Freestanding 2-in GaN layers using lateral overgrowth with HVPE

Hydride vapor phase epitaxy (HVPE) was used for the lateral overgrowth of thick GaN layers over masks of tungsten silicide nitride (WSiN). This mask material reduces sticking between the overgrown GaN and the mask and promotes the self-separation of the overgrown layers. Evaluation of the reflectance transient of the growing GaN layer indicates that the separation already occurs during growth and is caused by the intrinsic tensile strain of the growing GaN layer. This strain causes a strong concave bowing which is preserved even after cooling down.To reduce this residual bow of the freestanding GaN layers different approaches have been evaluated. It was found that the moment of separation is influenced by the mask geometry and that the temperature at this moment has an effect on the residual bow. The strain state of the template and the resulting bow at growth temperature are indicated to affect the residual bow as shown from the comparison of SiC- and sapphire-based GaN templates.