Abstract

We present a TEM analysis of a series of Si/SiGe resonant tunnelling diode structures which contain Si1-xGex quantum wells (x of 0.4 and 1.0) grown on a range of (001) Si1-yGey virtual substrates (y of 0.15, 0.2 and 0.3). It is found that the dislocation density in the graded region of the virtual substrate increases with the y parameter, as expected. The subsequent effect of this, however, is to increase the amplitude of RMS roughness of the substrate surface, which ranges from 2.0 to 6.7 rim. Quantum wells with x = 0.4 are found to be highly planar; however, at x = 1.0 the wells undulate significantly due to misfit strain.

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