|Photocurrent simulation in TH photoconductive detectors (Vol. 44 No. 1)|
The simulated signals are shown for two different gate fluences as well as the input THz field. The schematics on the right depict the reason for the difference between signals, which is caused by the saturation of the traps in the high fluence regime resulting in long lived mobile carriers which do not appear in the low fluence case.
Nowadays the most widely used spectroscopic technique in the terahertz band (0.1 to 10 THz) is called terahertz time-domain spectroscopy, which generates and detects pulses of terahertz light by triggering photoconductive antennae using infrared pulses from an ultrafast laser.
The influence of geometrical structure and semiconductor properties on the performance of photoconductive antennae has been studied extensively from the experimental point of view. However, theoretical studies on the semiconductor carrier dynamics of these devices have only emerged recently and have mostly focused on simulating the performance of emitters.
The present work develops a semi-classical Monte-Carlo model that can simulate ultrafast carrier dynamics in photoconductive detectors. The simulation tracks the motion of millions of charges under the electric field of a terahertz pulse at various times after their photo-generation taking into account the quantum mechanical scattering of each particle. By utilising a sequence of simulations the transient photocurrent was modelled precisely. In photoconductive detectors the rate at which electrons become trapped is an important parameter that determines how the measured current transient differs from the actual terahertz pulse's shape. By examining the role of carrier trapping at various illumination levels the authors demonstrated that high powers can distort the measured photocurrent. This model will set the path for further development of detectors of pulsed terahertz radiation by providing insights into semiconductor material design for that application.
E. Castro-Camus, M.B. Johnston and J. Lloyd-Hughes, ‘Simulation of fluence-dependent photocurrent in terahertz photoconductive receivers’, Semicond. Sci. Technol. 27, 115011 (2012)