Intraband absorption in Ge/Si self-assembled quantum dots

We have observed intraband absorption in Ge/Si self-assembled quantum dots. The self-assembled quantum dots are grown at 550 degrees C by chemical vap or deposition. Atomic force microscopy shows that the quantum dots have a s quare-based pyramidal shape (approximate to 100 nm base length) and a densi ty approximate to 2 x 10(9) cm(-2). Intraband absorption in the valence ban d is observed around 300 meV (4.2 mu m wavelength) using a photoinduced spe ctroscopy technique. The intraband absorption is in-plane polarized. It is attributed to bound-to-continuum transitions since the intraband energy cor responds to the energy difference between the Si band gap and the photolumi nescence energy of the quantum dots. The magnitude of the intraband absorpt ion saturates when the ground level of the quantum dots is filled. This fea ture allows the measurement of the in-plane absorption cross section of the intraband transition which is found as large as 2 x 10(-13) cm(2). (C) 199 9 American Institute of Physics. [S0003-6951(99)01403- 5].