Effect of doping location on photoconductive spectrum of SiGe quantum dots

Comparative analysis of photoconductive (PC) spectra obtained from SiGe quantum dots grown on Si shows large dependence on the location of doping. The sample with doping in the silicon barrier has much larger response than the sample in which the doping was placed in the wetting layer, i.e. in the self assembled dots. This is due to the penetration of the wave-function into the barrier in the first structure, as shown by the 1-D simulation. Several peaks in the infrared were observed, ranging from 70 to 220 meV, associated with inter-level transitions of holes in the valance band of the dot or the wetting layer. The overall spectra and the relative intensity of the various peaks change drastically with bias magnitude and polarity. The PC signals increase super-linearly with bias, indicating that the carriers are released into the quasi-continuum through tunneling.