GaAs Thin Films Research Articles

Homoepitaxial growth of device-grade GaAs using low-pressure remote plasma CVD

We have achieved the growth of high-quality, homoepitaxial 100 GaAs thin films at 0.5 mbar and 500 °C using a Remote Plasma Chemical Vapor Deposition (RP-CVD) reactor. With this process, we demonstrate a film growth rate up to 3 μm/h, comparable to the conventional MOCVD technique. The resulting films exhibit structural characteristics close to those of commercial GaAs wafers, with excellent crystalline quality as confirmed by SAED patterns and XRD rocking-curve measurements for the 004 peak with a FWHM of 0.004°. AFM measurements reveal a surface roughness of 0.2 nm, similar to that of a polished wafer. Analysis of the chemical composition – as determined through XPS surface and depth-profiled measurements – indicates that the film is homogeneous, with a constant III/V ratio of 1 throughout the whole layer, and has no detectable carbon or oxygen contamination. Additionally, the films demonstrate a sharp photoluminescence peak (FWHM of 55 meV), a p-type doping concentration of 1.1018 cm−3, and a hole mobility of 172 cm2 V⁻1.s⁻1. This work thus demonstrates a cost-effective growth method for III-V devices, enabled by the reduced gas consumption (only a few sccm, compared to tens of L/min in MOCVD) in RP-CVD operation at low pressure.

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.

High-efficiency ultra-thin GaAs solar cells based on ITO/Ag/ITO transparent electrodes and photonic crystals

Ultrathin photovoltaic technology has great potential to improve efficiency and reduce costs. However, achieving optical thickness requires an effective light capture strategy. In this study, for GaAs thin film solar cells with an active layer thickness of 500 nm, we adopt a combination strategy of front-end ITO/Ag/ITO transparent electrodes and back-end photonic crystals (PC). By employing the finite difference time domain (FDTD) simulation, we verify that ITO/Ag/ITO transparent electrodes and AlGaAs PC can effectively enhance the light-harvesting capacity of cells. The proposed cell structure has a spectral absorption rate (SAR) of 0.9781 in the visible wavelength range. To further optimize the photovoltaic performance parameters, we optimize the doping concentration of the pn junction in the cell. Finally, the short circuit current density Jsc, open circuit voltage Voc, fill factor (FF) and photoelectric conversion efficiency (PCE) of GaAs thin film solar cells are successfully increased to 31.10mAcm−2, 1.28V, 88.18% and 35.12%, respectively. This provides crucial experimental validation and theoretical guidance for advancing ultra-thin photovoltaic technology.

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.

Archimedes optimization algorithm based parameter extraction of photovoltaic models on a decent basis for novel accurate RMSE calculation

Solar photovoltaic (PV) technology stands as a promising alternative to conventional fossil fuel-based power generation, offering pollution-free and low-maintenance energy production. To harness its potential effectively, understanding the power generation process and accurately modeling solar PV systems are essential. Unfortunately, manufacturers often do not provide the necessary parameters for modeling solar cells, making it challenging for researchers. This research employs the Archimedes Optimization Algorithm (AOA), an optimization technique, to determine unknown parameters for the PVM752 GaAs thin film solar cell and the RTC France solar cell. The modeling of these solar cells utilizes both a Single Diode Model (SDM) and a Double Diode Model (DDM). Performance evaluations are conducted using the sum of individual absolute errors (SIAE) and a novel root mean square error (RMSE) method. Comparing the effectiveness of the AOA with other optimization methods, The RMSEs for the AOA applied to the SDM and DDM of RTC France solar cell were 3.7415 × 10–3 and 1.0033 × 10–3. Similarly, for PVM752 GaAs thin film solar cell were 1.6564 × 10–3, and 0.00106365, respectively. The SIAE values for both solar diode models of RTC France cells were 0.071845 and 0.021268, respectively. For the PVM752 GaAs thin film, the corresponding SIAE values were 0.031488 and 0.040224. The results highlight the efficiency of the AOA-based approach, showcasing consistent convergence and a high level of accuracy in obtained solutions. The suggested approach produces superior results with a lower RMSE compared to other algorithms, demonstrating its efficacy in determining solar PV parameters for modeling purposes.

A new method for direct extraction of ambipolar diffusion length in a thin film by scanning photoluminescence microscopy

In this study, we demonstrate a new method of scanning photoluminescence (PL) microscopy (SPLM) to directly extract the ambipolar diffusion length in a GaAs thin film. The PL intensity of the GaAs thin film was recorded while the excitation source scanned along a 400 nm wide slit between the metal masks to avoid the influence of surface recombination and light scattering at the sample edge. The experimental SPLM profile showed a simple-exponential-decay functional form and was numerically verified. A fitted decay length of 723 nm was extracted, which represents the ambipolar diffusion length of the GaAs thin film and agrees well with our previous study.

Miniaturised wideband bandpass filter with good selectivity based on 3D heterogeneous integrated passive device technology

AbstractThe miniaturised wideband filter with good frequency selectivity and wide stopband is proposed, which is based on three‐dimensional (3D) heterogeneous integrated passive device technology. The proposed sixth‐order wideband bandpass filter is based on the magnetic‐coupling‐loaded highpass‐lowpass lumped topology and implemented by the 3D heterogeneous integration process, integrating GaAs‐based and Glass‐based micro‐nano‐scale processes together. Then, lumped inductors are designed in the Glass substrate with low dielectric loss tangent and realised by a three‐dimensional spiral structure. Therefore, the inductors have high quality factors and small sizes. The lumped capacitors are designed using the GaAs thin film process. Finally, a prototype with a 3‐dB fractional bandwidth of 42% is designed and fabricated at 3.875 GHz (f0). The upper‐stopband attenuation higher than 30 dB is extended to more than 5.15f0. It occupies only 0.014 × 0.018 λ02 (1.1 × 1.42 mm2), where λ0 is the free‐space wavelength at f0.

Parametric estimation of photovoltaic systems using a new multi-hybrid evolutionary algorithm

Integrating solar photovoltaic (PV) systems into the modern power grid introduces a variety of new problems. The accurate modelling of PV is required to strengthen the system characteristics in simulation environments. Modelling such PV systems is reflected by a nonlinear I–V characteristic curve behaviour with numerous unknown parameters because there is insufficient data in the cells’ datasheet. As a result, it is always a priority to identify these unknown parameters. To extract features of solar modules and build high-accuracy models for modelling, control, and optimization of PV systems, current–voltage data is required. A hybrid evolutionary algorithm is proposed in this paper for precise and effective parameter estimation from experimental data of various PV models. The proposed algorithm is named as hybrid flower grey differential (HFGD) algorithm and is based on the hybridization of flower pollination algorithm (FPA), grey wolf optimizer (GWO), and differential evolution (DE) algorithm. For performance evaluation, CEC 2019 benchmark data set is used. To increase the accuracy of the output solutions, we also combined the Newton–Raphson approach with the proposed algorithm. Four PV cells/modules with diverse characteristics, including RTC France Single Diode Model (SDM), RTC France Double DM (DDM), Amorphous Silicon aSi:H, and PVM 752 GaAs Thin-Film, are used to validate the effectiveness as well as the feasibility of the proposed algorithm. The parameter results obtained through the utilization of HFGD algorithm have been compared with other evolutionary algorithms through aspects of precision, reliability, and convergence. Based on the outcomes of the comparison, it has been seen that the HFGD algorithm obtained the lowest root-mean-square error (RMSE) value. Friedman’s rank and Wilcoxon test are carried out for the statistical analysis of the proposed work. The I–V and P–V characteristics are drawn along with the box plot for different PV cells/modules. Statistical and experimental results show the superiority of the proposed algorithm with respect to its counterpart.

Numerical Simulations of Space Charge Waves Amplification Using Negative Differential Conductance in Strained Si/SiGe at 4.2 K

This paper introduces a two-dimensional (2D) numerical simulation of the amplification of space charge waves using negative differential conductance in a typical MOS silicon–germanium (SiGe)-based field-effect transistors (FET) and complementary metal oxide semiconductor (CMOS) technology at 4.2 K. The hydrodynamic model of electron transport was applied to describe the amplification of space charge waves in this nonlinear medium (i.e., the negative differential conductance). This phenomenon shows up in GaAs thin films at room temperature. However, this can be also observed in a strained Si/SiGe heterostructure at very low temperatures (T < 77 K) and at high electric fields (E > 10 KV/cm). The results show the amplification and non-linear interaction of space charge waves in a strained Si/SiGe heterostructure occurs for frequencies up to approximately 60 GHz at T = 1.3 K, 47 GHz at T = 4.2 K, and 40 GHz at T = 77 K. The variation of concentration and electric field in the Z and Y directions are calculated at 4.2 K. The electric field in the Z direction is greater than in the Y direction. This is due to the fact that this is the direction of electron motion. In addition to deep space applications, these types of devices have potential uses in terrestrial applications which include magnetic levitation transportation systems, medical diagnostics, cryogenic instrumentation, and superconducting magnetic energy storage systems.

Inverse design of omnidirectional coherent absorbers for optical power beaming applications.

An efficient photovoltaic power converter is a critical element in laser power beaming systems for maximizing the end-to-end power transfer efficiency while minimizing beam reflections from the receiver for safety considerations. We designed a multilayer absorber that can efficiently trap monochromatic light from broad incident angles. The proposed design is built on the concept of a one-way coherent absorber with inverse-designed aperiodic multilayer front- and back-reflectors that enable maximal optical absorption in a thin-film photovoltaic material for broad angles. We argue that the broad bandwidth is achieved through an optimization search process that automatically engineers the modal content of the cavity to create multiple overlapping resonant modes at the desired angle or frequency range. A realistic design is provided based on GaAs thin films with inverse-designed multilayer binary AlAs/AlGaAs mirrors. The proposed device can pave the way for efficient optical power beaming systems.

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-efficiency and cost-effective manufacturing of solar cells based on localized surface plasmonic resonance

Improving photovoltaic efficiency is essential to the early realization of universal solar cell application, which has proven to be the most promising solution to the global energy transition. Therefore, we propose a thin-film GaAs solar cell with TiO2 quantum dots, plasmonic Ag nanoparticles, and the AlGaAs window layer. First, we using the finite difference time domain method to simulate the electromagnetic wave propagation and the solar cell light absorption under set boundary conditions to test whether the TiO2 quantum dots and plasmonic Ag nanoparticles can improve the cell light-trapping ability. The results show that the light absorption of the cell can be maintained above 95% in the visible wavelength range of 300–721 nm, with an average absorption of 97.7%. The photoabsorption effect is particularly prominent at 558 nm, with an absorption rate of 99.86%. The p-n junction doping concentration and the molar fraction of the AlGaAs window layer were optimized to obtain better photovoltaic performance parameters. The results show that AlGaAs reduces incident light loss and possesses a higher potential barrier in the emitter region because of its wider band gap, effectively lowering carrier recombination rate and consequently enhancing the photovoltaics characteristics of the cell. The short-circuit current density, open-circuit voltage, and photoelectric conversion efficiency (PCE) of the thin-film GaAs solar cell improved to 30.01 mA/cm2, 1.247 V, and 33.43%, respectively. Thus, this study provides an effective strategy for high-performance fabrication of the thin-film solar cells, demonstrating significant potential for broad applications in cost-effective solar cell usage and mitigating the climate change crisis.

Computational Investigation of c-GaN/GaAs1–x N x /GaAs Heterojunction Solar Cell

GaN-based electronics have witnessed an increase in both research and industrial activities, first spurred by the successful demonstration of GaN LEDs, and are now expanding into transistors and photovoltaic cells. In addition, GaN/GaAs heterojunction devices are currently receiving much interest. In this study, we conduct rigorous optoelectronic computational analysis of cubic phase GaN (c-GaN)/GaAs heterojunction solar cells for a comprehensive understanding of the cell. We utilize a compositionally graded GaAs1–xNx buffer layer to reduce defect states at the heterojunction interface caused by a significant lattice mismatch between c-GaN and GaAs. Furthermore, we enhance the performance of the cell by optimizing GaAs absorber layer thickness and c-GaN buffer layer doping concentration. Moreover, we examine the effects of GaAs1–xNx/GaAs interface recombination velocity (IRV) on the cell. Overall, we achieve ~23% power conversion efficiency within 1.25- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> thin-film GaAs at low GaAs1–xNx/GaAs IRV. The analyses and results presented in this study demonstrate the vast application potential of c-GaN/GaAs heterojunction in high-efficiency solar cells.

The Co-Design of Broadband Diplexer and Quasi-Reflectionless Lowpass/Highpass TFIPD Filter Chip

A new ultra-miniaturized 5G N78 and N79 diplexer based on GaAs Thin Film Integrated Passive Device (TFIPD) technology is proposed in this brief. By a NiCr thin film resistor, the quasi-reflectionless lowpass/highpass filter can also be achieved on the same circuit structure without any increase of size. Circuit schematic is composed of serial-parallel inductances and capacitances, which generates out-of-band transmission zeros. The proposed design provides <2 dB insertion loss and >15 dB out-of-band rejection. Therefore, the GaAs-based TFIPD technology can support low-loss, high-precision, and miniaturized design desires of 5G radio-frequency (RF) front-end devices. Chip model is demonstrated through EM simulation, wafer fabrication, and measurement.

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.

Parameter extraction of photovoltaic models using atomic orbital search algorithm on a decent basis for novel accurate RMSE calculation

In the available literature, there are several methods and techniques are employed to extract the unknown parameters of solar cell. The performance of the method used is validated on the basis of Root Mean Square Error (RMSE) value. This work aims to promote a decent basis for proper investigation and the implementation of an optimization algorithm to extract solar unknown parameters. In this work, the true value of RMSE is calculated for the single diode model of the RTC France solar cell using 30 different methods published in several literatures. The obtained results show that the approach of calculating RMSE is not precise in most of the published literature. The Atomic Orbital Search algorithm is proposed as a new metaheuristic optimisation method to extract the parameters of a single diode, double diode and three diode models for RTC France and PVM752 GaAs thin film solar cell. Last, the performance of the proposed algorithm is compared with other different optimisation algorithms. It is observed that the proposed algorithm gives best results with less RMSE as compared to other algorithms. This work intends to provide a solid foundation for thorough analysis and implementation of an optimization technique to extract unknown solar parameters.

Design of GaAs-thin film solar cell using TiO2 hemispherical nanoparticles array

In this paper, GaAs-thin film solar cell based on the titanium dioxide (TiO2) hemispherical nanoparticles array with active layer thickness of 1 μm is proposed. To reflect the transmitted light into the active layer, a back reflector (BR) composed of SiO2/GaAs multilayer is applied at the backside of the GaAs active layer. Simulation results show that, TiO2 hemispherical nanoparticles can trap the light in the active layer and enhance the light absorption. In this way, TiO2 hemispherical nanoparticles array on the front of the GaAs active layer is applied. According to the outcomes, the photocurrent density (Jph) and power conversion efficiency (PCE) for a normally incident light are calculated as 30.44 (mA/cm2) and 28.67%, respectively. Compared to the conventional 1 μm GaAs thin film solar cell, the Jph and PCE are enhanced by 51.2% and 47%, respectively. Simulation results are obtained using the finite difference time domain (FDTD) method.

Comprehensive analysis of photon dynamics in thin-film GaAs solar cells with planar and textured rear mirrors

This study describes a comprehensive analysis of light trapping and photon recycling (PR) in thin-film GaAs solar cells, explicitly considering the effects of (non-perfect) light scattering at a textured rear mirror. We calculate the probabilities of escape, reabsorption in the absorber and parasitic absorption for internally generated photons, as well as the reflectance, absorptance and parasitic absorptance of externally incident photons. Combined with the internal luminescent efficiency to account for non-radiative recombination non-explicitly, but in a phenomenological manner, device performance metrics such as the short-circuit current density ( J s c ), open-circuit voltage ( V o c ) and its radiative limit, the external luminescent efficiency, the contribution of PR to the V o c and the power conversion efficiency ( P C E ) are derived. We analyze a typical thin-film GaAs solar cell architecture, consisting of an n-GaAs/p-InGaP heterojunction structure cladded by commonly employed front- and rear-side layer stacks. The probabilities of escape, reabsorption and parasitic absorption and the resulting performance metrics are presented as a function of absorber thickness, rear-mirror reflectivity, haze factor, internal luminescent efficiency, front grid coverage and band tailing. The simulations show that the implementation of a textured rear mirror reduces PR and its importance for device performance. In these textured cells, a high rear-mirror reflectivity and, thereby, efficient PR, is less crucial to achieve V o c values close to the radiative limit. The increased J s c in textured cells renders light trapping favorable for the P C E , regardless of absorber thickness and material quality and despite reduced PR. Furthermore, the impact of an absorbing front grid and lateral transport of internal luminescence on PR is estimated, emphasizing the importance of transparent (non-absorbing) contact layers, at the rear, but importantly, also at the front of the device. To conclude, P C E limits of 300-nm-thick GaAs solar cells are deduced in the context of an experimentally realized light-trapping scheme based on a randomly textured rear mirror. P C E s exceeding 25.5% are deemed realistic. • Photon recycling and light trapping are studied in textured thin-film GaAs cells • Ray-optical modeling yields probabilities of escape and (parasitic) absorption • Textured rear mirrors reduce photon recycling and its impact on cell performance • Light trapping improves efficiency for any absorber thickness and material quality • Efficiency limits of 300-nm GaAs cells are currently 25.5% and ultimately ¿28%

Efficient ion-slicing of 4-inch GaAs thin film for Si-based hetero-integration with ultra-smooth surface

Heterogeneous integration of single-crystalline GaAs thin film on a Si substrate provides a promising material platform for Si-based optoelectronic integration. In this work, based on the clarified splitting mechanism of GaAs, the ion implantation conditions for GaAs film transfer were optimized. It was found that the co-implantation of He and H ions is more efficient in exfoliating the GaAs thin film with a lower thermal budget and lower density of defects in comparison with the case of the single He/H ion implantation. With the Al2O3 as the bonding intermediate layer, a 4-inch GaAs film was successfully transferred onto the Si (100) substrate via the optimized ion-slicing technique. The surface treatments, including chemical mechanical polishing, ozone oxidation, and KOH cleaning, were explored to improve the surface quality of the as-transferred GaAs thin film to the level of epi-ready. After post-annealing at 400°C for 1 h, the quality of the transferred GaAs thin film was further improved with only 89.03 arcsec for the full width at half maximum of the X-ray rocking curve.