Contents lists available at ScienceDirect Optics Communications journal homepage: www.elsevier.com/locate/optcom Circuit modeling and performance analysis of photoconductive antenna Jitendra Prajapati ⁎ , Mrinmoy Bharadwaj, Amitabh Chatterjee, Ratnajit Bhattacharjee Department of Electronics and Electrical Engineering, Indian Institute of Technology Guwahati, Guwahati, Assam-781039, India ARTICLE INFO Keywords: Equivalent electrical circuit Laser-semiconductor interaction Photoconductive antenna (PCA) Pulsed thz system Sentaurus TCAD THz antenna ABSTRACT In recent years, several experimental and simulation studies have been reported on the terahertz (THz) generation using a photoconductive antenna (PCA). The major problem with PCA is its low overall efficiency, which depends on several parameters related to a semiconductor material, an antenna geometry, and characteristics of the laser beam. To analyze the effect of different parameters on PCA efficiency, accurate circuit modeling, using physics undergoing in the device, is necessary. Although a few equivalent circuit models have been proposed in the literature, these models do not adequately capture the semiconductor physics in PCA. This paper presents an equivalent electrical circuit model of PCA incorporating basic semiconductor device physics. The proposed equivalent circuit model is validated using Sentaurus TCAD device level modeling tool as well as with the experimental results available in the literature. The results obtained from the proposed circuit model are in close agreement with the TCAD results as well as available experimental results. The proposed circuit model is expected to contribute towards future research efforts aimed at optimization of the performance of the PCA system. 1. Introduction In recent years THz frequency band (100 GHz-10 THz) [1], which is between the microwave and optical frequency bands, is receiving a lot of attention due to its potential in several significant fields of applica- tion. Until recently, the THz band had not been utilized properly compared to other frequency bands mainly due to the lack of efficient and practical THz sources. Ultra-fast optical techniques for THz generation, have boosted the research in the THz band. Among all the ultra-fast optical techniques, THz generation based on photocon- ductivity is considered to be both simple and compact as compared to optical rectification and photo-mixing. A 3D schematic diagram of a PCA system is shown in Fig. 1. Investigations on PCA started with Auston switch [2], which was used for ultrafast switching by optoelec- tronic conversion techniques using Hertzian dipole structure. Using the same principle as described in Ref. [2] with different antenna geome- tries, many experimental studies have been performed to generate THz pulses with large bandwidth, high power and efficiency [3–6]. Although PCA is a common source for THz, its low efficiency has been considered as a major bottleneck [7]. The overall efficiency of PCA is a product of electrical efficiency, matching efficiency and radiation efficiency [7]. The low efficiency of PCA is primarily due to low electrical efficiency [8]. Electrical efficiency of a PCA determines how efficiently the optical power is converted to electrical power in the substrate. It can be increased by enhancing the coupling of optical power to the substrate material. In PCA, the radiated power depends on the rate of change of the current [1,3,9,10] and can be improved by generating an ultrafast and high amplitude current pulse. Intuitively, to achieve high efficiency and large bandwidth from PCA, current pulse with higher amplitude and shorter pulse width is required. The characteristics of the current pulse generated in PCA depends on several parameters including incident laser power, antenna geome- try and material parameters of the semiconductor substrate. Detailed analysis, incorporating semiconductor physics in PCA operation, is very crucial for developing an accurate model. As regards prior work in this area, to the best of the authors’ knowledge, mainly three equivalent circuit models of PCA had been reported in the literature [8,11,12]. In Ref. [11], the proposed circuit model being very simple and basic, fails to predict the local field distribution and voltages of the PCA accurately. In Ref. [12], the circuit model does not include: the carrier dynamics in the material and the change in the electric field at the gap due to polarization effect. In Ref. [8], an improved circuit model had been presented, but it fails to incorporate adequate device physics into the analysis of the circuit model. Also, the analysis carried out to evaluate the circuit components had several inconsistencies as reported in Ref. [13], where it has been pointed out that the model does not provide an accurate insight into physics involved in PCA operation and fails to model accurately the effect of different parameters on PCA perfor- mance. http://dx.doi.org/10.1016/j.optcom.2017.03.004 Received 23 November 2016; Received in revised form 13 February 2017; Accepted 2 March 2017 ⁎ Corresponding author. E-mail address: j.prajapati@iitgernet.in (J. Prajapati). Optics Communications 394 (2017) 69–79 0030-4018/ © 2017 Elsevier B.V. All rights reserved. MARK