GaInN Alloys Research Articles

Compositional effects on structural, electronic, elastic, piezoelectric and dielectric properties of GaInN alloys: a first-principles study.

We conduct a comprehensive theoretical analysis of wurtzite GaxIn1-xN ternary alloys, focusing on their structural, electronic, elastic, piezoelectric, and dielectric properties through rigorous first-principles calculations. Our investigation systematically explores the influence of varying Ga composition (x = 0%, 25%, 50%, 75%, 100%) on the alloy properties. Remarkably, we observe a distinctive non-linear correlation between the band gap and Ga concentration, attributable to unique slopes in the absolute positions of the valence band maximum and conduction band minimum with respect to Ga concentration. Our effective band structure analysis reveals the meticulous preservation of Bloch characters near band extrema, minimizing charge carrier scattering. Furthermore, we scrutinize deviations from linear Vegard-like dependence in elastic, piezoelectric, and dielectric constants. Additionally, our calculations encompass various optical properties, including absorption coefficient, reflectivity, refractive index, energy loss function, and extinction coefficient. We analyze their trends with photon energy, providing valuable insights into the optical behavior of GaxIn1-xN alloys. Our results, in excellent agreement with available experimental data, significantly contribute to a deeper understanding of the alloys' electronic properties. This study offers valuable insights that may illuminate potential applications of GaxIn1-xN alloys in diverse technological fields.

Frontispiece: GaN and GaxIn1−xN Nanoparticles with Tunable Indium Content: Synthesis and Characterization

Optoelectronic Devices A captivating peculiarity of GaInN alloys is a tunable band gap, depending on the Ga/In ratio, where the pure nitrides are bright yellow (GaN) or dark blue (InN). Gax In1-x N nanoparticles were prepared by a bottom-up approach (the urea glass route). The incorporation of an increasing amount of indium in the GaN structure is indicated by different colors (i.e., different band gaps), and the alloys are further investigated by TEM and optical microscopy. More information can be found in the Full Paper by C. Giordano et al. on page 18976 ff.

Study of wurtzite and zincblende GaN/InN based solar cells alloys: First-principles investigation within the improved modified Becke–Johnson potential

Wurtzite GaInN alloys with flexible energy gaps are pronounced for their potential applications in optoelectronics and solar cell technology. Recently the unwanted built-in fields caused by spontaneous polarization and piezoelectric effects in wurtzite (WZ) GaInN, has turned the focus towards zinc-blende (ZB) GaInN alloys. To comprehend merits and demerits of GaInN alloys in WZ and ZB structures, we performed a comparative study of the structural, electronic and optical properties of Ga1−xInxN alloys with different In concentration using first-principles methodology with density function theory with generalized gradient approximations (GGA) and modified Becke–Johnson (mBJ) potential. Investigations pertaining to total energy of GaInN for the both phases, demonstrate a marginal difference, reflecting nearly equivalent stability of the ZB–GaInN to WZ–GaInN. The larger ionic radii of indium (In), result in larger values of lattice parameters of Ga1−xInxN with higher In concentration. For In deficient Ga1−xInxN, at first, the formation enthalpies increase rapidly as the In content approaches to 45% in WZ and 47% in ZB, and then decreases with the further increase in In concentration. ZB–Ga1−xInxN alloys exhibit comparatively narrower energy gaps than WZ, and get smaller with increase in In contents. The smaller values of effective masses of free carriers, in WZ phase, than ZB phase, reflect higher carrier mobility and electrical conductivity of WZ–Ga1−xInxN. Moreover wide energy gap of WZ–Ga1−xInxN results in large values of the absorption coefficients comparatively and smaller static refractive indices compared to ZB–Ga1−xInxN. Comparable electronic and optical characteristics of the ZB–Ga1−xInxN to WZ–Ga1−xInxN endorses it a material of choice for optoelectronics and solar cell applications besides the WZ–Ga1−xInxN.

Structural stability of Mn-doped GaInAs and GaInN alloys

Phase stability of pseudo-ternary (Ga,In,Mn)As and (Ga,In,Mn)N alloys with zinc blende (ZB) and rock salt (RS) structures is investigated by means of the first principles full-potential linearized augmented plane-wave method. Calculated results predict that the ordered and disordered states are less favorable with respect to the phase separation. However, the Mn solubility into ZB GaAs increase as the In composition increases. In addition, the Mn-doped GaAs with xMn≲0.44 (and GaN with xMn≲0.63) favors the ZB structure over the RS structure regardless the In incorporation.

On the electronic properties of two-dimensional honeycomb GaInN and GaAlN alloys: a molecular analysis

We have performed first principles total energy calculations to investigate the structural and the electronic properties of two-dimensional honeycomb GaAlN and GaInN alloys. Calculations were done using a coronene-like (C(24)H(12)) cluster and for different numbers of Ga, Al, and In atoms. The exchange and correlation potential energies were treated within the generalized gradient approximation (GGA). The bond length, dipole moment, binding energy, and gap between the HOMO and the LUMO are reported as a function of x. The stability of the structures depends on the site of the substituted atom; for example, when three Ga atoms are substituted, the GaInN alloy becomes unstable. The gap in the GaAlN increases from 3.76 eV (GaN) to 4.51 eV (AlN), and in the GaInN decreases to 2.11 eV. The biggest polarity occurs when eight and four Ga atoms are substituted, for GaAlN and GaInN, respectively.

Nitrogen-electronegativity-induced bowing character in ternary zincblende Ga 1− xIn xN alloys

The origins of the bandgap bowing character in the common-anion ternary cubic Ga 1− x In x N alloys are investigated using the s p 3 s ∗ tight-binding (TB) method, including the spin–orbit coupling effects within the virtual-crystal approximation (VCA) framework. The method is used to calculate the band structure, density of states and charge ionization versus composition and valence-band offsets (VBO). The results are used to model some recently available experimental optical absorption (Abs) and photoluminescence (PL) data. Two unusual characteristics are discussed: (i) unlike the common-anion “direct-bandgap-based” ternary alloys, the GaInN alloys possess a clearly large bowing character. This behavior is found to be mainly caused by the electronegativity of nitrogen atoms, whose effects can induce a competition between the cation (Ga and In) atoms to establish a compromised ionization with the increasing indium content; (ii) a single composition-independent bowing parameter cannot describe the bandgap behavior. The decrease of bowing parameter with the increasing In content is found to be almost linear and likely to be caused by the composition fluctuation due to the large lattice relaxation. The results also show that the VBO between the two constituents is small ( VBO < 0.38 eV), consistent with the predictions of the common-anion rule and the state-of-the-art ab initio methods.

Optical, structural investigations and band-gap bowing parameter of GaInN alloys

We have performed a detailed investigation of the photoluminescence features taken at 2 K on a series of Ga x In 1− x N alloys grown by metal-organic vapour-phase epitaxy through the whole composition range. The evolution of the photoluminescence lineshape of GaInN alloys in the indium-rich region is dominated by doping effects rather than by band-gap tailing effects correlated to existence of random chemical crystal inhomogeneities. The lineshape of the photoluminescence indicates a residual electron concentration of about 10 18–10 19 cm −3 in the bulk part of the epilayers. The value we get for the bowing parameter is b=2.8 eV.

Tight-binding studies of the electronic band structure of GaAlN and GaInN alloys

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.

Discrete Steps in the Capacitance-Voltage Characteristics of GaInN/GaN Light Emitting Diode Structures

ABSTRACTA detailed modeling of the electronic bandstructure of GaInN alloys and GaInN/GaN heterostructures typically used for high efficiency light emitting diodes is of high relevance for future improvements. Here we are exploring opportunities to accurately quantify the carrier dynamics under forward and reverse voltage bias. In GaInN/GaN LED-type heterostructures we observe distinct steps in the junction capacitance as a function of bias voltage within the depletion regime. Up to three individual steps can be identified that correspond to alternating ranges of capacitive and resistive impedances. Our analysis suggests that we are quantitatively monitoring the electron concentration in each individual quantum well. The pronounced clarity of the data reveals a high level of epitaxial perfection and spatial homogeneity across the entire area of the junction.

Impact of low-temperature buffer layers on nitride-based optoelectronics

A historical overview and recent trends in the research and development of nitride-based light emitters are presented. The growth of GaN using a low-temperature-deposited buffer layer conductivity control, and the use of GaInN alloys, by which nonradiative recombination centers in nitrides are screened, have been employed to fabricate high-efficiency blue and green light-emitting diodes. Today, luminous flux efficiency of up to 50 lm/W at a specific wavelength is available. Electrical pumping has realized commercial laser diodes in the violet and blue regions. Several milestones in the realization of these achievements are reviewed. Future prospects of the nitride-based light emitters are also discussed.

Detailed structural analysis of semiconductors with X-ray scattering

Some of the most important material systems, GaInN alloys and quantum dot structures create interesting and complex challenges for structural analysis. This paper concentrates on the interpretation of the microstructure of both these materials, the former to assess the defect separation and the latter to obtain the shape and composition of the quantum dots. The methods used are based on mapping the X-ray intensity in reciprocal space and simulating proposed models to achieve good agreement with the experimental results. An indication of the reliability of these methods is presented. The simulation of the 0002 reciprocal space map of a 〈0 0 0 1〉 orientated InGaN/GaN sample yielded a range of dimensions of the perfect regions between defects of 60 and 220 μm. This comes from careful fitting of the tails of the scattering parallel to the surface plane. The average composition within an InGaAs quantum dot has been determined to a reliability of ±3% and the dimensions of these buried dots evaluated from simulating the reciprocal space maps using the in-plane scattering geometry.

Improved Radiative Efficiency using Self-Formed GaInN/GaN Quantum Dots Grown by Molecular Beam Epitaxy

GaInN/GaN heterostructures have been grown by molecular beam epitaxy (MBE) on c-plane sapphire substrates. The growth of Ga1—xInxN (x > 12%) alloy has been extensively studied. At low V/III ratio, the growth undergoes a Stranski-Krastanov transition giving rise to the formation of three-dimensional (3D) islands. On the other hand, a high V/III ratio promotes the two-dimensional (2D) layer-by-layer growth regime. The optical properties of Ga1—xInxN (x > 12%)/GaN heterostructures made from either a 3D GaInN layer or a 2D GaInN layer are similar. This indicates that the mechanism responsible for the peculiar optical properties of Ga1—xInxN (x > 12%)/GaN heterostructures is intrinsically due to self-formed quantum dots (QDs) that may arise from In clustering in the GaInN alloy. Actually, the properties of the GaInN/GaN QDs grown by MBE are very close to those grown by metal-organic chemical vapor deposition (MOCVD). As for MOCVD material, a high radiative efficiency is obtained correlatively with a giant Stokes shift and a very large carrier lifetime. The high efficiency of GaInN/GaN QDs is confirmed by gain measurements performed at room temperature. Finally, light-emitting diodes (LEDs) based on GaInN QDs have been fabricated. They demonstrate improved performances compared to LED based on homogeneous GaInN alloys.