News Article

Laytec Enables Crack Free A-plane GaN Layers

To achieve thick crack free a-plane GaN buffer layers, low temperature AlN interlayers (LT AlN IL) are used for strain engineering
It is known that some properties of GaN based light emitting quantum wells (QWs) can be improved by a-plane III nitrides.

However, during the hetero-epitaxial growth on r-plane sapphire substrates, a-plane GaN layers are tensely strained in the growth plane resulting in crack formation.

At the annual conference of the German Society for Crystal Growth (DGKK) last December, Matthias Wieneke of Otto-von-Guericke University in Magdeburg (Germany) reported about the impact of LT AlN IL on a-plane GaN films.

For the studies, his team applies EpiCurve TT AR - an in-situ metrology system with advanced curvature resolution (AR).

This tool uses three laser spots for the curvature measurements as shown in the figure below, and also provides information on wafer curvature asymmetry along two perpendicular directions as it is typical for a-plane III-N growth.

The in-situ curvature measurements are demonstrated in the figure by a red line for (spherical) curvature and a blue line for curvature asphericity. During the growth of the tensely strained a-plane GaN buffer layer, the curvature (red) increases, while it decreases after the insertion of LT AlN IL.

Thus, the interlayer reduces the tensile strain as in the case of c-plane GaN growth.

However, after the growth of the interlayers, the asphericity (blue in the figure) increases, which indicates an increase of anisotropic strain. This anisotropy has been proven by subsequent ex-situ X-ray diffraction measurements [2].

[1] M. Wieneke, abstract book ICMOVPE 2012

[2] M. Wieneke et al., abstract book DGKK 2013

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