K. Schmidegg

In situ spectroscopic ellipsometry of MOCVD-grown GaN compounds for on-line composition determination and growth control

Abstract In situ spectroscopic ellipsometry measurements were performed in the ultraviolet–visible spectral range during the growth of GaN and ternary compounds in a metal organic chemical vapor deposition reactor and compared with standard reflectivity data recorded in parallel. Special emphasis has been given to the characterization of the GaN nucleation layer formed on sapphire substrates, its annealing and the subsequent initial stages of GaN growth. Furthermore, the optical response of GaN and ternary compounds (AlGaN, InGaN) has been studied as a function of the substrate temperature up to 1200°C. In the context of the on-line monitoring of ternary alloy concentration, ellipsometric data has been recorded as a function of time (increasing thickness) during the growth of AlGaN with different Al content and displayed on the plane of the complex dielectric function. The resulting exponential spirals gave, at the convergence points, the optical constant of the growing material and, therefore, an evaluation of the composition already achieved at the beginning of the growth process.

In situ and real-time characterization of metal-organic chemical vapor deposition growth by high resolution x-ray diffraction

We present an x-ray diffractometer for the analysis of epitaxial layers during (in situ) metal-organic chemical vapor deposition (MOCVD). Our diffractometer has a conventional x-ray source, does not need a goniometer stage, and is not sensitive to precise adjustment of the samples before measurement. It allows us to perform measurements within a few seconds even from rotating and wobbling samples. The first results of laboratory tests performed with our x-ray diffraction system show that it is well suited for in situ and real-time monitoring of the MOCVD growth process. We were able to measure the growth rate of a cubic GaN layer and the intensity and peak position of Bragg reflections of the growing layer in less than 20 s only.

GaN:δ-Mg grown by MOVPE: Structural properties and their effect on the electronic and optical behavior

Abstract The effect of Mg δ -doping on the structural, electrical and optical properties of GaN grown via metalorganic vapor phase epitaxy has been studied using transmission electron microscopy, secondary ion mass spectroscopy, atomic force microscopy, X-ray diffraction, Hall effect measurements and photoluminescence. For an average Mg concentration above 2.14 × 10 19 cm - 3 , phase segregation occurs, as indicated by the presence of Mg-rich pyramidal inversion domains in the layers. We show that δ -doping promotes, in comparison to Mg continuous doping, the suppression of extended defects on the sample surface and improves significantly the morphology of the epilayers. Conversely, we cannot confirm the reduction in the threading dislocation density—as a result of δ -doping—reported by other authors. In the phase separation regime, the hole concentration is reduced with increasing Mg concentration, due to self-compensation mechanisms. Below the solubility limit of Mg into GaN at our growth conditions, potential fluctuations result in a red-shift of the emission energy of the free-to-bound transition.

Virtual interface approximation model applied to spectroscopic ellipsometry for on-line composition determination of metalorganic chemical vapor deposition grown ternary nitrides

In situ spectroscopic ellipsometry measurements in the ultraviolet-visible spectral range were performed during metalorganic chemical vapor deposition of GaN and AlGaN layers on sapphire. At first, the initial GaN–sapphire interface formation has been characterized and the optical response of the nitride layers for temperatures up to 1200 °C has been recorded. The data were used as the basis for evaluating kinetic ellipsometry measurements performed during growth: an algorithm, based on the virtual interface approximation model, has been developed and implemented to determine the layer composition of AlGaN multilayer structures in real time.

Characterization of metalorganic chemical vapor deposition growth of cubic GaN by in situ x-ray diffraction

X-ray diffraction is used for the in situ characterization of the growth of cubic GaN by metalorganic chemical vapor deposition. Our setup permits the simultaneous measurement of a wide angular range and requires neither goniometer nor exact sample positioning. Time-resolved measurements during growth give access to film thickness and growth rate as well as information on the chemical composition of ternary compounds. Additionally, the relaxation of the crystal lattice during heteroepitaxial growth of GaN on AlGaN can be measured directly.

In‐situ multiple wavelength ellipsometry for real time process characterization of nitride MOCVD

In‐situ multiple wavelength spectroscopic ellipsometry has been performed in real time upon metalorganic chemical vapor deposition of GaN and ternary AlxGa1−xN compounds on (0001) sapphire substrates. The obtained data have been used as a basis for evaluating kinetic ellipsometry measurements performed during the nucleation process: an algorithm based on the virtual interface approximation model has been developed and implemented in order to simultaneously determine the layer composition and the growth rate of ternary nitride compounds in real time. Furthermore, we demonstrate the possibility to control in‐situ and on‐line the thickness and thickness variation of the nucleation layer as‐grown and upon annealing by modeling the acquired complex dielectric function data by means of an adapted effective‐medium‐based method.