Hydrogen: A Relevant Shallow Donor in Zinc Oxide

Abstract

Electron paramagnetic resonance and Hall measurements show consistently the presence of two donors ( D1 and D2) in state-of-the-art, nominally undoped ZnO single crystals. Using electron nuclear double resonance it is found that D1 shows hyperfine interaction with more than 50 shells of surrounding 67Zn nuclei, proving that it is a shallow, effective-mass-like donor. In addition D1 exhibits a single interaction with a H nucleus ( a(H) = 1.4 MHz), thus H is the defining element. It is in agreement with the prediction of Van de Walle [Phys. Rev. Lett. 85, 1012 (2000)] that H acts as a donor in ZnO. The concentration of D1 is 6x10(16) cm(-3) emphasizing its relevance for carrier statistics and applications.

Evidence for photogenerated intermediate hole polarons in ZnO

“…This was indeed the case for r-TiO 2 , where IR spectra recorded after exposure to atomic H (chemical doping, leading to an n-doping of TiO 2 ) were very similar to those recorded after ultraviolet exposure (photon doping) 16 . Since spectra recorded after n-doping resulting from exposure to D-atoms [18][19][20] (see Supplementary Fig. 3) are clearly different from those recorded after ultraviolet exposure, we therefore regard the effects observed in the IR spectra as evidence for hole polarons.…”

High-frequency EPR and ENDOR spectroscopy on semiconductor nanocrystals

“…D 1.9552 values obtained for the interstitial hydrogen donor in a single crystal of ZnO. 8 The linewidth however corresponds very well with g jj g ? D 0.0017 obtained for the interstitial hydrogen donor and taking into account the random character of the powder sample.…”

“…This should be compared with our previous observation on the hydrogen-related shallow donor in a bulk crystal of ZnO where two ENDOR lines were found with a hyperfine splitting of 1.4 MHz. 8 We conclude that the observed ENDOR lines originate in the hydrogen atoms present in the Zn(OH) 2 capping layer where the density of the electronic wave function is very small.…”

“…2, symmetrically around the Zeeman frequency of 67 Zn (I D 5/2, abundance 4.1%) at 9.2 MHz, a broad, unresolved set of ENDOR lines of 67 Zn spins is observed. From the multitude of lines seen for a bulk crystal 8 it is clear that we are indeed dealing with a delocalized electron of a shallow donor that interacts with a The ENDOR transitions of the 67 Zn, 7 Li, and 1 H nuclear spins observed in the EPR signal I (Fig. 1) 7 Li.…”

“…This conclusion is in line with our observation that the electron density at the ZnO/Zn(OH) 2 interface, as measured from the linewidth of the 1 H ENDOR signal, increases with decreasing size of the particles. It is interesting to note that estimates of the electron density at the ZnO/Zn(OH) 2 interface, using either the width of the dip in the 67 Zn ENDOR signal or the linewidth of the 1 H ENDOR signal and using the amplification factors for Zn and H, 8 yield about the same value. Our conclusion that the electron density at the surface increases with decreasing size of the nanoparticle is at variance with the results of the calculations of Melnikov and Chelikowsky 15 for the P-doped Si nanoparticles.…”