Analytic models for solid state plasma of Si/Ge/Si heterogeneous and lateral SPiN diode

Silicon-based reconfigurable antenna, which is fabricated by heterogeneous and lateral surface PiN (SPiN), is an effective technology to achieve antenna miniaturization and enhance radar and wireless communication system performance. In this paper, the heterogeneous and lateral Si/Ge/Si SPiN diode is presented, that can weaken the band gap narrowing of the P + and N + region to improve the injection ratio of PN junction. And the electrical properties of the solid state plasma within the intrinsic region are also studied. Based on the bipolar diffusion model and Fletcher boundary condition, the analytic models of the junction voltage, the current density and the solid state plasma concentration distribution are established for a large injection current, and the numerical simulation has been carried out. Results show that the junction voltage increases linearly with the increase of applied voltage and the solid state plasma concentration at the boundary; and the current density increases exponentially with increasing junction voltage and the applied voltage, respectively. And the applied voltage and the current density of heterogeneous SPiN diode is lower than that of homogeneous SPiN diode under the same condition due to the difference of barrier heights between the heterojunction and homojunction. In addition, results also show that the value of the concentration decreases with increasing length of the intrinsic region; otherwise, it increases with increasing applied voltage and the doping concentration in the P+ and N+ regions. Under the same conditions, the solid state plasma concentration of the heterogeneous SPiN diode is nearly seven times that of homogeneous diode, which is in excellent agreement with the data published, giving the evidence for the validity of our method. The proposed models provide an effective reference for the design and application of silicon-based reconfigurable antennas.