Optical Properties Of Ga Research Articles

Correlation of interface structure and optical properties of Ga(N,As) and Ga(As,Bi) based type-II hetero structures

The type-II band alignment of particular III/V heterostructures is a promising route towards achieving certain wavelengths on specific substrates, which would not be possible with type-I structures. One example is telecommunication lasers on GaAs substrates. This study reports on the progress in combining dilute nitrides and dilute bismides in W-type hetero structures to improve the luminescence intensity, which is a fundamental prerequisite for future incorporation in a laser structure. Increasing the emission wavelength of these structures is challenging and the interface formation is critical, especially as two metastable materials are combined. Here, we investigate the impact of different interface configurations by growing Ga(N,As)/Ga(As,Bi) and Ga(As,Bi)/Ga(N,As) type-II structures. We employ metal–organic vapor phase epitaxy (MOVPE) to grow Ga(N,As) and Ga(As,Bi) layers and investigate the effects of interlayer thicknesses on the structural and optical properties of the hetero structures. The results indicate that − while the introduction of a GaAs interlayer can affect the direct and indirect transitions intensities − it does not significantly improve the interface quality. However, this is strongly influenced by the order in which the materials are grown. The growth of Ga(N,As) on Ga(As,Bi) shows no peculiarities, while the type II transition energy is shifted to lower energies when Ga(As,Bi) is grown on Ga(N,As). High-resolution X-ray diffraction (HR-XRD), photoluminescence (PL) spectroscopy, atomic force microscopy (AFM), and scanning transmission electron microscopy (STEM) were used to characterize the samples.

Structure, surface/interface chemistry and optical properties of W-incorporated β-Ga2O3 films made by pulsed laser deposition

The effect of oxygen partial pressure on the structure, morphology, chemical bonding, and optical properties of Ga–W–O films made by pulsed laser deposition is evaluated. Conditions were optimized to realize materials for deep UV-photodetectors.

Influence of Substrate-Target Distance on Structural and Optical Properties of Ga and (Al + Ga)-doped ZnO Thin Films Deposited by Radio Frequency Sputtering

Ga-doped ZnO and (Ga + Al) co-doped ZnO thin films were deposited on glass substrates by radio frequency magnetron sputtering for three distances d between a substrate–target. The influence of the distance between substrate–target upon structure, microstructure, vibrational properties, and optical band gap of the thin films was analyzed by X-ray diffraction, atomic force microscopy (AFM), Raman spectroscopy, and optical transmission measurements. The diffraction patterns revealed that the ZnO film crystallites are preferentially oriented with the (002) planes parallel to the substrate surface. AFM images show a smooth and uniform surface as well as a high compact structure. The Raman results reveal that the co-doping with Al + Ga introduces 2B1(low) band and leads to the increase of intensity for longitudinal-optic’s band. In the visible region, the average value of the transmittance was above 80%.

First-Principle Studies on the Ga and As Doping of Germanane Monolayer

The study of energetics, structural, the electronic and optical properties of Ga and As atoms substituted for doped germanane monolayers were studied by first-principles calculations based on density functional theory. Both of the two doping are thermodynamically stable. According to the band structure and partial density of the states, gallium is p-type doping. Impurity bands below the conduction band lead the absorption spectrum moves in the infrared direction. Arsenic doping has impurity level passing through the Fermi level and is n-type doping. The analysis of optical properties confirms the value of bandgap and doping properties.

First principles study on structural, electronic and optical properties of Ga1−xBxP ternary alloys (x = 0, 0.25, 0.5, 0.75 and 1)

The structural, electronic and optical properties of GaP, BP binary compounds and their ternary alloys Ga1−xBxP (x=0.25, 0.5 and 0.75) have been studied by full-potential linearized augmented plane wave (FP-LAPW) method within the framework of density functional theory (DFT) as implemented in WIEN2k package. Local density approximation (LDA) and generalized gradient approximation (GGA) as proposed by Perdew–Burke–Ernzerhof (PBE), Wu–Cohen (WC) and PBE for solid (PBESol) were used for treatment of exchange-correlation effect in calculations. Additionally, the Tran–Blaha modified Becke–Johnson (mBJ) potential was also employed for electronic and optical calculations due to that it gives very accurate band gap of solids. As B concentration increases, the lattice constant reduces and the energy band gap firstly decreases for small composition x and then it shows increasing trend until pure BP. Our results show that the indirect–direct band gap transition can be reached from x=0.33. The linear optical properties, such as reflectivity, absorption coefficient, refractive index and optical conductivity of binary compounds and ternary alloys were derived from their calculated complex dielectric function in wide energy range up to 30 eV, and the alloying effect on these properties was also analyzed in detail.

Effect of deposition pressure on the structural and optical properties of Ga2O3films obtained by thermal post-crystallization

β-Ga2O3films have been obtained by thermal annealing of amorphous thin films that were deposited by radio frequency magnetron sputtering.

A first-principles study of the effects of different Al constituents on Ga1−xAlxN nanowires

In order to investigate the influences of different Al constituents on Ga[Formula: see text]Al[Formula: see text]N nanowires, the formation energy, stability, band structure, densities of states and optical properties of Ga[Formula: see text]Al[Formula: see text]N nanowires with different Al constituents are calculated using first-principles plane-wave ultrasoft pseudopotential method. Results show that Ga[Formula: see text]Al[Formula: see text]N nanowires become more stable with increasing Al constituent. Bandgap of Ga[Formula: see text]Al[Formula: see text]N nanowires increases as the Al constituent increases but with a lower amplification compared with bulk Ga[Formula: see text]Al[Formula: see text]N. The peaks of static dielectric constants show a decreasing trend and move towards high-energy side as Al constituent increases. The absorption of Ga[Formula: see text]Al[Formula: see text]N nanowires shows an interesting phenomenon that it firstly increases and then decreases slightly as the Al constituent increases. Reflectivity of Ga[Formula: see text]Al[Formula: see text]N nanowires is much smaller than that of the bulk. The optical properties of Ga[Formula: see text]Al[Formula: see text]N nanowires show a blueshift effect as Al composition increases. According to these calculations, it is found that Ga[Formula: see text]Al[Formula: see text]N nanowires are appropriate to be applied into photoelectric detecting materials by adjusting the Al constituent of Ga[Formula: see text]Al[Formula: see text]N nanowires.

Density functional theories study on the properties of Ga1−xCrxAs

Abstract The structural, electronic, magnetic and optical properties of Ga 1 − x Cr x As (x = 0, 6.25%, 12.5%) have been studied by first-principles calculations based on the HSE hybrid density functional theories. The optical properties, including the complex dielectric function, optical refractive index, extinction coefficient and absorption coefficient are discussed for radiation up to 15 eV. The results predicate that the system of Ga 1 − x Cr x As exhibits typical half-metallic properties, in which Cr forms deep levels in the forbidden band and reduces the energy gap, increases static dielectric constant and obviously red-shifts the absorption edge. With the increase of the fraction of Cr, the material gradually exhibits noticeable anisotropy in the photon energy range of 0–5 eV. In addition, the p-d hybridization reduces the magnetic moment of Cr from its free space charge value of 3 μ B and a smaller atomic magnetic moments of As and Ga atoms are generated.

Optical properties of Ga and in doped CdS nanocomposites: An experimental and first principles study

Present work deals with Ga and In doped CdS nanocomposites by experimental and theoretical means. For theoretical simulations, we considered Supertetrahedron (Tn) cluster models of substitutionally and interstially (Ga, In) doped CdS. To mimic experimental conditions polyvinyl alcohol (PVA) chain fragments were allowed to cap the clusters. Structural and electronic properties have been calculated using density functional theory (DFT). Frontier molecular orbital (FMO) plots indicate that transfer of charge occurs between organic (polymer) and inorganic (semiconducting nanoclusters) moieties. The transfer of charge leads to longevity of hybrid nanocomposites. Nanocomposites have been synthesized by the in situ chemical method at room temperature and characterized using XRD, TEM, FTIR and UV spectroscopy. DFT has been employed to simulate optical properties. There is a good agreement in optical band gap calculated from experimental method and theoretical approach.

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 and optical properties of thermally evaporated Ga–In–Se thin films

In this paper, structural and optical properties of Ga – In – Se (GIS) thin films deposited by thermal evaporation technique have been investigated. The effect of annealing was also studied for samples annealed at temperatures between 300°C and 500°C. X-ray diffraction, energy dispersive X-ray analysis and scanning electron microscopy have been used for structural characterization. It was reported that increase of annealing temperature results with better crystallization and chemical composition of the films were almost same. Optical properties of the films were studied by transmission measurements in the wavelength range of 320–1100 nm. The direct bandgap transitions with energies in the range of 1.52 eV and 1.65 eV were revealed for the investigated GIS films. Photon energy dependence of absorption coefficient showed that there exist three distinct transition regions for films annealed at 400°C and 500°C. The quasicubic model was applied for these transitions to calculate crystal-field splitting and spin-orbit splitting energy values.

Growth of Ga- and N-polar GaN layers on O face ZnO substrates by molecular beam epitaxy

Gallium nitride (GaN) epitaxial layers have been grown on O face (0001¯) zinc oxide (ZnO) substrates by ammonia source molecular beam epitaxy. By adjusting the growth temperature and the III/V ratio during the nucleation stage, GaN layers with Ga (0001) or N (0001¯) polarities have been obtained. We show that low growth temperatures (<550°C) and Ga-rich conditions lead to Ga-polar layers, whereas higher growth temperatures (>600°C) and N-rich conditions lead to N-polar layers. Furthermore, the formation of a zinc gallate (ZnGa2O4) interfacial layer between GaN and ZnO has been evidenced, which is responsible for the growth of Ga-polar GaN layers. The structural and optical properties of Ga- and N-polar GaN layers have been characterized and Ga-polar GaN layers exhibit higher crystal quality.

Study on the electronic structure and optical properties of different Al constituent Ga1−xAlxAs

Using quantum mechanics GASTEP software package based on the first principle density function theory, the electronic structure and optical properties of Ga1−xAlxAs at different Al constituent are calculated. Result shows that with the increase of Al constituent, the band gap of Ga1−xAlxAs increases and varies from direct band gap to indirect band gap; the absorption band edge and the absorption peak move to high-energy side; the static reflectivity decreases. With the increasing of the incident photon energy, Ga1−xAlxAs shows metal reflective properties in certain energy range. With the increasing of Al constituent, static dielectric constant decreases and the intersection of dielectric function and the x-axis move towards high-energy side; the peak of energy loss function move to low-energy side and the peak value reduces.

Synthesis and Structural-Optical Properties of Ga-Doped ZnO Nanowires by Hot-Walled Pulsed Laser Deposition Method

Well-aligned single-crystalline zinc oxide (ZnO) and Ga doped ZnO (GZO) NWs (NWs) were successfully fabricated on Au film catalyzed sapphire substrate using vapor-liquid-solid (VLS) method in hot-walled pulsed laser deposition (HW-PLD). The structural and optical properties of Ga doped ZnO NWs have been investigated depending on various concentration of Ga dopants in ZnO NWs. As increasing Ga concentration, stacking faults were observed by using FE-SEM and an exciton bound to a neutral donor (D(0)X) peak was clearly observed by using PL spectra. From the structural and optical properties, the ZnO NWs by doping could be application to electronic and optoelectronic devices, such as nano-FETs, nano-inverters, nano-logic circuits and nano-sensors.

Dependences of the optical characteristics of Al x Ga1−x N films on the substrate composition and polarity

Optical properties of Ga- and N-polar triple nitrides AlxGa1−xN with molar fractions of aluminum from 0 to 0.6 are studied by a nondestructive contactless method of spectroscopic ellipsometry. Correlation dependences of the shift of the fundamental absorption edge and the behavior of the real and imaginary parts of the pseudodielectric function on the composition x and polarity of the AlxGa1−xN layers are revealed. It is verified that the polarity of the layers grown by molecular beam epitaxy is defined by the formation of the AlN nucleating layer.

Influence of Si co-doping on magnetic, electrical and optical properties of Ga1–x Mn x N film grown by MOCVD

A detailed study is presented on magnetic, electrical and optical properties of Ga1−xMnxN: Si film grown by metal organic chemical vapor deposition (MOCVD) with high-purity SiH4 as the Si dopant source. The room-temperature field dependence magnetization and zero-field-cooled (ZFC)/field-cooled (FC) measurements indicate that the film remains room-temperature ferromagnetism and it declines slightly after Si co-doping. However, room-temperature Hall measurements indicate that the electrical property of the film improves distinctly compared with Ga1−xMnxN. Cathode luminescence (CL) measurements show an obvious enhancement in luminous property and different peak strength changes at three different positions. Therefore, we demonstrate that Fermi level and the electron structure of Mn atoms will change with variation of the impurities co-doped and the intrinsic defects and this may be related with room-temperature ferromagnetism and the other corresponding properties of the film.

Optical properties of Ga(NAsP) lattice matched to Si

AbstractIII/V semiconductors containing dilute amounts of N exhibit remarkable features such as a strong increase of the effective mass of the electrons, a huge red‐shift of the band gap compared to the host material and a weak pressure dependence of the PL band position. We examined these features by studying the affect of N incorporation onto the band formation of the alloys Ga(NAs) and Ga(NP). The dispersion‐free N‐related impurity band interacts in a repulsive way with the conduction band of the host material. The novel As‐rich Ga(NAsP) alloy exhibits both the electronic as well as the mechanical properties to serve as an active laser material for III/V integration onto Si substrates. We studied the optical properties by means of photoluminescence, excitation and modulation spectroscopy as well as pressure dependence. Energies of the interband transitions within the MQW have been successfully simulated by a type I QW calculation, yielding a CB to VB offset ration of about 1:2. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Structural and optical properties of Ga 2(1− x) In 2 xO 3 films prepared on α-Al 2O 3 (0 0 0 1) by MOCVD

Ga 2(1− x) In 2 x O 3 thin films with different indium content x [In/(Ga + In) atomic ratio] were prepared on α-Al 2O 3 (0 0 0 1) substrates by the metal organic chemical vapor deposition (MOCVD). The structural and optical properties of the Ga 2(1− x) In 2 x O 3 films were investigated in detail. Microstructure analysis revealed that the film deposited with composition x = 0.2 was polycrystalline structure and the sample prepared with x up to 0.8 exhibited single crystalline structure of In 2O 3. The optical band gap of the films varied with increasing Ga content from 3.72 to 4.58 eV. The average transmittance for the films in the visible range was over 90%.

Improvement of electrical and optical properties of Ga and N co-doped p-type ZnO thin films with thermal treatment

Ga and N co-doped p-type ZnO thin films were epitaxially grown on sapphire substrate using magnetron sputtering technique. The process of synthesized Ga and N co-doped ZnO films was performed in ambient gas of N 2O. Hall measurement shows a significant improvement of p-type characteristics with rapid thermal annealing (RTA) process in N 2 gas flow, where more N acceptors are activated. The film rapid thermal annealed at 900 °C in N 2 ambient revealed the highest carrier concentration of 9.36 × 10 19 cm −3 and lowest resistivity of 1.39 × 10 −1 Ω cm. In room and low temperature photoluminescence measurements of the as grown and RTA treated film, donor acceptor pair emission and exciton bound to acceptor recombination at 3.25 and 3.357 eV, respectively, were observed.

Structural and optical properties of GaInAs∕GaAs and GaInNAs∕GaNAs multiple quantum wells upon postgrowth annealing

We have investigated structural and optical properties of Ga1−xInxAs∕GaAs and Ga1−xInxNyAs1−y∕GaNzAs1−z multiple quantum wells. The evolution of x-ray diffraction rocking curves during thermal treatment of the samples indicates that there is observable Ga∕In interdiffusion across the heterointerfaces at high sample temperatures. X-ray diffraction also indicates that the diffusion length of the atoms decreases with an increase in nitrogen concentration, while the interface roughness, which exhibits remarkable changes for the two different quantum wells, only plays a minor role in diffusion. Structural stability of the Ga1−xInxNyAs1−y∕GaNzAs1−z quantum wells against temperature variations is better than that of the Ga1−xInxAs∕GaAs quantum wells. These observations can be accounted for by assuming that nitrogen has a tendency to suppress Ga∕In interdiffusion across the heterojunctions.