency is obtained in this work.