Background impurities in Si_0.8Ge_0.2/Si/Si_0.8Ge_0.2n-type δ-doped QW

Abstract

Additional (residual) impurities in the barriers change the energy profile of a quantum well. This means that they alter the ionization energy for the impurity delta layer situated within the quantum well. In turn, this is accompanied by the change of a V‐shaped quantum well created by ionization of the delta layer. All of this is the subject of studies presented in this article. It has been shown that the most dramatic are the changes in the difference between the space‐quantized energy levels for an edge‐doped quantum well.

Background impurities and a delta-doped QW. Part I: Center doping

“…Here it has to be noted that in our earlier work [38] the data on the higher concentration were reported. It will be seen below, in the part 4 that a smaller concentration allows one to estimate a possible dynamic range of changing both IBEs and energy gaps between couples of neighboring space-quantized energy levels with changing concentration of the delta layer.…”

“…It means that the Si QW can be considered as subjected to the uniaxial strain along the growth direction z of the structure. This results in that the degeneracy of electron valleys in the conduction band of Si is removed and in our case of [100] growth direction the splitting between the four upper in energy valleys Δ 4 and two others Δ 2 is more than 110 meV [37,38,42]. In turn, such big splitting allows us to consider only the two lowest valleys (even at temperature T=300 K -see below) with the effective masses along the layer = m m 0.19 0  , and in the growth direction = m m 0.92 0 with m 0 being the free electron mass.…”

“…On the other hand, in order to make the considered QW structure closer to the real device, it is also necessary to take into account the BIs, and that is what this work is devoted to. At this point, however, we must mention that we have published some preliminary results on this topic earlier, in a short publication [38]. Here we present a more complete set of results with detailed (in our opinion) theoretical grounding.…”

“…We have made calculations for two concentrations of Phosphorus in the delta layer n δ =0.6×10 12 cm −2 and 9 At this temperature the structure of the space-quantized energy levels in the QW is the same for both center-and edge-doped QWs because of all the impurities in the delta-layer are neutral independently on their place within the QW. In [38] the results for center-doped QW were only presented.…”

“…The calculations are made for the most important experimental physics temperatures T=4, 77, and 300 K for a center-doped QW, while an edge-doped QW we only examine at T=4 K, as at this temperature the delta layers are neutral independently on their place inside the QW. The choice of two elevated temperatures (in [38] only temperature 300 K was examined) is conditioned by the fact that two temperatures allow one to estimate the dynamic range of changing both the IBE and (which is the most important)-the dynamic range of changing energy differences between couples of the neighboring energy levels against the ionization level of impurities in the delta layer.…”