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Question 1: Surface Transfer Doping of Diamond Diamond has large band gap of 5.47 eV. which makes diamond extremely insulating (i) 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 Diamond Surface Diamond acceptors acceptors y Evac Conduction Band e Conduction Band FCBM FCBM E E E LUMO EOU 4 LUMO HOMO ******* FVBM Valence Band VBM HOMO Valence Band Figure 1. Schematic diagram showing the energy level alignment before and after surface transfer doping. (ii) 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 at areal hole (number) density p, which depends the position of VBM relative to Fermi energy on the diamond surface us = EVBM - EF can be derived from Poisson's equation as follows: (1.1) le2 /2kT) when us <0 exp(u, for non-degenerate case and p(u) = 2kTc, E0 N° le2 - 1 + us s + 8 5/2 kT 13J1((1) u 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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Semiconductor Physics Questions
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