INDIRECT EXCITONS IN STRAINED GAXIN1-XAS INP QUANTUM-WELLS/

We present direct experimental evidence that in GaxIn1-xAs/InP quantum wells the bandstructure undergoes a direct-to-indirect gap transition in k-space above a critical value of x. We observe a drastical increa se of the measured radiative exciton lifetimes for samples where x > x (c), with x(c), depending on well width. Using a six-band k . p calcul ation of the valence subbands we show that for x > x(c) the valence ba nd maximum is at k not-equal 0, i.e. the bandstructure becomes indirec t.