Determination of Optimal ITO Current-Spreading Layer Parameters for LEDs Based on AlInGaN Heterostructures and Developing a Technology to Form Such Layers on p-GaN Surfaces

We presented and discussed the results of modeling the parameters and characteristics of an AlInGaN LED with an ITO current spreading layer. It is shown that for a planar LED, the fields of current density distribution, internal quantum efficiency, power released as heat, and optical radiation power have similar contours of the regions of maximum and minimum values. With a decrease in the contact resistance of ITO/p-GaN, there is a decrease in resistive losses, as a result of which the voltage drop and heat generation decrease. Significant heat generation at the ITO/p-GaN boundary leading to a decrease in the LED efficiency is observed at a contact resistance of more than 10–2 Ω cm2. On the other hand, a decrease in contact resistance leads to an increase in current constriction near metal electrodes. An increase in the thickness of the current spreading layer leads to a more uniform current distribution over the active area of the LED. But at the same time, the absorption of generated photons in the ITO volume increases. Thus, it was found that the most optimal thickness of the ITO current spreading layer is 130–150 nm, and the ITO/p-GaN contact resistance is in the range from 10–2 to 10–4 Ω cm2. When applying ITO to the surface of the p-GaN AlInGaN heterostructure, it was shown that the most effective technological solution is the deposition of a two-layer structure: a thin In + Sn metal film deposited by magnetron sputtering of an In (90%)/Sn (10%) target in an oxygen-free environment and an ITO film deposited in the same vacuum cycle with the addition of oxygen. This combination allows for specific contact resistance values of ITO/p-GaN at a level of 8 × 10–4 Ω cm2 with a transmittance of 94% at a radiation wavelength of 450 nm.