COMPOUND FORMATION AND LARGE MICROSTRAINS AT THE INTERFACE OF II-VI/III-V-SEMICONDUCTORS DETECTED BY RAMAN-SPECTROSCOPY

ZnSe epitaxial layers grown by different methods on GaAs (100) substrates were studied by micro-Raman spectroscopy. At the interface the formation of a Ga-Se compound, very probably the zincblende defect structure Ga2Se3, is observed. This situation is similar to that found in the II-VI/III-V heterosystems CdTe/InSb and CdS/InP. There the thermodynamically favoured III-VI compounds (In-Te and In-S respectively) were also detected at the interface. As a consequence the analysis of strains in the II-VI epitaxial overlayers has to take into account these interfacial reacted regions. Micro-Raman spectra taken on a (110) cleavage plane close (200 nm) to a ZnSe/GaAs interface show large frequency shifts of the 2TA/TO-TA and 2LO features in the second-order Raman spectra but only marginal ones in the first-order To Raman scattering. The amount of splitting corresponds to pressures up to 40 kbar (second-order scattering) and a few kbar (first-order scattering). This behaviour can be explained by assuming that Ga2Se3 forms clusters at the interface. Their size should be intermediate between the wavelengths of near-zone-centre phonons (100 nm) detected in a first-order scattering process and those of zone boundary phonons (1 nm) responsible for the structure in second-order Raman scattering spectra.