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1.
Strain-compensated InGaN quantum well (QW) active region employing tensile AlGaN barrier is analyzed. Its spectral stability and efficiency droop for dual-blue light-emitting diode (LED) are improved compared with those of the conventional InGaN/GaN QW dual-blue LED based on stacking structure of two In0.18Ga0.82N/GaN QWs and two In0.12Ga0.88N/GaN QWs on the same sapphire substrate. It is found that the optimal performance is achieved when the Al composition of strain-compensated AlGaN layer is 0.12 in blue QW and 0.21 in blue-violet QW. The improvement performance can be attributed to the strain-compensated InGaN-AlGaN/GaN QW that can provide a better carrier confinement and effectively reduce leakage current.  相似文献   

2.
The semi-empirical tight-binding (TB) approach with an sp3s* orbital basis is used to investigate the electronic band structure of cubic Ga1-xAlxN and Ga1-xInxN alloys. The spin–orbit splitting in the Hamiltonian and first- and second-neighbour interactions are considered to explore the gap evolution as a function of the concentration x. The TB parameters used in the studies were obtained within the virtual crystal approximation using those of the binary compounds AlN, GaN, and InN. The binary parameters are calculated by applying an empirical TB Hamiltonian taking into account first- and second-neighbour interactions. A direct to indirect gap transition is obtained for Ga1-xAlxN at x=0.60. In contrast, the Ga1-xInxN alloys exhibit direct-gap characteristics as a consequence of being formed by the direct-gap binary compounds GaN and InN. PACS 71.20.Nr; 71.23.-k; 71.55.Eq  相似文献   

3.
Al0.31Ga0.69N/AlN/GaN/InxGa1?xN/GaN heterostructures grown with the metal-organic chemical vapor deposition (MOCVD) technique with different InxGa1?xN back-barriers with In mole fractions of 0.05 ≤ x ≤ 0.14 were investigated by using XRD measurements. Screw, edge, and total dislocations, In mole fraction of back-barriers, Al mole fraction, and the thicknesses of front-barriers and lattice parameters were calculated. Mixed state dislocations with both edge and screw type dislocations were observed. The effects of the In mole fraction difference in the back-barrier and the effect of the thickness of front-barrier on crystal quality are discussed. With the increasing In mole fraction, an increasing dislocation trend is observed that may be due to the growth temperature difference between ultrathin InxGa1?xN back-barrier and the surrounding layers.  相似文献   

4.
The effect of built-in-polarization (BIP) field on thermal properties of InxGa1−xN/GaN heterostructure has been investigated. The thermal conductivity k of InxGa1−xN alloy has been estimated using Callaway's formula including the BIP field for In content x = 0, 0.1, 0.3, 0.5 and 0.9. This study reports that irrespective of In content, the room temperature k of InxGa1−xN/GaN heterostructure is enhanced by BIP field. The result predicts the existence of a characteristic temperature Tp at which both thermal conductivities (including and excluding BIP field) show a crossover. This gives signature of pyroelectric nature of InxGa1−xN alloy which arises due to variation of polarization with temperature indicating that thermal conductivity measurement can reveal pyroelectric nature. The pyroelectric transition temperature of InxGa1−xN alloy has been predicted for various x. The composition dependent nature of room temperature k for x = 0.1 and 0.5 are in line with prior experimental studies. The result can be used to minimize the self heating effect in InxGa1−xN/GaN heterostructures.  相似文献   

5.
In this report, we designed a light emitting diode (LED) structure in which an N-polar p-GaN layer is grown on top of Ga-polar In0.1Ga0.9N/GaN quantum wells (QWs) on an n-GaN layer. Numerical simulation reveals that the large polarization field at the polarity inversion interface induces a potential barrier in the conduction band, which can block electron overflow out of the QWs. Compared with a conventional LED structure with an Al0.2Ga0.8N electron blocking layer (EBL), the proposed LED structure shows much lower electron current leakage, higher hole injection, and a significant improvement in the internal quantum efficiency (IQE). These results suggest that the polarization induced barrier (PIB) is more effective than the AlGaN EBL in suppressing electron overflow and improving hole transport in GaN-based LEDs.  相似文献   

6.
《Current Applied Physics》2015,15(5):608-616
The state-of-the-art all-electron FLPAW method and the BoltzTrap software package based on semi-classical theory were adopted to explore the electronic structure and the optical and thermoelectric properties of Ga1−xInxN. Ga1−xInxN is predicted to be a direct band gap material for all values of x. Moreover, the band gap varies between 2.99 eV and 1.95 eV as x changes. Optical parameters such as the dielectric constant, absorption coefficient, reflectivity and refractive index are calculated and discussed in detail. The doping of In plays an important role in the modulation of the optical constants. The static dielectric constant ɛ(0) of Ga1−xInxN was calculated as 3.95, 3.99, 3.99 and 4.03 at x = 0.00, 0.25, 0.50 and 0.75, respectively. The static refractive index is 2.0 for pure Ga1−xInxN at x = 0.00. The thermal properties varied greatly as x fluctuated. The ternary alloy has large values for the Seebeck coefficient and figure of merit at high temperatures and is thus suitable for thermoelectric applications. Pure Ga1−xInxN at x = 0 exhibited ZT = 0.80 at room temperature, and at higher temperatures, the thermal conductivity decreased with increased In doping.  相似文献   

7.
The physical mechanisms leading to the efficiency droop of InGaN/GaN light-emitting diodes (LEDs) are theoretically investigated. We first discuss the effect of Auger recombination loss on efficiency droop by taking different Auger coefficients into account. It is found that the Auger recombination process plays a significant nonradiative part for carriers at typical LED operation currents when the Auger coefficient is on the order of 10−30 cm6 s−1. Furthermore, the InGaN/GaN multiple-quantum-well (MQW) LEDs with varied indium compositions in InGaN quantum wells are studied to analyze the wavelength-dependent efficiency droop. The simulation results show that the wavelength-dependent efficiency droop is caused by several different effects including non-uniform carrier distribution, electron overflow, built-in electrostatic field induced by spontaneous and piezoelectric polarization, and Auger recombination loss. These internal physical mechanisms are the critical factors resulting in the wavelength-dependent efficiency droop in InGaN/GaN MQW LEDs.  相似文献   

8.
用X射线衍射(XRD)技术和显微Raman散射方法对金属有机化学气相沉积(MOCVD)法生长的六方相InxGa1-xN薄膜样品进行了研究,观察到了相分离现象和LO声子-等离子耦合模(LPP+),讨论了InxGa1-xN的A1(LO)模被屏蔽的主要物理机制.同时,对Raman谱中E2和A1(TO)声子模进行了分析和讨论.在InxGa1-xN样品的低温Raman谱中还观察到单电子跃迁产生的Raman散射信号. 关键词: Raman散射 X射线衍射 相分离 应力 LO声子-等离子耦合  相似文献   

9.
《Current Applied Physics》2010,10(3):838-841
The low-temperature conductivity of InxGa1−xN alloys (0.06  x  0.135) is analyzed as a function of indium composition (x). Although our InxGa1−xN alloys were on the metallic side of the metal–insulator transition, neither the Kubo-Greenwood nor Born approach were able to describe the transport properties of the InxGa1−xN alloys. In addition, all of the InxGa1−xN alloys took place below the Ioeffe–Regel regime with their low conductivities. The observed behavior is discussed in the framework of the scaling theory. With decreasing indium composition, a decrease in thermal activation energy is observed. For the metal–insulator transition, the critical indium composition is obtained as xc = 0.0543 for InxGa1−xN alloys.  相似文献   

10.
宋杰  许福军  黄呈橙  林芳  王新强  杨志坚  沈波 《中国物理 B》2011,20(5):57305-057305
The temperature dependence of carrier transport properties of AlxGa1-xN/InyGa1-yN/GaN and AlxGa1-xN/GaN heterostructures has been investigated.It is shown that the Hall mobility in Al0.25Ga0.75N/In0.03Ga0.97N/GaN heterostructures is higher than that in Al0.25Ga0.75N/GaN heterostructures at temperatures above 500 K,even the mobility in the former is much lower than that in the latter at 300 K.More importantly,the electron sheet density in Al0.25Ga0.75N/In0.03Ga0.97N/GaN heterostructures decreases slightly,whereas the electron sheet density in Al0.25Ga0.75N/GaN heterostructures gradually increases with increasing temperature above 500 K.It is believed that an electron depletion layer is formed due to the negative polarization charges at the InyGa1-yN/GaN heterointerface induced by the compressive strain in the InyGa1-yN channel,which e-ectively suppresses the parallel conductivity originating from the thermal excitation in the underlying GaN layer at high temperatures.  相似文献   

11.
The effects of the In-mole fraction (x) of an InxGa1−xN back barrier layer and the thicknesses of different layers in pseudomorphic AlyGa1−yN/AlN/GaN/InxGa1−xN/GaN heterostructures on band structures and carrier densities were investigated with the help of one-dimensional self-consistent solutions of non-linear Schrödinger-Poisson equations. Strain relaxation limits were also calculated for the investigated AlyGa1−yN barrier layer and InxGa1−xN back barriers. From an experimental point of view, two different optimized structures are suggested, and the possible effects on carrier density and mobility are discussed.  相似文献   

12.
Two ultraviolet InGaN/GaN light emitting diodes (LEDs) with and without InGaN underlying layer beneath the multiple quantum wells (MQWs) were grown by metal-organic vapor phase epitaxy. Based on the photoluminescence excitation measurements, it was found that the Stokes shift of the sample with a 10-nm-thick In0.1Ga0.9N underlying layer was about 64 meV, which was smaller than that of the reference sample without InGaN underlying layer, indicating a reduced quantum-confined Stark effect (QCSE) due to the decrease of the piezoelectric polarization field in the MQWs. In addition, by fitting the photon energy dependence of carrier lifetime values, the radiative recombination lifetime of the sample with and without InGaN underlying layer were obtained about 1.22 and 1.58 ns at 10?K, respectively. The shorter carrier lifetime also confirmed that the QCSE in the MQWs was weakened after inserting the InGaN underlying layer. In addition, although the depth of carrier localization in the sample with InGaN underlying layer became smaller, the nonradiative recombination centers (NRCs) inside it decreased, and thus suppressed the nonradiative recombination process significantly according to the electroluminescence measurement results. Compared to the reference sample, the efficiency droop behavior was delayed in the sample with InGaN underlying layer and the droop effect was also effectively alleviated. Therefore, the enhanced light-emission efficiency of ultraviolet InGaN/GaN MQW LEDs could be attributed to the decrease of QCSE and NRCs.  相似文献   

13.
The aim of this work is to analyze theoretically the correlation energies, for neutral, positive and negative excitons and bi-excitons in the III–V nitride InxGa1−xN/GaN quantum dot; where x=17.5% denotes the indium concentration. So, we propose a model consistent with experimental observations that is small InxGa1−xN truncated pyramids with circular base lying on wetting layer, both buried into GaN matrix. The correlation energies of many-body complexes X, X, X+ and XX are investigated as a function of the quantum dot radius rc and the intrinsic electric field.  相似文献   

14.
We have calculated the spectral regime of subband transitions in AlxGa1−xN/GaN and AlxGa1−xN/InN single quantum wells. We used a simplified model to account for the internal electric fields, which modify the shape of the quantum well. Some of the parameters for these materials have not yet been firmly established. Therefore, we carried out the analysis for the extremes of the reported values of conduction band discontinuities and band gaps (in the case of InN). This analysis shows that the spectral regime of interband transitions for 1–4 nm thick wells has wavelengths above 0.5 μm for AlGaN/InN and above 0.8 μm for AlGaN/GaN and both heterostructures cover several μm wavelengths. The spectral variation with alloy composition is less pronounced in the AlxGa1−xN/InN single quantum wells due to the higher electric field present across the InN quantum well as compared to GaN. The results of these calculations are in good agreement with more rigorous theoretical approaches and available experimental values for AlxGa1−xN/GaN.  相似文献   

15.
Electrical characteristics of In0.05 Ga0.95N/Al0.07Ga0.9aN and In0.05 Ga0.95N/GaN multiple quantum well (MQW) ultraviolet light-emltting diodes (UV-LEDs) at 400hm wavelength are measured. It is found that for InGaN/AlGaN MQW LEDs, both ideality factor and parallel resistance are similar to those of InGaN/GaN MQW LEDs, while series resistance is two times larger. It is suggested that the Al0.07Ga0.93N barrier layer did not change crystal quality and electrical characteristic of p-n junction either, but brought larger series resistance. As a result, InGaN/AlGaN MQW LEDs suffer more serious thermal dissipation problem although they show higher light output efficiency.  相似文献   

16.
In this work, the structure of InxGa1−xN/GaN quantum dots solar cell is investigated by solving the Schrödinger equation in light of the Kronig-Penney model. Compared to p-n homojunction and heterojunction solar cells, the InxGa1−xN/GaN quantum dots intermediate band solar cell manifests much larger power conversion efficiency. Furthermore, the power conversion efficiency of quantum dot intermediate band solar cell strongly depends on the size, interdot distance and gallium content of the quantum dot arrays. Particularly, power conversion efficiency is preferable with the location of intermediate band in the middle of the potential well.  相似文献   

17.
The effect of the indium (In) composition of InxGa1−xN (GaN) waveguide layers on the performance of deep violet In0.082Ga0.918N/GaN double quantum well (DQW) laser diodes (LDs) emitting at 390 nm output emission wavelength has been numerically investigated. Simulation results indicated that by increasing In composition of the InxGa1−xN waveguide layers, the threshold current decreases, the slope efficiency, and differential quantum efficiency (DQE) increase, whereas the output power decreases. The increase in the In composition of the InGaN waveguide layers increases the refractive index and consequently increases the optical confinement factor (OCF) which result in the increase in the slope efficiency and DQE and the decrease in the threshold current. The decreasing movement of electron and hole carriers from the bulk waveguide layers to the active regions also causes to decrease the output power. A new LD structure with InGaN/GaN superlattice (SL) waveguide layers has been proposed to exploit the increased OCF of InGaN waveguide structures, and the enhanced electron and hole mobilities and the tunneling effect of the periodic structure of the SL structures. The results also showed that the use of InGaN/GaN SL waveguide structures effectively improves the output power, slope efficiency and DQE and decreases the threshold current of the LD compared with (In)GaN bulk waveguide structure.  相似文献   

18.
Light emitting diodes (LEDs) based on GaN/InGaN material suffer from efficiency droop at high current injection levels. We propose multiple quantum well (MQW) GaN/InGaN LEDs by optimizing the barrier thickness and high–low–high indium composition to reduce the efficiency droop. The simulation results reflect a significant improvement in the efficiency droop by using barrier width of 10 nm and high–low–high indium composition in MQW LED.  相似文献   

19.
In this work, we present a second nearest neighbour sp3s* semi-empirical tight-binding theory to calculate the electronic band structure of heterostructures based on group III-N binary semiconductors and their ternaries. The model Hamiltonian includes the second nearest neighbour (2nn) interactions, the spin–orbit splitting and the nonlinear variations of the atomic energy levels and the bond length with ternary mole fraction. Using this sp3s* tight-binding approach, we investigated the electronic band structure of Al1−xGaxN/GaN and In1−xGaxN/GaN heterostructures as a function of composition and interface strain for the entire composition range (0≤x≤1). There is an excellent agreement between the model predictions and experiment for the principal bandgaps at Γ, L and X symmetry points of the Brillouin zone for AlN, GaN and InN binaries and Al1−xGaxN and In1−xGaxN ternaries. The model predicts that the composition effects on the valence band offsets is linear, but on the conduction band offsets is nonlinear and large when the interface strain and deformation potential is large.  相似文献   

20.
The aluminium gallium nitride (AlGaN) barrier thickness dependent trapping characteristic of AlGaN/GaN heterostructure is investigated in detail by frequency dependent conductance measurements. The conductance measurementsin the depletion region biases (−4.8 V to −3.2 V) shows that the Al0.3Ga0.7N(18 nm)/GaN structure suffers from both the surface (the metal/AlGaN interface of the gate region) and interface (the AlGaN/GaN interface of the channel region) trapping states, whereas the AlGaN/GaN structure with a thicker AlGaN barrier (25 nm) layer suffers from only interface (the channel region of AlGaN/GaN) trap energy states in the bias region (−6 V to −4.2). The two extracted time constants of the trap levels are (2.6–4.59) μs (surface) and (113.4–33.8) μs (interface) for the Al0.3Ga0.7N(18 nm)/GaN structure in the depletion region of biases (−4.8 V to −3.2 V), whereas the Al0.3Ga0.7N (25 nm)/GaN structure yields only interface trap states with time constants of (86.8–33.3) μs in the voltage bias range of −6.0 V to −4.2 V. The extracted surface trapping time constants are found to be very muchless in the Al0.3Ga0.7N(18 nm)/GaN heterostructure compared to that of the interface trap states. The higher electric field formation across the AlGaN barrier causes de-trapping of the surface trapped electron through a tunnelling process for the Al0.3Ga0.7N(18 nm)/GaN structure, and hence the time constants of the surface trap are less.  相似文献   

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