Question 1: Surface Transfer Doping of Diamond
Diamond has large band gap of 5.47 eV. which makes diamond extremely insulating
Calculate the charge carrier density for intrinsic diamond at room temperature (300
Note: effective density of states in the valence for band it to of contain diamond at RT N. 3x1019 cm³
K). What the volume of diamond sample one mobile electron carrier?
effective density of states in the conduction band of diamond at RT Ne 1x1019 cm³
In order to use diamond as an electronic material by exploiting its numerous extraordinary
electronic properties, diamond needs to be doped. However, conventional bulk substitutional
doping using common impurities does not work well for diamond due to the very high activation
energy of dopants. For example, the activation energy of boron (energy difference between the B
acceptor level and diamond valence band) for p-type doping of diamond is 0.37 eV.
Before electron transfer
After equilibrium Surface
FVBM Valence Band
Figure 1. Schematic diagram showing the energy level alignment before and after
surface transfer doping.
Comment on the doping efficiency of boron for diamond at RT.
Due to this fundamental challenge in the bulk doping of diamond, considerable research efforts
have been devoted to developing novel doping method called surface transfer doping. Surface
transfer doping relies on spontaneous charge exchange between diamond and its surface dopants
across the interface (Figure 1). For example, in p-type surface transfer doping, when the acceptor
energy level of surface acceptors (e.g. lowest unoccupied molecular orbital, LUMO, for
molecular acceptors) is close to the diamond valence band maximum (VBM), electrons will be
spontaneously transferred from diamond valence band to the surface acceptors until
thermodynamic equilibrium is reached. As a result, diamond surface display p-type surface
conductivity due to the accumulated holes in diamond valence band which are confined to its
surface by the band-bending and the negatively charged surface acceptors. The depth integrated
areal hole (number) density p, which depends the position of VBM relative to Fermi energy
the diamond surface us = EVBM - EF can be derived from Poisson's equation as follows:
le2 /2kT) when us <0
exp(u, for non-degenerate case
2kTc, E0 N° le2 -
1 + us s +
when Us >0 (1.2)
for degenerate case
in which Er is the dielectric constant of diamond (&r = 5.8).
(viii) What determines the maximum achievable areal hole density on diamond? What is
your strategy in choosing the best-performing surface acceptors to enable p-type surface
transfer doping of diamond?
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