Performance of InGaN/GaN MQW LEDs Using Ga-Doped ZnO TCLs Prepared by ALD

Heavily Ga-doped ZnO (n±-GZO) films prepared by atomic layer deposition were used as transparent conducting layers (TCLs) on InGaN/GaN multiple quantum well (MQW) light emitting diodes (LEDs). It was found that N₂-annealed n⁺-GZO-coated InGaN/GaN MQW LEDs exhibited reduced forward voltage and enhanced light extraction under certain conditions. A forward voltage of 3.1 V at 20 mA was achieved for a 400°C N₂-annealed n⁺-GZO-coated InGaN/GaN MQW LED with a specific contact resistance of the n⁺-GZO on p-GaN contact being 4.1 × 10^-3 Ω cm². Compared to the same InGaN/GaN MQW LED structure with a commercial grade indium tin oxide (ITO) TCL, the 400 °C N₂-annealed n⁺-GZO-coated InGaN/GaN MQW LED shows an increment of light output power by 15% at 20 mA. It is believed that the enhanced light extraction of the n⁺-GZO-coated InGaN/GaN MQW LED is a consequence of a higher refractive index of n⁺-GZO than that of ITO.