Shallow versus deep hydrogen states in ZnO and HgO

Abstract

The muonium states mimicking interstitial hydrogen in ZnO and HgO are compared. Whereas in ZnO a theoretically predicted shallow donor state is confirmed, in HgO we find a considerably deeper state. The respective ionization temperatures are around 40 K and 150 K and the donor ionization energies are 19 ± 1 and 136 ± 3 meV, deduced from the temperature dependence of the µSR (muon spin-rotation) signal amplitudes. The µSR spectra provide a comprehensive characterization of the undissociated paramagnetic states: the hyperfine parameters, which measure the electron spin density on and near the muon, differ by a factor of ∼30. These define a hydrogenic radius of 1.1 nm in ZnO but indicate a much more compact electronic wavefunction in HgO, more akin to those of Mu * and the AA9 centre in Si. These data should largely carry over to hydrogen as a guide to its electrical activity in these materials.

Charge carrier and spin doping in ZnO thin films

“…Layers occupied by zinc atoms alternate with layers occupied by oxygen atoms. Electron doping in nominally undoped ZnO has been attributed to Zn interstitials, oxygen vacancies, or hydrogen [2][3][4][5][6][7]. The intrinsic defect levels that lead to n-type doping lie approximately 0.05 eV below the conduction band.…”

Hydrogen incorporation and diffusivity in plasma-exposed bulk ZnO

“…Recently, there has been much interest in the properties of hydrogen in ZnO and related oxides. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Theoretical predictions suggest that interstitial atomic hydrogen will introduce a shallow donor state in ZnO, [1][2][3][4] and this assertion is supported by some experimental data for its muonium counterpart, 5,6 by electron paramagnetic resonance data of bulk single crystals 7 and by the fact that hydrogen can lead to electron conduction in other wide-band-gap oxides such as SnO. 19 In addition, the presence of hydrogen in the growth or processing ambient can significantly affect the electrical and optical properties of ZnO, [9][10][11][12][13][14][15][16][17][18] but there is little systematic data available on its diffusivity and thermal stability when introduced by different methods.…”

Probing the shallow-donor muonium wave function in ZnO and CdS via transferred hyperfine interactions

“…This already argues against a compact molecular radical comparable with bond-centred hydrogen or muonium in Si or GaAs, for which the (muonium) dipolar parameters are 51 and 86 MHz, respectively [6]. Such a compact state may well be formed in HgO, for which the hyperfine and ionization parameters are all quite [7,8]) but we can reasonably exclude it for the materials of Table 1. For ZnO and CdS we can also state that all the muons which form paramagnetic centres are subject to the same superhyperfine interactions: there are not different components to the mSR signals according to the isotopic abundance of near neighbours.…”