BYThe study of the piemresistance of n-Si arising at uniaxial elastic deformation along the [lll] direction (in absence of current carrier redistribution between individual valleys) due to the deformation-induced change of the effective mas8 is of special interest /1, 2/. X along the [lll] direction. In this case the dependences of the components of the effective mass tensor on X can be represented as follows:A s shown in /3/, the isoenergetic ellipsoids become three-axial for stress 2 where r= 6 . 7 4~1 0 -~ cm /kp.At 3 II f"_ila the isoenergetic ellipsoids of n-Si a r e oriented in such a way that the axis corresponding to m2 (for each ellipsoid) lies in the plane containing the deformation axis and the great ellipsoid axis.The conductivity teneor of one valley (in terms of their main axes) has the where mN = (mlm2m3)1/3, no is the Maxwellian equilibrium distribution function of electrons,' b~, a r e the components of the relaxation time tensor depending on the pressure X owing to ma = fm), ko is the Boltzmann constant, T is the absolute temperature.Since rX *I for the entire.pressure interval, then (2) may be decomposed:~~ 1) proepekt Nauki, 252028 Kiev, u88R.where OL and d, a r e the conductivity components of one valley in absence of mechanical stress calculated in /4/ and J is the combination of some angular integrals included in ~~( x ) .For the parameters of n-Si we obtain J = 0.87. Based on (3) we have where K = 4 /Ull is the anisotropy parameter.The experimental curve 1 in Fig. 1 even qualitatively differs from the calculated results (straight line 3 in Fig. 1) carried out by (4). In addition, (4) proved to be independent of temperature at least in the interval 78 to 300 K contradicting the experimental data (curves 1 and 2 in Fig. 1). However /l/, the temperature dependence of the piezoresistance measured in n-Si a t great 2 II [lll] was explained by supposing that the curvature of the dispersion &$(k) changes with removal of the energy degeneracy a t the Brillouin zone boundary (Fig. 1). This is equivalent to the occurrence of non-parabolicity which shall be taken into account below.Let u s suppose that the non-parabolicity has the Kane form The best agreement between theory and experiment (Fig. 1) is obtained at Lo = 2 . 0~1 0 . cm b e r g . ~n this case the non-parabolicity is insignificant since X E w h k T r . 2~1 0 -~ 4: 1. However, for great X the non-parabollcity essentially determines the behaviour and the temperature dependence of the piezoresistance.

Strain-induced metal-insulator (MI) transitions have been observed in degenerately doped Si:Sb and Ge:Sb crystals at T = 4.2 K and for extremely high uniaxial pressures up to 5 GPa. It is shown that in both Si and Ge the transition from a metallic-type to an activated conductivity is determined by strain-induced changes of the conduction band parameters. The data obtained demonstrate that the effective mass donor approach and the scaling theory of localization describe well the MI transition phenomenona observed.

Institute of Semiconductors, Academy of Sciences of the Ukrainian SSR, Kiev The Determination of the Deformation Potential Constants in n-Germanium BY P. I. BARANSKII and V. V. KOLOMOETS It is known that the numerical values of the deformation potential constants determined by different methods (1 to 7) a r e characterized by a considerable uncertainty. It is easily shown that the scattering of literature data for Z (approximately from 16 up to 19 ev) cannot be eliminated by taking into account the temperature dependence of this parameter. Indeed we would expect Z (77) = Z (6.6) [l--6~l O -~x 7 0 . 4 ]~1 8 . 4 eV for 77 K taking into account Z = (19.2 +_ 0.4)eV for T = = 6.6 K and a temperature coefficient dL = -6x10 eV/deg, whereas the direct

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