In making a Quantum Dot LED, is there an ideal ITO resistivity (ohm/sq) that is used for optimal performance? I am aware that ITO on glass slide sellers list this specification often. Does sheet resistivity change the performance of an LED?
Dear Reed Petersen,
Sheet resistance (Rs) or surface resistance or surface resistivity is electrical property used to characterise thin films of conducting and semiconducting materials. It is a measure of the lateral resistance through a thin square of material, i.e. the resistance between opposite sides of a square.
The key advantage of sheet resistance over other resistance measurements is that it is independent of the size of the square - enabling an easy comparison between different samples. Another advantage is that it can be measured directly using a four-point probe. The sheet resistance of the electrodes will effect amount of current that reaches the LED, impacting its performance.
The resistivity and conductivity can be calculated if the sheet resistance and material thickness are known. This allows for the materials to be electrically characterised, purely by measuring their sheet resistance.
A low sheet resistance is preferable from electrical point of view, but the lower the sheet resistance, the lower the transmission of the ITO. To decide its optimum value depends on the current density & the amount of transparencey needed.
A 100 nm thick ITO layer shows a transparency above 80% in the visible part of the spectrum and provides a low sheet resistivity of 20 Ω/sq (Sigma Aldrich Co, St Louis, MO.)
Most LED manufacturers characterize a product's thermal resistance for only one drive current, ambient temperature, and junction temperature. However, these parameters may change when LEDs are packaged into a system, which in turn may change the thermal resistance coefficient.
I hope I have answered your question.
With Best Wishes,
Samir G. Pandya
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