  The p-symmetry of the hole wavefunction is associated with a weaker hyperfine
interaction as compared to electrons, thus making hole spin qubits attractive
candidates to implement long coherence quantum processors. However, recent
studies demonstrated that hole qubits in planar germanium (Ge) heterostructures
are still very sensitive to nuclear spin bath. These observations highlight the
need to develop nuclear spin-free Ge qubits to suppress this decoherence
channel and evaluate its impact. With this perspective, this work demonstrates
the epitaxial growth of $^\text{73}$Ge-depleted isotopically enriched
$^\text{70}$Ge/SiGe quantum wells. The growth was achieved by reduced pressure
chemical vapor deposition using isotopically purified monogermane
$^\text{70}$GeH$_\text{4}$ and monosilane $^\text{28}$SiH$_\text{4}$ with an
isotopic purity higher than 99.9 $\%$ and 99.99 $\%$, respectively. The quantum
wells consist of a series of $^\text{70}$Ge/SiGe heterostructures grown on Si
wafers using a Ge virtual substrate and a graded SiGe buffer layer. The
isotopic purity is investigated using atom probe tomography following an
analytical procedure addressing the discrepancies in the isotopic content
caused by the overlap of isotope peaks in mass spectra. The nuclear spin
background in the quantum wells was found to be sensitive to the growth
conditions. The lowest concentration of nuclear spin-full isotopes
$^\text{73}$Ge and $^\text{29}$Si in the heterostructure was established at
0.01 $\%$ in the Ge quantum well and SiGe barriers. The measured average
distance between nuclear spins reaches 3-4 nm in
$^\text{70}$Ge/$^\text{28}$Si$^\text{70}$Ge, which is an order of magnitude
larger than in natural Ge/SiGe heterostructures.
