Defects in ZnO

Between 30 and 100 K, the DAP transition at 3.220eV decreases and the adjacent e-A transition at 3.236eV increases. (Courtesy of K. Thonke [45].) 

Characteristically, defects represent one of the controversial areas of semiconductors, and ZnO is no exception, as the measurement techniques are not able to correlate 

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In recent years, there has been considerable effort to derive defect formation enthalpies of intrinsic defects in ZnO [108-110,113-117]. An example is shown in Fig. 1.13 [115]. Horizontal curves belong to neutral defects, curves with positive or negative slopes to charged donors or acceptors, respectively. The donor with the lowest formation enthalpy is the oxygen vacancy Vo, the acceptor with the lowest formation enthalpy the zinc vacancy Vzn-... 

Fig. 1.14. Dumbbell oxygen interstitial defects in ZnO in comparison to the ideal lattice structure and the octahedral oxygen interstitial [114,115]. The structure of the rotated dumbbell interstitial depends on the charge state. Copyright (2005) by the American Physical Society...

HYDROGEN-RELATED DEFECTS IN ZnO STUDIED BY IR ABSORPTION SPECTROSCOPY... 

Optics and Spectroscopy of Point Defects in ZnO Vladimir Nkitenko... 

Hydrogen-Related Defects in Zno Studied by IR Absorption Spectroscopy... 

Kim Y S, Park C H, Rich variety of defects in ZnO via an attractive interaction between O vacancies and Zn interstitials Origin of -type doping, Phys. Rev. Lett., 102, 086403, 2009. 

Hu J, Pan BC (2008) Electronic stmctures of defects in ZnO hybrid density functional studies. J Chem Phys 128 154706... 

Kohan AF, Ceder G, Morgan D, Van de Walle CG (2000) First-principles study of native point defects in ZnO. Phys Rev B 61(22) 15019-15027... 

The formation energies of native defects in ZnO have been calculated by several groups of theorists and the results generally agree [86,88-91). The results for oxygen and zinc vacancies, interstitials, and antisites in ZnO are shown in Figure 3.17 for the... 

Figure3.17 Calculated defectformation energies for main native point defects in ZnO as a function of the Fermi level under (a) zinc-rich conditions and (b) oxygen-rich conditions. Only the segments corresponding to the lowest formation energy values are shown. The zero of the Fermi level is set to the top of the valence band. Kinks for each defect indicate transitions between different charge states (0, —1, —2). (After Ref [88].)...

The first-principles calculations also provide information on the mobility of point defects, that is, their ability to diffuse at certain temperature. The estimated annealing temperatures, above which point defects are mobile, and the energy migration barriers for the native defects in ZnO are listed in Table 3.5. It is evident... 

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