Two types of fast-response germanium photodiodes

Two types of fast-response photodiodes have been prepared using a selective and controlled bath etching process. Both types are sensitive to visible and near infrared radiation (intrinsic photoconductivity). The first of these devices is in essence a flat fused p-n junction of from 2 to 30 microns base width. The germanium opposite the junction is the photosensitive window. Photodiodes of this type show good reproducibility and photosaturation characteristics. Response time for the thinner base devices is essentially limited by the detector load resistance and total circuit capacitance. Circuit rise and fall times of less than 0.05 µsec have been attained. Sensitive window areas have ranged from cm²to cm².