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 height are deposited by molecular beam epitaxy in the Stranski-Krastanov growth mode within the intrinsic region of a p⁺-i-p⁺ Si structure. For a broad excitation wavelength range between about 2 μm (620 meV) and 6 μm (207 meV), interlevel photocurrent is observed in normal incidence and waveguide 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.