An ultra-
high density data storage device using phase-change
diode memory cells, and having a plurality of emitters for directing beams of directed energy, a layer for forming multiple data storage cells and a layered
diode structure for detecting a memory or data state of the storage cells, wherein the device comprises a phase-change data storage layer capable of changing states in response to the beams from the emitters, and a second layer forming one layer in the layered
diode structure, the second layer comprising a material containing
copper,
indium and
selenium. A method of forming a diode structure for a phase-change data storage array, having multiple thin film
layers adapted to form a plurality of data
storage cell diodes, comprises depositing a first diode layer of CuInSe material on a substrate and depositing a second diode layer of phase-change material on the first diode layer.