Bulk InxGa1 Research Articles

First principles study on the structural stability and optoelectronic properties of InxGa1−xAs materials with different Indium component

The III–V ternary semiconductors InxGa1−xAs (0 ≤ x ≤ 1) have attracted a great deal of interests in electronics and optoelectronics due to their superior transport properties, high-efficiency thermoelectric applications and so on. In this work, the optoelectronic properties of bulk InxGa1−xAs materials and the phase transition of InxGa1−xAs nanowires (NWs) at different Indium (In) component have been investigated by first-principles calculation using density functional theory. Different calculation models have been chosen to simulate the (2 × 2 × 1) supercells of pure bulk InxGa1−xAs structures and the most stable one has been adopted for further calculation. NWs models of In0.25Ga0.75As and In0.75Ga0.25As have been employed to represent the In-rich and Ga-rich structures, respectively. Our calculation results have clearly shown that the In-rich nanostructure show more zinc-blende characteristic while the wurtzite phase exhibit dominating role in the Ga-rich NWs. The band gap of bulk models decreases with increasing the In component, which is well consistent with the theoretical formula. With the In component increasing, the lower valence band shifts toward high energy region and the peak value increases, while the absorption edge and peak value move to lower energy side and the static dielectric constant increases. The metal reflective properties emerge in certain photon energy range. Our results offer the guidance to make use of the different properties of InxGa1−xAs materials at different In component.

InGaN/GaN single-quantum-well microdisks

We have grown InxGa1−xN/GaN quantum wells atop GaN microdisk with γ-LiAlO2 substrate by using plasma-assisted molecular beam epitaxy. The structural and optical properties of the samples were analyzed by transmission electron microscopy, x-ray diffraction, cathodoluminescence, and photoluminescence measurements. Based on the measured results, we obtained the indium concentration of the InxGa1−xN/GaN single quantum well to be x = 0.25 with a band-gap energy of 2.31 eV, which is consistent with the bowing effect of bulk InxGa1−xN: Eg(x) = [3.42 − x * 2.65 − x * (1 − x) * 2.4] eV.

Electronic Structures and Optical Properties of Ga-Rich InxGa1−xN Nanotubes

The electronic structures and optical properties of single-walled Ga-rich zigzag InxGa1−xN nanotubes (NTs) are investigated using first-principles calculations. We find that In atoms substitute Ga atoms randomly in InxGa1−xN NTs, in which some typical In−N clusters, chains, and rings are embedded by chance. Both the electronic structures and optical properties insensitively depends on In distribution. A spiculate density of states (DOS) peak appears in the vicinity of the valence band maximum (VBM) and conduction band minimum. The imaginary part ε2 of the complex dielectric function has also a sharp peak related to the band edge absorption. The In doping can effectively adjust the band gap and enhance the peak of the band edge absorption and DOS. Unlike bulk InxGa1−xN alloys, the electron states at the VBM become extended for the NTs with various In distributions.

Application-oriented nitride substrates: The key to long-wavelength nitride lasers beyond 500 nm

We present results based on quantum mechanical estimates of the longest emission wavelength for nitride laser diodes grown on c-plane GaN/sapphire substrates. The results indicate that the absence of polarization-induced electric fields in nonpolar/semipolar GaN substrates does not necessarily guarantee that nitride lasers will operate at the longest possible wavelength for a given set of parameters. Our calculations suggest that the limit on the longest possible wavelength of nitride lasers is constrained by the lattice mismatch rather than by the strength of the polarization-induced electric field. Although it may be possible to develop lasers that approach the green portion of the electromagnetic spectrum (∼520 nm) by growing the structures on nonpolar/semipolar GaN substrates, the development of red and near-infrared nitride lasers appears extremely difficult by merely growing the structures on any crystallographic orientation of the GaN substrate. We suggest that efficient lasers emitting at the green, red, and near-infrared wavelengths can be developed by growing the laser structures on a proposed application-oriented nitride substrate (AONS) that is lattice-matched to the epilayers grown on it. The AONSs are bulk InxGa1−xN ternary substrates with Indium compositions chosen to lattice-match the epilayers to be grown on them. The concept of the AONS can be extended deep into the infrared region by increasing the Indium mole fraction of the quantum well layers in the active region of the laser and by choosing the AONS that best matches the specific wavelength desired. We believe it would be possible, by using this concept, to make nitride lasers at the fiber-optic communication windows at 1.3 and 1.55 μm, thus eliminating the need to use the hazardous arsenides/phosphides materials currently used to make the communications lasers.

Evidence of compositional inhomogeneity in InxGa1−xN alloys using ultraviolet and visible Raman spectroscopy.

In this paper we report a study of phase separation in bulk InxGa1−xN films grown by metal organic chemical-vapor deposition using mid-UV Raman spectroscopy. Evidence of phase separation is observed by the occurrence of low frequency shoulders identified as minority phase in the A1(LO) Raman mode. A phase transition in the alloy from the metastable to unstable region was found to be occurring at an indium concentration of about 25%. Raman spectroscopic results also indicate that the compositional inhomogenity in our samples increase, as would be expected, with depth in the film. A direct correspondence is also found between the percentage of indium concentration in the film and the amount of compositional inhomogenity.

Approach to reduce the residual strain in bulk InGaAs crystals grown by the multi‐component zone melting method

AbstractAn analytical study has been carried out to evaluate the quantitative amount of strain and its distribution in bulk Inx Ga1–x As crystals grown by the two‐step multi‐component zone melting (MCZM) method. With the combination of Raman scattering, photoluminescence and energy dispersive X‐ray experiments, it has been confirmed that there exists large amount of strain in bulk Inx Ga1–x As crystals grown by the two‐step MCZM method due to approximately exponential variation of composition from 0.06 to 0.29 in the first step growth process. Using an axially symmetrical strain model, the quantitative amount of strain and its distribution have been studied for various compositional profiles including the currently used profile. It has been found that the strain and its distribution are strongly dependent on the shape of the compositional profile. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spectroscopic investigation of strain induced by compositional variation in bulk InxGa1–xAs crystal grown by MCZM method

Raman scattering (RS), photoluminescence (PL) and energy dispersive X-ray (EDX) experiments have been carried out to investigate residual strain and hence to understand breakage issue in bulk Inx Ga1–x As crystal grown by multi component zone melting (MCZM) method. It is found from a comparison that there is a large discrepancy among the RS, PL and EDX results due to the strain induced by compositional variation in the crystal. The strain induced changes in TOGaAs and PL peak positions are found to be 4.04 cm–1 and 0.097 eV, respectively, for the variation of composition from 0.06 to 0.29 from the seed-end to the tail-end of the crystal. By assuming a simple one-dimensional strain distribution, the strain value corresponding to 4.04 cm–1/ 0.097 eV can be obtained of the order of 10–2, which is large enough for understanding the breakage issue in the crystal investigated here. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Study on polycrystallization in bulk InxGa1−xAs using micro-Raman and photoluminescence

Micro-Raman and photoluminescence experiments have been performed to characterize the polycrystalline region in the wafers cut from a bulk InxGa1−xAs crystal, which was found to be initiating from the inner part of the ingot, unlike the usual observation of polycrystallization starting from the peripheral part of an ingot. This indicates the existence of polycrystallization mechanism other than those relating to the boundary effects. The polycrystalline region was found to have a random fluctuation of composition. The possibility of drastic local fluctuation in composition, which can be occurred by convection-induced local supercooling, being the main cause of polycrystallization, is investigated here.

Temperature dependence of the photoluminescence properties and band gap energy of InxGa1−xAs/GaAs quantum wells

The effective band gap energy of InxGa1−xAs/GaAs strained quantum wells (QWs) is investigated by photoluminescence spectroscopy (PL) in the range 12–295 K. The temperature dependence of the band gap energy of strained QWs correlates well with that of bulk InxGa1−xAs of similar composition. Deviations from the band gap variation of bulk material at low temperatures (12–90 K) are interpreted in terms of exciton localization. The differences ΔE(12 K) between the measured PL peak energies and the expected transition energies at 12 K (obtained by simulating the measured temperature dependence of the PL peak positions by the well-known Varshni relation) are suggested to be closely related to the Stokes shifts that often exist between PL and PL excitation spectra of QWs. A linear relation is found between the PL full-width at half-maximum measured at 12 K and ΔE for a range of QWs prepared under different growth conditions. Excitonic recombination is inferred to be dominant in the PL transitions at the highest temperatures investigated—even at room temperature.

Magnetic resonance studies of InGaN-based quantum well diodes

Photoluminescence (PL) based optically detected magnetic resonance (ODMR) studies as well as electroluminescence detected and electrically detected magnetic resonance (ELDMR and EDMR, respectively) measurements of InxGa1−xN quantum wells were performed. In the ODMR, two PL-enhancing resonances were observed: an electron resonance and a hole resonance. The electron resonance is consistent with expectations for the g value in bulk InxGa1−xN for x ≈ 0.4 but deviates significantly in an x≈0.3 sample. Possible reasons for this include the effects of strain and confinement. The hole resonance is qualitatively similar to observations in Mg-doped GaN, but more isotropic in the x ≈ 0.3 diode than in the x ≈ 0.4 sample. We measure relatively long radiative lifetimes (as long as ∼0.2 ms) in the ODMR which facilitate the observation of the resonances and indicate that the electron and hole are spatially separated either by potential fluctuations within the quantum well or by the trapping of the hole at an acceptor in the player of AlGaN whch serves as one of the confining barriers. In the EDMR and ELDMR experiments, the signal is primarily due to a reduction in the nonradiative recombination at resonance. While the ODMR is alwyas emission-enhancing, the ELDMR is luminescence-quenching, supporting the notion that techniques are probing different centers.

Cyclotron resonance measurements of electron effective mass in strained AlGaAs/InGaAs/GaAs pseudomorphic structures

Electron effective mass in the InxGa1−xAs conduction channel of strained AlGaAs/InGaAs/GaAs pseudomorphic structures is measured using far-infrared cyclotron resonance techniques at 4.2 K. The measured cyclotron mass is heavier than the conduction-band-edge mass in bulk InxGa1−xAs. This result is explained by the large two-dimensional electron density realized in the structure, and the lattice strain that exists in the InxGa1−xAs layer.

Luminescence investigations of highly strained-layer InAs-GaAs superlattices

We describe photoluminescence investigations in InAs-GaAs superlattices in the thin layer limit (10–20 Å). The data, which are compared to theoretical results obtained from band structure calculations, yield an estimate of the conduction-band discontinuity of 550 meV at the interfaces. They also show that although the superlattice has a band gap (765 meV) close in energy to that of the corresponding bulk InxGa1−xAs alloy (800 meV), the band structures are very different. In the superlattice, electrons and light holes appear to be the important carriers, and they tend to be spatially separated, to the extent that this is meaningful in the thin layer limit.