Electroluminescence from controlled splits in CdS, CdSe, and GaAs0.2P0.8

The emission of visible (band-gap) radiation from current passed through controlled partial splits in n-type ∼5-Ω cm CdS has been studied in some detail. Some results are also reported for CdSe and GaAs0.2P0.8. Recombination occurs at the back-to-back surface barriers that occur in these materials at unhealed portions of the split. These barriers are effective at closed splits produced both in ultrahigh vacuum and in air for CdS and GaAs0.2P0.8 but only in high vacuum for CdSe. The radiation is emitted in a thin region at that side of the split which is biased in the forward direction. This is explained by a hole-tunnelling mechanism. Pulsed operation at room temperature and continuous operation (several seconds) at liquid-nitrogen temperatures gives light generation efficiencies in CdS of a few percent, at current levels in the region of 10 A cm−2. Such efficiencies have hitherto been unobtainable. Operation at about 50 A cm−2 results in failure which is shown to be due to breakdown of the surface barriers at isolated spots in the contact zone. A thin collodion layer between the surfaces greatly reduces this tendency.