Normal-incidence near 1.55 μm Ge quantum dot photodetectors on Si substrate

The development of Si-based photodetectors is very important due to their compatibility with the state-of-the-art Si planar technology. Photodetectors based on Ge quantum dots were studied. Three p-i-n structures containing Ge dots were grown by molecular beam epitaxy in Stranski-Krastanov mode. The dots were grown embedded in Si spacing layers on Si (100) substrates. The nominal Ge growth thickness in each layer was 1.2, 1.5 and 1.8 nm for the three samples, respectively. Photoluminescence measurement showed that the Ge dot related peak shift to lower energy with increasing the dot layer thickness. The materials were processed into p-i-n photodiodes with conventional processing methods. I-V measurement showed a low dark current density of 3×10^-5 A/cm² at -1 V. A strong photoresponse at 1.3-1.55 μm originating from Ge dots was observed. The response peak shifts with the Ge growth thickness. At normal incidence, an external quantum efficiency of 8% was achieved at 2.5 V. The dot layers were considered to trap the light in the intrinsic region, and thus increase the absorption.