engleski

Common origin of doping-limiting mechanisms in IIB-VI compounds and alloys

Wide-band-gap II-VI semiconductors have a potential for a variety of applications, especially in the areas of light-emitting and light-detecting devices, photovoltaic conversion (solar cells), X-ray and g-ray detection, etc., which is still hindered by great difficulties in achieving efficient doping from both n- and p-side. We have reviewed and analyzed present status of maximal dopability hitherto achieved on both p- and n- side in each of IIB-VI compounds and ternary or quaternary alloys. In this work we shall show that all these data (ranging from 1E20/cm3 to very low values), although obtained by different laboratories, different growth techniques, dopants, optimizations, etc., can be well predicted using a single variable: the ratio of covalent radii, R= rc(IIB)/rc(VI) of the constituent atoms of the particular IIB-VI compound or alloy. The importance of relative sizes of II and VI atom lies in the fact that their size determines the sizes of their respective vacancies, and therefore the ratio of the formation energies for these vacancies. Hence, the common origin of all different doping-limiting mechanisms (self-compensation by spontaneous formation of native defects, amphoteric behavior of several potential dopants, lattice relaxation around some doping atoms, insufficient solubility of the others, 'softness' of the lattice of the IIB-VI compounds, etc.) can be traced down to basic thermodynamic requirements for minimum energy of the system. The practical consequence is that the n- and p-type dopability of IIB-VI compounds as well as their ternary alloys can be predicted in a simple way.

II-VI semiconductors; doping; vacancy

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