The microstructural, luminescence properties and photoresponse of multilayer Ge(Si) quantum dots grown on Si (100) substrates are studied. The strain and composition of the dots are studied by synchrotron-radiation x-ray. The dots are found to be Si<SUB>0.58</SUB>Ge<SUB>0.42</SUB> alloy with 50% strain relaxed in average. The photoluminescence from the dots is observed up to room temperature. The thermal stability of the quantum dots is studied. P-i-n structures are grown with Ge(Si) dots embedded in the i-layer for photodetection investigation. The photoresponse wavelength of Ge(Si) dots covers the wavelength range of 1.3-1.52 mm and relatively high external quantum efficiency is obtained.
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 3x10-5A/cm2 at -1 V. A strong photoresponse at 1.3-1.55 mm 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.