Capacitance-voltage and admittance spectroscopy of self-assembled Ge islands in Si

We investigate the electrical properties of self-assembled Ge islands embed ded in Si Schottky diode structures by means of capacitance-voltage measure ments and admittance spectroscopy. The Ge islands form at T=550 degrees C b y self-assembly in the Stranski-Krastanow growth mode with an area density of 4.5x10(9) cm(-2). Their diameter and height are 70 and 6.5 nm, respectiv ely. A linear increase of the thermal activation energy observed in voltage -dependent admittance spectroscopy shows that the ensemble of Ge islands ha s a low, continuous, averaged density of states. (C) 2000 American Institut e of Physics. [S0003-6951(00)03443-4].