Structural Defects in Epitaxial III/V Layers

This chapter discusses structural defects in epitaxial III/V layers. The main interest in epitaxial semiconductor layers has been concentrated on the electronic quality of the material such as carrier mobility or photoluminescence (PL)-output. Therefore, the extended structural defects are often overlooked, even though they can be detrimental, especially in integrated circuit applications. Near-lattice-matched heteroepitaxy is the fundamental growth process for all optoelectronic semiconductor devices and for the most advanced digital devices on III/V semiconductors. However, lattice-mismatched heteroepitaxy provides increased flexibility for band-gap engineering. Strained-layer quantum wells have been used to control the band gap of the active region of semiconductor lasers, thereby permitting lasing at previously unattainable wavelengths. Stacking faults and twins are major defects observed in gallium arsenide (GaAs) heteroepitaxial layers grown on silicon (Si). However, it is not clear if stacking faults are always formed during growth or sometimes also during cooling. Oval defects have been attributed to several causes, such as surface contamination, Ga-spitting, Ga oxides, and particulates. To reduce the density of oval defects, it is necessary that the substrates be prepared carefully in an ultraclean environment to avoid carbon (C) or sulfur (S) contaminations and adhesion of particulates.