Benefits and side effects of high temperature anneal used to reduce threading dislocation defects in epitaxial Ge layers on Si substrates

In the first part of this work we studied the effect of annealing time and temperature on the degree of threading dislocations density (TDD) reduction in epitaxial Ge films grown by CVD on Si. We show, that one-step controlled nitrogen annealing at temperatures above 800 °C can decrease TDD of thick (1.6 µm) Ge layers with 1 order of magnitude from 1E+ 08/cm2 down to 1E+ 07/cm2. Our results indicate that when temperature is high enough (> 800 °C) time does not play a role anymore. Thus for a temperature of 850 °C the same degree of TDD reduction can be achieved for 3 as well for 30 min. In the second part of the work we demonstrate that the combination of cycled epi growth and high temperature annealing although beneficial for TDD reduction deteriorates the crystalline quality of the layers due to significant Si out-diffusion and SiGe formation. Ge on Si substrates with lower defect densities have been further characterized by leakage current measurements on diode structures. Our results indicate that the reduction of drain to bulk leakage is insignificant and does not correspond to 1 order of magnitude reduction in TDD. We therefore conclude that threading dislocations are not the dominant factor for reduced device performance.