Photoemission and photoluminescence from GaAs/GaA1As superlattices.

There has been a large amount of experimental and theoretical work on optical excitation between quantized levels of superlattices or quantum wells. Most results deal with level spectroscopy, but fewer are concerned with the transport of electrons perpendicular to the layers in absence of electric field. We report photoemission measurements in a GaAs/GaA1As superlattice covered by a GaAs surface activated to negative electron affinity by cesium and oxygen coadsorption. The original experimental apparatus allows heating up to 900K during sample activation, and cooling down to 30K by helium circulation. The photocurrent versus light excitation energy, i.e., the yield curve, shows definite step- like structures, which appear at the same energy positions as those present in the luminescence excitation spectrum.