Coulomb centers assisted tunneling in a δ-doped triple barrier SiGe heterostructure

A study of vertical transport in δ-doped SiGe/Si heterostructures is presented. An asymmetrical triple barrier structure was grown with a δ-layer of boron impurity in the center of a narrow quantum well. The growth procedure was followed by conventional processing including photolithography, plasma etching and magnetron sputtering. Secondary-ion mass-spectroscopy depth profiling and high resolution x-ray diffraction were used to control the as-grown structure. The conductance of the structure was measured at liquid helium temperature and analyzed. All pronounced resonances were identified. The resonant feature near 60 mV is attributed to impurity-assisted tunneling, which is supported by calculation of the binding energy of the acceptor in the narrower quantum well.