III-V compound process development using photoluminescence lifetime

The development of processing techniques for the Al_xGa_1-xAs alloys for solar cells was expedited by using photoluminescence lifetime as a processor monitor. The active region was part of an isotype double heterostructure. The variation of lifetime with growth temperature and starting material is shown. It is found that the effect of higher-temperature Al_xGa_1-xAs processing appears to be the partial removal of Shockley-Read-Hall recombination centers that are present in the starting materials used in organometallic vapor-phase epitaxy growth. The nature of these centers is unknown but may be related to the impurity oxygen or water vapor in the materials. As all reported work indicates a steep drop in minority carrier lifetime with aluminum concentration, one might suspect the purity of the metal-organic aluminum compound as the source of these impurities. The superior minority carrier properties of liquid-phase-epitaxy (LPE)-grown Al_xGa_1-xAs result primarily from the purer starting materials used in LPE growth.