Epitaxial Growth of AlN on (0001) Sapphire: Assessment of HVPE Process by a Design of Experiments Approach

Abstract

Abstract:This study aims to present the interest of using a design of experiments (DOE) approach for assessing, understanding and improving the hydride vapor phase epitaxy (HVPE) process, a particular class of chemical vapor deposition (CVD) process. The case of the HVPE epitaxial growth of AlN on (0001) sapphire will illustrate this approach. The study proposes the assessment of the influence of 15 process parameters on the quality or desired properties of the grown layers measured by 9 responses. The general method used is a screening design with the Hadamard matrix of order 16. For the first time in the growth of AlN by CVD, a reliable estimation of errors is proposed on the measured responses. This study demonstrates that uncontrolled release of condensed species from the cold wall is the main drawback of this process, explaining many properties of the grown layers that could be mistakenly attributed to other phenomena without the use of a DOE. It appears also that the size of nucleation islands, and its corollary, the stress state of the layer at room temperature, are key points. They are strongly correlated to the crystal quality. Due to the intrinsic limitations of the screening design, the complete optimization of responses cannot be proposed but general guidelines for hydride (or halogen) vapor phase epitaxy (HVPE) experimentations, in particular with cold wall apparatus, are given.

Prediction of dislocation density in AlN or GaN films deposited on (0001) sapphire

“…In GaN films, density values between 5x10 9 cm -2 to 5x10 10 cm -2 for domain sizes evaluated in the 200-500 nm range were found [7,23,24]. Close values between 5 to 8x10 10 cm -2 were determined in AlN films for domains between 20 to 50 nm [4,10,20,25,26]. The mean rotation angle between domains together with the domain size and the dislocation density are usually not available for the same film in the literature.…”

Green upconversion improvement of TiO2 codoped Er3+-Yb3+ nanoparticles based thin film by adding ALD-Al2O3 for silicon solar cell applications

“…The deposition process while respecting DOE approach is performed. More details on the experimental steps of the DOE approach used can be found in a previous study [23]. After deposition, the substrates are pre-heated on a heating plate for 1 min at 200°C in order to evaporate the rest of the solvent.…”

Modeling multilayer coating systems in solar receivers

“…Successive stages including the growth of islands, impingement of islands and their coalescence take place to form a continuous surface, and thus grain boundaries. The film thickness just after islands coalescence is usually of the order of 30 nm or less [12]. Subsequently, the film evolves by grain coarsening and grain growth, which leads to further thickening [13].…”