The influence of the photovoltaic effect on the surface electric field in GaN

Abstract

The surface potential barrier is an important issue for design and development of semiconductors devices, particularly based on heterostructures. It can be investigated with the electromodulation (EM) spectroscopy, as this technique allows the study of a surface electric field. However, the latter may be altered significantly by the photovoltaic (PV) effect. In this paper we present comprehensive studies of the influence of the PV effect on the surface electric field established using contactless electroreflectance (CER) and photoreflectance in dark and bright experimental configuration. Materials under investigation are the so called ‘van Hoof’ GaN structures with upward and downward band bending. This kind of sample architecture enables the probing of the built-in electric field through the investigation of Franz-Keldysh oscillations observed in the measured spectrum. It is shown that results obtained in bright configuration are more susceptible to PV effect than in dark configuration, however even for dark configuration this effect should not be neglected. What is more, it is highlighted that due to reduction of PV effect, CER enables more precise investigation of surface electric field than PR experiment. Relative changes in the surface electric field obtained for different lighting power densities are determined and discussed in this article.