The ionisation of impurity states of Sb in Ge, connected with L‐ and X‐valleys of the conduction band

Abstract

It is known that in the conduction band of Ge in addition to the four <lll>-type valleys (L-valleys) there a r e the six <l?O>-type valleys (X-valleys known as Si valleys), spaced in absence of a deformation 0.18 eV above the L-valleys.A s was shown i n /l/, a t uniaxial elastic compression 3 II[lOO] and mechanical s t r e s s P > 2 1~1 0~ N/m2, two X-valleys a r e positioned lawer than the L-valleys. All L-valleys a t 3 II [loo] are equally raised in energy scale. From the data of /1/ i t follows also that the electron effective mass mx and its anisotropy K", for the X-valleys a r e essentially different from the corresponding parameters for the L-valleys. The ionisation energy of a shallow local level is determined by the parameters of the valley connectingthis level/2 to 4/ on condition that k a >> 1 (a is the radius of the orbit of electrons connected with the impurity centre, ko is the distance between the valley minima in the wave vector space /5/). In the case of Ge this condition is sufficiently well fullfilled for the shallow donors Sb, A s , P both for the L-and X-valleys. However, owing to the difference between band parameters of the L-and X-valleys, the ionisation energies of impurity states, connected with Ulese valleys ( E . and EL ) must differ essentially.Since the value of the impurity breakdown field is directly determined by the ionisation energy of the impurity, in the present note the dependence of the impurity breakdown field of Sb states on the uniaxial compressive stress w a s investigated on samples of n-Ge doped with Sb (Nsb = 3 . 2~1 0~' m-3) at 4.2 K. The results of measurements a r e presented in Fig. 1. In region I the breakdown is caused by the ionisation in L-valleys of electrons from donor levels of 0 X 1 1) Prospekt Nauki 115, 252028 Kiev, USSR.

Dose dependence of tensoresistance for the symmetrical orientation of the deformation axis relatively to all isoenergetic ellipsoids in γ-irradiated (60Co) n-Si crystals

“…Moreover, since the effective masses of charge carriers and their anisotropy for ∆ 1 -and L 1 -valleys should be significantly different; it is natural to assume that the ionization energy of shallow impurity levels for these valleys also should differ. The experiments on the study of low-temperature impact ionization of neutral donors [8] confirmed the theoretical assumption that each energy minimum has its own energy level of the same impurity.…”