Deformed layers observed at the interface between a Sn‐doped epitaxial layer and a Cr‐doped substrate in GaAs

摘要

Interfacial deformed layers existing in GaAs epitaxial wafers are conveniently observed on a {110} cleavage face by means of a room‐temperature photoetching technique with a slightly modified Abrahams‐Buiocchi etchant. Examination is mainly confined to vapor‐grown GaAs samples composed of an 0.4‐μ‐thick Sn‐doped epitaxial layer [n? (6–10) ×1016 cm-3] and a Cr‐doped semi‐insulating substrate. It is established that the deformed layer results from thermal stress imposed on the arsenic depletion layer generated at the substrate surface in the preheating stage prior to growth. The strain field is found to extend more than 10 μ into the substrate side and even into the epitaxial layer side. Electron mobility in the submicron epitaxial layer is lowered by the presence of this strain field. However, this can be improved from 10 to 30% by annealing. It is also found that dislocations are generated in the deformed layer when the imposed stress is increased by coating the back side of the substrate with a SiO2 film. The dislocation density increases rapidly, but the deformed‐layer thickness gradually decreases as the SiO2 film thickness increases. Slip dislocations are generated from the periphery of the epitaxial wafer during the cooling process. This is due to stress concentration at the periphery.