Modelling of hole mobilities in heavily doped strained SiGe

Abstract

Low-field hole mobilities have been calculated for heavily relaxed and strained doped SiGe alloy layers with Ge contents varying from 0 to 50%, using a novel semi-analytical bandstructure model which incorporates the effects of strain on the valence band of the alloy. We obtain poor results compared with experiment for mobilities in heavily doped Si, and attribute this to (i) a failure of the Born approximation at low carrier energies and (ii) the omission of additional effects associated with heavy doping and high carrier concentrations. For the strained doped and intrinsic alloy we observe that both the in-plane and out-of-plane hole drift mobilities increase with increasing Ge content relative to those for Si. These enhancements are due mainly to the effects of strain, and to a lesser extent due to alloying with Ge, but are offset by the presence of alloy scattering. Our results are sensitive to the details of the models used for scattering by ionized impurities; however, the large uncertainties and scatter of the experimental data preclude accurate estimates of the alloy potential. We find that an alloy potential of 2.0 eV gives an in-plane mobility consistent with experimental data for intrinsic material. Our calculations for heavily doped layers are affected by uncertainties in the value of the alloy potential and highlight a need for a better quantitative understanding of the scattering processes which are important in heavily doped alloy layers.

Hall effect and ionized impurity scattering in Si(1−x)Gex

“…Our alloy scattering potential was U 0 = 0.51eV. Note that some authors [9,10], on the basis of fits to mobilities and other transport parameters, prefer a stronger alloy scattering potential (∼ 1eV); other discussions of the effect of alloy potential (and high impurity concentrations) can be found in [19,20]. We do not expect our results for r H to be particularly sensitive to the strength of the alloy potential, as alloy scattering is isotropic.…”

SiGe HBTs for application in BiCMOS technology: I. Stability, reliability and material parameters

“…Considerable work on these topics has been done at Princeton University [19], at IMEC [20][21][22][23][24] and by other groups [25][26][27][28]. Recently several papers have appeared on the mobility [29][30][31][32][33] and on BGN [34][35][36][37]. Simulations and material parameters are discussed in section 4.…”

“…Briggs et al [32] have calculated majority hole mobilities in the doped and strained SiGe alloys using the Monte Carlo method. Calculations were made for four doping concentrations, 0, 10 17 , 10 18 and 10 19 cm −3 .…”

High field transport in strained Si/GeSi double heterostructure: A Fokker–Planck approach

“…9 More recently, hole transport parameters have been analyzed for this type of system. 10 While the electronic transport properties of low field, low temperature Si/GeSi heterostructures are more or less well understood, 11 the situation is not the same for high electric fields. For high field transport, the effects of size quantization are usually negligible and we can work within three dimensional models for the valley structure.…”

“…Monte Carlo calculations of high electric field mobilities and drift velocities for electronic transport along the Si channel of Si/Ge x Si 1−x were reported by various authors [5][6][7][8] and also applied in the study of modulation-doped field-effect transistor (MODFET) structures [9]. More recently, hole transport parameters have been analyzed for this type of systems [10]. While the electronic transport properties of low field, low temperature Si/GeSi heterostructures are more or less well understood [11], the situation is not the same for high electric fields.…”