We have developed a physics based analytical model for the calculation of threshold voltage, two dimensional electron gas（2DEG） density and surface potential for Al Ga N/Ga N metal oxide semiconductor high electron ...We have developed a physics based analytical model for the calculation of threshold voltage, two dimensional electron gas（2DEG） density and surface potential for Al Ga N/Ga N metal oxide semiconductor high electron mobility transistors（MOSHEMT）. The developed model includes important parameters like polarization charge density at oxide/Al Ga N and Al Ga N/Ga N interfaces, interfacial defect oxide charges and donor charges at the surface of the Al Ga N barrier. The effects of two different gate oxides（Al_2O_3 and HfO_2/ are compared for the performance evaluation of the proposed MOSHEMT. The MOSHEMTs with Al_2O_3 dielectric have an advantage of significant increase in 2DEG up to 1.2 10^（13） cm^2 with an increase in oxide thickness up to 10 nm as compared to HfO_2 dielectric MOSHEMT. The surface potential for HfO_2 based device decreases from 2 to –1.6 e V within10 nm of oxide thickness whereas for the Al_2O_3 based device a sharp transition of surface potential occurs from 2.8to –8.3 e V. The variation in oxide thickness and gate metal work function of the proposed MOSHEMT shifts the threshold voltage from negative to positive realizing the enhanced mode operation. Further to validate the model,the device is simulated in Silvaco Technology Computer Aided Design（TCAD） showing good agreement with the proposed model results. The accuracy of the developed calculations of the proposed model can be used to develop a complete physics based 2DEG sheet charge density and threshold voltage model for Ga N MOSHEMT devices for performance analysis.展开更多
The effect of annealing on vertically aligned TiO2 NWs deposited by glancing angle deposition（GLAD）method on Si substrate using pressed and sintered TiO2 pellets as source material is studied.The FE-SEM images revea...The effect of annealing on vertically aligned TiO2 NWs deposited by glancing angle deposition（GLAD）method on Si substrate using pressed and sintered TiO2 pellets as source material is studied.The FE-SEM images reveal the retention of vertically aligned NWs on Si substrate after annealing process.The EDS analysis of TiO2NWs sample annealed at 600 ℃ in air for 1 h shows the higher weight percentage ratio of ～2.6（i.e.,72.27%oxygen and 27.73%titanium）.The XRD pattern reveals that the polycrystalline nature of anatase TiO2 dominates the annealed NWs sample.The electrical characteristics of Al/TiO2-NWs/TiO2-TF/p-Si（NW device） and Al/TiO2-TF/p-Si（TF device） based on annealed samples are compared.It is riveting to observe a lower leakage current of ～1.32 × 10^-7 A/cm^2 at ＋1 V with interface trap density of-6.71 × 10^11eV^-1cm^-2 in NW device compared to ～2.23 × 10^-2 A/cm^2 in TF device.The dominant leakage mechanism is investigated to be generally Schottky emission;however Poole-Frenkel emission also takes place during high reverse bias beyond 4 V for NWs and 3 V for TF device.展开更多
文摘We have developed a physics based analytical model for the calculation of threshold voltage, two dimensional electron gas（2DEG） density and surface potential for Al Ga N/Ga N metal oxide semiconductor high electron mobility transistors（MOSHEMT）. The developed model includes important parameters like polarization charge density at oxide/Al Ga N and Al Ga N/Ga N interfaces, interfacial defect oxide charges and donor charges at the surface of the Al Ga N barrier. The effects of two different gate oxides（Al_2O_3 and HfO_2/ are compared for the performance evaluation of the proposed MOSHEMT. The MOSHEMTs with Al_2O_3 dielectric have an advantage of significant increase in 2DEG up to 1.2 10^（13） cm^2 with an increase in oxide thickness up to 10 nm as compared to HfO_2 dielectric MOSHEMT. The surface potential for HfO_2 based device decreases from 2 to –1.6 e V within10 nm of oxide thickness whereas for the Al_2O_3 based device a sharp transition of surface potential occurs from 2.8to –8.3 e V. The variation in oxide thickness and gate metal work function of the proposed MOSHEMT shifts the threshold voltage from negative to positive realizing the enhanced mode operation. Further to validate the model,the device is simulated in Silvaco Technology Computer Aided Design（TCAD） showing good agreement with the proposed model results. The accuracy of the developed calculations of the proposed model can be used to develop a complete physics based 2DEG sheet charge density and threshold voltage model for Ga N MOSHEMT devices for performance analysis.
文摘The effect of annealing on vertically aligned TiO2 NWs deposited by glancing angle deposition（GLAD）method on Si substrate using pressed and sintered TiO2 pellets as source material is studied.The FE-SEM images reveal the retention of vertically aligned NWs on Si substrate after annealing process.The EDS analysis of TiO2NWs sample annealed at 600 ℃ in air for 1 h shows the higher weight percentage ratio of ～2.6（i.e.,72.27%oxygen and 27.73%titanium）.The XRD pattern reveals that the polycrystalline nature of anatase TiO2 dominates the annealed NWs sample.The electrical characteristics of Al/TiO2-NWs/TiO2-TF/p-Si（NW device） and Al/TiO2-TF/p-Si（TF device） based on annealed samples are compared.It is riveting to observe a lower leakage current of ～1.32 × 10^-7 A/cm^2 at ＋1 V with interface trap density of-6.71 × 10^11eV^-1cm^-2 in NW device compared to ～2.23 × 10^-2 A/cm^2 in TF device.The dominant leakage mechanism is investigated to be generally Schottky emission;however Poole-Frenkel emission also takes place during high reverse bias beyond 4 V for NWs and 3 V for TF device.
