Effect of overgrowth temperature on the mid-infrared response of Ge/Si(001) quantum dots

Ge/Si quantum dots fabricated by molecular-beam epitaxy at 500 degrees C are overgrown with Si at different temperatures T-cap, and their mid-infrared photoresponse is investigated. The photocurrent maximum shifts from 2.3 to 3.9 mu m with increasing T-cap from 300 to 750 degrees C. The best performance is achieved for the detector with Tcap 600 degrees C in a photovoltaic mode. At a sample temperature of 90K and no applied bias, a responsivity of 0.43mA/W and detectivity of 6.2 x 10(10) cmHz(1/2)/W at lambda = 3 mu m were measured under normal incidence infrared radiation. The device exhibits very low dark current (I-dark = 2 nA/cm(2) at T = 90K and U = -0.2 V) and operates until 200 K. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3682304]