Charge accumulation in a type-II Ge/Si heterostructure

The main motivation for mixing a small amount of Ge into Si for example by the self-organized growth of a stack of Ge dots into Si [1], is the controlled modification of the electronic band structure in strained Si namely charge carrier mobility and optical transition probabilities [2]. We report on charge accumulation in fivefold stacks of Ge quantum dots embedded in the n-region of a p+n-Si diode. By means of thermal admittance spectroscopy, capacitance voltage and deep level transient spectroscopy measurements [3] electron confinement in the type II Ge/Si-heterostructures, barrier effects of the quantum wells and wetting layers and defect states in the n-region of the sample associated with the surrounding Si-matrix have been probed. By relating these results to the self consistently modeled electronic band-structure and capacitance voltage characteristic charge accumulation in quantum confined electron states in the investigated type II Ge/Si-heterostructures is clearly revealed.
[1] A. Malachias, T. H. Metzger, M. Stoffel, O.G. Schmidt and V. Holy, Thin Solid Films 515, 5587 (2007)
[2] O.G. Schmidt and K. Eberl, Phys. Rev. B 61, 20 (2000)
[3] M. Gonschorek, H. Schmidt, J. Bauer, G. Benndorf, G. Wagner, G.E. Cirlin and M. Grundmann, Phys. Rev. B 74, 115312 (2006)