We investigated the surface chemistry and valence band (VB) structure of as-grown thin InN(0001)-2 Â 2 films as well as their change upon the exposure to oxygen and water. The InN films were grown by plasma-assisted molecular beam epitaxy (PAMBE) and in situ characterized by reflection high electron energy diffraction (RHEED) and photoelectron spectroscopy (UPS, XPS). The oxygen and water exposure was directly performed on the as-grown, contamination-free InN surfaces at room temperature and leads to changes in the chemical surface states as well as the electronic properties. For 2 Â 2 reconstructed InN surfaces one observes directly after growth a surface state at the Fermi-edge which decreases continuously with oxygen and water exposure. Furthermore, two oxygen related electronic states develop in the VB at binding energies at around 5 and 10 eV. For water exposure a third weak state around 8 eV is additionally observed. The impact of oxygen and water on the work function F as well as the variation of surface band bending was investigated. In both cases for initially 2 Â 2 reconstructed surfaces a reduction in the downward band bending is found, while F increases in the case of oxygen exposure but in the case of interaction with water a reduced work function is observed. The oxygen uptake rates reveal a higher reactivity of water with InN surfaces compared to oxygen. Furthermore, during oxidation and water exposure different chemical oxygen bonds are formed, but a direct assignment to In-O or N-O bonds is difficult due to changes in the In3d and N1s XPS core level peak shape.

The influence of selected donor- and acceptor-type adsorbates on the electronic properties of InN(0001) surfaces is investigated implementing in-situ photoelectron spectroscopy. The changes in work function, surface band alignment, and chemical bond configurations are characterized during deposition of potassium and exposure to oxygen. Although an expected opponent charge transfer characteristic is observed with potassium donating its free electron to InN, while dissociated oxygen species extract partial charge from the substrate, a reduction of the surface electron accumulation occurs in both cases. This observation can be explained by adsorbate-induced saturation of free dangling bonds at the InN resulting in the disappearance of surface states, which initially pin the Fermi level and induce downward band bending.

In this work we investigate the interaction of potassium and water with 2×2 reconstructed InN(0001) surfaces prepared by plasma‐assisted molecular beam epitaxy. The influence of adsorbate‐substrate‐interaction on surface properties is characterized in‐situ by photoelectron spectroscopy. Potassium exposure leads to a strong reduction in the work function Φ to 1.6 eV revealing a charge transfer from the adsorbate to the InN surface. In parallel, a reduction of the surface downward band bending by 0.2 eV and hence a reduced electron accumulation density is observed. While interaction of water with clean InN(0001)‐2×2 surfaces induces only minor changes in the surface band bending, water adsorption at potassium covered InN(0001) leads to a reversal of the K‐induced reduction in surface band bending and a slight increase of Φ to 2.4 eV. These results show that surrounding water modifies the interaction of potassium with InN(0001) surfaces. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The interaction of n-type GaN(0001) surfaces with potassium and water is investigated using photoelectron spectroscopy, with special focus on adsorbate–substrate charge-transfer processes and water dissociation. Potassium atoms adsorb at the surface, forming a distinct surface dipole layer. For very low K coverage, the attached ionized K adsorbates result in a drop of the work function and the released electrons induce a reduction of the initial upward band bending. After stabilization of both quantities in the sub-monolayer regime, a reverse effect is observed for higher K coverage up to one monolayer (ML), exceeding the upward band bending of the clean surface. If the K-covered surface is exposed to water, hydroxyl groups are formed, whereas during long K and H2O coadsorption, a potassium hydroxide film grows. In both cases, a further reduction of the work function and an abrupt change in the surface depletion layer is recorded. For the coadsorption, initially an electron accumulation layer forms at the surface, approaching flat band conditions for higher KOH thickness. Overall, the surface band bending can be drastically modified in the range between +0.5 and −0.6 eV. These observations clearly show that the electron density at the GaN(0001) surface can be reversibly tuned by alkali-based adsorbates. Different reactions are observed, which are directly linked to the charge-transfer processes and chemical reactions induced by the K 4s electrons.

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Fast silicon detectors are crucial for a lot of applications, [1] e.g., the experiments at large hadron collider (LHC) at CERN to obtain timeresolved trajectories of particles. A concept to realize such fast silicon detectors are the low-gain avalanche detectors (LGAD). They combine the advantages of normal n-i-p-diodes such as a low noise with a large signal of avalanche multiplication diodes. [2] LGADs operate with a gain of about 10. The avalanche multiplication region is usually obtained by deep boron doped layers. [3] Nevertheless, these LGADs have a drawback if they are irradiated. The gain layer "disappears" after irradiation as a consequence of a deactivation of the gain layer doping species, which is usually boron. [4,5] This means that, e.g., boron, loses after irradiation its properties as an acceptor to provide a negative space charge.In this contribution, the focus is first on LGAD device manufacturing at CiS. Afterward, an experiment is described and discussed, which investigates the acceptor removal phenomenon for the three acceptors boron, gallium, and indium in silicon. Therefore, boron, gallium, and indium were implanted into silicon. Additionally, coimplantation of carbon, oxygen, nitrogen, and fluorine was made. It was found in the literature that for carbon co-implantation the acceptor removal effect can be reduced. [6] Therefore, this study investigates different co-implantation species if they have an impact on the acceptor removal phenomenon. The samples underwent an activation anneal and were then investigated by 4-point-probe (4pp), low temperature photoluminescence spectroscopy (LTPL) and secondary ion mass spectrometry (SIMS) before and after irradiation with electrons and protons.