Optical, structural investigations and band-gap bowing parameter of GaInN alloys (original) (raw)
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Small band gap bowing in In1−xGaxN alloys
Applied Physics Letters, 2002
High-quality wurtzite-structured In-rich In 1-x Ga x N films (0 ≤ x ≤ 0.5) have been grown on sapphire substrates by molecular-beam epitaxy. Their optical properties were characterized by optical absorption and photoluminescence spectroscopy. The investigation reveals that the narrow fundamental bandgap for InN is near 0.8eV and that the bandgap increases with increasing Ga content. Combined with previously reported results on the Ga-rich side, the bandgap versus composition plot for In 1-x Ga x N alloys is well fit with a bowing parameter of ~ 1.4 eV. The direct bandgap of the In 1-x Ga x N system covers a very broad spectral region ranging from near-infrared to near-ultraviolet.
Alloy effects in GaInN/GaN heterostructures
We show that the large band offsets between GaN and InN and the heavy carrier effective masses preclude the use of the Virtual Crystal Approximation to describe the electronic structure of Ga1−xInxN/GaN heterostructures while this approximation works very well for the Ga1−xInxAs/GaAs heterostructures.
Applied Physics Letters, 2002
Using the radio-frequency ͑rf͒ sputtering deposition technique, we have grown GaInN x As 1Ϫx thin films on glass substrates at room temperature. The concentration of nitrogen in the films was found to depend mainly on the rf power used to excite the growth plasma. X-ray diffractograms show that the films have small grain sizes and present a broad diffraction band centered close to the ͑002͒ diffraction peak of hexagonal GaN. Electron dispersive spectroscopy measurements report N concentrations of xϳ0.8 and In concentrations of about 3% indicating that we have grown GaInN x As 1Ϫx alloys in the GaN-rich side. The absorption spectra measured by the photoacoustic technique show that these semiconductor films have band-gap energies ranging between 1.69 and 2.56 eV, when the rf sputtering power is varied in the range 30-80 W. Thus, we show the feasibility to grow GaInN x As 1Ϫx thin films with high N concentrations in which we can tune the band-gap energy in the red-blue portion of the visible spectrum, by a careful control of the growth parameters.
Using large (500-1000 atoms) pseudopotential supercell calculations, we have investigated the effects of atomic short-range order SRO on the electronic and optical properties of dilute and concentrated GaAsN, GaInN, and GaInAs alloys. We find that in concentrated alloys the clustering of like atoms in the first neighbor fcc shell e.g., N-N in GaAsN alloys leads to a large decrease of both the band-gap and the valence-to-conduction dipole transition-matrix element in GaAsN and in GaInN. On the other hand, the optical properties of GaInAs depend only weakly on the atomic SRO. The reason that the nitride alloys are affected strongly by SRO while GaInAs is affected to a much lesser extent is that in the former case there are band-edge wave-function localizations around specific atoms in the concentrated random alloys. The property for such local-ization is already evident at the dilute isolated impurity and impurity-pair limits.
Control of stress and crystalline quality in GaInN films used for green emitters
Journal of Crystal Growth, 2008
We succeeded in growing almost completely relaxed, high-quality, thick GaInN films on an m-plane GaN template with grooves along the /0 0 0 1S direction, using lateral-growth technology. Reciprocal space mapping of asymmetrical X-ray diffraction confirmed almost complete relaxation. By transmission electroscopic characterization, the growth of GaInN film with a threading dislocation density of approximately 1 Â10 8 cm À2 was confirmed.
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.
Positron-annihilation measurements and nuclear reaction analysis utilizing the 14 N(d,p) 15 N and 14 N(d,He) 12 C reactions in conjunction with Rutherford backscattering spectrometry in the channeling geometry were used to study the defects in as-grown GaInNAs materials grown by molecular beam epitaxy using a radio-frequency plasma nitrogen source. Our data unambiguously show the existence of vacancy-type defects, which we attribute to Ga vacancies, and nitrogen interstitials in the as-grown nitride–arsenide epilayers. These point defects, we believe, are responsible for the low luminescence efficiency of as-grown GaInNAs materials and the enhanced diffusion process during annealing.
The short-wavelength edge of intrinsic photoluminescence in diluted GaN x As1 − x alloys
Semiconductors, 2009
The diluted GaN x As 1 -x alloys containing up to several percent of nitrogen are of considerable interest for basic research and applications in devices due to the extremely profound effect of the relatively small content of nitrogen atoms on the band gap of the material. According to the empiric band anticrossing (BAC) model , this effect is due to the fact that the N atom substituting for the As atom forms a highly localized state of symmetry a 1 , with the energy level falling within the conduction band at the energy E N from the top of the valence band. Interaction of this state with delocalized states of the conduction band of the GaAs matrix induces mixing and anticrossing of these states, resulting in some modification of the energy spectrum of the conduction band of the crystal. In the context of the simple model of two energy lev els, whose interaction is treated as a perturbation, it can be found that the conduction band is split into two subbands E ± (k) and the dependence of the energy on the wave vector k in each of the split subbands is described by the expressions defining the energy eigenvalues of an electron in the conduction band [1]: