Surface Conductivity of Diamond: A Novel Doping Mechanism

2006 ◽  
Vol 48 ◽  
pp. 93-102 ◽  
Author(s):  
Jürgen Ristein ◽  
Paul Strobel ◽  
Lothar Ley

One of the most amazing features of diamond is the p-type surface conductivity which occurs when intrinsic material is hydrogen terminated and brought into contact with appropriately chosen adsorbates. Experiments during the last decade have revealed the different roles of the surface acceptors and of the covalent carbon-hydrogen surface bonds: providing unoccupied electronic states, and lowering the energy barrier for electron transfer from the diamond, respectively. The simplest and historically first method to supply surface acceptors, i.e. exposing hydrogenated diamond to air, provides, unfortunately, the most complex electronic system acting as surface acceptors, namely solvated ions within atmospheric wetting layers. In that case electron transfer is accompanied by a red-ox reaction that finally induces the hole accumulation. A much simpler case of transfer doping has been demonstrated for C60F48 as molecular surface accpeptors. In this case, the doping yield as a function of surface coverage can be modelled quantitatively by the transfer doping mechanism. Also, pure C60 can be adopted for transfer doping, but the formation of the van-der-Waals solid is required in this case to circumvent the electron correlation energy for charge transfer to a single fullere cage. The C60 layers can be stabilized by oxygen-mediated polymerisation without loosing their doping efficiency.

Relativistic ab initio calculations of inter-ionic potential energies are used to develop a reliable non-empirical method for predicting the properties of ionic solids containing the heaviest ions. A physically realistic method for describing the non-negligible differences between free and in-crystal ion wavefunctions is described. Functions are presented for describing the partial quenching, arising from ion wavefunction overlap, of the standard long-range form of the inter-ionic dispersive attractions. These attractions are shown to be distinct from the contributions to the inter-ionic potentials that arise from that portion of the electron correlation energy which is nonzero solely because of overlap of the ion wavefunctions. The results presented for NaCl, MgO and the fluorides of Li, Na, Ag and Pb show that these modifications overcome the deficiencies of previous calculations. Ab initio predictions of the closest cation-cation and anion-anion short-range interactions, which are not available from semi-empirical fits to experimental data, are presented. The non-point coulombic interactions between pairs of anions, derived by adding the dispersive attractions to the short-range interactions, are compared with previous semi-empirical and approximate ab initio results. The uncorrelated short-range inter-ionic potentials computed exactly are compared with those predicted from electron-gas theory. The use of the electron-gas approximation to describe any of these potentials degrades the quality of the predicted crystal properties.


2010 ◽  
Vol 257 (5) ◽  
pp. 1634-1637 ◽  
Author(s):  
Qingwei Li ◽  
Jiming Bian ◽  
Jingchang Sun ◽  
Hongwei Liang ◽  
Chongwen Zou ◽  
...  
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