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.
Highlights
AlN films have a large number of attractive properties including a high thermal conductivity, high resistivity, wide band-gap and high chemical resistance [1]
In order to extract general trends from experiments realized in this particular chemical vapor deposition (CVD) reactor with the design of experiments (DOE) method, we will try to sort out what is just technical optimization and what is of first interest for the CVD community
We have assessed the performance of a cold wall HT-hydride vapor phase epitaxy (HVPE) process by using a DOE approach for AlN growth
Summary
AlN films have a large number of attractive properties including a high thermal conductivity, high resistivity, wide band-gap and high chemical resistance [1]. The most attractive perspective for AlN-base devices is in the field of deep-ultraviolet light-emitting diodes working at extremely short wavelengths [5]. For this last application, the most serious challenge is the reduction of defect density in thin films grown on foreign substrates, which limits both efficiency and reliability of the devices [6,7]. The most successful methods to provide substrates of high structural quality are the PVT method [8] or a combination of PVT and HVPE methods [14,15] They provide AlN substrates with low dislocation densities (
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