Nondestructive and Quantitative Evaluation of a GaAs Epitaxial Layer Covered With a Silicon Nitride Insulating Thin Film After a Highly Accelerated Temperature and Humidity Stress With the Use of Photoreflectance Spectroscopy

We demonstrate that photoreflectance spectroscopic measurements of Franz-Keldysh oscillations are applicable to nondestructively quantify the changes in surface Fermi level and surface recombination velocity of semiconductors after reliability stress tests. The present sample, a two-layer homoepitaxial structure consisting of a top undoped GaAs epilayer and a bottom n-type GaAs epilayer, were initially covered with a silicon nitride insulating thin film. This sample was subjected to the highly accelerated temperature and humidity stress. Initially, we estimated the built-in electric field strength from the Franz-Keldysh oscillations. We found that the built-in electric field strength is enhanced after the acceleration stress. Next, we performed the numerical analysis of the built-in electric field strength as a function of probe-light power density. From the above-mentioned numerical analysis, we clarified that the surface recombination velocity of the top undoped GaAs epilayer is enhanced by a factor of two. In contrast, the surface Fermi level is hardly changed. We discuss this phenomenon from the viewpoint of the formation of the surface defects that enhance the surface recombination velocity.