Increase In Internal Quantum Efficiency Research Articles

Introducing boron gallium nitride as carriers’ source layer for efficient near-ultraviolet microLED

Abstract This study explored the impact of boron gallium nitride (BGaN) in buffer layer and hole source layer. We employed B0.05Ga0.95N which reduced the lattice mismatch as well as the electric field. BGaN not only minimized the number of electrons leaking out of quantum wells (QWs) but also improved the hole injection. It is evident from our simulations that internal quantum efficiency (IQE) is enhanced significantly as more carriers are available for radiative recombination in multiple quantum wells (MQWs). Along with the increase in IQE, droop is also reduced in BGaN ultraviolet light-emitting diodes. Significantly high luminous power and emission intensity were observed along with slight blueshift because of minimized quantum confinement stark effect (QCSE).

Design of a metasurface deflector for guided absorption enhancement in a Si PIN photodiode

We numerically demonstrated a surface-illuminated Si PIN photodiode (PD) structure with a metasurface composed of etched isosceles triangle pillars that can enhance sensitivity in the near-infrared wavelength range (NIR) by enabling directional scattering (DS) of photons. The metasurface is designed to act as a deflector to increase the absorption efficiency by extending the photon dwell time. This is particularly effective in thin intrinsic layers (i-layers) of silicon, surpassing the capabilities of conventional omnidirectional scattering gratings. Our results show a 3.5-fold increase in internal quantum efficiency over wavelengths above 0.9 µm compared to the structure without metasurface. The absorption enhancement brought about by directional scattering is not limited to thin i-layers; it can potentially improve a wide range of photodiode geometries and structures. Furthermore, the proposed structure, consisting of an all-Si layer and a simple geometric etching process, makes it compatible with foundry fabrication methods and opens up new possibilities for expanding applications of Si PDs.

Reduced Surface Recombination in Extended-Perimeter LEDs toward Electroluminescent Cooling.

III-V semiconductor light-emitting diodes (LEDs) are a promising candidate for demonstrating electroluminescent cooling. However, exceptionally high internal quantum efficiency designs are paramount to achieving this goal. A significant loss mechanism preventing unity internal quantum efficiency in GaAs-based devices is nonradiative surface recombination at the perimeter sidewall. To address this issue, an unconventional LED design is presented, in which the distance from the central current injection area to the device's perimeter is extended while maintaining a constant front contact grid size. This approach effectively moves the perimeter beyond the lateral spread of current at an operating current density of 101-102 A/cm2. In p-i-n GaAs/InGaP double heterojunction LEDs fabricated with varying sizes and perimeter extensions, a 19% relative increase in external quantum efficiency is achieved by extending the perimeter-to-contact distance from 25 to 250 μm for a front contact grid size of 450 × 450 μm2. Utilizing an in-house developed Photon Dynamics model, the corresponding relative increase in internal quantum efficiency is estimated to be 5%. These results are ascribed to a significant reduction in perimeter recombination due to a lower perimeter-to-surface area (P/A) ratio. However, in contrast to lowering the P/A ratio by increasing the front contact grid size of LEDs, the present method enables these improvements without affecting the required maximum current density in the microscopic active LED area under the front contact grid. These findings aid in the advancement of electroluminescent cooling in LEDs and could prove useful in other dedicated semiconductor devices where perimeter recombination is limiting.

Lasing Threshold Reduction of AlGaN‐Based Ultraviolet‐C Laser Diodes Using Strain Relaxed Lower Cladding Layer

The dependence of the performance of ultraviolet‐C (UV‐C) laser diodes on the strain relaxation of lower cladding layer (LCL) is numerically investigated. As the strain relaxation increases from 0% to 100%, the threshold current density decreases from 25 to 12.7 kA cm−2, and the slope efficiency increases from 0.039 to 0.087 W A−1, thanks to an increase in internal quantum efficiency (IQE). The improvement of IQE is mainly due to the enhanced hole injection resulting from the increased hole concentration in the distributed polarization doping layers and the reduced hole blocking barrier height of the upper waveguide layer with increasing the strain relaxation. Additionally, the effective screening of the polarization field within the quantum well ameliorates the quantum‐confined Stark effect, further improving the IQE. Our study reveals that strain relaxed LCL is imperative to achieve low‐threshold UV‐C laser diodes.

Contribution of the photoluminescence effect of the stain etched porous silicon in improvement of screen printed silicon solar cell performance

In this work, we investigate the potential use of porous silicon (PS) nanostructures stain etched into photovoltaic technology as one possible way to increase the silicon solar cell (SC) efficiency at low cost. The process is based on a combination of texturization and porous silicon formed by metal assisted etching which used the screen printed front grid contact. The photoluminescence (PL), the reflectivity spectra of the PS layers, spectral response and electrical measurements are presented and discussed. As a result, the short circuit current density was improved by more than 21%. We observed an increase in internal quantum efficiency (iQE) in the region where the PL of the PS layers appears and the minority carriers’ diffusion length is enhanced by more than 60 . We report the correlation between the converter PL intensity and iQE and we demonstrate that the photoluminescence properties and the increased photocurrent result in an improvement of the solar cell efficiency.

Near-Ultraviolet Light-Driven Photocathodic Activity for (001)-Oriented BiOCl Thin Films Synthesized by Mist Chemical Vapor Deposition.

Semitransparent and homogeneous bismuth oxychloride (BiOCl) thin films with (001) preferred orientation were synthesized on polycrystalline Sn:In2O3-glass substrates by mist chemical vapor deposition. The films showed photocathodic activity even under near-ultraviolet light within the band gap due to the in-gap states induced by oxygen vacancies. Higher synthesis temperatures resulted in a significant increase of photocurrent density under ultraviolet light. While the longer lifetime of photocarriers led to an increase of internal quantum efficiency, the larger band-edge absorption significantly contributed to the higher external quantum efficiency.

Simultaneously improve the Purcell factor and internal quantum efficiency of light-emitting diodes via surface plasmon by metal conic structure

Recent advances in the development of surface plasmons (SPs) enhanced LED have provided a great opportunity to enhance either the internal quantum efficiency (IQE) or the spontaneous emission rate (SE) by employing specific metal structures. However, it is still challenging to simultaneously achieve high IQE and Purcell factor (Fp), which demonstrates the SE enhancement, without sacrificing the electrical performance of LEDs. Herein, we designed and investigated a conic metal structure applied to LEDs by comprehensively considering the electrical, optical, and data transmission performance of devices. Conic structures with various heights were implemented to investigate the variation trends of IQE and Fp with the structure design, accompanied by the planar structures as references. A more than five times increase in IQE and almost five times increase in Fp were demonstrated experimentally even with a coupling distance of 100 nm, by employing this conic structure. The theoretical analysis was verified by the experimental results and revealed the mechanism of high Fp and IQE toward high SP–photon coupling efficiency and initial IQE. This study provides a universal strategy to enhance the performance of luminous efficiency and modulation speed of LEDs without sacrificing electrical properties, making them viable for the integration of lighting, display, and communication.

Light extraction efficiency and internal quantum efficiency of fully UVC-transparent AlGaN based LEDs

The light extraction efficiency (LEE), external quantum efficiency (EQE), and current–voltage characteristics of deep ultraviolet light emitting diodes (DUV-LEDs) with different aluminum mole fractions in the p-AlGaN layers have been investigated. Optimizing the p-AlGaN layer composition requires a tradeoff between reducing the absorption losses and limiting the increases in the p-contact resistance and operation voltage. AlGaN multiple quantum well LEDs emitting around 263 nm with different AlGaN:Mg short period super lattices (p-SPSL) ranging from x = 33% (UV-absorbing) to x = 68% (UV-transparent) average aluminum mole fraction have been explored. DUV-LEDs with different p-contact metals and UV-reflectivities have been characterized by electroluminescence measurements and analyzed by ray-tracing simulations. The comparison shows an increased operating voltage and a five-fold increase of the on-wafer EQE with a maximum value of 3.0% for DUV-LEDs with UV-transparent p-SPSL (x = 68%) and UV-reflective indium contacts in comparison to LEDs with a UV-absorbing p-SPSL (x = 33%). Ray-tracing simulations show that the increase in EQE can be partially ascribed to a 2.5-fold improved LEE in combination with a two-fold increase in internal quantum efficiency.

(Keynote) Dynamics of Electron Transfer in Enhanced Water Splitting Under Modal Strong Coupling Conditions

Metallic nanoparticles such as gold (Au) and silver (Ag) nanoparticles shows light absorption and scattering at the arbitrary wavelength of visible and near-infrared regions based on localized surface plasmon resonances (LSPRs). LSPRs which are collective oscillations of conductive electrons give rise to the enhancement of near-field and are expected as a light harvesting optical antenna for light energy conversion devices We have successfully developed the plasmon-induced artificial photosynthesis systems such as water splitting and ammonia synthesis systems as well as solid-state plasmonic solar cells based on the principle of plasmon-induced charge separation between gold nanoparticles (Au-NPs) and semiconductor.[1]-[6] Recently, the plasmon-induced charge separation has received considerable attention as a novel strategy for solar energy conversion.[7],[8] However, in general Au-NPs loaded semiconductor photoelectrode, the insufficient absorption limits its solar energy conversion efficiency. Aiming at the enhancement of light absorption, in the present study, we apply the principle of modal strong coupling to plasmonic water splitting using Au-NPs/titanium dioxide (TiO2) thin-film/Au-film (ATA) photoelectrode.[9],[10] Furthermore, the dynamics of the hot electron transfer under the modal strong coupling conditions are further studied by transient reflection spectroscopy.Modal strong coupling between the Fabry–Pérot nanocavity mode of the TiO2thin-film/Au-film and the LSPR mode of the Au-NPs is induced when their resonant frequencies overlap. To increase the coupling strength in this modal strong coupling regime, a key feature of the ATA photoelectrode is partially inlaying of Au-NPs into the TiO2 nanocavity by several nanometers. Under a three-electrode system measurement with a saturated calomel electrode (SCE) as a reference electrode, a Pt wire as a counter electrode and an electrolyte of KOH (0.1 mol/dm3), we demonstrated that the action spectrum of incident photon to current conversion efficiency (IPCE) exhibited two bands, which almost corresponds to the absorption spectrum of ATA. The IPCE of ATA is extraordinarily enhanced as compared to that of Au-NPs/TiO2photoanode. Most importantly, under the modal strong coupling conditions, the internal quantum efficiency (IQE) of the photocurrent generation is also enhanced at the wavelengths of strong coupling induced hybrid branches. The increase in IQE implies the possibility of increasing the generation of hot electrons in the modal strong coupling regime. The plasmon-induced water splitting using a two-electrode system was also quantitatively measured. To understand the IQE enhancement under the strong coupling conditions, the dynamics of the hot electrons transfer from Au-NPs to TiO2 were further explored by transient measurement using a visible pump/infrared probe (at 3500 nm) femtosecond transient reflection spectrometers. An ultrafast hot electrons injection from Au-NPs to TiO2 was observed. Interestingly, under the strong coupling conditions, the hot electrons excited in the ATA photoelectrode that fabricated on Al film instead of Au film exhibited a much longer lifetime than that on Au film. The contributions for the long lifetime of the injected electrons to TiO2 are also discussed. References Nishijima, K. Ueno, H. Misawa et al. J. Phys. Chem. Lett. 1, 2031 (2010). Zhong, K. Ueno, Y. Mori, X. Shi, T. Oshikiri, K. Murakoshi, H. Inoue, H. Misawa, Angew. Chem. Int. Ed., 53,10350(2014).Oshikiri, K. Ueno, H. Misawa, Angew. Chem. Int. Ed., 53, 9802 (2014).Oshikiri, K. Ueno, H. Misawa, Angew. Chem. Int. Ed., 55,3942 (2016).Nakamura, T. Oshikiri, K. Ueno, H. Misawa et al. J. Phys. Chem. Lett., 7, 1004 (2016).V. Hoang, K. Hayashi, K. Ueno, H. Misawa et al. Nat. Commun., 8, 771 (2017).Ueno, T. Oshikiri, H. Misawa, ChemPhysChem, 17, 199 (2016).Ueno, T. Oshikiri, Q. Sun, X. Shi, H. Misawa, Chem. Rev., 118, 2955 (2018). Shi, K. Ueno, T. Oshikiri, Q. Sun, K. Sasaki, H. Misawa, Nat Nanotechnol., 13, 953 (2018).Y. Cao, T. Oshikiri, X. Shi, K. Ueno, J. Li, H. Misawa, ChemNanoMat, 5, 1008 (2019).

(Keynote) Dynamics of Electron Transfer in Enhanced Water Splitting Under Modal Strong Coupling Conditions

Metallic nanoparticles such as gold (Au) and silver (Ag) nanoparticles shows light absorption and scattering at the arbitrary wavelength of visible and near-infrared regions based on localized surface plasmon resonances (LSPRs). LSPRs which are collective oscillations of conductive electrons give rise to the enhancement of near-field and are expected as a light harvesting optical antenna for light energy conversion devices We have successfully developed the plasmon-induced artificial photosynthesis systems such as water splitting and ammonia synthesis systems as well as solid-state plasmonic solar cells based on the principle of plasmon-induced charge separation between gold nanoparticles (Au-NPs) and semiconductor.[1]-[6] Recently, the plasmon-induced charge separation has received considerable attention as a novel strategy for solar energy conversion.[7],[8] However, in general Au-NPs loaded semiconductor photoelectrode, the insufficient absorption limits its solar energy conversion efficiency. Aiming at the enhancement of light absorption, in the present study, we apply the principle of modal strong coupling to plasmonic water splitting using Au-NPs/titanium dioxide (TiO2) thin-film/Au-film (ATA) photoelectrode.[9],[10] Furthermore, the dynamics of the hot electron transfer under the modal strong coupling conditions are further studied by transient reflection spectroscopy.Modal strong coupling between the Fabry–Pérot nanocavity mode of the TiO2thin-film/Au-film and the LSPR mode of the Au-NPs is induced when their resonant frequencies overlap. To increase the coupling strength in this modal strong coupling regime, a key feature of the ATA photoelectrode is partially inlaying of Au-NPs into the TiO2nanocavity by several nanometers. Under a three-electrode system measurement with a saturated calomel electrode (SCE) as a reference electrode, a Pt wire as a counter electrode and an electrolyte of KOH (0.1 mol/dm3), we demonstrated that the action spectrum of incident photon to current conversion efficiency (IPCE) exhibited two bands, which almost corresponds to the absorption spectrum of ATA. The IPCE of ATA is extraordinarily enhanced as compared to that of Au-NPs/TiO2photoanode. Most importantly, under the modal strong coupling conditions, the internal quantum efficiency (IQE) of the photocurrent generation is also enhanced at the wavelengths of strong coupling induced hybrid branches. The increase in IQE implies the possibility of increasing the generation of hot electrons in the modal strong coupling regime. The plasmon-induced water splitting using a two-electrode system was also quantitatively measured. To understand the IQE enhancement under the strong coupling conditions, the dynamics of the hot electrons transfer from Au-NPs to TiO2were further explored by transient measurement using a visible pump/infrared probe (at 3500 nm) femtosecond transient reflection spectrometers. An ultrafast hot electrons injection from Au-NPs to TiO2was observed. Interestingly, under the strong coupling conditions, the hot electrons excited in the ATA photoelectrode that fabricated on Al film instead of Au film exhibited a much longer lifetime than that on Au film. The contributions for the long lifetime of the injected electrons to TiO2are also discussed.

Performance of InGaN/GaN Light Emitting Diodes with n-GaN Layer Embedded with SiO2 Nano-Particles

We demonstrate high-performance InGaN/GaN blue light emitting diodes (LEDs) embedded with an air-void layer produced by a dry-etch of nano-pillars in an n-GaN layer grown on patterned sapphire substrate (PSS), filling the space between nano-pillars with SiO2 nano-particles (NPs) and subsequent epitaxial overgrowth. The structure exhibits enhanced output power compared to similarly grown reference conventional LED without the air-void layer. This change in growth procedure contributes to the increase of internal quantum efficiency (IQE) and light extraction efficiency (LEE) resulting in a 13.5% increase of light output. LEE is 2 times more affected than IQE in the modified structure. Simulation demonstrates that the main effect causing the LEE changes is due to the emitted light being confined within the upper space above the air-void layer and thus enhancing the light scattering by the SiO2 NPs and preferential light via front surface.

Fabrication and evaluation of plasmonic light-emitting diodes with thin p-type layer and localized Ag particles embedded by ITO

Light-emitting diodes (LEDs) have been demonstrated with a thin p-type layer using the plasmonic effect. Optimal LED device operation was found when using a 20-nm-thick p+-GaN layer. Ag of different thicknesses was deposited on the thin p-type layer and annealed to form the localized Ag particles. The localized Ag particles were embedded by indium tin oxide to form a p-type electrode in the LED structure. By optimization of the plasmonic LED, the significant electroluminescence enhancement was observed when the thickness of Ag was 9.5 nm. Both upward and downward electroluminescence intensities were improved, and the external quantum efficiency was approximately double that of LEDs without the localized Ag particles. The time-resolved photoluminescence (PL) decay time for the LED with the localized Ag particles was shorter than that without the localized Ag particles. The faster PL decay time should cause the increase in internal quantum efficiency by adopting the localized Ag particles. To validate the localized surface plasmon resonance coupling effect, the absorption of the LEDs was investigated experimentally and using simulations.

Analytical model of front texturization effect on silicon solar cell with porous silicon at the backside

In this work, we proposed a theoretical model and an analytical solution to the complete set of equations needed for determining the effect of the front surface texturization and the multiple-pass light trapping on the performance of an n++/n+/p/p+ solar cell having a porous multi-layer structure at the backside (p+ type). The increase in internal quantum efficiency (IQE), contributions of the different cell regions to IQE, enhancement of conversion efficiency, and effects of multiple-pass light trapping and physical parameters of each region were simulated and evaluated in comparison with n++/n+/p/p+ flat solar cells. Overall, the findings revealed that, for the same physical parameters of the different regions of the solar cells, the textured cells have better IQE and better conversion efficiency than the flat ones. The cell conversion efficiency can be improved by 1.25%. This is due to an increase of the light path offered by a textured structure. Moreover, the effect of multiple-pass light trapping on the IQE is more profound at long wavelength range 0.9–1.15 µm. This effect is almost saturated after four passages for both flat and textured cells.

Dependence of radiative and nonradiative recombination on carrier density and Al content in thick AlGaN epilayers

Dynamics of radiative and nonradiative recombination of non-equilibrium carriers is investigated in thick AlGaN epitaxial layers with Al content ranging from 0.11 to 0.71. The internal quantum efficiency (IQE) in the epilayers was obtained using two approaches: either estimated from PL measurements or calculated using the recombination coefficients of a simple ABC model, retrieved by fitting the kinetics of light induced transient gratings (LITG). At photoexcited carrier densities below ~1019 cm−3, both approaches provided similar IQE values indicating that the simple ABC model is applicable to analyze carrier recombination at such carrier densities. The increase in IQE at higher carrier densities slowed down for the values extracted from PL considerably faster than for those obtained from LITG transients. This discrepancy is explained in terms of the mixed nature of the rate coefficient B caused by the onset of the density-activated nonradiative recombination at high carrier densities.

Bifacial potential of single‐ and double‐sided collecting silicon solar cells

AbstractBifacial applications are a promising way to increase the performance of photovoltaic systems. Two silicon solar cell concepts suitable for bifacial operation are the passivated emitter, rear totally diffused (PERT) and the both sides collecting and contacted (BOSCO) cell concepts. This work investigates the bifacial potential of these concepts by means of in‐depth numerical device simulation and experiment with a focus on the impact of varying material quality. It is shown that the PERT cell concept (representing a structure with front‐side emitter only) requires high‐minority‐carrier‐diffusion‐length substrates with Lbulk > 3 × W (with cell thickness W) to exploit its bifacial potential, while the BOSCO cell (representing a structure with double‐sided emitter) can already utilise its bifacial potential on substrates with significantly lower diffusion lengths down to Lbulk ≈ 0.5 × W. Experimentally, BOSCO cells with and without activated rear‐side emitter are compared. For rear‐side illumination, the activated rear‐side emitter is measured to increase internal quantum efficiency at wavelengths λ < 850 nm by up to 45%abs (factor of 9) and 30%abs (factor of 2) for cells processed on p‐type multicrystalline silicon substrates with Lbulk ≈ 0.3 × W and Lbulk ≈ 2.6 × W, respectively. For PERT cells processed on n‐type Czochralski‐grown silicon substrates, an according increase in internal quantum efficiency for rear‐side illumination of more than 20%abs (factor of 1.3) is measured when changing from a substrate with Lbulk ≈ 3.0 to 10.0 × W. The performed simulations and experiments demonstrate that the BOSCO cell concept is a promising candidate to successfully exploit bifacial gain also on low‐ to medium‐diffusion‐length substrates such as p‐type multicrystalline silicon, while PERT cells require a high‐diffusion‐length substrate to utilise their bifacial potential. Furthermore, the BOSCO cell concept is shown to be a promising option to achieve highest output power densities, even when using lower quality and therefore possibly more cost‐effective silicon substrates. Copyright © 2016 John Wiley & Sons, Ltd.

Solid-state colloidal CuInS2 quantum dot solar cells enabled by bulk heterojunctions.

Colloidal copper indium sulfide (CIS) nanocrystals (NCs) are Pb- and Cd-free alternatives for use as absorbers in quantum dot solar cells. In a heterojunction with TiO2, non-annealed ligand-exchanged CIS NCs form solar cells yielding a meager power conversion efficiency (PCE) of 0.15%, with photocurrents plummeting far below predicted values from absorption. Decreasing the amount of zinc during post-treatment leads to improved mobility but marginal improvement in device performance (PCE = 0.30%). By incorporating CIS into a porous TiO2 network, we saw an overall drastic improvement in device performance, reaching a PCE of 1.16%, mainly from an increase in short circuit current density (Jsc) and fill factor (FF) and a 10-fold increase in internal quantum efficiency (IQE). We have determined that by moving from a bilayer to a bulk heterojunction architecture, we have reduced the trap-assisted recombination as seen in changes in the ideality factor, the intensity dependence of the photocurrent and transient photocurrent (TPC) and photovoltage (TPV) characteristics.

Internal quantum efficiency improvement in polysilicon solar cells with porous silicon layer on the rear side

The present paper reports on a simulation study carried out to determine and optimize the effect of porous silicon (PS) layer at the rear side on the performance of thin polysilicon solar cells. It analytically solved the complete set of equations necessary to determine the contribution that this material has with regard to the internal quantum efficiency (IQE) of the cell when acting as a backside reflector. The contribution of the different regions of the cell, the increase in IQE, and the effects of high porosity and number of PS layers were derived and compared to conventional BSF solar cells. The findings revealed that the IQE of the solar cell with a PS layer at the backside was higher than that of conventional BSF, particularly in terms of medium and long wavelength range λ > 0.5 μm. This improvement was more significant with thin cells, large grain widths, and well-passivated grain boundaries. Furthermore, while the use of the PS layer had a significant effect on the contribution of the base, it exerted no effect on the contribution of the emitter and depletion regions. Overall, the maximum level of IQE improvement was recorded with three double-porosity structures in the PS layer, reaching a high porosity value of about 80 %.

Effect of the Barrier Thickness on the Optical Properties of InGaN/GaN/Al2O3 (0001) LED Heterostructures

The results of numerical and experimental study of the electric field strength, photoluminescence wavelength, and internal quantum efficiency of InGaN/GaN (0001) blue LED heterostructures consisting of InGaN multiple quantum wells and GaN barrier layers with the thicknesses of 3, 10, and 15 nm are presented. It is shown that a decrease in the thicknesses of the GaN barrier layers results in a blue shift of the wavelength of LED structures and in an increase of internal quantum efficiency of the structure at high excitation power density.

Multiscale Modeling of Plasmon-Enhanced Power Conversion Efficiency in Nanostructured Solar Cells.

The unique optical properties of nanometallic structures can be exploited to confine light at subwavelength scales. This excellent light trapping is critical to improve light absorption efficiency in nanoscale photovoltaic devices. Here, we apply a multiscale quantum mechanics/electromagnetics (QM/EM) method to model the current-voltage characteristics and optical properties of plasmonic nanowire-based solar cells. The QM/EM method features a combination of first-principles quantum mechanical treatment of the photoactive component and classical description of electromagnetic environment. The coupled optical-electrical QM/EM simulations demonstrate a dramatic enhancement for power conversion efficiency of nanowire solar cells due to the surface plasmon effect of nanometallic structures. The improvement is attributed to the enhanced scattering of light into the photoactive layer. We further investigate the optimal configuration of the nanostructured solar cell. Our QM/EM simulation result demonstrates that a further increase of internal quantum efficiency can be achieved by scattering light into the n-doped region of the device.

Effects of quantum well growth temperature on the recombination efficiency of InGaN/GaN multiple quantum wells that emit in the green and blue spectral regions

InGaN-based light emitting diodes and multiple quantum wells designed to emit in the green spectral region exhibit, in general, lower internal quantum efficiencies than their blue-emitting counter parts, a phenomenon referred to as the “green gap.” One of the main differences between green-emitting and blue-emitting samples is that the quantum well growth temperature is lower for structures designed to emit at longer wavelengths, in order to reduce the effects of In desorption. In this paper, we report on the impact of the quantum well growth temperature on the optical properties of InGaN/GaN multiple quantum wells designed to emit at 460 nm and 530 nm. It was found that for both sets of samples increasing the temperature at which the InGaN quantum well was grown, while maintaining the same indium composition, led to an increase in the internal quantum efficiency measured at 300 K. These increases in internal quantum efficiency are shown to be due reductions in the non-radiative recombination rate which we attribute to reductions in point defect incorporation.