| Nowadays,near infrared(NIR)photodetectors have played an important role in the high developing information society.Germanium(Ge)is considered as one of the most ideal materials for NIR photodetectors,due to its large absorption coefficient at NIR wavelengths,high carrier mobilities,and process compatibility with Silicon(Si)architecture.Moreover,among the various types of photodetectors,Schottky photodetector have many advantages in terms of simple process,low production cost,and high response speed.In this thesis,we focus on the Fermi-level pinning effect in contact between metal and Ge,searching methods to modulate the Schottky barrier height of metal/n-Ge contacts;We use a highly conductive and transparent indium-doped tin oxide(ITO)film to replace the traditional metal electrodes to fabricate NIR Si and Ge Schottky photodiodes.The main works and innovations are listed as following:1.Tin(Sn)was introduced into Ge for the preparation of a thin GeSnOx film by thermal oxidation.It is found that Ge suboxides could be effectively suppressed by the oxidation of Sn-doped Ge,which strongly alleviated the Fermi-level pinning effect between metal and n-Ge.This resulted in the strong correlation between the Schottky barrier heights of metal/GeSnOx/n-Ge contacts and metal work functions.Additionally,the oxidation of Sn-doped Ge was also proved to be an effective way of passivating the interface between high-k dielectrics and Ge.The leakage current density of the Pt/HfO2/Ge structure could be remarkably decreased by formation of an ultrathin GeSnOx layer between metal and Ge.2.We proposed a method to insert a conducting oxide(ITO)interfacial layer between metal and n-Ge to to modulate the Schottky barrier height of metal/n-Ge contacts while avoiding the series resistance caused by interfacial layer.Then by merging the high doped n-type Ge substrate obtained by ion implantation with laser annealing,we obtain a low specific contact resistivity of 1.2×10-7?·cm2 for Al/ITO/n+-Ge contact.3.We proposed a method to insert an ultra-thin metallic film between transparent conductive electrode ITO and n-Si(or n-Ge)to fabricate high-performance ITO/n-Si and ITO/n-Ge Schottky diodes.A well-behaved ITO/Ag/n-Si Schottky photodiode with a high rectification ratio(±1 V)of 4 × 105 and low dark current density(-1 V)of 2.4 × 10-6 A/cm2 was achieved,in which substantial responsivity for wavelengths from 360 to 1650 nm was realized for diode through both inter-band absorption from Si and internal photoemission form Schottky contact.Analogously,a well-behaved ITO/Au/n-Ge Schottky photodiode with a high rectification ratio(±1 V)of 1013 and low dark current density(-1 V)of 1.4 x 10-3A/cm2 was achieved,in which substantial responsivity for wavelengths from 800 to 1650 nm was realized for diode through inter-band from Ge.4.Ge materials with smooth surface and high-quality crystallinity were epitaxially grown on Si and SOI substrate using low temperature buffer technique.The impacts of excimer laser annealing on the crystallinity of Ge epilayers were investigated.And then,an annealing approach of combing excimer laser annealing and high temperature annealing for long time was proposed to treat the samples of Ge epilayers,resulting in a futher improvement fo crystal quality of the Ge epilayers.5.We proposed a method to epitaxially grown an ultra-thin Sicap layer at the surface of Ge epilayer to preparate a Si-based ITO/Ge Schottky diode.With 430 nm thick Ge epilayer,a minimum dark current of 2.0 ×10-7 A and an optical responsixity of 0.19 A/W at 1550 nm wavelength was achieved for SOI-based ITO/Ge Schottky photodetector.This responsixity was excelled in reported Si-based Ge photodetector with the same thickness of Ge epilayer,benefited from the high transmissivity of ITO electrode and high reflectivity of SOI substrate.6.The ITO/Al2O3/n-Ge and ITO/HfO2/n-Ge Schottky photodiodes with high rectification ratio and high photocurrent gain voltage were achieved.The high photocurrent gains had been obtained at 1310 and 1550 nm wavelength even at low bias voltage for both detectors.Specially,a high responsivity of 12.5 A/W was achieved for ITO/Al2O3(2nm)/n-Ge detector,measured under illumination by a 1310 nm laser at a low reverse bias voltage of-4V,and its correspondence's external quantum efficiency is 1192%?... |
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