Optical Writing and Electro-Optic Imaging of Reversible Space Charges in Semi-Insulating CdTe Diodes.

Adriano Cola,Antonio Valletta,Lorenzo Dominici

doi:10.3390/s22041579

Abstract

Deep levels control the space charge in electrically compensated semi-insulating materials. They limit the performance of radiation detectors but their interaction with free carriers can be favorably exploited in these devices to manipulate the spatial distribution of the electric field by optical beams. By using semi-insulating CdTe diodes as a case study, our results show that optical doping functionalities are achieved. As such, a highly stable, flux-dependent, reversible and spatially localized space charge is induced by a line-shaped optical beam focused on the cathode contact area. Real-time non-invasive imaging of the electric field is obtained through the Pockels effect. A simple and convenient method to retrieve the two-dimensional electric field components is presented. Numerical simulations involving just one deep level responsible for the electrical compensation confirm the experimental findings and help to identify the underlying mechanism and critical parameters enabling the optical writing functionalities.

Highlights

Semiconductor devices rely on electric fields in order to provide suitable paths for the free charge carriers
The main consequence of the optical irradiation, which occurs on the cathode side is a huge increase in the electric field close to the anode, maximum at the transverse position of irradiation xirr and, as expected, laterally symmetric with respect to this axis
We have shown that optical doping is feasible across the planar electrode surface of

Summary

Introduction

Semiconductor devices rely on electric fields in order to provide suitable paths for the free charge carriers. A viable route to overcome this limitation is offered by optical doping, defined here as an optical perturbation leading to a spatially localized and stable modification of the charges. In this regard, scanning light beams have been recently used to permanently write monolithic integrated circuits on a two-dimensional semiconductor, via irreversible processes such as direct defect creation [1]. Permanent optical doping was realized in the active channel layer of thin films transistors resulting in the enhancement of their parameters [3]. Reversible optical doping has been often shown in monolayers, such as WS2 [4] or, more frequently, graphene [5,6,7,8,9]

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Conclusion