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The influence of isovalent impurity of germanium upon the electrophysical properties of silicon

The influence of isovalent impurity of germanium upon the electrophysical properties of silicon
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The developing of modern engineering demands the investigation of new semiconductor materials. Crystals of solid solutions Si are of great interest in this respect. Solid solutions of Si with the concentration of additional component of about 1% are regarded as semiconductors doped with isovalent impurities [1]. When doping the crystals of silicon with atoms of germanium inner local stresses arise as a result of difference between the covalent radii of Si (1.17 ) and isovalent impurity of Ge (1.22 ), deforming the crystal lattice, changing its constant and thus influencing upon electrophysical properties of the crystal.

The paper presents the results of the investigation of electrophysical parameters and piezoresistanse effects in the crystals Si of n-type with a concentration of germanium NGe=2101921020cm-3 by measuring temperature dependencies of conductivity, Hall coefficient, piezoresistance and piezo-Hall-effect. The object of the investigation were the crystals grown by Chokhralsky method with content of oxygen of (68)1017cm-3. The measurements of control samples without isovalent impurity of germanium (IIGe) were performed for comparison.

Figure 1 shows the temperature dependences of electron mobility  on the temperature in pure n-silicon (curve 1) and in n-silicon with different concentration of IIGe (dependences 2,3). Numbers of curves in Figure 1 correspond to the numbers of samples in Table 1.

Table 1

N 

cm N10-13

cm-3 NGe10-19

cm-3 N010-17

cm-3 300K

cm2/Vs 77K


1 130 3.1 - 7 1500 23000

2 81 5.1 2 6 1500 21000

3 65 6.2 4 6 1500 19500

4 50 9 7 6.5 1450 18500

5 98 4 20 6 1480 16400

Detailed experimental and theoretical investigations of electron mobility in n-silicon [2] showed that in the region of mainly phonon scattering it is determined both by in-valley and inter-valley scattering. Theoretical calculations, performed with account of scattering on long wave acoustic phonons and inter-valley pulse scattering at interaction of electrons and the phonons of corresponding averaged temperatures 1=190 K and 2=630 K, show the sufficiently detailed coincidence with the experiment in a wide temperature range 77450 K. It is confirmed by plot 1, Fig.1, which also shows the contributions of different scattering mechanisms according to [2]. Plot 1 has a distinctive bending in 100K range. Such behavior of the curve and the deviation from the dotted line which determines the temperature dependency of electron mobility in pure n-silicon at scattering on acoustic oscillations of the lattice may be explained by the increasing contribution of inter-valley scattering at T100 K. As it is seen in Fig.1, the slope of the dependency lg()=lg(T) changes from 1.5 to 2.3. The change of power exponent in dependency T-m in the region of phonon scattering for n-silicon is revealed in paper [3], in which the authors assume that the abrupt decrease of  at NGe1020cm-3 testifies to the change of phonon spectrum and to the elastic stress relaxation via formation of modular structure of crystals. As it is seen in Fig. 1, the identity of all the curves slopes in practically important temperature range of 220450K with the major contribution of inter-valley scattering testifies to the principal role of inter-valley scattering.

The decrease of electron mobility at temperatures T

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Реферат на тему: The influence of isovalent impurity of germanium upon the electrophysical properties of silicon

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