THz Detection by HBT Justified by Nonlinear Analytical Modeling and TCAD Simulation

Transistor operation beyond cutoff frequency as THz signal rectifiers has attracted increasing attention, lately. As a result, further development of different models has been carried out of the rectification and detection of this THz signal within different transistor structures. The common theory for THz detection by FETs is based on the well-known plasma wave model. However, recently reported THz rectification in HBT devices challenged this plasma wave model, as it may not apply to the THz detection and rectification within HBTs. We propose a simple nonlinear analytical model for describing the induced THz rectified signals in HBTs. This nonlinear analytical model is not only applicable to HBTs but also to FETs. Our proposed model is primarily based on the Taylor series expansion of the device's multivariable, nonlinear static I-V characteristics function. We validate our proposed analytical model by performing TCAD simulations for a typical SiGe HBT structure for both unbiased and biased collector operation modes. The results of the simulations demonstrate good agreement with the suggested nonlinear analytical model. Furthermore, we present a parametric study to investigate the contribution of effective device parameters such as base length, base width, base doping, emitter doping, and collector doping on the behavior of the HBT as a THz rectifier. The findings of this study shed light on the effects of these parameters and their role in shaping the performance of the HBT as a THz rectifier.