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 °C are overgrown with Si at different temperatures Tcap, and their mid-infrared photoresponse is investigated. The photocurrent maximum shifts from 2.3 to 3.9 μm with increasing Tcap from 300 to 750 °C. The best performance is achieved for the detector with Tcap = 600 °C in a photovoltaic mode. At a sample temperature of 90 K and no applied bias, a responsivity of 0.43 mA/W and detectivity of 6.2 × 1010 cmHz1/2/W at λ = 3 μm were measured under normal incidence infrared radiation. The device exhibits very low dark current (Idark = 2 nA/cm2 at T = 90 K and U = −0.2 V) and operates until 200 K.