Comprehensive Studies of High-Linearity Position-Sensitivity Detectors With Theoretical Consideration on Lateral Photovoltaic Currents

Detective properties of a GaAs-based position sensitive detector (PSD) employing a very thin, highly doped p
⁺
-GaAs layer as a resistive layer were investigated. In addition to photovoltaic voltages, photovoltaic currents from a three-terminal PSD with two lateral electrodes and one transverse common electrode were also studied. In particular, lateral photovoltaic currents flowing into the two lateral electrodes and/or their differential values, instead of transverse photovoltaic currents were used as output signals. To do so, a PSD itself without power supply was proposed to realize its suitability for applications. When a 2 mW 638 nm light spot was used as an input, a position sensitivity of
$38.5~\mu \text{A}$
/mm, a correlation coefficient (or linearity) of > 0.999, and a nonlinearity (or position error) of 1.25% were obtained for our GaAs-based PSD with a long distance of 14 mm between two lateral electrodes. Besides, an equivalent circuit with a point solar cell was proposed to successfully explain these photovoltaic currents found in various configured 2-terminal and 3-terminal PSDs.