Effect of p-GaN Layer and High-k Material in InGaN/GaN LED for Optical Performance Enhancement (original) (raw)
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The calculation model of tunneling current through GaN/InGaN/GaN heterostructure in InGaN-based LED using the transfer matrix method employed to verify the result of calculation of tunneling current implemented analytically. The analytical method applied through solving theoretically the Schrödinger equation, whereas, the transfer matrix method divided the solution area into a less size of N segment compared to the observed potential width size, where the potential energy of each segment was assumed constant. Verification employed to the thickness of depletion region and bias voltage variations. The obtained result has shown that the analytical result of calculation simmilar with the calculation result using transfer matrix method. The calculation model was then extended to calculate the tunneling current for different temperature.
Optics Express, 2014
(NPNPN-GaN) junctions embedded between the n-GaN region and multiple quantum wells (MQWs) are systematically studied both experimentally and theoretically to increase the performance of InGaN/GaN light emitting diodes (LEDs) in this work. In the proposed architecture, each thin P-GaN layer sandwiched in the NPNPN-GaN structure is completely depleted due to the built-in electric field in the NPNPN-GaN junctions, and the ionized acceptors in these P-GaN layers serve as the energy barriers for electrons from the n-GaN region, resulting in a reduced electron over flow and enhanced the current spreading horizontally in the n-GaN region. These lead to increased optical output power and external quantum efficiency (EQE) from the proposed device.
Japanese Journal of Applied Physics, 2008
Electroluminescence (EL) efficiency of the InGaN-based light-emitting diode (LED) is the present subject of discussion. An equivalent circuit model was introduced to treat explicitly four independent current components: leakage, radiative, nonradiative, and carrier overflow. This model was used to explain the internal quantum efficiency (IQE) as a function of current, temperature, and material quality. In the low-current range, efficiency became strongly dependent on temperature as leakage and nonradiative recombination currents related to material quality shared a large part of the total current. In the highcurrent range, the reduced efficiency was explained by electron-overflow current. Electron-overflow current was increased by reducing temperature via freeze-out of holes. When leakage current and carrier overflow were suppressed effectively in the intermediate current range on high-quality devices, hole freeze-out was observed experimentally in electroluminescence intensity as temperature was varied.
Efficiency Enhancement of InGaN LEDs With an n-Type AlGaN/GaN/InGaN Current Spreading Layer
IEEE Electron Device Letters, 2011
This letter reports an InGaN light-emitting diode (LED) structure that has an n-type Al 0.1 Ga 0.9 N/GaN/In 0.06 Ga 0.94 N current spreading layer under its multiple-quantum-well active region. As indicated by simulation, the Al 0.1 Ga 0.9 N/GaN/In 0.06 Ga 0.94 N heterostructure induces a higher electron concentration than an n-AlGaN/GaN cladding layer and an n-GaN/InGaN current spreading layer that are used in conventional LEDs. As a result, the proposed n-type spreading layer is expected to alleviate current crowding and improve external quantum efficiency. Experimentally, the light output uniformity across the chips is greatly improved. The output power and wall-plug efficiency are enhanced by about 18.2% and 22.2% at an injection current of 350 mA for the LEDs employing the new double-heterostructure current spreading layer.
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...
Microscopic, electrical and optical studies on InGaN/GaN quantum wells based LED devices
We report here on the micro structural, electronic and optical properties of a GaN-based InGaN/GaN MQW LED grown by the MOVPE method. The present study shows that the threading dislocations present in these LED structures are terminated as V pits at the surface and have an impact on the electrical and optical activity of these devices. It has been pointed that these dislocations were of edge, screw and mixed types. EBIC maps suggest that the electrically active defects are screw and mixed dislocations and behave as nonradiative recombinant centres.
Technical Physics Letters, 2009
It is established that the low frequency noise density S in InGaN/GaN based light emitting diodes (LEDs) operating a current densities j > 20 A/cm 2 depends on the current density as S ~ j 3. This depen dence is indicative of the formation of new nonradiative recombination centers, which may account for a drop in the external quantum efficiency of LEDs operating at high current densities.
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.
Semiconductors, 2011
A comprehensive study of blue light emitting diodes based on quantum well InGaN/GaN struc tures with external quantum efficiencies η of up to 40% has been carried out. It is shown that, in the general case, the manner in which the efficiency depends on the current density j is determined by the competition of contributions to the radiative recombination of localized and delocalized carriers. The contribution of the latter grows with worsening structural organization of the nanomaterial, increasing temperature and drive current, and decreasing width of the depleted layer in the active region (under zero bias). The steepest effi ciency droop relative to the maximum value (by up to a factor of 2 at j ≈ 50 A cm-2) is observed in the case of heavy doping of the n + region (to 10 19 cm-3) and upon appearance of compensated layers in the active or p + region. At j > 50 A cm-2 , the contribution of delocalized carriers is predominant and the current dependences of efficiency are of uniform type, approximated with η(j) ∝ j-b , where 0.2 < b < 0.3.