A theory is given for the design of junction diodes which can simultaneously exhibit high photosensitivity and a reverse-biased dark charge-storage time greater than 1/30 second with calculations specifically carried out for silicon and germanium photo-junctions. The charge-storage problem associated with the use of narrower bandgap materials as vidicon targets is thus overcome, and a microarray of such junctions can be used as the photosensitive target at room temperature. Experimental data are presented for single element photo junctions in silicon, constructed according to the theoretical specifications for obtaining long time dark state charge storage. It is established that present state-of-the-art microelectronic technology is applicable to the production of the mosaic junction arrays necessary for constructing a completed camera tube.