Acceptor impurities ionization energy

Free electrons and holes produced by photoexcitation with energies above Eg can form free exciton (see Sect. 3.3.2), but a free electron (hole) can also recombine with a hole (electron) of a neutral acceptor (donor). The energy of the photon produced by this e-A0 or AD° recombination is Eg — E1 + k T/2 where A is the ionization energy of the acceptor or of the donor and T the electron or hole temperature, which is close to the lattice temperature for moderate excitations close to Es. In high-purity samples and at very low temperature, these lines can be sharp and when identified, they allow a good estimation of the impurity ionization energies when the value of Eg is known accurately. 

Element as impurity Electron donor (D) or acceptor (A) Ionization energy gap, conductance tWd eV, from valence band... 

The energy barrier of a depletion layer (the potential across a depletion layer I I) is called the Schottky barrier in semiconductor physics. Assuming that all the impurity donors or acceptors are ionized to form a fixed space charge in the depletion layer, we obtain the following approximate equation, Eqn. 5—75, for the thickness of depletion layer, dx, [Memming, 1983] ... 

The bivalent substitutional impurities of group-IVA elements such as C, Si, Ge, Sn, or Pb also produced double shallow acceptor levels with the ionization energy of 0.721 eV for C, 0.919 eV for Si, 0.792 eV for Ge, 1.034 eV for Sn, and 1.283 eV for Pb, respectively. Some bivalent substitutional impurities of another type of group-VIIIA elements such as Ne, Ar, Kr, or Xe did not produce any energy levels in the band gap by the substituting host O atom. As expected, the acceptor levels produced by the impurities of group-VA and -IVA elements at the O site were single or double acceptors, respectively. Quantitave analysis of these shallow acceptors produced by the monovalent and bivalent substitutional impurities will be made in Section 4.2. 

We roughly attempted to compare the acceptor ionization energies between the experimental and calculated values, for the monovalent substitutional impurities of group-VA elements at the host O site. The comparison was made for group-VA elements because of the existence of the most reliable data for them. The experimental values [20,22,29-31] of the acceptor activation energies for group-VA elements were already described in Section 4.1 to be 0.170-0.200 eV for N,... 

TABLE 3 Ionization energy (eV) of some acceptor impurities in the most common SiC polytypes. 

In practice the results of these measurements are the subject of controversy. A solid can contain various impurities (e.g., Zn and Zn in ZnO) and can have both donor and acceptor levels. The measurements can be carried out on the isolated solid or in the presence of reactants. Interpretation of conductivity, ionization energy, and work function data is difficult. Once again, surface effects must be examined separately from effects inside the lattice. 

Diarra M, Niquet Y-M, Delerue C, Allan G (2007) Ionization energy of donor and acceptor impurities in semiconductor nanowires importance of dielectric confinement. Phys Rev B 75 045301... 

The activation energy Ei is the normal acceptor ionization energy, associated with transitions from the acceptor ground state to the valence band, and is observed in all samples provided the acceptor concentration is not too high. The activation energy E2 can be observed only in the intermediate concentration range and is associated with conduction in an impurity band. When the acceptor concentration is small 2 is close to Ei, but when the acceptor concentration is increased, so that there is an appreciable overlap between the wave functions of neighboring... 

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