  The transport properties of hot holes in silicon at cryogenic temperatures
exhibit several anomalous features, including the emergence of two distinct
saturated drift velocity regimes and a non-monotonic trend of the current noise
versus electric field at microwave frequencies. Despite prior investigations,
these features lack generally accepted explanations. Here, we examine the
microscopic origin of these phenomena by extending a recently developed
ab-initio theory of high-field transport and noise in semiconductors. We find
that the drift velocity anomaly may be attributed to scattering dominated by
acoustic phonon emission, leading to an additional regime of drift velocity
saturation at temperatures $\sim 40$ K for which the acoustic phonon occupation
is negligible; while the non-monotonic trend in the current noise arises due to
the decrease in momentum relaxation time with electric field. The former
conclusion is consistent with the findings of prior work, but the latter
distinctly differs from previous explanations. This work highlights the use of
high-field transport and noise phenomena as sensitive probes of microscopic
charge transport phenomena in semiconductors.
