Search

Date of Conference: 1-6 February 2020 Conference Name: SPIE OPTO, 2020: Gallium Nitride Materials and Devices XV 2020 In this work, the effect of introducing a photonic crystal network of silicon nitride (SiN) micro-domes on the backside of silver coated gallium nitride (GaN) based light emitting diodes (LEDs) was studied. First, sapphire side of the top emitting LEDs, which is the bottom surface of the LEDs, is coated with silver (Ag). Light emitted towards the sapphire substrate is reflected upwards to the top surface and the amount of light extracted from the LED is expected to increase. In an alternative approach, SiN micro-domes forming a two dimensional photonic crystal, 2 μm in diameter and 80 nm in height in average, are deposited on the light emitting surface of the device with a period of 2 μm. Coating the backside with Ag has increased the efficiency of a top emitting LED by 11%. By introducing the SiN photonic crystal onto the Ag backside coated sample, total internal reflection is reduced via scattering and the amount of light emitted has been increased by 30% at 5·104 mA/cm2. Integration of SiN micro-domes with Ag coating has significantly impacted light extraction which has been shown to increase the efficiency of GaN based LEDs. Fabrication process and the results are discussed in detail.

WOS: 000430037600030, We investigate the effect of InGaN stress compensation layer on the properties of light emitting diodes based on InGaN/GaN multiple quantum well (MQW) structures with step graded electron injectors. Insertion of an InGaN stress compensation layer between n-GaN and the step graded electron injector provides, among others, strain reduction in the MQW region and as a result improves epitaxial quality that can be observed by 15-fold decrease of V-pit density. We observed more uniform distribution of In between quantum wells in MQW region from results of electro- and photoluminescence measurement. These structural improvements lead to increasing of radiant intensity by a factor of 1.7-2.0 and enhancement of LED efficiency by 40%. (C) 2018 Elsevier Ltd. All rights reserved., Scientific and Technological Research Council of Turkey [113G042]; TUBITAK, Financial support for this work is provided by the Scientific and Technological Research Council of Turkey (Grant No: 113G042). Ismail Altuntas acknowledges the Ph.D. Grant support from TUBITAK. We thank UNAM-National Nanotechnology Research Center at Bilkent University for access to fabrication and characterization equipment.

WOS: 000425566100069, Enhancement of InGaN/GaN based light emitting diode performance with step graded electron injectors through a two-step passivation is reported. Perimeter passivation of LED dies with SiO2 immediately following ICP mesa etch in addition to conventional Si3N4 dielectric surface passivation leads to decrease in the reverse bias leakage current by a factor of two as well as a decrease in the shunt current under forward bias by an order of magnitude. Mitigation of the leakage currents owing to the two-step passivation leads to significant increase in the radiant intensity of LEDs by more than a factor of two compared to the conventional single step surface passivation. Further, micro-dome patterned surface of Si3N4 passivation layer allow enhanced light extraction from LEDs. (C) 2017 Elsevier Ltd. All rights reserved., Scientific and Technological Research Council of Turkey (TUBITAK) [113G042]; TUBITAK, Financial support for this project was provided by the Scientific and Technological Research Council of Turkey (TUBITAK) [Grant No: 113G042]. Ismail Altuntas, acknowledges the Ph.D. Grant support from TUBITAK. We thank to UNAM-National Nanotechnology Research Center at Bilkent University for the use of fabrication and characterization equipment.

The effect of delta-doping of In0.06Ga0.94N barriers with Mg on the quantum efficiency of blue light-emitting-diodes (LEDs) with active regions composed of 6 (hex) 3-nm In0.15Ga0.85N is investigated. Compared to the reference sample, delta-doping of the first barrier on the n-side of the LED structure improves the peak external quantum efficiency (EQE) by 20%, owing to the increased hole concentration in the wells adjacent to the n-side, as confirmed by numerical simulations of carrier distributions across the active region. Doping the second barrier, in addition to the first one, did not further enhance the EQE, which likely indicates compensation of improved hole injection by degradation of the active region quality due to Mg doping. Both LEDs with Mg delta-doped barriers effectively suppress the drop of efficiency at high injection when compared to the reference sample, and the onset of EQE peak roll-off shifts from similar to 80 A/cm(2) in the reference LED to similar to 120 A/cm(2) in the LEDs with Mg delta-doped barriers. (C) 2015 AIP Publishing LLC.