Dieter Schmeisser

Surface chemistry and Fermi level movement during the self-cleaning of GaAs by trimethyl-aluminum

The removal of the native oxides from NH4OH-cleaned p-GaAs (100) by exposure to trimethyl-aluminum (TMA) was studied by in situ photoelectron spectroscopy using synchrotron radiation. The reduction of high-valence As- and Ga-oxides occurred through different routes: while As3+ was reduced to As(1±Δ)+ suboxides (with 0 ≤ Δ ≤ 1), Ga3+ was directly removed. The surface Fermi level was shifted by about 100 meV towards the valence band edge upon TMA exposure. This indicates that removing the native oxide of GaAs by TMA is insufficient to create interfaces between GaAs and Al2O3 with defects densities below the 1012 cm−2 range.

Room‐Temperature Atomic Layer Deposition of Al2O3: Impact on Efficiency, Stability and Surface Properties in Perovskite Solar Cells

In this work, solar cells with a freshly made CH3 NH3 PbI3 perovskite film showed a power conversion efficiency (PCE) of 15.4 % whereas the one with 50 days aged perovskite film only 6.1 %. However, when the aged perovskite was covered with a layer of Al2 O3 deposited by atomic layer deposition (ALD) at room temperature (RT), the PCE value was clearly enhanced. X-ray photoelectron spectroscopy study showed that the ALD precursors are chemically active only at the perovskite surface and passivate it. Moreover, the RT-ALD-Al2 O3 -covered perovskite films showed enhanced ambient air stability.

In situ measurements of the atomic layer deposition of high-k dielectrics by atomic force microscope for advanced microsystems

We investigated in situ the atomic layer deposition (ALD) of high-k dielectrics for advanced microsystems by ultra high vacuum (UHV) atomic force microscope (AFM). With our equipment we examined the surface topography of the substrate and the thin high-k films without breaking the vacuum and therefore without contaminating the sample with external agents. Following the full analysis of the Si(001)/SiO2 substrates we started the ALD process. After each ALD cycle using tetrakis-di-methyl-amido-Hf (TDMAHf), and H2O as precursors, we studied the relation between the film growth and the root mean square surface roughness, surface fractal dimension and correlation length. Additional information about the ALD was extracted from the statistical description of the surface by the height histogram together with the surface skewness and kurtosis parameters. The in situ studies of the ALD process with the UHV/AFM system were correlated with the experiments performed by means of synchrotron radiation photoelectron spectroscopy for understanding the fundamental properties of the ALD of high-k thin films on Si(001)/SiO2 substrates.

Control of the Crystalline Polymorph, Molecular Dipole and Chain Orientations in P(VDF-HFP) for High Electrical Energy Storage Application

The electroactive β-phase is induced in poly(vinylidene fluoride-hexafluoropropylene) [P(VDFHFP)] copolymer films without the help of traditional stretching techniques. We doped silver nanoparticles in P(VDF-HFP) to induce β-phase as well as control the chain and dipole orientations. The Grazing incidence reflection (GIR) infrared spectroscopy is used to confirm the molecular dipole orientations and crystalline polymorph for ultra thin films. The capability of the ferroelectric response is confirmed from the dynamic contact electrical force microscopy (DCEFM) study.

Ultrathin TaN/Ta barrier modifications to fullfill next technology node requirements

A physical vapor deposition tool for 300 mm wafers was coupled with an angle resolved photoelectron spectroscopy tool (ARXPS) and used to study the growth of TaN single layer and TaN/Ta double layer diffusion barriers. The nitrogen content of TaN was adjusted by controlling the nitrogen flow and by varying the deposition power. We describe a process recipe that allows us to decrease the TaN thickness while still maintaining the Ta layer in the low resistivity α-phase. The process recipe was developed on blanket wafers and evaluated in a test structure for high performance CMOS products.