Nitride-based green light-emitting diodes with high temperature GaN barrier layers (original) (raw)
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Nitride-Based Green Light-Emitting Diodes With Various p-Type Layers
IEEE/OSA Journal of Display Technology, 2007
High-quality InGaN-GaN multiquantum well (MQW) light-emitting diode (LED) structures were prepared by temperature ramping method during metalorganic chemical vapor deposition (MOCVD) growth. It was found that we could reduce the 20-mA forward voltage and increase the output intensity of the nitride-based green LEDs by increasing the growth temperature of GaN barrier layers from 700 C to 950 C. The 20-mA output power and maximum output power of the nitride-based green LEDs with high temperature GaN barrier layers was found to be 2.2 and 8.9 mW, respectively, which were more than 65% larger than those observed from conventional InGaN-GaN green LEDs. Such an observation could be attributed to the improved crystal quality of GaN barrier layers. The reliability of these LEDs was also found to be reasonably good.
400-nm InGaN-GaN and InGaN-AlGaN multiquantum well light-emitting diodes
IEEE Journal of Selected Topics in Quantum Electronics, 2002
Rcenctly, tremendous progress has been achieved in GaN-based blue and green lightemitting diodes (LEDs). These blue/green LEDs have already been extensively used in fullcolor displays and high-efficient light sources for traffic light lamps. Although these blue/ green LEDs are already commercially available, it is still difficult to achieve LEDs emitting at even shorter wavelength regions, such as ultraviolet (UV) region. Short wavelength emitters are of interest for various fluorescence-based chemical sensing applications, high efficiency lighting, flame detection, and possibly optical storage applications. Conventional nitridebased multiquantum well (MQW) LEDs use InGaN as the material for well layers and GaN as the material for barrier layers. To achieve a short wavelength emitter, one needs to reduce the indium composition in the well layers so as to increase its bandgap energy. However, a reduction in indium composition in the well layers will result in a small bandgap discontinuity at the well/barrier interfaces. Thus, the quantum well depth in the MQW active region will become smaller and the carrier confinement effect will be reduced. As a result, severe carrier leakage problem might occur in the short wavelength InGaN-GaN MQW LEDs. One possible way to solve this problem is to use AlGaN or AlGaInN as the barrier layers instead of GaN. The quaternary AlGaInN permits an extra degree of freedom by allowing independent control of the bandgap and lattice constant. Thus, the use of quaternary AlGaInN for barrier layers could potentially offer better carrier confinement while minimizing lattice mismatch issues. However, it is much more difficult to grow high-quality AlGaInN than AlGaN. Since the bandgap energy of AlGaN is also larger than that of GaN, InGaN-AlGaN MQW should still be able to provide a better carrier confinement, as compared to InGaN-GaN MQW. Also, since the lattice constant of AlGaN is smaller while the lattice constant of InGaN is larger than that of GaN base layer, it is possible to achieve a strain compensated InGaN-AlGaN MQW on GaN with proper composition ratios in InGaN and AlGaN layers. As a result, we could increase the effective MQW critical thickness, and thus reduce the probability of relaxation occurred within the MQW active region. In this study, InGaN-GaN LED and InGaN-AlGaN LED will both be fabricated. The optical and electrical properties of these LEDs will be reported.
Journal of Luminescence, 2012
Thermal effects on the optoelectrical characteristics of green InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) have been investigated in detail for a broad temperature range, from 30 1C to 100 1C. The current-dependent electroluminescence (EL) spectra, current-voltage (I-V) curves and luminescence intensity-current (L-I) characteristics of green InGaN/GaN MQW LEDs have been measured to characterize the thermal-related effects on the optoelectrical properties of the InGaN/GaN MQW LEDs. The experimental results show that both the forward voltages decreased with a slope of À 3.7 mV/K and the emission peak wavelength increased with a slope of þ 0.02 nm/K with increasing temperature, indicating a change in the contact resistance between the metal and GaN layers and the existence of a band gap shrinkage effect. The junction temperature estimated from the forward voltage and the emission peak shift varied from 25.6 to 14.5 1C and from 22.4 to 35.6 1C, respectively. At the same time, the carrier temperature decreased from 371.2 to 348.1 1C as estimated from the slope of high-energy side of the emission spectra. With increasing injection current, there was found to be a strong current-dependent blueshift of À 0.15 nm/mA in the emission peak wavelength of the EL spectra. This could be attributed to not only the stronger band-filling effect but also the enhanced quantum confinement effect that resulted from the piezoelectric polarization and spontaneous polarization in InGaN/GaN heterostructures. We also demonstrate a helpful and easy way to measure and calculate the junction temperature of InGaN/GaN MQW LEDs.
Journal of Electronic Materials, 2006
We investigated the electrical and structural qualities of Mg-doped p-type GaN layers grown under different growth conditions by metalorganic chemical vapor deposition (MOCVD). Lower 300 K free-hole concentrations and rough surfaces were observed by reducing the growth temperature from 1,040°C to 930°C. The hole concentration, mobility, and electrical resistivity were improved slightly for Mg-doped GaN layers grown at 930°C with a lower growth rate, and also an improved surface morphology was observed. In0.25Ga0.75N/GaN multiple-quantum-well light emitting diodes (LEDs) with p-GaN layers grown under different conditions were also studied. It was found from photoluminescence studies that the optical and structural properties of the multiple quantum wells in the LED structure were improved by reducing the growth temperature of the p-layer due to a reduced detrimental thermal annealing effect of the active region during the GaN:Mg p-layer growth. No significant difference in the photoluminescence intensity depending on the growth time of the p-GaN layer was observed. However, it was also found that the electroluminescence (EL) intensity was higher for LEDs having p-GaN layers with a lower growth rate. Further improvement of the p-GaN layer crystalline and structural quality may be required for the optimization of the EL properties of long-wavelength (∼540 nm) green LEDs.
Temperature-dependent light-emitting characteristics of InGaN/GaN diodes
Microelectronics Reliability, 2009
Temperature-dependent light-emitting and current-voltage characteristics of multiple-quantum well (MQW) InGaN/GaN blue LEDs were measured for temperature ranging from 100 to 500 K. The measurement results revealed two kinds of defects that have pronounced impact on the electroluminescent (EL) intensity and device reliability of the LEDs. At low-temperature (<150 K), in addition to the carrier freezing effect, shallow defects such as nitrogen vacancies or oxygen in nitrogen sites can trap the injected carriers and reduces the EL intensity. At high temperature (>300 K), deep traps due to the structure dislocations at the interfaces significantly reduce the efficiency for radiative recombination though they can enhance both forward and reverse currents significantly. In addition, the significant enhancement of trap-assisted tunneling current causes a large heat dissipation and results in a large redshift of the emission peak at high temperature.
Materials Science in Semiconductor Processing, 2021
This work presents an interesting observation on a possible growth regime transition from diffusion-limited to desorption-limited at Multi-Quantum Well (MQW) growth structure. In common practices, this transition is normally observed by increasing the growth temperature. However, in this work, this phenomenon is noticed by increasing the V/III ratio during the Indium Gallium Nitride/Gallium Nitride (InGaN/GaN) MQW growth process. By increasing the nitrogen (N)-precursors, the V/III of MQW growth structure was varied at three different ratios of 5109, 6387 and 7664 respectively. The X-ray Diffraction (XRD) peaks measured on these three devices reveals the highest Indium (In) incorporation of ~11.2% is obtained at 5109 ratios followed by 6387 ratios with ~5.0% and ~0.0% incorporation for 7664 ratios. Additionally, the EDX mapping also discloses the presence of In element on the p-GaN surface and it reduces significantly with the increase of the MQW V/III ratios. This trend implies the MQW growth process was occurred under diffusion-limited regime, which also affects the p-GaN upper layer. However, XRD results shows that the increment of MQW V/III ratios depreciates the MQW thicknesses, which manifests that the growth condition changed to metal-limited or N-rich regime, where the important reactants start to desorb from the sample. This leads to the low growth rate of InGaN/GaN layer and degrades the devices performance. The blue shift of InGaN peaks in photoluminescence spectra has support the notion of In reduction at high MQW V/III ratios. At 20 mA, the devices of 5109 and 6387 ratios with a forward voltage of 3.57 V and 3.95 V produce electroluminescence peak at 443.74 nm and 487.45 nm, respectively. Despite the 5109 sample exhibits the highest In percentage, green speckles were produced at low optical threshold voltage due to the proliferation of localization states induced by the In clusters. The device also experiences the higher reverse current leakage compared to 6387 device due to higher threading dislocation density.
Applied Physics Letters, 2010
We report on Mg doping in the barrier layers of InGaN/GaN multiple quantum wells (MQWs) and its effect on the properties of light-emitting diodes (LEDs). Mg doping in the barriers of MQWs enhances photoluminescence intensity, thermal stability, and internal quantum efficiency of LEDs. The light output power of LEDs with Mg-doped MQW barriers is higher by 19% and 27% at 20 and 200 mA, respectively, than that of LEDs with undoped MQW barriers. The improvement in output power is attributed to the enhanced hole injection to well layers in MQWs with Mg-doped barriers.
Light-emitting devices (LEDs) with higher performance, lower energy demand and minimal environmental impact are needed. With wide-band gaps and high emission efficiencies, III-V nitride semiconductors are useful for LEDs in short-wavelength regions. A multiple quantum well (MQW LED), based on InGaN/GaN, is proposed. The structure involves GaN(n)/InxGa1−xN(i)/GaN(i)/AlGaN(p)/GaN(p), where GaN(n) and GaN(p) have different dopants to formulate the junction at which electric field occurs, InxGa1−xN(i) is a 3 nm-thick intrinsic quantum well with (x) as indium mole fraction, GaN(i) is barrier intrinsic layer and AlGaN(p) is a 15 nm-thick electron blocking layer (EBL). Simulation is performed by Tcad-Silvaco. Various characteristics such as current versus voltage (I-V) plots, luminosity power, band diagram, spectrum response, radiative recombination rate and electric field effect, have been investigated. By controlling the InxGa1−xN(i) number of quantum wells and their indium mole fraction...
Luminescence studies on green emitting InGaN/GaN MQWs implanted with nitrogen
Scientific reports, 2015
We studied the optical properties of metalorganic chemical vapour deposited (MOCVD) InGaN/GaN multiple quantum wells (MQW) subjected to nitrogen (N) implantation and post-growth annealing treatments. The optical characterization was carried out by means of temperature and excitation density-dependent steady state photoluminescence (PL) spectroscopy, supplemented by room temperature PL excitation (PLE) and PL lifetime (PLL) measurements. The as-grown and as-implanted samples were found to exhibit a single green emission band attributed to localized excitons in the QW, although the N implantation leads to a strong reduction of the PL intensity. The green band was found to be surprisingly stable on annealing up to 1400°C. A broad blue band dominates the low temperature PL after thermal annealing in both samples. This band is more intense for the implanted sample, suggesting that defects generated by N implantation, likely related to the diffusion/segregation of indium (In), have been o...