Improved electrical characteristics of porous germanium photodiode obtained by phosphorus ion implantation

Abstract

Germanium–based photodetectors are the standard technology used for radiometric measurement in the IR spectral range. Shallow PN+ junctions were obtained by using ion implantation in p–type germanium. N–type doping was achieved by phosphorus implantation at a dose of 1 × 1015 cm−2 doses and an energy of 150 keV followed by annealing at 600°C for 2 h. In order for the new detector to be used as a standard for radiometric measurement, a porous layer is introduced on the active surface. After metallisation by thermal evaporation of indium (In) on the front side and gold (Au) on the back side, the new porous germanium–based photodetector is essentially done. The electrical behaviour of this porous germanium photodiode is characterised by current–voltage measurements that are compared to the I–V characteristic of classical germanium photodiodes. The results of this study show a huge increase of the photocurrent, a significant increase of the shunt resistance and low series resistance. Effects of low shunt resistance are also discussed. AFM showed that the porous layer contributes to trap the incident optical radiation and to reduce the reflection coefficient fluctuations of the front face of the photodiode.