Inhomogeneous strain relaxation in triple-barrier p-Si/SiGe nanostructures

Resonant tunneling measurements are used to probe size-induced strain relaxation in p-Si/SiGe triple-barrier nanostructures with a narrow (similar to 10 Angstrom) middle barrier, where the confined subbands depend strongly on the strain and bias-dependent coupling between the two neighboring quantum wells. In structures with 2.0 greater than or equal to D greater than or equal to 0.25 mu m diameter, shifts in the strain-dependent subband energies are clearly observable in the tunneling current. Further, in the smallest structures (D less than or equal to 0.17 mu m), tunneling through discrete states confined by inhomogeneous-strain-induced lateral potentials dominates the I(V). Magnetotunneling measurements on a D = 0.17 mu m structure reveal a similar to 75-Angstrom effective length of the strain-induced lateral confinement potential. Based on our previous measurements of double-barrier nanostructures and the finite element calculations of the strain distribution in these triple-barrier structures, we conclude that the I(V) peak shifts in larger devices are due to uniform strain relaxation, whereas in smaller devices the fine structure in the I(V) is due to coupled inhomogeneous-strain-induced discrete quantum-dot or ring states in neighboring wells. [S0163-1829(99)14347-9].