Abstract
Fabrication of indium tin oxide (ITO) was optimized for InGaN-based amber/red light-emitting diodes (LEDs). A radiofrequency sputtering reduced the sheet resistivity of ITO at low pressures, and a subsequent two-step annealing resulted in a low sheet resistivity (below 2×10-4 Ωcm) and high transmittance (over 98%) in the amber and red regions between 590 nm to 780 nm. Double ITO layers by sputtering could form an excellent ohmic contact with p-GaN. Application of the double ITO layers on amber and red LEDs enhanced light output power by 15.6% and 13.0%, respectively, compared to those using ITO by e-beam evaporation.
Highlights
During the past decade there has been a tremendous development of III-nitride semiconductors and their visible-UV optoelectronic devices, especially efficient blue light-emitting diodes (LEDs) for bright and energy-saving white light sources [1,2,3,4,5]
The efficiency of InGaN-based LEDs is still low in the amber and red regions due to the strong quantum-confined Stark effect (QCSE) and high defect density in high-In-content InGaN quantum wells (QWs) [7,8]
For the contacts with p-GaN layers, double indium tin oxide (ITO) layers were utilized in both amber and red LEDs, which achieved a lower forward voltage and higher light output power compared to an ITO layer by e-beam evaporation
Summary
During the past decade there has been a tremendous development of III-nitride semiconductors and their visible-UV optoelectronic devices, especially efficient blue light-emitting diodes (LEDs) for bright and energy-saving white light sources [1,2,3,4,5]. ITO could be deposited by magnetron sputtering and obtained the transmittance above 90% with optimized oxygen flow rate [28,29] These deposition processes usually introduce oxygen gas and adopt high-temperature conditions, complicating the process and requiring additional configurations for facilities. We systematically investigated the performance of ITO deposited by RF sputtering or e-beam evaporation Both sheet resistivity and transmittance were optimized for InGaN-based amber and red LEDs. We propose a two-step annealing process under O2-containing and O2-poor atmospheres (in sequence), achieving a low sheet resistivity below 2×10−4 Ωcm and high transmittance of more than 98% in the 590 nm to 780 nm wavelength range. For the contacts with p-GaN layers, double ITO layers were utilized in both amber and red LEDs, which achieved a lower forward voltage and higher light output power compared to an ITO layer by e-beam evaporation
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