Research Of Germanium-tin PIN Photodetectors

Semiconductor Ge Sn material is a versatile material system that attracting significant research interests due to its several unique and beneficial properties,such as tuning the Sn composition to modulate the band structures that indicates the ability to show a direct band gap,high electron and hole mobilities and the compatibility with conventional Si process technology,making it an ideal material platform for co-integration of Si compatible photonics devices and high speed CMOS intedrated circuits.For Ge Sn photo detectors,the cut-off wavelength of the response spectral of PDs can be extended into the near-infrared or mid-infrared wavelength ranges,by tuning the Sn composition in the active absorption layer.The wavelength tunable Ge Sn photo detectors can be achieved,which can detect all range of the near-infrared or mid-infrared.Based on the first principle,the Ge Sn alloys primary cells are built.The modified models of Ge Sn material band structures with different content of Sn are got.By analyzing the material band gap values,doping concentrations.etc material parameters,and various work temperatures,the variation rules of Ge Sn photo detectors are obtained.Based on the above,a kind of Ge Sn photo detectors structure is designed.The simulation result shows that,the Ge Sn photo detector has a high quantum efficiency,high responsivity,and low dark current.The main area and contents of this dissertation are as follows.1?Ge Sn alloys band structure and photoelectricity characterBased on the first principle,the Ge Sn material primary cells with different composition of Sn are created.Based on the density functions theory plane wave method,the band structures of Ge Sn binary alloys with different content of Sn are calculated.And the modified Ge Sn band structures are obtained.Based on the semi-classical approach by treating the electrons as Bloch wave,the absorption coefficient formula is derived.And the absorption coefficient model is obtained.The variation of Ge absorption coefficient with different temperature is studied.2?Photo detectors performance studyThe influence of band gap values,absorption coefficient,doping concentration.etc material parameters and various work temperatures is analysed.The result shows that the smaller the material band gap value,the larger the dark current is.The extension to longer wavelength of the spectral is achieved based on the smaller band gap value,that is,the absorption coefficient is increased due to the smaller band valure.Absorption coefficient determines the magnitude of the quantum efficiency.And the quantum efficiency affects the responsivity directly.Improving the doping concentration of P-region or N-region can suppresses the magnitude dark current.Reducing the work temperature can also suppress the dark current,which makes the device work properly.The dark current increases 10 times,if the work temperature increases 40 K.Photocurrent signal varies linearly with the input optical power.The modified diode current-voltage model is obtained.The modified model can express the diode current-voltage characteristics in both darkroom and illumination conditions.Based on the Ge Sn material character and the principles of the photo detectors,a kind of high performance Ge Sn PIN photodetector is designed.3?Ge Sn PDs simulation and results analysisThe absorption coefficient of semiconductor materials determines the quantum efficiency of the photo detectors.The direct and indirect band gap energy of semiconductor Ge Sn materials with Sn composition at 0%,2%,4%,6%,8%,and 10% are calculated.Due to the Ge Sn absorption coefficient model,the Ge Sn absorption coefficient is calculated with different Sn content.Using TCAD sentaurus software,the designed photodetector is simulated and obtains the key parameters,such as the quantum efficiency,responsivity,dark current and photocurrent,and frequency response.The simulation result indicates that Ge Sn photodetector shows a high quantum efficiency and responsivity,low dark current,and good frequency response.The photodetectors quantum efficiency increases with Sn content.And the cut-off wavelength of the Ge Sn photodetector response spectral extends to longer wavelength.The 1.17A/W responsivity is obtained with Sn content at 2%.The cut-off wavelength extends into mid-infrared with the Sn composition greater than 6%.With Sn composition at 10%,the cut-off wavelength is 2.48?m,the peak wavelength at 2.3?m and peak responsivity is 1.3A/W.The magnitude of the dark current with Sn composition up to 10% is greater 100 times compared to Ge.This paper has a great guiding significient for designing high performance photo detectors,and provides the important basis theory for experiment.