Piezoelectric interaction in controlling the effective electron temperature and the non-ohmic mobility characteristics in GaN and other III–V compounds at low lattice temperature

In a compound semiconductor that lacks inversion symmetry, the free electrons interact simultaneously with the piezoelectric and acoustic phonons. This combined interaction principally controls the electrical transport at low lattice temperatures. Again, at low temperatures, the electrons in some of the compounds may be significantly perturbed for comparatively low fields, say, even for a fraction of a Vcm−1 or so, which effectively seems to be high enough, and the material exhibits electrical nonlinearity. Such a perturbed ensemble then attains a field dependent effective electron temperature Te, which exceeds the lattice temperature TL. The relative importance of the piezoelectric interaction in controlling the field dependence of the effective electron temperature, and therefrom, the non-ohmic mobility characteristics have been analyzed here under the condition of low lattice temperature. The numerical results obtained for InSb, InAs, and GaN are studied in detail. When compared with the experiments, the results here seem to give the same qualitative picture with respect to the variation of the non-ohmic mobility with the electric field for the indium compounds. The results, being interesting, stimulate further work in the same field.

Effect of MnCO3 on ZnO-Pr6O11-Co2O3-Cr2O3 Varistor Ceramics

0~1.5mol% MnCO3doped ZnO-Pr6O11-Co2O3-Cr2O3varistor ceramics were synthesized by conventional oxides mixing procedure. The effect of MnCO3variations on the microstructure, phase constituents and electric field–current density (E-J) characteristics of the ceramics were studied by SEM, XRD examinations and standard E-J test. The result showed the electrical nonlinearity exponents and breakdown voltage of the ceramics increased from 38 and 1296V/mm of the un-doped one to 52 and 1420V/mm respectively with the addition of 0.5mol% MnCO3; meanwhile, the leak current density was reduced from 4.35μA/cm2 to 2.05 μA/cm2. Further doping MnCO3deteriorated the overall varistor properties of the ceramics by remarkably decreasing the density of the ceramic, and the main reason causing the density drop was ascribed to the hindering effect of the well dispersed perovskite-like Pr0.95Mn0.9393O3particles formed mainly within the ZnO grain boundary areas.

The Effects of Bi2O3 Doping on the Electrical Characteristics of SnO2 Based Varistors

Bi2O3 is an important additive in the composition of ZnO varistors. However, the effect of Bi2O3 on novel SnO2 based varistors is still unclear. This paper reports the nonlinear electrical characteristics of (98.95-x)mol%SnO2-0.5mol%CoO-0.05mol%Nb2O5- xmol% Bi2O3 (x = 0, 0.05, 0.1, 0.5 mol%) system, and the influence of sintering temperature is also investigated. The addition of Bi2O3 can improve the electrical nonlinearity of SnO2-CoO-Ta2O5 based varistors, this may be due to the higher barrier height and barrier voltage. The optimum Bi2O3 doping level is between 0.1-0.5mol% and the optimum sintering temperature is 1350°C.