Vertical and lateral mid-infrared photocurrent study on Ge quantum dots in Si

In this paper we discuss photocurrent measurements in normal incidence geometry performed on sell-assembled Ge dots in Si. The "classical" detector concept with vertical photocurrent is compared to a new one which is based on in-plane photoconductivity and is only realizable with dots. The active region of the samples consists of ten layers of Ge dots formed by self-assembly in the Stranski-Krastanov growth mode with lateral dimensions of about 20 nm and a height of about 1.5 nm. The mid-infrared photocurrent measurements show the typical line shape of bound-to-con tinuum transitions. The responsivity of the lateral device of 10 mA/W is about twice that of the vertical structure, furthermore the peak maximum at 284 meV is shifted by about 40 meV towards smaller energies. This is explained using a model involving carrier transfer to the modulation doping layer.