| New kinds of semiconductors have been developed towards the infrared and terahertz bands applications via two paths.One way is form radio frequency,microwave,millimeter wave,terahertz to far infrared.The other way is from ultraviolet light,visible light,near infrared,far infrared to terahertz band.The integration of the optical,electrical,magnetic,wave devices and the interconnection of micro-circuit system on the same semiconductor wafer is a hot topic in the future.Epitaxial growth of wafer-size infrared and terahertz-band semiconductor films,in-situ device array integration,and interconnected into integrated circuits are the recent international scientific topics.There are several technique bottlenecks in this area,such as controlling the dislocation density of heteroepitaxial semiconductor thin films on large-size silicon wafers,breaking the limit of the infrared and terahertz bands of doped semiconductor thin films,exploring the fabrication process of 4-inch wafer-size infrared and terahertz bands information detection as well as modulation array devices.This thesis just carried out researches focused on the above scientific issues and technique bottlenecks.The research achievements are demonstrated as follows:1.The growth mechanism of the wafer-size germanium-tin?GeSn?and germanium-bismuth?Ge Bi?films using ultra-high vacuum chemical vapor deposition?UHV/CVD?and molecular beam epitaxy?MBE?techniques has been studied.The diffusion and distribution of gas molecules in the chamber,the physical and chemical reaction of the films on the surface of the substrate,the calculation of the large-size film thickness and the components uniformity have been systematically investigated.The results are important to guide the subsequent growth of high quality GeSn and GeBi thin films.It also laid a foundation for the photoelectric application of Ge1-xRx?R=Si,Sn,Bi?semiconductor films.2.The idea of inserting patterned Ge or Si meta-material film to serve as high-relaxation simulated buffer layer has been proposed.The pattern element and array model have been theoretically established.The optimal size of meta-material patterns was found by theoretical simulations.The buffer layers were prepared by MBE and UHV/CVD systems at low substrate temperature.Dislocation density and relaxation can be controlled by changing the nano-size?process and annealing?of the metamaterial layer,tuning the contents of Ge in Si1-xGex and Ge1-xSnx epitaxial layers and varying film thicknesses.The relaxation degree of the prepared film is more than 94%,and the tensile stress of epitaxial layer film can be completely released into the meta-material buffer layer.The chemical corrosion dislocation method EPD and AFM analysis indicate that the dislocation density is between 5.0×105/cm2 and 8.0×105/cm2 with a surface roughness between 0.4 nm and 2.0 nm.The meta-material buffer layer has high strain relaxation,low dislocation density,low surface roughness and thin buffer layer thickness.The approach is efficient to grow high-quality Ge1-xRx series films,which can be utilized to make infrared photodetectors with low-dark current density.3.Wafer-size?3 to 5 inch?infrared and terahertz dual-band optoelectronic semiconductor films were grown for the first time.Single crystalline Ge1-xSnx films with thicknesses of 100-200 nm were grown on p-type silicon substrate using in-situ two-step method by UHV-CVD and MBE,respectively.The effects of two-step growth,in-situ annealing,substrate temperature,film thickness,tin content and oxidation on the microstructures,direct bandgap,infrared and terahertz band properties of large-size semiconductor thin films were systematically studied.The results show that the film has a roughness between 0.4-1.0 nm and the oxidation rate is less than 0.1%.It is found that the film has obvious broadband absorption and transmission window in the0.8?m-2.6?m band and 0.1-1.6 THz band,respectively.The light response in near-infrared region is 0.367-0.486 A/W,while the light response value in far-infrared is0.020-0.036 A/W.There is strain induced direct bandgap between 0.843eV and 0.860eV with Sn content above 8.2%.4.4-inch n-type Ge1-xBix semiconductor were originally designed and epitaxially grown using low temperature?<150??MBE method.The microstructure analysis show that a relatively high proportion of amorphous phase and a small amount of oxide phase existed.Atomic force microscopy?AFM?and X-ray photoelectron spectroscopy?XPS?measurements show that Bi was precipitated in high Bi content samples.The microstructure and properties of the films can be improved by in-situ growth process improvement,selection of doped substrates,change of film composition,film thickness optimization and so on.Raman spectroscopy shows that the Ge-Bi peak shifted to the right with the increase of Bi content.It proves that the strain induced bandgap existed in the thin film with Bi content more than 10%.The direct bandgap of Ge Bi film is 0.854eV,while the indirect band gap of the GeBi film is narrowed to 0.640 eV.The responsivity of the GeBi photodetector is 0.40 A/W to 0.20 A/W in a wavelength range of 800 nm to 2300 nm.The responsivity of the GeBi photodetector is 0.03A/W to 0.036A/W in a wavelength range of 4?m to 15?m.Furthermore,the absorption and transmittance properties of the GeBi films can be tailored with tuning Bi content.5.Infrared photodetector and terahertz wave modulator have been fabricated based on GeBi semiconductor thin films.Chips on 4-inch wafers have been successfully realized.N-type GeBi and p-type Si substrate formed into“p-Si/n-GeBi”shallow junctions.The Bi dopant concentration was generally between 4.80×1016-7.01×1017.Photodetectors and terahertz wave modulators were fabricated using standard microelectronics process.I-V characteristic,dark current and photocurrent test showed that GeBi/Si junctions can be used as broadband infrared photodetectors?800-2300 nm?.The minimum dark current density is 2.133 mA/cm2?-1V,100?m×50?m?.The maximum light responsivity is 0.80 A/W,while the photocurrent density is 297.94mA/cm2?-1V,100?m×50?m?.PN junction can be used as a terahertz wave modulator at the same time.The test shows that the maximum modulation bandwidth is up to 1.0THz,the maximum modulation rate is 1 MHz,the maximum modulation depth is 15%.GeSn films with high Sn content?greater than 8%?were doped with phosphorus using thermal diffusion doping.The doping depth was controlled between 50 nm and180 nm.The concentration was about 5.6×1016.The heterostructure films formed typical“n-GeSn/i-GeSn/p-Si”PIN shallow junction.PIN photodetectors and terahertz modulators with device areas of?50×50?m2 to?1000×1000?m2 were prepared by standard lithography process.Dark current and infrared photocurrent test indicated that the photoelectric properties were closely related to the thickness of i region and the depth of n-type doping region.The optimal i region thickness is 40 nm,while the optimum n-type doping depth is about 80 nm.The minimum dark current density is 0.10mA/cm2?-1V bias?.The maximum photocurrent density is 0.78 mA/cm2?±1V bias?and 38 mA/cm2?±5V bias?.The optimal thickness of i region and doping depth for terahertz modulators are 20 nm and 50 nm,respectively.The modulator bandwidth and modulation rate are 1.0 THz and 500 kHz,respectively.The modulation depth is 26.7%. |
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