  We investigate the transport of holes through $AlAs/In_{.10}Ga_{.90}As$
resonant tunneling diodes which utilize $In_xGa_{1-x}As$ prewells in the
emitter with $x=0,.10,$ and $.20$. The data show an increase in peak current
and bias at resonance and a concurrent increase in the peak-to-valley ratio
with increasing x. We explain this enhancement in tunneling as due to
confinement (or localiz- ation) of charges in the prewell and the formation of
direct heavy(light) hole to heavy(light) hole conduction channels as a
consequence.
