On the Czochralski growth of Si<i>x</i>Ge1−<i>x</i> crystals as substrates for strained Ge quantum well heterostructures

This investigation showcases the viability of producing SixGe1−x bulk single crystals via the Czochralski technique. A high Si content in Ge-rich SiGe wafers is highly desirable for various applications in quantum technology, particularly as strain-relaxed buffers for the realization of hole spin qubits in strained Ge quantum well heterostructures. The focus lies on the bulk crystal growth of such materials and their chemical and structural quality. For this, the Czochralski process, starting from a highly pure Ge seed and melt, utilizing continuous feeding by dissolution of Si rods was performed.Si0.16Ge0.86 wafers with a diameter of up to 15 mm obtained from the bulk crystal exhibited homogeneous structural quality in contrast to the conventionally used epitaxial strain-relaxed SiGe buffers. The compositional fluctuations of Si measured throughout the wafer were below 0.4 at. % in addition to a dislocation density below 3 × 106 dislocations/cm2. Interestingly, the central region of the wafer displayed no measurable compositional fluctuations and contained less than 105 dislocations/cm2. Furthermore, the difficulties and limits of growing such SiGe crystals are discussed, such as the continuous dissolution of Si during growth and the formation of oxides in the melt during growth. The current observations indicate significant potential for further enhancement of the crystal quality and to realize higher Si concentrations using the Czochralski technique.