  The Landauer-Buettiker formalism combined with the tight-binding transfer
matrix method is used to describe the results of recent experiments: the high
tunneling magnetoresistance (TMR) in (Ga,Mn)As-based trilayers and highly
polarized spin injection in p-(Ga,Mn)As/n-GaAs Zener diode. For both TMR and
Zener spin current polarization, the calculated values agree well with those
observed experimentally. The role played in the spin dependent tunneling by
carrier concentration and magnetic ion content is also studied.
