EFFECTIVE MASSES IN IN1-XGAXAS SUPERLATTICES DERIVED FROM FRANZ-KELDYSH OSCILLATIONS

In1-xGaxAs superlattices with InP or In1-xGaxAsyP1-y barriers show in small fields, below the onset of Stark localization, Franz-Keldysh osc illations that give direct access to the miniband mass. The mass at th e bottom of the first miniband is similar to that of the wells. A seco nd set of oscillations is observed at the saddle-point edge, which poi nts to a smaller mass on top of the first miniband. A very small mass, 0.014m(0) is obtained for the minimum of the second miniband. Stark l ocalization in this band is not observed, most likely due to efficient tunneling into higher bands.