DISLOCATIONS IN SEMICONDUCTORS P. Haasen To cite this version: P. Haasen. DISLOCATIONS IN SEMICONDUCTORS. Journal de Physique Colloques, 1966, 27 (C3), pp.C3-30-C3-38. 10.1051/jphyscol:1966305. jpa-00213115 HAL Id: jpa-00213115 https://hal.archives-ouvertes.fr/jpa-00213115 Submitted on 1 Jan 1966 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. JOURNAL DE PHYSIQUE Colloque C 3, suppliment au no 7-8, Tome 27, juillet-aolit 1966, page C 3-30 DISLOCATIONS IN SEMICONDUCTORS (Institut fiir Metallphysik, Universitat Gottingen, Allemagne) RBsum6. - L'auteur rksume les proprietks des dislocations dans les semiconducteurs, notamment leur vitesse de glissement et leur influence sur les proprKtCs de transport et donne quelques appli- cations. Abstract. - Properties of dislocations in semiconductors are reviewed, mainly dislocation velocities and influence on transport properties. Applications are described. 1. Introduction. - Since 1952 it is known that the mean velocity v is then defined by the distance AB = Ax elemental semiconductors Ge and Si lose their characte- divided by At if Axis proportional to At. v depends ristic brittleness at temperatures above two thirds of on the length I of the dislocation segment moving, on their melting temperatures and become as ductile as the angle between its Burgers vector b and its line fcc metals [l]. Ge and Si crystals have a diamond direction, and on other material parameters as will cubic structure (the related 111-V compounds like be shown below. If N and v are known from such InSb have a sphalerite structure) and slip on ( l11 ) microscopic experiments, the macroscopic strain planes in 110 > directions as expected from their rate i follows for any fixed temperature and stress from fcc translation symmetry. Slip occurs by the move- = bNv (1) ment of dislocations. These defects can be made E visible particularly easy in these materials by etching, if all N dislocations are assumed to be moving with infrared, X-ray, or electron transmission techniques, the same velocity v. E (E, z) is measured in a static see [l]. In the studies which are described below dislo- creep experiment at constant stress (or in a dynamic cation intersections with a surface are etch pitted and test at constant strain rate ; the latter yields the stress- dislocation densities are counted, up to N = 10' cmw2 strain curve z = Z(E,E)). We will discuss in the follo- by optical microscopy, and above that value by replica wing how this dependence E(&, 7) is made up by that methods. Dislocation velocities are measured by of its constituents N(t, E) and v(%,R) according to Johnston and Gilman's [2] double etching technique theory and experiment. The relation between z and N outlined in figure 1. A dislocation ending in the sur- determines work hardening, that between N and E face at A moves to B between two etches by the action dislocation multiplication. These two processes are of a stress z in the slip plane during the time At. The of general interest. In a semiconductor the dislocation velocity may / ,"i depend on doping (As or Ga) as we will see. This is related to the core structure and the atomic mechanism ofcalculate. motion Onof thea dislocation, inverse effect which of dislocationswe have tried affec- to l' f /?'.Q/ l I f ting semiconducting properties, some new facts have l I become known recently which will briefly be mentio- I 1 ned below. Plastic deformation of semiconductors may 'C, Af have technical applications in the future, as is also indicated in this report. This paper is based heavily . on the work of members of the Gottingen Institut, \,'0 j! particularly Dr. H. Alexander, Dr. E. Peissker, Dr. R. Labusch, Dipl. Phys. S. Schafer, W. Schroter, FIG.1. - Measuring dislocation velocity and K. Berner, whose cooperation is gratefully acknow- by double etching. ledged. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1966305 DISLOCATIONS IN SEMICONDUCTORS C3-31 2. Dislocation velocity and core structure. - The InSb such that U is proportional to their respective Johnston-Gilman technique for measuring v was melting temperatures T,. Furthermore, U is about first applied to semiconductors by Chaudhuri et al. [3]. half the activation energy of self diffusion. m decreases These authors produced a linear dislocation array by in the order InSbjGelSi, 2 > m > 1. In metals, on scratching the side of a crystal at room temperature fol- the other hand, values of m 9 1 are measured and B lowed by heating. Then these dislocations were moved is rather temperature independent. Thus dislocations by bending the crystal between three wedges. This in the diamond structure move in a quasi-viscous created an inhomogeneous stress distribution and manner and rather slowly for T d TJ2. Schafer [5] has recently repeated these measure- ments on Ge under improved experimental conditions. In his experiments a homogeneous stress acted on a few dislocation rings of known diameter I and of known dislocation character. He finds a similar z and T dependence of v (slightly larger m, smaller U at lower T)as did Chaudhuri et al. [3] in addition to a definite dependence of v on the angle between b and V rp SLW-'J Screw 0- o/O--O o/O' o/O' FIG. 3. -Dislocation velocity in Ge vs. loop length according to [5] T = 440 "C, 7 = 0,466 kg/rnm2 line direction and on the loop size I, see figure 3. Screws move faster than edges, especially at higher temperatures, and long dislocations move faster than Shear stress T(kg/mm2) short ones due to the line tension. + The motion of a dislocation in the diamond structure, as characterized above, can be described atomistically FIG. 2. - Dislocation velocity in Ge vs. by the formation of kink pairs in the Peierls potential, stress according to [3]. see figure 4. A calculation of the kink formation energy yields the v(z) relation in a rough manner as shown <"l1 <110), in figure 2. It is described by v = B(T)zm, where nz 1.5 f 0.2 and B(T) = B, e-'IkT , (see figure 6) . (2) For intrinsic Ge U = 1.6 + 0.05 eV, rather inde- pendent of z*. A similar relation holds for Si and (*) A relation U - z -1 as has been proposed by Gilman 141, does not hold for Ge or Si up to stresses of G/100, G = shear modulus. FIG. 4. - Kink formation in the Peierls potential. C3-32 P. HAASEN by Labusch [6] is based on Peierls'model and on the known elastic properties of the diamond structure, His results for a screw dislocation in Ge are : Peierls potential 0,225 eV, Peierls force 212 kg/mm2, kink pair formation energy 1,75 eV, kink potential 0,M eV. The movement of the kink along the Peierls potential (in the kink potential) thus appears to be relatively easy and is little influenced by the mutual attraction of the double kink partners. The (almost) linear stress dependence of v probably stems from the difference in formation rates of forward and backward kink pairs. The increase in velocity with increasing dislocation length characterizes the back stress of the line tension. Screw dislocations are rarely found in electron trans- mission surveys of the slip plane of deformed Ge [7], probably because they move faster than edges. The latter appear to be responsible for work hardening. We will return to this point later. Patel et al. [S] have recently measured dislocation velocities in otherwise dislocation-free crvstals of heavily doped Ge. Results obtained at 500 OC and FIG. 6. - Dislocation velocity vs. temperature z = 6 kg/mm2 are shown in figure 5 for additions of at z = 6 kg mm -2 according to [a]. IMPURITY CONCENTRATION/CM~ FIG. 5. -Dislocation velocity in Ge vs. doping, T = 500 oC, z = 6 kg mm -2, according to 181. As, Ga, Sn. No effect of doping is seen on the intrinsic range while for concentrations c 2 10" cm-3, where the material becomes extrinsic at this temperature, As eases and Ga hinders dislocation movement. Sn (or Si) have no effect on v even at higher c. The velocity becomes again independent of c (As, Ga) at the highest c and thus depends on doping qualitatively as the Fermi level. In terms of eq. (2) both B, and U appear to be affected by c, but not m. Figure 6 shows the temperature dependence of v for a number of dopings. This diagram resembles that of the diffusion constant vs. temperature and doping plotted accor- ding to Valenta et al. [g] in figure 7. From this Patel et al. [8] propose that both dislocation velocity and RG. 7. -Diffusion coefficient in Ge diffusion may be influenced by the abundance and at various Ievels of doping according to [9]. DISLOCATIONS IN SEMICONDUCTORS C3-33 mobility of vacancies. That is difficult to believe, There is a row of dangling bonds (the density of although the distorted dislocation core of a 600-dis- which approaches zero for the screw orientation), location may be assumed rather pictorially to move some of which, according to Read, accept an electron like a row of vacancies [101.