High-quality In0 Research Articles

Indium content, doping and thickness related impacts on nonpolar (In,Ga)N solar cell performance: Numerical investigation

Analytical model to evaluate the photovoltaic performance via the short circuit current density, open circuit voltage, fill factor, and efficiency of nonpolar (In,Ga)N solar cells at room temperature is conducted via this paper. The Indium content and structure thickness including the doping concentration impacts are assessed to obtain the optimum values that yield high efficiencies. The band gap energy, reverse saturation current density, and carrier mobility are the important factors that govern how the solar cell performance characteristics change with the adjusted parameters. The solar cell characteristics are calculated for American Society for testing and Materials experimental data related to 1-sun AM1.5D, AM1.5G, and AM0 spectra. A high quality In0.42Ga0.58N(1.42eV) solar cell with a 3μm thickness, 1017cm−3 doping concentration and reflection coefficient of about 15% can display as optimum efficiency as 25.43%,25.16% and 22.87% under respectively 1-sun AM1.5G, AM1.5D and AM0 illuminations. The optimum AM1.5G related photovoltaic conversion efficiency is reached for FF=89.2%, Voc=1.12V and Jsc=28.63mA.cm−2.

Thermally induced metastability of InGaAs single-layer for highly strained superlattices by metal-organic chemical vapor deposition

In this study, the metastability of In0.68Ga0.32As layers on InP substrates was investigated at various growth temperatures. The thickness of each metastable In0.68Ga0.32As layer was 40 nm, which is four times the critical thickness of the stable lattice with a stress of approximately 1%. The surface morphologies and roughness of the metastable In0.68Ga0.32As layers were highly sensitive to the growth conditions. Cross-hatches were observed on their surfaces when they were grown at various growth temperatures, and over this range, the surface roughness varied from 0.11 nm to 0.16 nm. The lowest surface roughness of 0.11 nm was achieved at 770 °C, and the metastable In0.68Ga0.32As layer showed a flat surface morphology with terraces parallel to the step edges. These results corresponded to those of the strain relaxation analysis of the metastable In0.68Ga0.32As layers using X-ray diffraction spectra. The In0.68Ga0.32As layer grown at 770 °C was almost fully strained, whereas those grown at other growth temperatures were relieved by approximately 10%. The flat surface morphologies and almost fully strained lattices suggested that the growth conditions were suitable for preparing high-quality superlattices with well-defined interfaces. The intuitive results of the metastable In0.68Ga0.32As single layers were utilized to grow high-quality In0.67Ga0.33As/Al0.64In0.36As superlattices with a reduction in the misfit dislocation by 41.8%. The results obtained herein suggest that the growth conditions for superlattices can be easily and efficiently optimized using the metastability of the materials.

Pt/(InGa)2O3/n-Si Heterojunction-Based Solar-Blind Ultraviolet Photovoltaic Detectors with an Ideal Absorption Cutoff Edge of 280 nm.

Ga2O3 is a popular material for research on solar-blind ultraviolet detectors. However, its absorption cutoff edge is 253 nm, which is not an ideal cutoff edge of 280 nm. In this work, by adjusting the ratio of In/Ga elements in the films, a high-quality (In0.11Ga0.89)2O3 film with an absorption cutoff edge of 280 nm was obtained, which owns a uniform surface and preferred orientation. On this basis, a solar-blind ultraviolet photovoltaic detector was constructed based on the Pt/(In0.11Ga0.89)2O3/n-Si heterojunction. When the device is exposed to 254 nm UV light, its open-circuit voltage (VOC) can reach 354 mV. Under 0 V bias, the device has a responsivity of 0.48 mA/W with a rise time of 0.47 s and a decay time of 0.37 s; under -7 V bias, the device achieves a responsivity of 16.96 mA/W with a rise time of 0.17 s and a decay time of 0.33 s. The spectral response characteristics of the device show that it has a selective response to solar-blind ultraviolet light (cutoff wavelength is 280 nm) with a rejection ratio (R254 nm/R310 nm), which is greater by more than two orders of magnitude. This work provides a good reference for adjusting the band gap of Ga2O3-based films and broadening their application fields.

Improved quality of In0.30Ga0.70As layers grown on GaAs substrates using undulating step-graded GaInP buffers

High quality In0.30Ga0.70As layers on GaAs substrates were obtained using compositional undulating step-graded Ga1-xInxP (x = 0.48–0.78) buffers grown by metal-organic chemical vapor deposition. The density of threading dislocation is about 4.0 × 106 cm−2 and the root-mean-square roughness is only 5.20 nm, which is much better than those grown on the conventional step-graded metamorphic buffer. On one hand, the reversed GaInP layers reduce the distribution imbalance of α dislocations between the (1 1 1) and (−1 −1 1) slip planes, which promote dislocation glide. On the other hand, the inserted tensile strained GaInP layers change the direction of dislocation glide and facilitate dislocation annihilations, which effectively confine the threading dislocations in the buffer. Overall, this work provides a promising way to obtain virtual substrates for the achievement of desired metamorphic devices.

Damage-Free Smooth-Sidewall InGaAs Nanopillar Array by Metal-Assisted Chemical Etching.

Producing densely packed high aspect ratio In0.53Ga0.47As nanostructures without surface damage is critical for beyond Si-CMOS nanoelectronic and optoelectronic devices. However, conventional dry etching methods are known to produce irreversible damage to III-V compound semiconductors because of the inherent high-energy ion-driven process. In this work, we demonstrate the realization of ordered, uniform, array-based In0.53Ga0.47As pillars with diameters as small as 200 nm using the damage-free metal-assisted chemical etching (MacEtch) technology combined with the post-MacEtch digital etching smoothing. The etching mechanism of InxGa1-xAs is explored through the characterization of pillar morphology and porosity as a function of etching condition and indium composition. The etching behavior of In0.53Ga0.47As, in contrast to higher bandgap semiconductors (e.g., Si or GaAs), can be interpreted by a Schottky barrier height model that dictates the etching mechanism constantly in the mass transport limited regime because of the low barrier height. A broader impact of this work relates to the complete elimination of surface roughness or porosity related defects, which can be prevalent byproducts of MacEtch, by post-MacEtch digital etching. Side-by-side comparison of the midgap interface state density and flat-band capacitance hysteresis of both the unprocessed planar and MacEtched pillar In0.53Ga0.47As metal-oxide-semiconductor capacitors further confirms that the surface of the resultant pillars is as smooth and defect-free as before etching. MacEtch combined with digital etching offers a simple, room-temperature, and low-cost method for the formation of high-quality In0.53Ga0.47As nanostructures that will potentially enable large-volume production of In0.53Ga0.47As-based devices including three-dimensional transistors and high-efficiency infrared photodetectors.

Growth of high-quality In0.28Ga0.72Sb/AlSb/GaSb/GaAs heterostructure by metalorganic chemical vapor deposition for single-channel Sb-based complementary metal–oxide–semiconductor applications

The growth of high-quality In0.28Ga0.72Sb epilayer on an AlSb/GaSb/GaAs heterostructure by metalorganic chemical vapor deposition is demonstrated. The In0.28Ga0.72Sb epilayer has a fully relaxed surface roughness of ∼1.0 nm and a low threading dislocation density of ∼6.2 × 106 cm−2. The valence band offset (VBO) of 3.11 eV and conduction band offset (CBO) of 3.21 eV for an Al2O3/In0.28Ga0.72Sb interface extracted from X-ray photoemission spectroscopy data highlight its suitability for use in single-channel InGaSb-based complementary metal–oxide–semiconductor (CMOS) applications. The type-I straddling gap of an In0.28Ga0.72Sb/AlSb heterojunction with a VBO of 0.47 eV and CBO of 0.65 eV is also sufficient to prevent both electron and hole leakage currents in CMOS devices.

Materials growth and band offset determination of Al2O3/In0.15Ga0.85Sb/GaSb/GaAs heterostructure grown by metalorganic chemical vapor deposition

The ternary InxGa1-xSb epilayers grown on GaAs substrates by metalorganic chemical vapor deposition using a GaSb buffer layer have been demonstrated. High–resolution transmission electron microscopy micrographs illustrate an entirely relaxed GaSb buffer grown by the interfacial misfit dislocation growth mode. A high quality In0.15Ga0.85Sb epilayer was obtained on the GaSb surface with the very low threading dislocation densities (∼8.0 × 106 cm−2) and the surface roughness was 0.87 nm. The indium content of the InxGa1-xSb epilayer depends significantly on the growth temperature and approaches to a saturated value of 15% when the growth temperature was above 580 °C. Based on the X-ray photoelectron spectroscopy analyses, the valence band offset and the conduction band offset of Al2O3 with the In0.15Ga0.85Sb/GaSb/GaAs heterostructure are 3.26 eV and 2.91 eV, respectively. In addition, from the O1s energy-loss spectrum analysis, the band gap of Al2O3 is found to be ∼6.78 ± 0.05 eV.

Preparation and characterization of In0.82Ga0.18As PIN photodetectors

Using two-step growth method and buffer layer annealing treatment, the double heterojunction structures of In0.82Ga0.18As epilayer capped with InAs0.6P0.4 layer were prepared on InP substrate by low pressure metal organic chemical vapor deposition (LP-MOCVD). Based on the high quality In0.82Ga0.18As structures, the In0.82Ga0.18As PIN photodetector with cut-off wavelength of 2.56 μm at room temperature was fabricated by planar semiconductor technology, and the device performance was investigated in detail. The typical dark current at the reverse bias V R=10 mV and the resistance area product R 0 A are 5.02 μA and 0.29 Ω·cm2 at 296 K and 5.98 nA and 405.2 Ω·cm2 at 116 K, respectively. The calculated peak detectivities of the In0.82Ga0.18As photodetector are 1.21×1010 cm·Hz1/2/W at 296 K and 4.39×1011 cm·Hz1/2/W at 116 K respectively, where the quantum efficiency η=0.7 at peak wavelength is supposed. The results show that the detection performance of In0.82Ga0.18As prepared by two-step growth method can be improved greatly.

Effect of InxGa1 − xAs interlayer on the properties of In0.3Ga0.7As epitaxial films grown on Si (111) substrates by molecular beam epitaxy

High-quality In0.3Ga0.7As films have been epitaxially grown on Si (111) substrate by inserting an InxGa1−xAs interlayer with various In compositions by molecular beam epitaxy. The effect of InxGa1−xAs interlayer on the surface morphology and structural properties of In0.3Ga0.7As films is studied in detail. It reveals that In0.3Ga0.7As films grown at appropriate In composition in InxGa1−xAs interlayer exhibit smooth surface with a surface root-mean-square roughness of 1.7nm; while In0.3Ga0.7As films grown at different In composition of InxGa1−xAs interlayer show poorer properties. This work demonstrates a simple but effective method to grow high-quality In0.3Ga0.7As epilayers on Si substrates, and brings up a broad prospect for the application of InGaAs-based optoelectronic devices on Si substrates.

Staggered band gap n+In0.5Ga0.5As/p+GaAs0.5Sb0.5 Esaki diode investigations for TFET device predictions

We study in this paper the epitaxial growth and electrical characterization of an n+In0.5Ga0.5As/p+GaAs0.5Sb0.5 Esaki diode lattice matched to (001)-oriented InP substrate. First, the effects of molecular beam epitaxy growth temperature and group-V growth rates on the GaAsxSb1−x composition are characterized by means of X-ray diffraction (XRD). It is found that GaAsxSb1−x lattice constant is mainly determined by the Sb4 incorporation rather than the As4 one. After optimization, high quality In0.54Ga0.46As(Si)/GaAs0.52Sb0.48(Be) heterostructure is confirmed by XRD, Transmission electron microscope (TEM) and Secondary Ion Mass Spectroscopy (SIMS) profiles meeting requirements for sub-60mV/dec operating devices. Esaki tunnel diodes are then fabricated to be used as a prediction of Band-To-Band Tunneling (BTBT) for Tunnel Field-Effect transistors (TFETs). The results are compared to previously reported n+/p+In0.5Ga0.5As homojunction diodes, showing a ×60 factor improvement of BTBT current density for the same electric field with an excellent average Peak-to-Valley Current Ratio (PVCR) of 14.

Structural properties of In0.53Ga0.47As epitaxial films grown on Si (111) substrates by molecular beam epitaxy

In0.53Ga0.47As epitaxial films are grown on 2-inch diameter Si (111) substrates by growing a low-temperature In0.4Ga0.6As buffer layer using molecular beam epitaxy. The effect of the buffer layer thickness on the as-grown In0.53Ga0.47As films is characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy and transmission electron microscopy (TEM). It is revealed that the crystalline quality and surface morphology of as-grown In0.53Ga0.47As epilayer are strongly affected by the thickness of the In0.4Ga0.6As buffer layer. From TEM investigation, we understand that the type and the distribution of dislocations of the buffer layer and the as-grown In0.53Ga0.47As film are different. We have demonstrated that the In0.4Ga0.6As buffer layer with a thickness of 12nm can advantageously release the lattice mismatch stress between the In0.53Ga0.47As and Si substrate, ultimately leading to a high-quality In0.53Ga0.47As epitaxial film with low surface roughness.

Droplet epitaxy growth of telecom InAs quantum dots on metamorphic InAlAs/GaAs(111)A

We demonstrated the droplet epitaxial growth of InAs quantum dots on a GaAs(111)A substrate, which emitted at telecommunication wavelengths. A high-quality metamorphic In0.52Al0.48As layer was formed by inserting three monolayers of InAs between GaAs(111)A and InAlAs. InAs quantum dots were grown on the InAlAs surface by droplet epitaxy. They exhibited a laterally symmetrical shape owing to the C3v symmetry of the {111} surface. The photoluminescence signals of capped quantum dots indicated broadband spectra covering wavelengths from 1.3 to 1.55 µm. Thus, our dots are potentially useful for constructing entangled photon sources compatible with current telecommunication networks.

Control of metamorphic buffer structure and device performance of InxGa1−xAs epitaxial layers fabricated by metal organic chemical vapor deposition

Using a step-graded (SG) buffer structure via metal-organic chemical vapor deposition, we demonstrate a high suitability of In0.5Ga0.5As epitaxial layers on a GaAs substrate for electronic device application. Taking advantage of the technique’s precise control, we were able to increase the number of SG layers to achieve a fairly low dislocation density (∼106 cm−2), while keeping each individual SG layer slightly exceeding the critical thickness (∼80 nm) for strain relaxation. This met the demanded but contradictory requirements, and even offered excellent scalability by lowering the whole buffer structure down to 2.3 μm. This scalability overwhelmingly excels the forefront studies. The effects of the SG misfit strain on the crystal quality and surface morphology of In0.5Ga0.5As epitaxial layers were carefully investigated, and were correlated to threading dislocation (TD) blocking mechanisms. From microstructural analyses, TDs can be blocked effectively through self-annihilation reactions, or hindered randomly by misfit dislocation mechanisms. Growth conditions for avoiding phase separation were also explored and identified. The buffer-improved, high-quality In0.5Ga0.5As epitaxial layers enabled a high-performance, metal-oxide-semiconductor capacitor on a GaAs substrate. The devices displayed remarkable capacitance–voltage responses with small frequency dispersion. A promising interface trap density of 3 × 1012 eV−1 cm−2 in a conductance test was also obtained. These electrical performances are competitive to those using lattice-coherent but pricey InGaAs/InP systems.

Growth and characterization of In0.17Al0.83N thin films on lattice-matched GaN by molecular beam epitaxy

InxAl1−xN thin films were grown on c-plane GaN templates by plasma-assisted molecular beam epitaxy. The effect of the growth temperature on the quality and surface morphology of these InxAl1−xN thin films were examined. The alloy composition, crystalline quality and surface morphology were characterized by high-resolution x-ray diffraction, scanning electron microscopy, and atomic force microscopy. A very narrow growth temperature for high-quality In0.17Al0.83N was identified between 520 and 530°C. At the optimized growth temperature around 525°C, the In0.17Al0.83N thin films on lattice-matched GaN templates were grown with excellent crystalline quality. The value of full width at half maximum of the In0.17Al0.83N (0002) peak is 249.6arcsec, which is among the best results reported to date. The root mean square surface roughness of the In0.17Al0.83N thin films is as low as 0.47nm.

Quality-enhanced In0.3Ga0.7As film grown on GaAs substrate with an ultrathin amorphous In0.6Ga0.4As buffer layer

Using low-temperature molecular beam epitaxy, amorphous In0.6Ga0.4As layers have been grown on GaAs substrates to act as buffer layers for the subsequent epitaxial growth of In0.3Ga0.7As films. It is revealed that the crystallinity of as-grown In0.3Ga0.7As films is strongly affected by the thickness of the large-mismatched amorphous In0.6Ga0.4As buffer layer. Given an optimized thickness of 2 nm, this amorphous In0.6Ga0.4As buffer layer can efficiently release the misfit strain between the In0.3Ga0.7As epi-layer and the GaAs substrate, trap the threading and misfit dislocations from propagating to the following In0.3Ga0.7As epi-layer, and reduce the surface fluctuation of the as-grown In0.3Ga0.7As, leading to a high-quality In0.3Ga0.7As film with competitive crystallinity to that grown on GaAs substrate using compositionally graded InxGa1-xAs metamorphic buffer layers. Considering the complexity of the application of the conventional InxGa1-xAs graded buffer layers, this work demonstrates a much simpler approach to achieve high-quality In0.3Ga0.7As film on GaAs substrate and, therefore, is of huge potential for the InGaAs-based high-efficiency photovoltaic industry.

Study of the Growth and Dislocation Blocking Mechanisms in InxGa1−xAs Buffer Layer for Growing High-Quality In0.5Ga0.5P, In0.3Ga0.7As, and In0.52Ga0.48As on Misoriented GaAs Substrate for Inverted Metamorphic Multijunction Solar Cell Application

AbstractEffects of growth conditions and buffer structures on crystal quality of 1.9-eV In

Design of InxGa1−xAs buffer layers for epitaxial growth of high-quality In0.3Ga0.7As films on GaAs substrates

A phase field model is developed to simulate In0.3Ga0.7As thin films grown on an GaAs substrate with different buffer layer structures. Using this newly developed phase field model, an optimal step graded InxGa1−xAs buffer layer structure with four sub-layers of x = 0.09, 0.18, 0.27, and 0.33 is then proposed for epitaxial growth of high-quality In0.3Ga0.7As film on GaAs substrate. The strain distribution analysis by using the phase field model reveals that the compressive strain in this optimal heterostructure is partially balanced by the tensile strain caused by the uppermost two layers of In0.3Ga0.7As grown on top of In0.33Ga0.67As, which results in high-quality In0.3Ga0.7As film. The subsequent epitaxial growth of In0.3Ga0.7As films on GaAs substrates demonstrates that the surface RMS roughness and the full width at half maximum of X-ray rocking curve of as-grown In0.3Ga0.7As film with the optimal buffer layer structure are as low as 0.56 nm and 116′′, respectively, indicating very high film quality. These experimental results confirm the high effectiveness of the proposed approach to design buffer layer structure using our newly developed phase field model. This phase field model should be able to extend to hetero-epitaxial growth of other material systems apart from InGaAs.

In(Ga)As quantum dots on InGaP layers grown by solid-source molecular beam epitaxy

We report the growth of In(Ga)As quantum dots (QDs) on In0.48Ga0.52P layers with and without GaAs spacer layers using solid-source molecular beam epitaxy. We can grow high quality and high density In0.4Ga0.6As and InAs QDs on In0.48Ga0.52P layers. In0.4Ga0.6As QDs with 2nm GaAs spacer layers have high uniformity, which is confirmed by performing a photoluminescence measurement with a full-width at half maximum of 24meV. We can control the energy difference between the In0.48Ga0.52P conduction band and the QD energy state by employing GaAs spacer layers and InAs QDs, which is a useful technique for realizing optimal intermediate-band solar cells fabricated using In(Ga)As QD structures in an In0.48Ga0.52P matrix.

Effects of growth temperature on high-quality In0.2Ga0.8N layers by plasma-assisted molecular beam epitaxy

High-quality In0.2Ga0.8N epilayers were grown on a GaN template at temperatures of 520 and 580 °C via plasma-assisted molecular beam epitaxy. The X-ray rocking curve full widths at half maximum (FWHM) of (10.2) reflections is 936 arcsec for the 50-nm-thick InGaN layers at the lower temperature. When the growth temperature increases to 580 °C, the FWHM of (00.2) reflections for these samples is very narrow and keeps similar, while significant improvement of (10.2) reflections with an FWHM value of 612 arcsec has been observed. This improved quality in InGaN layers grown at 580 °C is also reflected by the much larger size of the crystalline column from the AFM results, stronger emission intensity as well as a decreased FWHM of room temperature PL from 136 to 93.9 meV.

The Growth of High Quality In0.4Ga0.6N Film on Si(111) Substrate without Phase Separation for Photovoltaic Device Applications

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