Single crystal mobility

Boron Phosphide (BP). Boron phosphide is extrinsic at room tenqterature, and the transport is limited by impurity scattering. Figure 4.1-60 shows the temperature dependence of the conductivity, carrier concentration, and Hall mobility of several samples. In n-doped single crystals, electron mobilities of the order of 30-40 cm /V s have been found at 300 K in p-doped single crystals, mobilities around 500cm /Vs have been measured at 300 K. 

Calculations of this type are carried out for fee, bcc, rock salt, and hep crystal structures and applied to precursor decay in single-crystal copper, tungsten, NaCl, and LiF [17]. The calculations show that the initial mobile dislocation densities necessary to obtain the measured rapid precursor decay in all cases are two or three orders of magnitude greater than initially present in the crystals. Herrmann et al. [18] show how dislocation multiplication combined with nonlinear elastic response can give some explanation for this effect. 

The shock-induced micromechanical response of <100>-loaded single crystal copper is investigated [18] for values of (WohL) from 0 to 10. The latter value results in W 10 Wg at y = 0.01. No distinction is made between total and mobile dislocation densities. These calculations show that rapid dislocation multiplication behind the elastic shock front results in a decrease in longitudinal stress, which is communicated to the shock front by nonlinear elastic effects [pc,/po > V, (7.20)]. While this is an important result, later recovery experiments by Vorthman and Duvall [19] show that shock compression does not result in a significant increase in residual dislocation density in LiF. Hence, the micromechanical interpretation of precursor decay provided by Herrmann et al. [18] remains unresolved with existing recovery experiments. 

At room temperature, NiAl deforms almost exclusively by (100) dislocations [4, 9, 10] and the availability of only 3 independent slip systems is thought to be responsible for the limited ductility of polycrystalline NiAl. Only when single crystals are compressed along the (100) direction ( hard orientation), secondary (111) dislocations can be activated [3, 5]. Their mobility appears to be limited by the screw orientation [5] and yield stresses as high as 2 GPa are reported below 50K [5]. However, (110) dislocations are responsible for the increased plasticity in hard oriented crystals above 600K [3, 7]. The competition between (111) and (110) dislocations as secondary slip systems therefore appears to be one of the key issues to explain the observed deformation behaviour of NiAl. 

Mobilities up to 1.5 cm2 V-1 s 1 have been obtained for films deposited on hcale substrates [94—96]. As in the case of oligothiophenes, this has been attributed to a highly ordered morphology, close to that of a single crystal [94]. However, high values are only obtained under very acute deposition parameters (in particular an opti... 

We Finally note that the MTR model is a priori more appropriate to disordered materials. It is not expected to give good results with single crystal OFET, especially when the mobility becomes temperature-independent (see Section 14.6.1.2). However, it has recently been invoked in the case of poly thiophene [112], the mobility of which is also thermally activated. 

Pb also crystallizes in the fee system and therefore the same dependence of EamQ on the crystallographic orientation should be expected. Quite surprisingly, Ecm0 varies in the sequence (112) (110)> (100) >(111),135 i.e., exactly the other way round. Although the authors of the measurements do not remark on this apparent anomaly, a possible explanation can be sought in the surface mobility of Pb atoms at room temperature, which may lead to extensive surface reconstruction phenomena. It doesn t seem possible to clarify this aspect for the time being, since the most recent studies on the pzc of Pb single-crystal faces date back almost 20 years. 

T. T. M. (2004) Effect of impurities on the mobility of single crystal pentacene. Appl. Phys. Lett., 84, 3061-3063. 

Housmans THM, Koper MTM. 2005b. CO oxidation on stepped Rh[n(lll) x (111)] single-crystal electrodes Anion effects on CO surface mobility. Electrochem Commun 7 581-588. 

In the study of the M dependence of I and V of extended chain single crystals (FCSCs), samples were isothermally crystallized from the melt into the hexagonal (= disordered mobile ) phase at high pressure (P = 0.4 GPa). The range of AT was 3.3-9.4 K. 

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