Increasing the sensitivity of laser ultrasonic detection in GaAs photo-EMF configuration under external DC bias

Abstract

Summary form only given. Due to simplicity and robustness adaptive photodetectors based on the photo-EMF effect are considered promising for various applications, and in particular for laser ultrasonic detection. The most important drawback of these photodetectors is relatively low current response:/spl les/10/sup -3/ A/W for typical GaAs devices with several tens of interference fringes in the interelectrode spacing. Since the dominating noise of the detection configuration is the current noise of the transimpedance amplifier (/spl sim/ 1pA//spl radic/Hz for operational amplifiers with bipolar transistors), this reduces dramatically the signal-to-noise ratio in the detected signal. Various changes were proposed to increase the current response, and in particular, longitudinal configuration of the device and asymmetric interdigitated planar system of contacts. We demonstrate that external DC bias can also increase the response of the GaAs photo-EMF detectors significantly.