GaAs Films Research Articles

The Construction and Mechanism Study of High-Speed Carrier Transport Channel in Gallium Arsenide Homojunction Toward High-Performance Photoelectrochemical Photodetector.

The energy band structure and surface/interface properties are prerequisite for not only preserving the intrinsic material quality but also manipulating carrier transport behavior for photoelectrochemical (PEC) photodetection. How to precisely design/regulate the band structure and surface/interface properties of semiconductor materials is the key to improving the performance of PEC photodetection. Herein, the quintuple heterotypic homojunction (QH) GaAs film is fabricated with a gradient energy band via plasma-assisted molecular beam epitaxy for constructing a high-speed carrier transport channel in PEC photodetection, which can efficiently drive the separation and transport of photogenerated electron-hole pairs. The designed QH-GaAs-based PEC photodetector exhibits excellent performances, compared with bare i-GaAs, delivering an ultrashort rise/decay times of only 1.1/1.1ms and a high responsivity of 20.4mAW-1 at 0V under 850nm illumination. Strikingly, an ultrahigh detectivity with 1.46×1012 Jones is achieved. More importantly, the QH-GaAs device can stably operate underwater seawater environment. This study provides a novel strategy for designing and fabricating multiple heterotypic homojunction with gradient energy band to boost charge transport dynamics for PEC fields.

Enhanced Antireflection and Absorption in Thin Film GaAs Solar Cells Using Dielectric Composite Nanostructures

This study investigates the application of dielectric composite nanostructures (DCNs) to enhance both antireflection and absorption properties in thin film GaAs solar cells, which are crucial for reducing production costs and improving energy conversion efficiency in photovoltaic devices. Building upon previous experimental validations, this work systematically explores the underlying theoretical mechanisms using the finite difference time domain (FDTD) method to analyze the light interaction with the proposed DCNs. The results show that the combination of Mie resonance, Fabry–Perot resonance, and guided resonance, induced by the surface structuring of the DCNs, significantly enhances light absorption in the active layer, particularly at longer wavelengths. For solar cells featuring a 500-nm-thick absorber layer, SARL-decorated solar cells demonstrated an average reflectivity of 12.18%, whereas those incorporating DCNs exhibited a significantly reduced average reflectivity of 4.52%. These findings indicate that DCNs structures are highly effective in enhancing the performance of thin and ultra-thin GaAs solar cells by minimizing surface reflection and increasing photon utilization, offering a promising solution for high efficiency, cost effective photovoltaic devices.

Design perspectives of a thin film GaAs solar cell integrated with Carrier Selective contacts and anti-reflection coatings: Optical and device analysis

III-V thin-film solar cells (SCs) have shown exceptional optoelectronic properties and remarkable power conversion efficiency (PCE), attributed to their outstanding charge transport, efficient photon trapping, adaptability, and recycling of photons. In particular, incorporating anti-reflective coatings (ARCs) made from wide-bandgap oxides has proven effective in reducing optical losses, with reductions as low as 20 % being reported. Furthermore, the use of carrier-selective contacts in these designs not only eliminates the need for complex doped junctions but also simplifies the fabrication process, further enhancing their performance. Despite these advancements, relatively few studies have explored the integration of both ARCs and carrier-selective contacts in gallium arsenide (GaAs)-based thin-film solar cells. This gap represents a significant opportunity for improving the efficiency and performance of these devices. To address this, we present a GaAs thin-film solar cell incorporating an ARC layer for enhanced light-trapping and optimized photon absorption. In addition, we integrate carrier-selective contacts using titanium dioxide (TiO2) as the electron transport layer and molybdenum oxide (MoO3) as the hole transport layer, ensuring effective charge separation and collection. Our optical analysis demonstrates that, with an optimized ARC thickness, the optical losses in the 380 nm-thick GaAs absorber layer can be limited to 20 %. Moreover, by maintaining a surface recombination velocity (SRV) of 103 cm/s and a carrier lifetime of 10μs, the proposed design achieves an impressive PCE of approximately 23 %. This study highlights the potential of combining ARCs and carrier-selective contacts to push the performance of GaAs thin-film solar cells to new heights, paving the way for more efficient, and cost-effective photovoltaic technologies.

Indepth doping assessment of thick doped GaAs layer by scanning spreading resistance microscopy

Scanning spreading resistance microscopy (SSRM) measurements were performed on GaAs thick films grown by hydride vapor phase epitaxy technology under different growth conditions to evaluate their carrier concentrations. For this purpose, a calibration curve was established based on a multilayer staircase structure grown by molecular beam epitaxy. The dopant calibration range measured by secondary ion mass spectrometry is from 5 × 1016 to 1019 cm−3. An abnormal phenomenon in the calibration process was explained by taking into account the parasitic parallel resistance of the calibration samples. Finally, the calibration curve was used to quantitatively analyze the carriers inside the Zn doping p-type GaAs film from 4 × 1016 to 1018 cm−3 range. We demonstrate here the applicability of SSRM to the in-depth analysis of thick epilayers, providing new inputs for the control of thick film technologies.

Effects ofAs8structure formation on the surface morphology and internal microstructure of GaAs thin films.

Gallium arsenide (GaAs) materials have the advantages of high electron mobility, electron saturation drift rate, and other irreplaceable semiconducting properties. They play an important role in the electronics, solar and other fields. However, during GaAs film sedimentary growth, As atoms can undergo segregation to formAs8clusters because of the influence of external factors, which affect the surface morphology and internal structure of these films. In this study, a series of investigations on the deposition and growth of GaAs crystal films were performed. Additionally, the deposition and growth of GaAs thin films were simulated using molecular dynamics. The influence of As8clusters on the surface morphology and internal structure of GaAs films at different incidence angles, velocities and substrate temperatures was studied by using 'defect analysis technology' and 'diamond structure identification' in open source software, along with surface roughness and radial distribution function. Results show that with increasing incident angle, the number ofAs8clusters decreases and film density increases. Increasing incident velocity increases the irregular movement ofAs8clusters in air, and their deposition on the film surface affects the morphology of the film, and the surface roughness increases first and then decreases. Additionally, we investigated the effect of different substrate temperatures on the film surface. Results show that at a substrate temperature of 1173 K, the number ofAs8clusters in the film decreases or the As8clusters disappear, heterogeneous nucleation occurs in the film, and the crystallization rate increases. Although the dislocation line associated with nucleation may affect the mechanical and optical properties of the film, it considerably reduces the annealing effort after the deposition and growth.

High performance GaAs ultrathin film solar cell based on optimized antireflection coating and dielectric nano-cylinders

This study presents an ultrathin crystalline GaAs solar cell consists of titanium dioxide (TiO2) nano-cylinders partially embedded in the GaAs film and covered by a proper antireflection coating. For light trapping over the solar spectrum and consequently, enhancing the optical and electrical characteristics of the cell, the thickness and refractive index (RI) of the antireflection coating and the embedding depth of the nano-cylinders in the GaAs film have been optimized. Also, aluminum (Al) metallic layer is applied at the backside of the cell to obtain a higher absorption at longer wavelengths due to photon reflection into the GaAs film. In the suggested solar cell, improvements of 70.65 % and 78.12 % in the short current density (JSC) and the power conversion efficiency are obtained, respectively compared to the conventional GaAs solar cell (Case 1).

Thermal Optical Fiber Sensor Based on GaAs Film for Fluid Velocity Measurement

Thermal Optical Fiber Sensor Based on GaAs Film for Fluid Velocity Measurement

Epitaxial growth of high-quality GaAs on Si(001) using ultrathin buffer layers

The direct growth of III–V semiconductors on silicon holds tremendous potential for photonics applications. However, the inherent differences in their properties lead to defects in the epitaxial layer, including threading dislocations (TDs), antiphase boundaries (APBs), and thermal cracks, significantly impacting device performance. Current processes struggle to suppress these defects simultaneously, necessitating the development of methods to inhibit TDs and APBs in a thin buffer on silicon. This study introduces a GaSb buffer layer during GaAs epitaxy on a silicon (001) substrate. This approach successfully suppresses defect formation by promoting the formation of interfacial misfit dislocation arrays at both the AlSb/Si and GaAs/GaSb interfaces. The resulting GaAs layer exhibits a step-flow surface with a rough mean square of ∼3.8 nm and a full width at half maximum of 158 arcsec. Remarkably, the growth is achieved without any observable interfacial intermixing. Building on this platform, InAs/GaAs quantum dots are grown with a density of 3.8 × 1010 cm−2, emitting at a wavelength of 1288 nm. This breakthrough holds immense promise for developing high-quality GaAs films with reduced defect densities on silicon for O band lasers, laying the foundation for the mass production of silicon-based integrated circuits.

Theoretical exploration of photoemission characteristics of GaAs nanowire array cathode based on photon-enhanced thermionic emission

The theoretical photoemission models of single GaAs nanowire and nanowire array cathode based on photon-enhanced thermionic emission (PETE) mechanism are respectively developed by utilizing two-dimensional continuity equations. Based on the built models in this work, the effect of several key factors on the quantum efficiency are also discussed. Results show that GaAs nanowire cathode exhibits the superiority of photoemission performance compared with GaAs film cathode at the spectral range of 300∼600 nm. Besides, the optimal wire diameter of GaAs nanowire cathode is in the range of 340∼360 nm. In addition, the nanowire cathode with low electron affinity of 0.3 eV achieves PETE effect under low temperature of 400 K, which is conducive to improve the stability of cathode. Moreover, increasing the incident light angle or decreasing the array spacing provides an effective method of obtaining high quantum efficiency of nanowire array cathode. Furthermore, the numerical difference between quantum efficiency and effective quantum efficiency implies that the low collection efficiency of emitted electrons is the main issue that hinders the application of PETE cathodes of GaAs nanowire array. The proposed GaAs nanowire array model would provide theoretical guidance for optimum design of PETE cathodes with nanoarray structure.

Study of the free carrier characteristics and surface morphology of AlGaAs/GaAs thin films deposited using MOCVD

Ultra-low loss optical thin films find broad applications in fields such as vertical-cavity surface-emitting lasers and optical atomic clocks. The main optical losses in AlGaAs/GaAs distributed Bragg reflectors (DBRs) prepared using metal-organic chemical vapor deposition (MOCVD) arise from absorption loss caused by free carriers within the layers and scattering loss caused by surface roughness. In this study, we fabricated AlGaAs and GaAs single-layer thin films with varying Al compositions on substrates of three crystal orientations and under different V/III ratios. The dependence of carrier concentration and surface morphology on different substrates and growth conditions was investigated. Thin films grown on substrates with three different crystal orientations exhibited three distinct growth modes (step-flow mode, SK mode, and FM mode). The impact of the V/III ratio on the growth mode was found to be complex. Higher V/III ratios resulted in poorer morphology for films grown on (100) substrates, while better morphology was observed on (211) B substrates. Furthermore, the surface morphology of films grown on (100) 15° off substrates showed less sensitivity to changes in the V/III ratio. With increasing Al composition, the carrier concentration of the films significantly increased. Elevating the V/III ratio proved effective in suppressing the incorporation of carbon, thereby reducing the carrier concentration of AlGaAs films. GaAs films exhibited a low carrier concentration at an appropriate V/III ratio. Additionally, the distinct abilities of different substrates to adsorb impurities exerted a significant impact on the carrier concentration of the films. This study demonstrates that, under optimal conditions, it is feasible to fabricate AlGaAs/GaAs Bragg mirrors with low carrier concentration and relatively small roughness on (100) 15° off substrates.

Nucleation Selectivity and Lateral Coalescence of GaAs over Graphene on Ge(111).

We use epitaxial lateral overgrowth (ELO) to produce semimetallic graphene nanostructures embedded in a semiconducting GaAs matrix for potential applications in plasmonics, THz generation and detection, and tunnel junctions in multijunction solar cells. We show that (1) the combination of low sticking coefficient and fast surface diffusion on graphene enhances nucleation selectivity at exposed regions of the substrate and (2) high growth temperatures favor efficient lateral overgrowth, coalescence, and planarization of epitaxial GaAs films over the graphene nanostructures. Our work provides a more complete understanding of ELO using graphene masks, as opposed to more conventional dielectric masks, and enables new types of metal/semiconductor nanocomposites.

Room Temperature NUV‐To‐NIR Up‐ and Down‐Conversion Photoluminescence in Erbium‐Doped GaAs

AbstractErbium (Er)‐doped III‐V semiconductors are promising for optoelectronic devices due to the unique intra‐4f electronic transitions of Er3+; however, the Er‐related luminescence at room temperature has always been challenging to obtain. In this work, High crystalline quality ErAs:GaAs films are grown with self‐assembled ErAs nanoparticles embedded within the GaAs matrix by molecular beam epitaxy. Rich photoluminescence spectra in a broad wavelength ranging from near‐ultraviolet to near‐infrared are observed at room temperature and confirmed to be Er‐related. A carrier‐mediated energy transfer up‐conversion mechanism is proposed, and the pump power‐dependent photoluminescence results reveal that the excited‐state absorption is governed by a single photonic process. The efficient interaction and energy transfer between the semiconductor matrix and Er3+ ions offered by this unique nanocomposite material provide a promising route to achieve novel optoelectronic devices with the potential to cover a broad wavelength range.

Design Optimization of Gas Distribution System for Large‐Scale Capacity GaAs‐MOCVD

AbstractIn the flexible photovoltaic (PV) industry, increment of the metal‐organic chemical vapor deposition (MOCVD) deposition zone is crucial to reducing the cost of ownership and increasing the power conversion efficiency (PCE). This implies that the larger closed coupled showerhead (CCS) of MOCVD system should be used in the manufacture of flexible gallium arsenide (GaAs) PV thin‐film solar cells. Currently, Aixtron Crius II is the largest commercial CCS reactor for GaAs deposition with 55 × 2 inches circular wafers. As the size of the carrier and showerhead increases, the deposition uniformity and gas flow stability become more difficult to control. To address these issues, previous studies have investigated the effects of geometric and process parameters of MOCVD on the vertical process gas inlet, with either a rotating carrier model represented by Veeco using high‐speed rotating carrier (Turbo Disc), and Aixtron using low‐speed rotating planetary carrier, or a horizontal process gas injector with a rotating carrier. However, these efforts have limited further capacity scale‐up. In this study, numerical simulations and fluid visualization experiments are conducted, based on previous research on thermal uniformity, for design optimization of a gas distribution system in a large square GaAs‐MOCVD reactor. The achieved reactor capacity is 36 × 4 inches square wafers in one process cycle, and the optimal average deposition rate and deposition uniformity of GaAs film are ≈0.430 µm min−1 and 0.93%, respectively.

Doping Properties of GaAs Film Grown by Molecular Beam Epitaxy

In order to make GaAs-based devices widely applicated in high-frequency and mobile communication, we use molecular beam epitaxy to grow GaAs thin films, and achieve the enhancement of GaAs thin film mobility and the increase of band width by doping control techniques. In our experiments, we use Si as dopant source to obtain GaAs thin films with high doping concentration, and we prepare and test the samples with different dopant source temperatures to achieve the regulation of the band gap, film luminescence intensity, surface roughness and mobility. The doping concentration of the prepared GaAs thin film layer was achieved at 1250 °C with Si doping source of 2.07 × 1018 cm−3, the mobility was 2097 cm2/V·s, and the photoluminescence(PL) intensity was increased by 100 times compared with the non-doped film.

High-Performance Flexible GaAs Nanofilm UV Photodetectors

Flexible ultraviolet (UV) photodetectors have attracted extensive research interest due to their potential applications in personal UV monitoring, UV electronic eye, anti-UV gloves, and other wearable systems. In this study, we present a highly sensitive flexible UV photodetector based on an ultrathin GaAs layer that is produced using a metal–organic chemical vapor deposition method and epitaxial lift-off film transfer technology. Device performance analysis reveals that the photodetectors made of a 50 nm thick GaAs layer have excellent sensitivity to 365 nm light. Specifically, the responsivity, specific detectivity, and external quantum efficiency could reach as high as 99.01 A W–1, 1.51 × 1012 Jones, and 3.37 × 104%, respectively, at −2 V bias voltage, which are comparable to many UV photodetectors made from conventional wide band gap semiconductors. Such outstanding UV response properties are related to the very high absorption coefficient for UV light and carrier mobility of an ultrathin GaAs film. Equally importantly, the mechanical flexibility resulting from reducing the film thickness allows the device to maintain its photoelectric properties even after more than 500 bending cycles. The totality of these results suggests that our flexible UV photodetectors have strong potential applications in future wearable devices.

Study of surface morphology in GaAs by hydrogen and helium implantation at elevated temperature

In this work, the surface morphology and internal defect evolution process of GaAs substrates implanted with light ions of different fluence combinations are studied. The influence of H and He ions implantation on the atomic mechanism of the blister phenomenon observed after annealing is investigated. Raman spectroscopy is used to measure the surface stress change of different samples before and after implantation and annealing. Optical microscopy and atomic force microscopy are used to characterize the morphology changes of the GaAs surface under different annealing conditions. The evolution of bubbles and defects in GaAs crystals is revealed by transmission electron microscopy. Through this study, it is hoped that ion implantation fluence, surface exfoliation efficiency and exfoliation cost can be optimized. At the same time, it also lays a foundation for the heterointegration of GaAs film on Si.

Study of Nitridation Effect on Structural, Morphological, and Optical Properties of GaAs Film Growth on Silicon Substrates via Close Space Vapor Transport Technique

In this work, Gallium Arsenide (GaAs) films growth via Close Space Vapor Transport (CSVT) technique on n-type Silicon (Si) substrates (100) and its nitridation effect in the ammonia (NH3) environment is reported. The GaAs films were grown at 800, 900, and 1000 ∘C, and the nitridation process was carried out at 900 ∘C with an NH3:H2 gasses ratio. The GaAs films with and without nitridation process were analyzed using X-ray diffraction (XRD), Raman spectroscopy, Diffuse Reflectance Spectroscopy, and Scanning Electron Microscopy with Energy Dispersive X-ray analysis (SEM-EDX). Grazing incidence X-ray diffraction measurements of GaAs films nitrided confirm a polycrystalline GaN wurtzite structure with preferential orientation along (002), and additionality, a crystallographic plane (310) of low intensity is observed in 2θ=52.18∘ corresponding to Ga2O3. The average quantification results in weight (Wt. %) of GaAs films nitrided was determined by EDS; Ga∼79, N∼17.1, O∼2 and As∼1.8 Wt. %. The presence of GaN, GaxOy, Si, and GaAs modes were found by Raman measurements, demonstrating a partial nitriding. The band gap estimation by diffuse reflectance was between 3.2 and 3.38 eV such values are close to that reported for bulk GaN (3.4 eV). The presence of oxygen in the structure could be related to substrates or the GaAs source.

Epitaxial lift-off method for GaAs solar cells with high Al content AlGaAs window layer

The epitaxial GaAs substrate lift-off (ELO) technique is widely used to produce thin film III–V semiconductor optoelectronic devices. However, the hydrofluoric (HF) acid used in the process forbids the incorporation of active AlGaAs device layers with high Al content due to its selective etching. In this work, a new ELO method is presented, which allows for the protection of AlGaAs layers against the HF acid attack. The method is used here to prepare and analyse thin film GaAs solar cells containing Al0.85Ga0.15As window layer. We employ a sacrificial GaAs buffer and device perimeter pre-processing that covers the exposed edges with back contact metals and electroplated Cu. A comparison of the epitaxially lifted GaAs solar cells with identical cells prepared by substrate etching demonstrates identical photovoltaic figures of merit and confirms the viability of the AlGaAs protection approach. In addition to applications in thin film photovoltaics, this ELO method can be applied to solid-state lasers and single-photon emitters employing AlGaAs-based Bragg reflectors, among other III–V semiconductor optoelectronic devices.

InAs/GaAs quantum-dot lasers grown on on-axis Si (001) without dislocation filter layers.

InAs/GaAs quantum dot (QD) laser monolithically grown on silicon is one of the potential approaches to realizing silicon-based light sources. However, the mismatch between GaAs and Si generates a high density of threading dislocations (TDs) and antiphase boundaries (APBs), which trap carriers and adversely affect device performance. In this paper, we present a simple method to reduce the threading dislocation density (TDD) merely through GaAs buffer, eliminating the intricate dislocation filter layers (DFLs) as well as any intermediate buffer layers whose compositions are different from the target GaAs. An APB-free epitaxial 2.5 µm GaAs film was grown on exact Si (001) by metalorganic chemical vapor deposition (MOCVD) with a TDD of 9.4 × 106 cm-2. InAs/GaAs QDs with a density of 5.2 × 1010 cm-2 were grown on this GaAs/Si (001) virtual substrate by molecular beam epitaxy (MBE) system. The fabricated QD laser has achieved a single facet room temperature continuous-wave output power of 138 mW with a threshold current density of 397 A/cm2 and a lasing wavelength of 1306 nm. In this work, we propose a simplified method to fabricate high-power QD lasers, which is expected to promote the application of photonic integrated circuits.

Si‐Doping of Low‐Temperature‐Grown GaAs Heterostructures on (100) and (111)A GaAs Substrates

Utilizing the amphoteric property of silicon impurity in GaAs (111)A for acceptor doping of low‐temperature‐grown (LTG‐) GaAs films and LTG‐GaAs‐based heterostructures for THz photoconductive applications is proposed and realized. The electronic properties of superlattice structures {LTG‐GaAs/GaAs:Si} grown by molecular beam epitaxy on (100) and (111)A GaAs substrates are experimentally investigated, where GaAs:Si are silicon‐doped GaAs layers grown at standard conditions. The use of GaAs substrates with surface orientation (111)A results in spatially indirect p‐type doping of LTG‐GaAs layers. In addition, the charge redistribution at the LTG‐GaAs/GaAs:Si interfaces, due to the presence of silicon atoms in GaAs:Si layers and antisite point defects in adjacent LTG‐GaAs layers, is also analyzed by means of band structure modeling.