Intra-valence band photocurrent measurements on Ge quantum dots in Si

We have investigated p-doped Ge quantum dots embedded in Si using mid-infrared photocurrent spectroscopy. The samples were grown on n^--Si (100) Substrates using solid-source MBE. The Ge dots form by self assembly at T = 510 °C in the Stranski-Krastanov growth mode. They have a diameter of approximately 25 nm and a height of 2 nm. Photocurrent measurements have been performed on vertical as well as on lateral structures. In both geometries, a broad photoresponse is obtained from the dots for excitation between 200 and 600 meV. The photocurrent maximum is at approximately 324 meV for the vertical and at approximately 284 meV for the lateral structure. This shift in the lateral structure can be explained by transport of the photoexcited carriers within the Ge wetting layer.