Berlin 2015 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 81: Heterostructures and interfaces
HL 81.6: Talk
Thursday, March 19, 2015, 16:15–16:30, EW 201
Depth dependence of the ionization energy of shallow hydrogen donor states in ZnO and CdS — •Thomas Prokscha1, Hubertus Luetkens1, Elvezio Morenzoni1, Gerard Nieuwenhuys1,2, Andreas Suter1, Max Döbeli3, Michael Horisberger4, and Ekaterina Pomjakushina4 — 1LMU, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland — 2Kamerlingh Onnes Laboratory, Leiden University, 2300 RA Leiden, The Netherlands — 3Ion Beam Physics, ETH Zurich, CH-8093 Zurich, Switzerland — 4LDM, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
The ionization energy of shallow hydrogen-like muonium (Mu) donor states in nominally undoped ZnO and CdS (0001) crystals has been measured in a near-surface region (10 - 180 nm depth) by using low-energy muons, and in the bulk using conventional muon spin rotation (µSR) [1]. The implantation depth of the muons is varied by tuning the implantation energy of the low-energy muons between 2.5 and 30 keV. The ionization energy of the shallow Mu donor is lowered by about 10 meV compared to its bulk value at a mean depth of 100 nm, and continuously decreasing on approaching the surface. At a depth of about 10 nm the ionization energy is reduced by 25 - 30 meV. The same reduction is observed at a Au/ZnO interface. We attribute this change to the presence of electric fields due to band bending at the surface/interface. Using a simple one-dimensional model the depth profile of the electric field can be determined.
[1] T. Prokscha et al., arXiv:1408.6972, accepted for publication in Physical Review B.