DIRECT-TO-INDIRECT ENERGY-GAP TRANSITION IN STRAINED GAXIN1-XAS INP QUANTUM-WELLS/

We present direct experimental evidence that in GaxIn1-xAs/InP quantum wells the band structure undergoes a direct-to-indirect gap transitio n in k space above a critical value of x. We observe a drastic increas e 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 calculat ion of the valence subbands, we show that for x > x(c) the valence ban d maximum is at k not-equal 0, i.e., the band structure becomes indire ct.