High Quality AlxGa1 Research Articles

Wet Chemical Synthesis of AlxGa1−xAs Nanostructures: Investigation of Properties and Growth Mechanisms

This study focuses on the wet chemical synthesis of AlxGa1−xAs nanostructures, highlighting how different deposition conditions affect the film morphology and material properties. Electrochemical etching was used to texture GaAs substrates, enhancing mechanical adhesion and chemical bonding. Various deposition regimes, including voltage switching, gradual voltage increase, and pulsed voltage, were applied to explore their impact on the film growth mechanisms. SEM analysis revealed distinct morphologies, EDX confirmed variations in aluminum content, Raman spectroscopy detected structural disorders, and XRD analysis demonstrated peak position shifts. The findings emphasize the versatility and cost-effectiveness of wet electrochemical methods for fabricating high-quality AlxGa1−xAs films with tailored properties, showing potential for optoelectronic devices, high-efficiency solar cells, and other advanced semiconductor applications.

Stimulated emission of AlGaN layers grown on sapphire substrates using ammonia molecular beam epitaxy

By optimising the growth temperature of the AlGaN layers and using high-temperature AlN buffer layers, high-quality AlxGa1 – xN layers (x = 0.15, 0.21, 0.26, and 0.3) were obtained, in which stimulated emission in the UV spectral range 330 – 297 nm was implemented with the threshold intensity of excitation Ith ≈ 0.7 – 1.4 MW cm−2, respectively. It is found that the threshold value of the stimulated emission of AlGaN layers grown by molecular beam epitaxy is largely determined by the intensity of the process of thermal decomposition of GaN, which affects the surface morphology and, consequently, the amount of optical scattering loss. It is shown that no pronounced localisation of nonequilibrium charge carriers occurs in the AlGaN layers, which is manifested in the absence of a large Stokes shift and in the realisation of optical amplification at transitions in an electron-hole plasma, and also indicates a relatively homogeneous material composition.

Ultraviolet-C Photodetector Fabricated Using Si-Doped n-AlGaN Nanorods Grown by MOCVD

Aluminum gallium nitride (AlxGa1–xN) alloy films and nanostructures have attracted extensive research attention for ultraviolet (UV) and deep ultraviolet optoelectronic applications. However, the morphology-controlled growth of high-quality AlxGa1–xN quasi one-dimensional nanostructures has been limited by the complex multicomponent phase diagram and inhomogeneous composition distribution. Here, we demonstrated the growth of Si-doped n-type compositionally uniform Al0.45Ga0.55N nanorods employing a metal organic chemical vapor deposition (MOCVD) technique for the application in UV-C photodetectors. A two-step growth process, namely, growth of undoped GaN seeds and subsequent growth of n-AlGaN nanorods over GaN seeds, has been developed. Various characterization techniques have been used to study the crystalline quality, orientation, and optical properties of the realized nanorods. Field emission scanning electron microscopy revealed a uniform distribution of vertically aligned n-AlGaN nanorods over the Ga...

Structural and optical characterization of AlGaN/GaN layers

High quality AlxGa1−xN layers have been grown on c-plane sapphire substrate by Metal Organic Vapor Phase Epitaxy. The aluminum (Al) composition was varied from 15% to 51%. When the flow rate of trimethylaluminum was increased, the growth rate was found to be decreased. The crystalline quality of AlGaN layers has been evaluated using High Resolution X-ray Diffraction rocking curves. Reciprocal Space Mapping results confirmed that at low Al composition (x=0.15), AlGaN layers are found to be fully strained. At high Al composition (x=0.33, 0.51), AlGaN layers are relaxed by generation of cracks due to lattice mismatch. The optical properties of AlGaN/GaN layers have been investigated by room temperature photoluminescence. With increasing Al content, the AlGaN emission peak has been found to shift towards higher energies. The surface morphology and roughness of AlGaN have been studied by Atomic Force Microscopy. Root Mean Square roughness values have been found to increase with the increase of Al.

Intersubband transitions at atmospheric window in AlxGa1−xN/GaN multiple quantum wells grown on GaN/sapphire templates adopting AlN/GaN superlattices interlayer

Defects and strain control in AlxGa1−xN/GaN multiple quantum wells (MQWs) for intersubband transitions (ISBTs) at atmospheric window grown on GaN/sapphire templates by metal-organic chemical vapor deposition have been investigated adopting strain modulation technique using AlN/GaN superlattices (SLs) interlayer. It is found that cracking in the MQWs can be effectively avoided adopting AlN/GaN SLs interlayer. It is demonstrated that AlN/GaN SLs interlayer acts as a flexible layer and relieves most of the tensile strain through buried microcracks in AlN/GaN SLs interlayer. The intersubband absorptions at 3.6–4.1 μm wavelength region have been observed on the crack-free AlxGa1−xN/GaN MQWs. Our results open up prospects to realize crack-free and high quality AlxGa1−xN/GaN MQWs on GaN/sapphire templates for ISBTs devices at 3–5 μm atmospheric window.

Dynamics of relaxation and trapping of excitons in Al x Ga 1– x As films

Carrier relaxation in high quality AlxGa1–xAs (x up to 5%) epilayers has been investigated by means of time resolved photoluminiscence. The time for the excitonic PL to reach the maximum intensity shows a non-monotonic behaviour with increasing excitation density, which is attributed to the competition between exciton localization and carrier-carrier scattering. The increase of the Al content enhances the alloy scattering and increases the number of localization sites, moderately accelerating the dynamics. A four-level rate equation model qualitatively describes the influence of trapping in the exciton dynamics at low excitation densities. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

High-Quality AlxGa1−xN Using Low Temperature-Interlayer and its Application to UV Detector

Low-temperature (LT-) AlN interlayer reduces tensile stress during growth of AlxGa1−xN, while simultaneously acts as the dislocation filter, especially for dislocations of which Burger’s vector contains [0001] components. UV photodetectors using thus-grown high quality AlxGa1−xN layers were fabricated. The dark current bellow 50 fA at 10 V bias for 10 μm strip allowing a photocurrent to dark current ratio greater than one even at 40 nW/cm2 have been achieved.

High-Quality AlxGa1−xN Using Low Temperature-Interlayer and its Application to UV Detector

AbstractLow-temperature (LT-) AlN interlayer reduces tensile stress during growth of AlxGa1−xN, while simultaneously acts as the dislocation filter, especially for dislocations of which Burger's vector contains [0001] components. UV photodetectors using thus-grown high quality AlxGa1−xN layers were fabricated. The dark current bellow 50 fA at 10 V bias for 10 [.mu]m strip allowing a photocurrent to dark current ratio greater than one even at 40 nW/cm2 have been achieved.

High quality self-nucleated AlxGa1−x N layers on (00.1) sapphire by low-pressure metalorganic chemical vapor deposition

High quality AlxGa1−xN alloy films with x<0.4 have been prepared on self-nucleated (00.1) sapphire substrates by low-pressure metalorganic chemical vapor deposition. It has been shown that the lattice constant of the films varies linearly with alloy composition x (Vegard’s law is obeyed) and that homogeneous and inhomogeneous strain and alloy clustering are minimized in these self-nucleated AlxGa1−xN films. Consistent with their reduced strain and chemical uniformity, the derived optical band gaps of these AlxGa1−xN films also show a linear dependence on alloy composition x, yielding a bowing parameter b≊0 eV.

Effect of structural and chemical parameters on the optical properties of highly strained AlGaAs/InGaAs/AlGaAs quantum wells

The realization of high-quality AlxGa1−xAs/In0.26Ga0.74As/AlyGa1−yAs single quantum wells on GaAs(001) substrates for the entire range of Al compositions, 0≤x, y≤1.0 is being reported. The effect of replacing the AlGaAs alloy in the barriers with (AlAs)m(GaAs)n short-period superlattice is also examined and presented. The photoluminescence (PL) transition energies are calculated within a model in which the effect of strain is also included. Analysis of the PL transition energies as a function of the well width and the Al and In contents in the barriers and the well reveals that the exciton peak position is most sensitive to variation in the In content in the well. Possible causes of this variation are discussed.

Growth of AlxGa1−x as by metalorganic chemical vapor deposition using trimethylgallium and trimethylamine alane

High-quality AlxGa1−xAs layers with aluminum arsenide contentx up to 0.34 have been grown in a low pressure metalorganic chemical vapor deposition (MOCVD) system using trimethylgallium (TMG), trimethylamine alane (TMAA) and arsine. The carbon content in these films depended on growth conditions but was in general lower than in those obtained with trimethylaluminum (TMA) instead of TMAA in the same reactor under similar conditions. Unlike TMA grown layers, the TMAA grown AlxGa1−xAs layers, (grown at much lower temperature—down to 650° C), exhibited room temperature photolu-minescence (PL). Low temperature (25 K) PL from these films showed sharp bound exciton peaks with a line width of 5.1 meV for Al0.25Ga0.75As. A 39 period Al0.28Ga0.72As (5.5 nm)/GaAs (8.0 nm) superlattice grown at 650° C showed a strong PL peak at 25 K with a line width of 5.5 meV attesting to the high quality of these layers.

High quality AlxGa1−xAs grown by organometallic vapor phase epitaxy using trimethylamine alane as the aluminum precursor

High quality AlxGa1−xAs has been grown by low-pressure (30 Torr) organometallic vapor phase epitaxy (OMVPE) using a novel precursor, trimethylamine alane (TMAAl), as the aluminum source. The epilayers exhibited featureless surface morphology, very strong room-temperature photoluminescence (PL), and excellent compositional uniformity (x=0.235±0.002 over a 40 mm diameter). The residual carbon incorporation, which determined the background doping, depended largely upon the choice of gallium precursor. Using triethylgallium, carbon incorporation could be largely suppressed ([C]≪1016 cm−3). The carbon-related emission intensity was less than the bound exciton emission in low-temperature (1.6 K) PL even at excitation powers as low as 50 μW cm−2. By sharp contrast, the use of trimethylgallium led to much higher C concentrations (2–5×1017cm−3). Under appropriate conditions, therefore, the use of TMAAl produces extremely high purity AlGaAs of superior quality to AlGaAs grown using conventional precursors.

Investigation of electrical and photoluminescent properties of MBE-grown Al x Ga1?x As layers

The electrical and photoluminescent (PL) properties of Al x Ga{1−x}As layers grown by MBE have been investigated. Some experimental factors, e.g. vacuum conditions, substrate growth temperature and As/group-III flux ratio, have been considered. Undoped AlGaAs layers exhibit slight p-type characteristics due to C accepters and its concentration is lower than 1015cm−3. Both n- and p-type AlGaAs layers achieve semi-insulated high resistance when the substrate temperature is lower than 580° C. The experimental results are comparable to other reports. In summary, the excellent vacuum environment, higher substrate temperature (T s>580° C) and lower As/group-III flux ratio are the necessary conditions for growing high quality Al x Ga1−x As layers.

Carbon-doped AlxGa1−xAs-GaAs quantum well lasers

Data are presented demonstrating that carbon (C) can be used as the active p-type dopant in high-quality AlxGa1−xAs-GaAs quantum well laser crystals. We show, by fabricating three different types of stripe geometry laser diodes (oxide stripe, hydrogenated stripe, and impurity-induced layer-disordered stripe), that C is a stable dopant and compatible in behavior with typical integrated-circuit style of device processing. The data suggest that more complicated laser geometries are possible on C-doped material because of minimal pattern ‘‘undercutting’’ after processing by, for example, hydrogenation or impurity-induced layer disordering.

Epitaxial growth of AlxGa1−xAs by low-pressure MOCVD

Epitaxial layers of AlxGa1−xAs grown from trimethylaluminum, trimethylgallium, and arsine in a low-pressure (10 Torr) MOCVD system were examined by Hall coefficient and photoluminescence measurements. The carrier concentration of undoped n-type AlxGa1−xAs increases as the V/III ratio and/or growth temperature increases. The carrier concentration of p-type epilayers decreases with increasing V/III ratio. The emission peak intensity from near-band transitions at room temperature increases with increasing growth temperature when epilayers are grown from the same source materials. It should be noticed that the peak intensity of AlxGa1−xAs layers grown from different arsine cylinders varied significantly. The origins will be discussed. Ten Torr low-pressure MOCVD can provide high-quality AlxGa1−xAs epilayers which are comparable to the best values reported for layers grown at atmospheric pressure.

Low-temperature photoluminescence in AlxGa1−xAs grown by molecular beam epitaxy

We report the first observation of free exciton transitions (X), as well as donor and acceptor bound exciton transitions (D0X, D+X, and A0X), in the high-resolution photoluminescence (PL) spectra of high-quality AlxGa1−xAs layers grown by molecular beam epitaxy (MBE) over the composition range 0.01≤x<0.2. This observation contrasts markedly with several previous investigations of AlxGa1−xAs samples of somewhat higher composition (x>0.2) in which only one or two bound exciton transitions have been reported together with the typically observed carbon free-to-bound transitions (e,A0). From a systematic study of MBE growth and PL spectral characterization, we find that both the free and bound exciton transitions of the AlxGa1−xAs layers correlate to their counterparts in high-purity MBE GaAs layers and that their photon energies increase linearly with increasing x value, as expected for these low AlAs mole fraction samples. At compositions as low as 2.1%, and as high as 12.5%, spectral linewidths of D0X transitions were found to be as narrow as 0.3 and 2 meV, respectively, in reasonably good agreement with the recent PL linewidth predictions of Singh and Bajaj which are based on a theory of alloy scattering. These observations confirm the high quality of the low x-value AlxGa1−xAs samples which were grown to thicknesses between 1 and 2 μm at substrate temperatures approaching 700 °C in a MBE system having low background impurity contamination.

Pressure dependence of AlxGa1−xAs light emitting diodes near the direct-indirect transition

High-pressure studies on high quality AlxGa1−xAs double heterostructure light emitting diodes (LEDs) grown by liquid phase epitaxy (LPE) are presented. The AlxGa1−xAs active region varies in composition from x∼0.25 to x∼0.53, i.e., through the important region of the direct-indirect crossover (x≡xc≊0.45). The pressure coefficient of the Γ conduction band is observed to decrease (∼1 meV/kbar for x∼0.25 to x∼0.53) with increasing Al concentration, which is in accord with alloy disorder and band-edge bowing. Indirect-gap (X) recombination radiation of significant intensity is observed and provides evidence for the high quality of the LPE diodes. High-pressure measurements, and the corresponding increase in energy of the direct band edge and decrease in the indirect band edge, show that the light emission is a strong function of the carrier distribution in the Γ and X conduction-band minima. Comparison LEDs fabricated from a crystal (x∼0.37) grown by metalorganic chemical vapor deposition exhibit nearly similar behavior as the LPE LEDs with application of pressure but with an order of magnitude lower light emission.

The growth of high quality Alx Ga1−xAs by molecular beam epitaxy and its application to double-heterojunction lasers

The molecular beam epitaxial (MBE) growth of high quality Si‐doped (n‐type) and Be‐doped (p‐type) Alx Ga1−xAs with 0<x<0.4 is reported. Room temperature mobilities and radiative recombination efficiencies comparable to those of high quality liquid phase epitaxial (LPE) and organometallic vapor phase epitaxial (OMVPE) material have been obtained. MBE grown double‐heterojunction lasers with Al0.07 Ga0.93As active layers have been fabricated. Broad area lasers having threshold current densities between 880 and 1000 A/cm2 and narrow stripe lasers having threshold currents as low as 84 mA are reported. These values are comparable to the best results for LPE and OMVPE lasers with similar structures.

Growth of High-Quality AlxGa1−xAs By OMVPE for laser devices

Optimum conditions are reported for the growth of high-quality AlxGa1_xAs by means of vapor phase epitaxy from organometallic compounds (OMVPE). Typical values of mobili-ty and radiative recombination efficiency are reported, showing that OMVPE material quality is the same as that grown by liquid phase epitaxy (LPE). OMVPE-grown DH narrow-stripe lasers with Al.06Ga.94As active layers show minimum threshold currents of85 mA, comparable to the best lasers with similar structures produced by LPE.