High-sensitivity position-sensitive detectors to low-power light spots

Abstract

This work reported on detecting properties of a p(+)-i-n(+) position-sensitive detector (PSD) which has a thin heavily-doped p+-GaAs layer and a thick lightly-doped i-GaAs layer as a resistive layer and an optical absorption layer, respectively. Two lateral electrodes on the p+-GaAs layer were separated by a distance of 12 mm to provide lateral photovoltaic voltages. The p(+)-GaAs layer with a small resistivity produces a long diffusion length for excess holes. Thus, a high linearity of > 99.8 % and a detection error of < 3.2 % are achieved when a visible light spot with a low power of < 3 mW is used. Measured sensitivities as a function of light-spot power are also indicative of a small power constant of 1.4 mW for a 638 nm light spot. A power efficiency of 9.66 mV.mm(- 1)mW(-1) at 0.5 mW is obtained. Together with mature optoelectronic and microelectronic technologies, the proposed structure is very promising for a high-sensitivity PSD to low-power light-spot detection. On the other hand, response times of the PSD reflecting light on and off were also studied for further understanding insight the positioning mechanism. Measured results reveal that transverse depth where electron-hole pairs generated is one of key factors influencing the response time.