Compositional Ordering in InxGa1-xN and its influence on optical properties (original) (raw)
Related papers
2000
The effect of In on the structural and optical properties of In x Ga 1-x N/GaN multiple quantum wells (MQWs) was investigated. These were five-period MQWs grown on sapphire by metalorganic chemical vapor deposition. Increasing the In composition caused broadening of the high-resolution x-ray diffraction superlattice satellite peak and the photoluminescence-excitation bandedge. This indicates that the higher In content degrades the interface quality because of nonuniform In incorporation into the GaN layer. However, the samples with higher In compositions have lower room temperature (RT) stimulated (SE) threshold densities and lower nonradiative recombination rates. The lower RT SE threshold densities of the higher In samples show that the suppression of nonradiative recombination by In overcomes the drawback of greater interface imperfection.
Journal of Crystal Growth, 2007
We systematically investigate the compositional inhomogeneity near surface, interface, and dislocation in In x Ga 1Àx N thin films on GaN(0 0 0 1) by using our empirical interatomic potential and the Monte Carlo (MC) method. The compositional inhomogeneity is discussed by evaluating individual contribution such as strain relief at the surface and the interface between In x Ga 1Àx N and GaN with/ without misfit dislocations. The empirical potential calculations reveal that the dislocation core energy for bulk InN (1.51 eV) is smaller than that of GaN (1.81 eV). This suggests that In atoms preferentially reside in the lattice sites near the dislocation core in In x Ga 1Àx N. The MC simulation clarifies that In surface segregation is found in In x Ga 1Àx N thin films pseudomorphically grown on GaN(0 0 0 1), where the surface composition of In is greater than that of bulk In composition because of strain relief and bond energy profit of In atoms at the surface. Further MC simulation for the system including both surface and misfit dislocations implies that the In atoms segregate at the surface strongly while In atoms segregate near the misfit dislocations weakly. r
2008 33rd IEEE Photovolatic Specialists Conference, 2008
The III-nitride material system with band gap ranging from 0.7eV to 6.2eV has substantial potential to develop high-efficiency solar cells. The III-nitride materials are grown by MOCVD on a lattice mismatched sapphire substrate (0001). This paper presents the generation of extended crystalline defects and their spatial distribution in the GaN and In0.12Ga0.88N layers as a function of In0.12Ga0.88N thickness. The material is characterized by photoluminescence, and the primary peak intensity is observed to increase with thickness, up to 200 nm, but the intensity diminishes with further increase in thickness. Additional photoluminescence peaks are observed for In0.12Ga0.88N thicknesses greater than 100 nm. These observations are attributed to extended crystalline defects and are characterized by high resolution x-ray diffraction. A detailed analysis of these extended crystalline defects is presented based on rocking curves, symmetric and asymmetric reciprocal space maps. The crystalline defects are unavoidable during epitaxial growth, but knowledge of their generation process yields better control over them.
Band gaps and lattice parameters of 0.9 μm thick InxGa1−xN films for 0⩽x⩽0.140
Journal of Applied Physics, 2002
The c 0 lattice parameter, band gap, and photoluminescence spectra of n-type 0.9 m thick In x Ga 1Ϫx N films with xϭ0, 0.045, 0.085, and 0.140 were examined. The c 0 lattice parameter followed Vegard's law using c 0 ϭ0.5185 nm for GaN and c 0 ϭ0.569 nm for InN. Band gap measurements by photocurrent spectroscopy fit well with data published by one other research group, with the combined set being described by the equation E g ϭ3.41Ϫ7.31xϩ14.99x 2 for 0 рxр0.15. Photoluminescence measurements with a pulsed nitrogen laser showed a peak well below the measured band gap, as well as significant luminescence above the measured band gap. The above-gap luminescence appears to be due to band filling by the high intensity laser pulses.
Microscopy and Microanalysis, 2013
The growth of high-quality indium (In)-rich InXGa1−XN alloys is technologically important for applications to attain highly efficient green light-emitting diodes and solar cells. However, phase separation and composition modulation in In-rich InXGa1−XN alloys are inevitable phenomena that degrade the crystal quality of In-rich InXGa1−XN layers. Composition modulations were observed in the In-rich InXGa1−XN layers with various In compositions. The In composition modulation in the InXGa1−XN alloys formed in samples with In compositions exceeding 47%. The misfit strain between the InGaN layer and the GaN buffer retarded the composition modulation, which resulted in the formation of modulated regions 100 nm above the In0.67Ga0.33N/GaN interface. The composition modulations were formed on the specific crystallographic planes of both the {0001} and {0114} planes of InGaN.
2009
InGaN based, blue and green light emitting diodes (LEDs) have been successfully produced over the past decade. But the progress of these LEDs is often limited by the fundamental problems of InGaN such as differences in lattice constants, thermal expansion coefficients and physical properties between InN and GaN. This difficulty could be addressed by studying pure InN and In x Ga 1-x N alloys. In this context Ga-rich In x Ga 1-x N (x≤ 0.4) epilayers were grown by metal organic chemical vapor deposition (MOCVD). X-ray diffraction (XRD) measurements showed In x Ga 1-x N films with x= 0.37 had single phase. Phase separation occurred for x ~ 0.4. To understand the issue of phase separation in Ga-rich In x Ga 1-x N, studies on growth of pure InN and In-rich In x Ga 1-x N alloys were carried out. InN and In-rich In x Ga 1-x N (x~0.97-0.40) epilayers were grown on AlN/Al 2 O 3 templates. A Hall mobility of 1400 cm 2 /Vs with a carrier concentration of 7x10 18 cm-3 was observed for InN epilayers grown on AlN templates. Photoluminescence (PL) emission spectra revealed a band to band emission peak at ~0.75 eV for InN. This peak shifted to 1.15 eV when In content was varied from 1.0 to 0.63 in In-rich In x Ga 1-x N epilayers. After growth parameter optimization of In-rich In x Ga 1-x N alloys with (x= 0.97-0.40) were successfully grown without phase separation. Effects of Mg doping on the PL properties of InN epilayers grown on GaN/Al 2 O 3 templates were investigated. An emission line at ~ 0.76 eV, which was absent in undoped InN epilayers and was about 60 meV below the band edge emission peak at ~ 0.82 eV, was observed to be the dominant emission in Mg-doped InN epilayers. PL peak position and the temperature dependent emission intensity corroborated each other and suggested that Mg acceptor level in InN is about 60 meV above the valance band maximum. Strain effects on the emission properties of InGaN/GaN multiple quantum wells (MQWs) were studied using a single blue LED wafer possessing a continuous variation in compressive strain. EL emission peak position of LEDs varies linearly with the biaxial strain; a coefficient of 19 meV/GPa, characterizes the relationship between the band gap energy and biaxial stress of In 0.2 Ga 0.8 N/GaN MQWs.
V-defects and dislocations in InGaN/GaN heterostructures
Thin Solid Films, 2005
In the growth of InGaN/GaN multi-quantum well (MQW) heterostructures by metal organic chemical vapor deposition, V-defects attached to threading dislocations have been observed and investigated. Energy-dispersive X-ray analysis and conventional transmission electron microscopy studies were carried out in order to determine the In composition and investigate the behavior of the dislocations. The Vdefects are limited by {1011} lattice planes, they are attached to threading dislocations and may start at the third quantum well. The associated dislocation runs up into the overgrown GaN layer. Some (a+c) dislocations were shown to decompose inside the multi-quantum well, giving rise to a misfit segment in the c-plane and a V-shape defect. D