Rüdiger Goldhahn

Otto-von-Guericke University Magdeburg | OvGU · Institute of Physics (IfP)

The interplay between band gap renormalization and band filling (Burstein-Moss effect) in n-type wurtzite GaN is investigated. For a wide range of electron concentrations up to 1.6×1020cm−3 spectroscopic ellipsometry and photoluminescence were used to determine the dependence of the band gap energy and the Fermi edge on electron density. The band g...

We systematically investigate the influence of free-electron concentrations from 1.5×10^17cm−3 up to 1.6×10^21cm−3 on the optical properties of single-crystalline In2O3 in the cubic bixbyite structure. Dielectric functions of bulk crystals and epitaxial films on various substrates are determined by spectroscopic ellipsometry from the mid-infrared (...

We perform a theoretical and experimental study of the optical properties of a CH3NH3PbI3 perovskite prepared by a vapor-assisted solution process, motivated in part by very high photovoltaic cell efficiencies. Several widespread theoretical approaches are used in an attempt to determine the most appropriate approach which would reproduce the exper...

The ordinary and extraordinary infrared dielectric functions of α-Ga2O3 thin films with the corundum structure were investigated. The films were grown by mist chemical vapor epitaxy on (10-10) sapphire substrates in (10-10) surface orientation. They were doped by the donor tin with the resulting free-electron concentrations between 10^17 and 10^19...

The ordinary dielectric functions (DFs) of rutile GexSn1−xO2 thin films grown by pulsed laser deposition have been obtained by spectroscopic ellipsometry from the near infrared to the ultraviolet range. Additionally, the Ge content x and the lattice parameters were determined by energy dispersive x-ray spectroscopy and x-ray diffraction, respective...

ScN is an emerging transition metal nitride with unique physical properties arising from the d electrons of Sc. In this letter, we present the results of optical characterization techniques: spectroscopic ellipsometry, Raman spectroscopy, and photoluminescence measurements of a 40−µm-thick fully relaxed, and only weakly n-type doped (n=1.2×1018cm−3...

We recently published a study concerning femtosecond pump–probe absorption edge spectroscopy of cubic GaN (fundamental bandgap: 3.23 eV), resulting in the transient dielectric function. In the present study, we continue our investigations of those pump–probe measurements by determining the time-dependent transition energy at the Fermi-vector betwee...

An ultra-fast change of the absorption onset for zincblende gallium-nitride (zb-GaN) (fundamental bandgap: 3.23 eV) is observed by investigating the imaginary part of the dielectric function using time-dependent femtosecond pump–probe spectroscopic ellipsometry between 2.9 and 3.7 eV. The 266 nm (4.66 eV) pump pulses induce a large electron–hole pa...

The syntheses of the new ligands 3‐(pyrazol‐1‐yl)methylpropanoate (L1) and 3‐(2,4‐dimethylpyrazol‐1‐yl)methylpropanoate (L2) and their complexation with palladium(II) have been instigated. In our hands L1 is best prepared by a Michael addition catalyzed by CaCO3 and L2 by a catalyst and solvent free reaction. Both L1 and L2 react with PdCl2(COD) to...

The anisotropic dielectric functions (DF) of corundum structured m-plane α-(Al_xGa_1-x)_2O_3 thin films (up to x=0.76) grown on m-plane sapphire substrate by metalorganic chemical vapor deposition (MOCVD) have been investigated. Infrared (IR) and visible-ultraviolet (UV) spectroscopic ellipsometry yields the DFs, while X-ray diffraction revealed th...

In this contribution, the first amidinate and amidine derivatives of p-carborane are described. Double lithiation of p-carborane (1) with n-butyllithium followed by treatment with 1,3-diorganocarbodiimides, R–N=C=N–R (R = iPr, Cy (= cyclohexyl)), in DME or THF afforded the new p-carboranylamidinate salts p-C2H10B10[C(NiPr)2Li(DME)]2 (2) and p-C2H10...

A series of new alkynylamidinate complexes of selected first and second row transition metals has been synthesized and fully characterized. Treatment of MCl2 precursors (M=Mn, Fe, Co) with 2 equiv. of the lithium alkynylamidinates Li[c‐C3H5−C≡C−C(NR′)2] ⋅ THF (R′=ⁱPr (2), Cy (cyclohexyl) (2)) afforded a series of binuclear complexes of the type M2[...

Redshift of the absorption onset and amplitude increase in the ultraviolet complex dielectric function (DF) of corundum-like alpha-(Ti_xGa_1-x)_2O_3 with increasing Ti content is presented. alpha-Ga2O3 thin film samples alloyed with Ti up to x =0.61 are grown from plasma enhanced atomic layer deposition. They are characterized by ultraviolet spectr...

By employing a mixed SnO2 + Sn source, we demonstrate suboxide molecular beam epitaxy (S-MBE) growth of phase-pure single-crystalline metastable SnO (001) thin films on Y-stabilized ZrO2 (001) substrates at a growth rate of ∼1.0 nm/min without the need for additional oxygen. These films grow epitaxially across a wide substrate temperature range fro...

By employing a mixed SnO$_2$+Sn source, we demonstrate suboxide molecular beam epitaxy growth of phase-pure single crystalline metastable SnO(001) thin films at a growth rate of ~1.0nm/min without the need for additional oxygen. These films grow epitaxially across a wide substrate temperature range from 150 to 450{\deg}C. Hence, we present an alter...

The current library of amidinate ligands has been extended by the synthesis of two novel dimethylamino‐substituted alkynylamidinate anions of the composition [Me 2 N–CH 2 –C≡C–C(NR) 2 ] – (R = i Pr, cyclohexyl (Cy)). The unsolvated lithium derivatives Li[Me 2 N–CH 2 –C≡C–C(NR) 2 ] ( 1 : R = i Pr, 2 : R = Cy) were obtained in good yields by treatmen...

Ga2O3 and its polymorphs are attracting increasing attention. The rich structural space of polymorphic oxide systems such as Ga2O3 offers potential for electronic structure engineering, which is of particular interest for a range of applications, such as power electronics. γ‐Ga2O3 presents a particular challenge across synthesis, characterisation,...

The optical properties of a single-phase corundum-structured In 2 O 3 epilayer grown by a mist chemical vapor deposition method have been studied. Raman scattering measurements on a c face and on a lateral face reveal all of the seven Raman-active modes of the corundum structure, with good adherence to the Raman selection rules. Three out of the fo...

Ga2 O3 and its polymorphs are attracting increasing attention. The rich structural space of polymorphic oxide systems such as Ga2 O3 offers potential for electronic structure engineering, which is of particular interest for a range of applications, such as power electronics. γ-Ga2 O3 presents a particular challenge across synthesis, characterisatio...

Time-dependent femtosecond pump-probe spectroscopic ellipsometry studies on zincblende gallium-nitride (zb-GaN) are performed and analyzed between 2.9-3.7eV. An ultra-fast change of the absorption onset (3.23eV for zb-GaN) is observed by investigating the imaginary part of the dielectric function. The 266nm (4.66eV) pump pulses induce a large free-...

The heteroepitaxial growth of lattice mismatched layers is crucial for modern semiconductor device fabrication, but it is a significant challenge in epitaxy. Growth of lattice mismatched materials creates strain in the epitaxial layer, which is usually relaxed by introducing crystal defects deteriorating the device performance. Remote epitaxy on gr...

A series of brightly colored alkaline earth metal 1,3-dimethylviolurates M(Me2Vio)2 have been prepared and fully characterized. The title compounds AE(Me2Vio)2·nH2O (AE = Mg, n = 6 (3); AE = Ca, n = 8 (4), AE = Sr, n = 6 (5); AE = Ba, n = 4 (6)) were obtained by neutralizing 1,3-dimethylvioluric acid monohydrate (=H(Me2Vio)·H2O; 2) with 0.5 equiv....

Ga$_2$O$_3$ and its polymorphs are attracting increasing attention. The rich structural space of polymorphic oxide systems such as Ga$_2$O$_3$ offers potential for electronic structure engineering, which is of particular interest for a range of applications, such as power electronics. $\gamma$-Ga$_2$O$_3$ presents a particular challenge across synt...

The simplest picture of excitons in materials with atomic-like localization of electrons is that of Frenkel excitons, where electrons and holes stay close together, which is associated with a large binding energy. Here, using the example of the layered oxide V2O5 , we show how localized charge-transfer excitations combine to form excitons that also...

Increase of light extraction efficiency (LEE) and total output power of UV LEDs emitting at 265 nm and 310 nm, respectively, after encapsulation with a UV-transparent silicone are studied. Raytracing simulations suggest that a properly placed hemispherical encapsulation with a refractive index in the range from 1.4 to 1.8 enhances the LEE from 8% t...

The simplest picture of excitons in materials with atomic-like localization of electrons is that of Frenkel excitons, where electrons and holes stay close together, which is associated with a large binding energy. Here, using the example of the layered oxide V2O5, we show how localized charge-transfer excitations combine to form excitons that also...

We report the heteroepitaxial growth of single-crystalline bixbyite (In1−xGax)2O3 films on (111)-oriented yttria-stabilized zirconia substrates using plasma-assisted molecular beam epitaxy. A pure In2O3 buffer layer between the substrate and (In1−xGax)2O3 alloy is shown to result in smoother film surfaces and significantly improved crystallinity. T...

A series of new homoleptic first‐row transition metal and yttrium tris(alkynylamidinate) complexes have been synthesized and fully characterized. The starting materials [c‐C3H5–C≡C–C(NR)2]Li·THF (1: R = iPr, 2: R = Cy; Cy = cyclohexyl) were obtained in high yields by employing a modified literature procedure. In the course of this study, the unprec...

Gallium oxide is a promising candidate for several future electronic devices to replace common technologies. For this reason, an understanding of fundamental physical processes is needed. In this work, we investigate the Raman excitations of a α-Ga2O3 thin film under temperature variation from 80 K up to 790 K. This yields detailed information abou...

The influence of Ga incorporation into cubic In2O3 on the electronic and vibrational properties is discussed for (In1−x,Gax)2O3 alloy films grown by molecular beam epitaxy. Using spectroscopic ellipsometry, a linear dependence of the absorption onset on the Ga content x is found with a blueshift of up to 150 meV for x = 0.1. Consistently, the funda...

Selective area growth of cubic gallium nitride is investigated in a plasma assisted molecular beam epitaxy setup. 380 μm thick silicon (001) and 10 μm thick 3C-silicon carbide (001), grown on 500 μm silicon (001), were used as substrates and structured with silicon dioxide masks. Selective area growth on silicon and 3C-silicon carbide was tested fo...

In this work, we show the heteroepitaxial growth of single-crystalline bixbyite (In$_{1-x}$Ga$_x$)$_2$O$_3$ films on (111)-oriented yttria-stabilized zirconia substrates using plasma-assisted molecular beam epitaxy under various growth conditions. A pure In$_2$O$_3$ buffer layer between the substrate and (In$_{1-x}$Ga$_x$)$_2$O$_3$ alloy is shown t...

Light emitting diode structures emitting in the ultraviolet spectral range are investigated. The samples exhibit defect luminescence bands. Synchrotron-based photoluminescence excitation spectroscopy of the complicated multi-layer stacks is employed to assign the origin of the observed defect luminescence to certain layers. In the case of quantum w...

The influence of Ga incorporation into cubic In$_2$O$_3$ on the electronic and vibrational properties is discussed for (In$_{1-x}$,Ga$_x$)$_2$O$_3$ alloy films grown by molecular beam epitaxy. Using spectroscopic ellipsometry, a linear dependence of the absorption onset on the Ga content $x$ is found with a blueshift of up to 150 meV for $x = 0.1$....

The linear optical response of the ultrawide bandgap h‐BN is investigated by spectroscopic ellipsometry. The ordinary dielectric function of h‐BN is determined up to 25 eV on a high‐quality single‐crystal platelet. The direct bandgap and the high‐energy transitions have been characterized with the aid of ab initio self‐consistent GW calculations an...

We present a quantitative description of the change in optical properties of zincblende aluminium-gallium-nitride thin films dependent on the free-carrier concentration due to band filling and renormalization effects. Free-electron concentrations above 10(20) cm(-3) in GaN are achieved by introducing germanium as a donor. Spectroscopic ellipsometry...