Cross-Correlated Current Noise Spectroscopy and Detection of Shot Noise in Organic Light-Emitting Diodes*

Noise spectroscopy is a powerful technique for probing electrical processes in materials and has been utilized to great effect to study inorganic devices. Organic semiconductors, however, present two problems: high resistance, due to molecular disorder; and high device capacitance, due to their planar structure. The associated high RC constants limit the bandwidth of voltage noise measurements. Current noise measurements allow one to circumvent the bandwidth issue, but the currents are often orders of magnitude smaller than the input noise of the amplifier itself. In this talk, we will show that cross-correlation methods present a way to overcome this obstacle. We will discuss the basic concepts of the cross-correlation technique and the system we have developed to implement it. We will then discuss its use in the current noise measurements of a variety of materials and devices, for instance phosphorescent and fluorescent organic light-emitting diodes. Finally, we will discuss our work using this technique to detect shot noise, which we have associated with percolative transport in organic materials.