Intra-valence band photocurrent spectroscopy of self-assembled Ge dots in Si

Intra-valence band photocurrent investigations of self-assembled Ge dots in Si are reported. Boron-doped Ge dots of about 70 nm diameter and 6.5 nm he ight are deposited by molecular beam epitaxy in the Stranski-Krastanov grow th mode within the intrinsic region of a p(+)-i-p(+) Si structure. For a br oad excitation wavelength range between about 2 mu m (620 meV) and 6 mu m ( 207 meV), interlevel photocurrent is observed in normal incidence and waveg uide geometry. The absorption is attributed to transitions from hole states bound in the Ge dots to continuum states. The photocurrent can be measured up to T=100 K without any significant decrease of the responsivity. (C) 20 00 American Institute of Physics. [S0003-6951(00)02108-2].