Study of hole transport through minibands in symmetrically strained Ge_xSi_1-x/Si superlattices

The hole transport through the minibands of symmetrically strained Ge_xSi_1-x/Si superlattices is observed. The superlattices are grown on unstrained Ge _{x 2}Si_{1- x 2}/Si buffer layers. Two peaks are observed from the current-voltage (I-V) and conductance-voltage (dI/dV) measurements, which are due to conduction of light holes through minibands in the superlattice. The second peak shows a negative differential resistance (NDR) region below 100 K. The energies of the minibands are estimated by thermionic emission analysis of current-voltage-temperature (I-V-T) data. Also, we have studied the long wavelength (10 μm) infrared absorption of these superlattice samples by photocurrent measurement. The measured photocurrent as a function of bias shows characteristics similar to the I-V characteristics. The preliminary data on polarization dependence of the photocurrent suggest that the infrared absorption occurs between lighth hole minibands.