  We grow $^{28}$Si/SiGe heterostructures by reduced-pressure chemical vapor
deposition and terminate the stack without an epitaxial Si cap but with an
amorphous Si-rich layer obtained by exposing the SiGe barrier to dichlorosilane
at 500 {\deg}C. As a result, $^{28}$Si/SiGe heterostructure field-effect
transistors feature a sharp semiconductor/dielectric interface and support a
two-dimensional electron gas with enhanced and more uniform transport
properties across a 100 mm wafer. At T = 1.7 K we measure a high mean mobility
of (1.8$\pm$0.5)$\times$10$^5$ cm$^2$/Vs and a low mean percolation density of
(9$\pm$1)$\times$10$^{10}$ cm$^{-2}$. From the analysis of Shubnikov-de Haas
oscillations at T = 190 mK we obtain a long mean single particle relaxation
time of (8.1$\pm$0.5) ps, corresponding to a mean quantum mobility and quantum
level broadening of (7.5$\pm$0.6)$\times$10$^4$ cm$^{2}$/Vs and (40$\pm$3)
$\mu$eV, respectively, and a small mean Dingle ratio of (2.3$\pm$0.2),
indicating reduced scattering from long range impurities and a low-disorder
environment for hosting high-performance spin-qubits.
