Analytical calculation of effective densities of states, intrinsic carrier concentration and ionized doping concentration in strained Si1−xGex alloys on (001) Si substrates at room and low temperatures
✍ Scribed by Zhang Wan-rong; Zeng Zheng; Luo Jin-sheng
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 476 KB
- Volume
- 36
- Category
- Article
- ISSN
- 0011-2275
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✦ Synopsis
In this paper, the effective densities of states for the conduction and valence bands, Nc and N,, the intrinsic carrier concentration ni and the ionized doping concentration in strained Si,_,Ge, layers grown on (001) Si substrates are analytically calculated, and their temperature and Ge fraction dependence studied. It is found that whereas ni increases quasi-exponentially, the ionized doping concentration increases (carrier freeze-out is mitigated at low temperatures compared with that in Si) and Nc, Nv and the product Nc.Nv decrease rapidly due to the effect of strain in the Si,-,Ge, layers as the Ge fraction increases. Furthermore, as the temperature becomes lower, the decrease in Nc, Nv and the product Nc.Nv become more rapid and the increase in ni becomes more evident. In addition, it is also found that for strained Si,_,Ge, layers with low and high Ge fractions, respectively, Nc, Nv and the product Nc.Nv normalized by those in Si depend on temperature Tstrongly versus slightly, which is consistent with the results of Prinz et a/. 01996 Elsevier Science Limited Keywords: SiGe alloy; strain; effective densities of states; intrinsic carrier concentration; carrier freeze-out
Physical models
Models for NC, NV and ni
In strained Si,,Ge, alloys grown on Si substrates, with increasing Ge fraction x, the energies of the X and L conduction band minima approach each other. Furthermore, the