不同掺杂剂锗硅单晶的张电阻特性

Tensoresistance in single crystals of germanium and silicon with different dopants but under practically equal charge carrier concentrations have been investigated.The features of ρ_X /ρ₀ = f (X) function, which depend on individual physical-chemical properties of dopants, have been discussed in this paper.

Electronic properties of many-valley semiconductors are determined by their band structure as well as availability, energy spectrum and spatial distribution of electrically active impurities and defects in the bulk of crystal. With mass production of semiconductor electronics devices, to meet the modern requirements of reproducibility and stability of their characteristics is possible only when using materials with high homogeneity of parameters. This is particularly important in microelectronics in the manufacture of large- and very large-scale integrated microcircuits and power semiconductor devices. Today, it became clear that further increasing the density of integrated microcircuits, their reliability and efficiency, obviously, can not be realized only by improving technology and restricting microinhomogeneities of physicochemical properties in semiconductor materials. Therefore, the problem of microinhomogeneities research has been and remains urgent to date.

Defects are usually separated by two large groups: 1) one-dimensional, two-dimensional, three-dimensional ones that disturb the crystal structure at considerable distances; 2) point defects that disturb the crystal structure over relatively small distances. The first group includes dislocations, dislocation networks, grain boundaries and twins, different defects of packing, nuclei of a new phase, clusters of point defects. These defects are formed, as a rule, in the process of growing crystals, during plastic deformation, as well as under irradiation by heavy particles of a high energy.

Impurity atoms are the second major type of point  defects, which are introduced into the semiconductor crystal during its growth, as well as under diffusion or  by ion implantation. These point defects can be placed  both in the lattice sites, and in the interstitial positions of  the crystal lattice. If the impurity atom in its physical  and chemical properties is similar to the atoms of matrix,  then it is usually placed in a vacant lattice site. In  the case when its properties are very different from  those of matrix atoms, it is located between the lattice  sites. In many-valley semiconductors, all atoms of  the periodic system can serve as impurities. This fact  allows obtaining a wide range of electronic properties of  crystals.

Fig1

When the concentration of dopant impurity rises,  interaction between impurity atoms appears and their  energy levels are changed just as the atomic electronic  levels split in the band during formation of the crystal.  The impurity band appears as a result of this interaction. When the concentration of the impurity atoms with  shallow levels is higher than 1018 сm^-3, their ionization  energy is reduced to almost zero as a result of the  expansion of the impurity band and its confluence with  the conduction or valence bands. Semiconductor acquires metallic properties; it becomes a semimetal or a  degenerate semiconductor.

Dopant impurities affect on the character of charge  carriers movement, and the latter are scattered by the  ionized and neutral impurity atoms, which significantly  affects on the phenomena of electronic transport.  Impurity atoms, as a lattice defects, affect on the other  physical, chemical, optical, and magnetic properties of  semiconductors, as well as actively interact with the  radiation defects. These processes lead to the  change in the energy spectrum of the impurity states in  the forbidden band.

Characteristic features of the physical properties  of many-valley semiconductors are determined by the  symmetry of crystal lattice and the nature of interatomic  interaction. To investigate crystals, uniaxial elastic  deformation is often applied, which causes the change  not only in interatomic distances but also in symmetry of  lattice, and results in the most significant changes in  their energy spectrum. This, in turn, determines the  corresponding changes in their electronic properties, the  study of which provides the valuable information about  the investigated object.