Comparative study on residual strain profiles in GaAs substrates grown by LEC and VB techniques

Abstract

Residual strain profiles have been experimentally and theoretically compared between the two different growth techniques preparing GaAs substrates. One is the vertical boat (VB) technique and the other is the liquid-encapsulated Czochralski technique. It is found from the experimental observations that the residual strain profile of VB substrate is simple bowl-shaped, in which the residual strain value is high near the peripheral region, while the residual strain profile of LEC substrate is more complex and fourfold-symmetrical, in which the residual strain value is high in the inner regions as well as near the peripheral regions. In order to explain this experimental observation, we have estimated the thermal stress caused during the crystal growth by computer analysis. Thermal stress during VB growth is dominantly caused near the solid-liquid interface. On the other hand, strong thermal stress is caused during LEC growth both near the surface of boric oxide encapsulant and near the solid-liquid interface. It is therefore concluded that the observed difference of residual strain profiles may be coming mainly from the temperature profile difference between VB and LEC techniques.