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We investigate the unexpected high-energy electroluminescence (EL) peaks observed in long-wavelength InGaN light-emitting diodes (LEDs) with ground state emission peaks between ∼495 and 685 nm by studying the EL spectra of LEDs with varying quantum well (QW) thicknesses and indium compositions. In addition to the ground state emission, two high-energy emission peaks were observed in the LEDs with thick QWs and high indium compositions. The less energetic high-energy emission peak (2.4–2.6 eV) is attributed to the optical transitions involving excited states. Factors influencing the excited state transitions, such as the QW thickness and indium compositions, were also examined by simulations to better understand the occurrence of these transitions. The more energetic high-energy emission peak (2.8–3.1 eV) originates from V-defect sidewalls and was verified through micro-photoluminescence measurements. Identification of the high-energy emission peaks is essential as it enables targeted epitaxial or growth optimizations to minimize or eliminate these undesirable emission peaks. This work demonstrates the importance of using thin QWs to suppress the unwanted high-energy emissions due to excited state transitions and V-defect sidewalls for long-wavelength InGaN LEDs. [ABSTRACT FROM AUTHOR]

A III-nitride red LED with an active region temperature of 835 °C on a Si substrate utilizing a strain-relaxed template (SRT) is demonstrated. The peak wavelength blueshifts from 670 nm at 1 A/cm2 to 636 nm at 150 A/cm2. The on-wafer external quantum efficiency was 0.021% at 7 A/cm2 with an emission wavelength of 655 nm. The LED grown on a Si substrate exhibited a 116 nm redshift when compared to a co-loaded LED grown on sapphire. This is attributed to the difference in strain state for the III-nitride layers grown on Si compared to sapphire, allowing for more indium to be incorporated in the LED grown on Si. This suggests efficient III-nitride red LEDs and µLEDs on Si with a SRT can be realized with further material, device structure, and processing optimizations. [ABSTRACT FROM AUTHOR]

Nitride based light emitting diodes (LEDs) have demonstrated very high efficiency in the blue and green wavelength ranges. For full color LED based displays, efficient and small sized devices emitting in the three primary colors - red, green and blue are required. While phosphide based red LEDs are highly efficient, high surface recombination velocities limit their scaling to small dimensions. Nitride emitters can be scaled to smaller sizes, however for longer emission wavelength such as yellow, orange, and red, the indium content in the active region of the devices needs to be >30%. Due to the large lattice mismatch between GaN and InN, the needed high indium content introduces a large strain in the structure, often resulting in poor material quality. Recently, a novel technique to mitigate this lattice mismatch induced strain was demonstrated with the use of compliant porous GaN underlayer based substrates. In our previous reports, we have discussed the surface morphology, strain state evolution and device demonstrations using these substrates, however a detailed discussion regarding the pore cross-sections and dislocation propagation for each generation of these porous GaN substrates was yet to be reported. In this work, we will discuss the cross-sectional transmission electron microscopy (TEM) results of these substrates across multiple stages of the substrate technology development. [ABSTRACT FROM AUTHOR]

A highly relaxed InGaN buffer layer was demonstrated over a full two-inch c-plane sapphire substrate by metalorganic chemical vapor deposition. The InGaN buffer layer was grown on a 100 nm GaN decomposition stop layer with a 3 nm thick high indium composition InGaN underlayer. After thermal decomposition of the underlayer at 1000 °C, a 200 nm thick In0.04Ga0.96N buffer showed 85% biaxial relaxation measured by a high resolution x-ray diffraction reciprocal space map. When used as a pseudo-substrate for the regrowth of InGaN/InGaN multi-quantum wells, the sample showed a 75 nm red-shift in room temperature photoluminescence when compared to a co-loaded GaN template reference. The longer emission wavelength is associated with higher indium incorporation in the InGaN layers from the lessening of the compositional pulling effect caused by compressive strain. Using this technique, a simple red light emitting diode was demonstrated with an active layer growth temperature of 825 °C and a peak wavelength of 622 nm at a current density of 20 A cm−2. This work represents a unique method to relax a III-nitride based layer over a full substrate. [ABSTRACT FROM AUTHOR]

In this study, two methods to tune the emission wavelength of micro-LEDs fabricated on tile patterned compliant GaN-on-porous-GaN pseudo-substrates (PSs) are presented. The mechanical flexibility of porous GaN was utilized to relax the strain induced during the growth of light-emitting diode (LED) structures with n- and p-InGaN layers and enhance the indium incorporation via the composition pulling effect. The first approach involved only varying the size of the PS square tiles used for LED structure regrowth, from 20 × 20 μm2 to 8 × 8 μm2. Higher n-InGaN base layer relaxation with decreasing tile size resulted in a red shift of emission from 525 nm to 561 nm with no change in the growth conditions. The second method involved changing the mole fraction, x, of the n-InxGa1−xN base layer of the LED structure from 0.04 to 0.09 by reducing growth temperature, while maintaining the high temperature growth conditions of the multi-quantum well (MQW) and p-InGaN targeting 530 nm emission. The resulting wavelength shift was a remarkable 536–616 nm due to the stronger composition pulling effect, providing a pathway to enable high indium content MQW active regions to be grown at high temperature. [ABSTRACT FROM AUTHOR]

Nonpolar m-plane (1100) InGaN-based light emitting diodes (LEDs) grown on low-extended defect density bulk m-plane GaN substrates offer great potential for high performance devices due to the absence of polarization-related internal electric fields. To optimize the quantum well (QW) structure, systematic sets of near blue-ultraviolet LEDs using different well widths, barrier widths, and QW periods were packaged and tested. With increasing current, high power LEDs were realized with fairly flat external quantum efficiency and blueshift-free peak wavelength for QWs with thicknesses from 8 to 20 nm, barrier widths from 10 to 22 nm, and QW numbers from 4 to 10. [ABSTRACT FROM AUTHOR]

Review: 49 refs. [ABSTRACT FROM AUTHOR]