[en] In this work we address three-dimensional heterojunctions, demonstrating that photoluminescence from defect-free, Ge/SiGe multiple quantum well (MQW) micro-crystals grown on deeply patterned Si(001) and Si(111) substrates exhibit similar radiative intensity and analogous spectral shape. The finite lateral size and faceted top morphology of the micro-crystals guarantee the absence of dislocations threading through the MQW structure and the dominance of radiative recombination at slanted $\{113\}$ facets. Our approach yields superior optical quality in comparison to state-of-the-art MQWs grown on SiGe/Si(001) linearly graded buffers. (paper)