Studies of In0.53Ga0.47As/InP Superlattice Mixing and Conversion

Sealed ampoule Zn diffusions into an unstrained In0.53Ga0.47As/InP superlattice are observed to preferentially induce cation (In, Ga) interdiffusion. The extent of interdiffusion is monitored in these studies by SIMS (secondary ion mass spectrometry). In some cases, Zn entirely displaces In in the InP layers forming an In1−xGaxAs/Zn3P2 superlattice. Under still more stringent conditions, all In and Ga is replaced, resulting in a Zn3As2/Zn3P2 superlattice. These structures are capable of supporting considerable strain due to the absence of grown-in defects. TEM (transmission electron microscopy) micrographs of several samples reveal defect free highly strained layers with thicknesses exceeding the predicted critical values. A high dose Zn implant was examined in which mixing proceeded until the Zn concentration dropped below a threshold concentration of approximately 1020 cm−3 during the anneal. These results, in total, strongly support a kickout mechanism for Zn induced mixing. Si diffusion was observed, in one case, to induce comparable cation and anion interdiffusion, thereby reducing the layer bandgap disparity, as opposed to Zn which increases the difference in layer bandgaps. Almost no interdiffusion was induced by Si diffusion from MBE (molecular beam epitaxy) polycrystalline Si films, due either to the very high resultant Si concentrations or to the capping effect of the film. The data suggest that both anion and cation site defects play a role in the Si induced mixing process.