Role Of Doping Research Articles

Van Hove singularities and the role of doping in the stabilization, synthesis and superconductivity of HgBa 2Ca n−1Cu nO 2n+2+δ

The electronic structure and Fermi surface of the recently discovered HgBa 2Ca n-1 Cu n O 2 n+2+δ superconductors have been determined using the full potential linear muffin-tin orbital method and precise structural information determined with neutrons by Radaelli et al. Whereas for stoichiometric HgBa 2CuO 4 (Hg-1201) the only band crossing the Fermi energy derived from the CuO antibonding state is half-filled, an additional HgO band that crosses E F exists in the case of HgBa 2CaCu 2O 6 (Hg-1212) and HgBa 2Ca 2CuO 4O 8 (Hg-1223). Thus, stoichiometric HgBa 2CuO 4 is expected to be a Mott insulator with dopants essential for forming the normal metallic state that leads to superconductivity at 95 K, in contrast to two other members of the Hg family that are expected to be “self-doped” to a metallic normal state. As in Hg-1201, the electronic structure is two-dimensional and is dominated by van Hove singularities (vHS's) to which E F is pinned by dopants whose calculated concentration is found to agree well with that determined by Radaelli et al. for Hg-1212 for their maximum T c = 128 K sample. Finally, predicted doping levels for stabilizing a large volume of the high- T c Hg-1223 phase - and hence its highest T c - are made on the basis of pinning E F to the vHS.

Segregation of Magnesium to the Internal Surface of Residual Pores in Translucent Polycrystalline Alumina

For the first time direct evidence for Mg segregation to the surface of pores within translucent polycrystalline alumina grains has been found using energy dispersive X‐ray spectroscopy (EDXS) and convergent beam electron diffraction (CBED) in an analytical electron microscope (AEM) on a submicrometer scale. This supports the model that MgO dopant increases the surface diffusivity which, in turn, increases the pore mobility. The MgO dopant's role in retarding grain growth in combination with the enhanced pore mobility allows the achievement of nearly full density and translucency in alumina.

The effect of sputter cleaning on Au/GaAs contacts and the role of doping

The effects of Ar-ion sputtering on electrical properties of Au contacts on (100) GaAs and the role of doping concentration have been studied. The n-GaAs was doped with 1017 or 1018 cm−3 Si or with 1018 cm−3 Te and the p-GaAs with 1018 or 1019 cm−3 Zn. After either chemical etching or Ar-ion beam cleaning of the GaAs, Au contacts were formed by evaporation in ultrahigh vacuum (10−9 Torr). Ion bombardment with Ar+ produced clean but nonstoichiometric, damaged GaAs surfaces. Contacts on chemically cleaned GaAs were either (nearly) ohmic or Schottky, depending upon the dopant and concentration. On sputtered GaAs, all the contacts showed soft rectification but did not act as purely Schottky contacts. The type of dopants, i.e., n or p, caused differences in the I-V behavior, but the behavior for different dopants of the same type was very similar. Sputtering increased the depletion depth on all the samples, and the depletion depth became larger as the ion energy increased and/or the dopant concentration decreased. The electrical behavior of the sputtered samples is suggested to result from the creation of a compensated layer with deep defect states. The deep level states are postulated to be related to defects resulting from sputtering.

Chemical recovery of damage fragments in gamma-irradiated doped potassium nitrate

Isothermal annealing of total reducing species, (NO 2 -)'; nitrite, NO 2 - and nonnitrite reducing species, Δ(NO 2 -) in gamma-irradiated pure as well as doped (Ba 2+) potassium nitrate has been investigated between 393–433 K in order to determine the order of the recovery process, the energy of activation, the role of doping, and the fraction ϕ recovered as a function of temperature. The data have been analysed in the light of diffusion controlled mechanisms as well as conventional chemical kinetics. It is found that the fractions of the damage (NO 2 -)' and NO 2 - recovered by the first and the second order mechanisms are, respectively, 0.41 and 0.38, 0.42 and 0.38 with different energies of activation.

Photoluminescence assessment of solar cell materials

Photoluminescence is a technique useful to the understanding of semiconductors. The emission spectrum reveals the relative distribution of states that are linked by radiative transitions. The kinetics of the radiative process indicate how localized the transitions may be. The emission efficiency measures the importance of non-radiative competing processes that are detrimental to carrier survival. In this paper we discuss the photoluminescence of hydrogenated amorphous silicon (a-Si:H), we consider the importance of hydrogen, the role of doping and the effect of temperature and we point out where this measurement technique may be useful to the improvement of solar cell performance.