# Study of the Photo-Response of Doped GaAs with Aging
## 1 Introduction  
Users of semiconductor materials assume that they are inert materials that do not change over time. However, it is useful to check whether or not their physical properties have been affected over time since they were produced. The warranty duration of devices, for which climatic conditions play an important role, is decided based on the efficiency of operation. The aging process can affect the structural and optical properties of aging-sensitive materials. Changes in the structural properties of the material can be caused by phase transformations and the deformation or damage of the surface over time. These structural changes will cause changes in optical, electrical, thermal and other responses. Thus, the classification of materials can be carried out in three differentiated parts based on their response to aging: short, long and very-long material sensitivity to aging. In many scientific research labs, experiments are performed with semiconductor wafers, whether purchased or manufactured. If the experiment is non-destructive, those samples are stored on shelves under ambient conditions for several years before another experiment. However, it is often not taken into account that there is a slow internal dynamic within the solid material that can alter its physical properties over time. On the other hand, the devices manufactured in companies are encapsulated to protect them from environmental conditions, but the aging process continues over time. Aging is one of these types of degradation that can affect the performance of devices designed with these materials [1, 2]. In the last decades, some theoretical and experimental studies have shown a growing interest in the analysis of the effects of aging and the rate of degradation in semiconductor materials [3, 4] and luminescent ceramics [5]. These studies are carried out with the purpose of understanding, simulating and mitigating their impact during the design phase of devices for technological and industrial applications, as described by [PERSON] and his group [6]. Semiconductor degradation is due to the accumulation of defects in the crystalline structure of the material. Several studies have explored the aging of semiconductor materials. [PERSON] et al. [7] carried out an investigation on the optical response of doped and undoped ZrO\({}_{2}\) epitaxialfilms and observed a decrease in the energy band as the aging time increased. On the other hand, [PERSON] et al. [8] applied different experimental techniques to analyze failures in high-power semiconductor lasers subjected to accelerated aging. All these works show that the study of the aging of semiconductor materials is still a current topic and some techniques have even been used to accelerate the aging process for analysis in the laboratory [9; 10; 11]. In particular, [PERSON] et al. [12] studied the formation of monodefects in GaAs when exposed to high-energy proton irradiation. GaAs is a widely studied semiconductor material with multiple applications in electronic and optoelectronic devices. We selected GaAs for this study because it is a widely characterized semiconductor material, which allows comparisons to be made with our measurements. In this work, we study the aging dynamics through optical techniques such as photoluminescence (PL) and photorelectance (PR), during three periods of time over 26 years on doped and undoped GaAs epitaxial films that are exposed to the environment.