Compound Semiconductor Materials Research Articles

A generalized mathematical modeling and performance analysis of GaAs, m-Si and Ge single - junction solar PV cells

Earlier theoretical approaches have analyzed the performance of semiconductor materials for the influence of temperature and band gap which is implemented in solar photovoltaic systems. This paper investigates the detailed mathematical analysis of single junction semiconductor materials such as Gallium Arsenide (GaAs), mono-crystalline Silicon (m-Si) and Germanium (Ge) solar cells parameters namely, Band gap (Eg), reverse saturation current (Io), shunt resistance (Rsh), Short circuit current (Isc), open circuit voltage (Voc), Fill factor (FF), Maximum Power (Pmax) and Efficiency (Ƞ) for temperature ranging from 273K (≈0°C) to 373K (≈100°C). The optimized cell parameters values are obtained under Air Mass 1.5 Global spectrum (Area = 100cm2 and Irradiance = 100 mW/cm2 for the semiconductor materials (GaAs, m-Si and Ge)) at 300K (≈25°C) are compared to identify the higher efficiency and open circuit voltage. Among the semiconductor materials, the single junction GaAs compound semiconductor material is identified with better efficiency and optimized open circuit voltage. A generalized mathematical model of semiconductor materials is developed using single diode equivalent circuit model under SIMULINK platform and it is used to observe the effect of different temperature, irradiance levels, series resistance and shunt resistance values on the performance of solar cells. The discussion is extended for a 2KW PV array for the semiconductor materials (GaAs, m-Si and Ge) under different temperature and irradiance levels. Evaluating the performance of a PV array, rather than individual cells, provides a more comprehensive understanding of how the chosen semiconductor materials function as part of a larger solar energy system.

Atomic layer deposition and application of group III nitrides semiconductor and their alloys

Group III nitride semiconductors, such as GaN, AlN, and InN, are an important class of compound semiconductor material, and have attracted much attention, because of their unique physicochemical properties. These semiconductors possess excellent characteristics, such as wide direct bandgap, high breakdown field strength, high electron mobility, and good stability, and thus are called third-generation semiconductors. Their alloy materials can adjust their bandgaps by changing the type or proportion of group III elements, covering a wide wavelength range from near-ultraviolet to infrared, thereby achieving wavelength selectivity in optoelectronic devices. Atomic layer deposition (ALD) is a unique technique that produces high-quality group III nitride films at low temperatures. The ALD has become an important method of preparing group III nitrides and their alloys. The alloy composition can be easily controlled by adjusting the ALD cycle ratio. This review highlights recent work on the growth and application of group III nitride semiconductors and their alloys by using ALD. The work is summarized according to similarities so as to make it easier to understand the progress and focus of related research. Firstly, this review summarizes binary nitrides with a focus on their mechanism and application. In the section on mechanism investigation, the review categorizes and summarizes the effects of ALD precursor material, substrate, temperature, ALD type, and other conditions on film quality. This demonstrates the effects of different conditions on film growth behavior and quality. The section on application exploration primarily introduces the use of group III nitride films in various devices through ALD, analyzes the enhancing effects of group III nitrides on these devices, and explores the underlying mechanisms. Additionally, this section discusses the growth of group III nitride alloys through ALD, summarizing different deposition methods and conditions. Regarding the ALD growth of group III nitride semiconductors, there is more research on the ALD growth of AlN and GaN, and less research on InN and its alloys. Additionally, there is less research on the ALD growth of GaN for applications, as it is still in the exploratory stage, while there is more research on the ALD growth of AlN for applications. Finally, this review points out the prospects and challenges of ALD in preparation of group III nitride semiconductors and their alloys.

Variability of temperature on the electrical properties of heterostructured CIS/Cds through SCAPS simulation for photovoltaic applications

Renewable energy research has received tremendous attention in recent years in a quest to circumvent the current global energy crisis. This study carefully selected and simulated the copper indium sulfur ternary compound semiconductor material with cadmium sulfide owing to their advantage in photovoltaic applications. Despite the potential of the materials in photovoltaic devices, the causes of degradation in the photovoltaic efficiency using such compound semiconductor materials have not really been investigated. However, electrical parameters of the materials such as open circuit voltage, short circuit current density, and fill factor have been extensively studied and reported as major causes of degradation in materials’ efficiency. Furthermore, identifying such electrical characteristics as a primary degradation mechanism in solar cells, this study work is an ardent effort that investigates the materials' electrical behavior as a cure to the degradation associated with compound semiconductor-based photovoltaic. In this study, we numerically characterized the electrical properties such as fill factor, open circuit voltage, short circuit current density, power conversion efficiency, net recombination rate, net generation rate, generation current density, recombination current density, hole current density, electrons current density, energy band diagram, capacitance–voltage, electric field strength of the heterostructured CIS/CdS compound semiconductor material using SCAP-1D. We also investigated the effect of temperature on the electrical properties of heterostructured materials. The obtained results reveal the uniformity of the total current density in the material despite the exponential decrease in the electron current density and the exponential increase in hole current density. The extracted solar cell parameters of the heterostructured CIS/CdS at 300 K are 18.6% for PCE, 64.8% for FF, 0.898 V for Voc, and 32 mA cm−2 for Jsc. After the investigation of the effect of temperature on the CIS/CdS compound semiconductor material, it was observed that the solar cell was most efficient at 300 K. The energy band gap of the CIS/CdS compound semiconductor material shrinks with an increase in temperature. The highest net recombination rate and recombination current is at 400 K, while the net generation rate and generation current density are independent of temperature. The study, on the other hand, gave insights into the potential degradation process, and utilizing the study’s findings could provide photovoltaic degradation remediation.

Recent Advances in III–V Compounds/Polymer Hybrid Solar Cells

The combination of III–V compound semiconductor materials and organic semiconductor materials to construct hybrid solar cells is a potential pathway to resolve the problems of conventional doped p–n junction solar cells, such as complexities in fabrication process and high costs. This review presents the recent progress of organic–inorganic hybrid solar cells based on polymers and III–V semiconductors, from materials to devices. The available growth process for planar/nanostructured III–V semiconductor materials, along with patterning and etching processes for nanostructured materials, are reviewed. As an emphasis of this review, advanced device structure designs are reviewed for facilitation of carrier collection and high efficiency, at planar structure level and nanowire structure level, respectively. Optimization pathways for efficiency enhancement are discussed with respect to polymer layers and surface/interface passivation, respectively. Finally, perspectives on the future development of such hybrid cells are presented.

Direct bonding of LiNbO3 and GaAs at room temperature by using activated Si atom layer

Heterogeneous integration of LiNbO3 and GaAs at room temperature has been achieved by using an activated Si atom interlayer, which demonstrate effectiveness in the fabrication of GaAs based LiNbO3 wafer. By using the activated Si atom interlayer as the adhesive layer, 4-inch LiNbO3 wafer is successfully directly bonded to the surface of GaAs wafer. The wafer bonding rate reaches over 95%. After bonding, the LiNbO3/GaAs bonding pair is cut into 10 × 10 mm2 square bonded chips. After annealing, the maximum bonding strength of square bonded chips exceeds 22 MPa. This means that the bonding strength of LiNbO3/GaAs wafer can be comparable to that of bulk materials. The characterization results of the bonding interface confirm that the intermediate amorphous Si layer is effective in improving the bonding strength and quality of LiNbO3/GaAs heterojunction. Heterogeneous integration of LiNbO3 with GaAs and other Ⅲ-Ⅴ compound semiconductor materials is conducive to reducing the area occupied by optical communication platforms and improving the overall efficiency of devices.

Accurate prediction of semiconductor bandgaps based on machine learning and prediction of bandgaps for two-dimensional heterojunctions

The bandgap value of materials has a profound impact on their properties and applications. Presently, with the development of high-throughput calculations, the bandgap of most materials is simulated and calculated using the density functional theory (DFT). Nevertheless, the bandgap of materials calculated in this way is often accompanied by large errors and long time consuming. Besides, the bandgap results obtained in different experimental environments are different. Therefore, finding a method to calculate the material bandgaps quickly and accurately is imminent. In this work, the Machine Learning (ML) method is used to predict the bandgap of semiconductor materials. Four different machine learning models are trained and tested through the feature processing, which can accurately predict the bandgap of the material by the hybrid density functional (HSE06) method, of which the average mean absolute error (MAE) is 0.142 eV and the coefficient of determination (R2) is 0.977. Moreover, in order to better predict the bandgap of local small-sample semiconductor materials, the federal learning framework is employed to forecast small-sample datasets under different experimental conditions. Then, the four ML models are used to the prediction of materials and compared the results with the local calculation results. The results indicate that the bandgap error of compound semiconductor materials is 2∼10%, and the bandgap error of 2D heterojunctions semiconductor materials is 5∼30%. In addition, the ML models are also utilized to the Materials Project database, in which the bandgap of about 53170 semiconductor materials is successfully predicted. In conclusion, the work not only provides a method to accurately predict the bandgap of compound semiconductor materials, but also supplies an effective idea for the prediction of the bandgap of semiconductor materials in local small data sets, which accelerating the development of the application of semiconductor materials.

Band-to-band tunneling switches based on two-dimensional van der Waals heterojunctions

Quantum mechanical band-to-band tunneling is a type of carrier injection mechanism that is responsible for the electronic transport in devices like tunnel field effect transistors (TFETs), which hold great promise in reducing the subthreshold swing below the Boltzmann limit. This allows scaling down the operating voltage and the off-state leakage current at the same time, and thus reducing the power consumption of metal oxide semiconductor transistors. Conventional group IV or compound semiconductor materials suffer from interface and bulk traps, which hinder the device performance because of the increased trap-induced parasitics. Alternatives like two-dimensional materials (2DMs) are beneficial for realizing such devices due to their ultra-thin body and atomically sharp interfaces with van der Waals interactions, which significantly reduce the trap density, compared to their bulk counterparts, and hold the promise to finally achieve the desired low-voltage operation. In this review, we summarize the recent progress on such devices, with a major focus on heterojunctions made of different 2DMs. We review different types of emerging device concepts, architectures, and the tunneling mechanisms involved by analytically studying various simulations and experimental devices. We present our detailed perspective on the current developments, major roadblocks, and key strategies for further improvements of the TFET technology based on 2D heterojunctions to match industry requirements. The main goal of this paper is to introduce the reader to the concept of tunneling especially in van der Waals devices and provide an overview of the recent progress and challenges in the field.

Compound Semiconductors – A Plethora of Possibilities for Future Electronic & Photonic Devices

The advent of integrated circuits (IC), primarily made from silicon (Si), revolutionised the electronics industry in the past century. However, with the increasing complexity of applications over the years in terms of higher speed, smaller size, low noise, high power handling capacities coupled with lower cost, triggered a wider use of compound semiconductors in some specific applications. The properties of these compound semiconductors can be modulated by changing the combination of constituent elements, thereby altering the bandgap suitable for the chosen application. Over the years, many elements from groups III & V and II & VI of the periodic table have been combined to create newer compositions with unique properties suitable for various critical applications. Nowadays, even IV-IV materials like SiGe, etc. are also explored. The higher internet speeds, backed up by a very strong fibre optic network, higher computing speeds and many other related applications have also triggered the development of photonic devices in addition to various electronic devices. Various compound semiconductor materials are found to exhibit very good performance in terms of reliability, size, production scalability, speed and many other pertinent issues as required. With the recent pace of development, future devices will require further enhancements. The wide range of applications required will also present greater complex challenges. So, the need for finding newer compound semiconductor materials with wider bandgaps and specialised characteristics is on the rise. In the present work, the authors have made an attempt to review the applications of compound semiconductor-based devices in the fields of energy, defense, biomedical (including wearable sensors) and optoelectronic applications. It is estimated that newer materials developed through research in the coming days will significantly improve the quality of life for the entire human civilization

Changes to the Editorial Board

It is my pleasure to welcome Dr. Mina Rais-Zadeh to the Editorial Board of IEEE Electron Device Letters. A biography and picture of Dr. Rais-Zadeh can be found below. Her subject areas are compound semiconductor devices, materials, processing and packaging, sensors and actuators, and emerging technologies and devices

Modeling Insights Into the Assembly Challenges of Focal Plane Arrays

Ongoing technological advances in photodetector material growth and processing, readout integrated circuits, and robust hybridization (packaging) methods for assembling high-resolution and small-pitch size pixel arrays are the main enabling factors for pushing the frontiers of high-performance Focal Plane Array (FPA) technologies for imaging systems. This paper details the development of analytical and numerical models and demonstrates their use to generate insights into the feasibility of two flip-chip assembly processes for packaging infrared (IR) detector chips. The modelling studies focus on the challenges of forming the indium interconnection arrays in the case of the FPA technologies using Group III-V compound semiconductor materials and ultra-fine pitch pixel array layouts. The accurate alignment of the IR detector chip onto the readout chip in the case of high-density pixel architectures is a critical requirement for the packaging process. To gain better understanding of this requirement, which has a clear implication for the quality and subsequent reliability performance of the FPA, compression and reflow bonding process models are developed using suitable modeling approaches and methods and then demonstrated for two distinctive focal plane array design configurations. The novelty of this work is in the developed modeling capabilities utilizing different computational methods, from large deformation and contact analysis finite element to energy-based and harmonic motion mechanics, to characterize and optimize the mechanical and dynamic non-linear behavior of the indium solder joints and their formation during FPA packaging. The feasibility of bonding techniques for different resolution FPAs and under flip-chip misalignment conditions is assessed. The modeling results pointed to a very strict, sub-micrometer flip-chip placement accuracy requirement for the assembly of FPAs with ultra-fine indium bump array resolution.

InAs nanowire arrays for room-temperature ultra-broadband infrared photodetection.

Detection of short-wave infrared (SWIR) and mid-wave infrared (MWIR) emissions remains challenging despite their importance in many emerging applications, including night vision, space imaging and remote sensing. III-V compound semiconductor materials such as InAs have an ideal band gap covering a spectral regime from near-infrared (NIR), SWIR to MWIR. However, due to their high dark current, InAs photodetectors normally require a low-temperature operation, which has greatly limited their practical applications. Here, we report the engineering of InAs nanowire arrays to achieve efficient photodetection of light at wavelengths ranging from NIR to MWIR (3500 nm). By using selective area metal-organic vapour-phase epitaxy, we optimise the nanowire growth temperature and V/III ratio to achieve wurtzite (WZ)-based InAs nanowire arrays with a high WZ density of ∼67%. Due to the n-type background doping of the InAs nanowires and the p-type InAs substrate used for nanowire growth, a p-n junction is formed, and an ultrawide room-temperature photoresponse ranging from 500 to 3500 nm is obtained under zero bias. It is found that the waveguide modes supported by the InAs nanowires result in a high peak responsivity of 0.44 A W-1 and a detectivity of 1.25 × 1010 cm √Hz W-1 at a wavelength of 1600 nm, a bias voltage of only -0.1 V and a relatively high operating temperature of 150 K. Such a strong light trapping effect in the InAs nanowires also leads to significantly lower reflection compared to that observed in planar photodetectors, and thus strong absorption in the substrate extending the photoresponse up to the InAs bandgap edge of 3500 nm. Our work shows that through careful material optimisation and device design, InAs nanowire arrays are promising for the development of high-performance ultra-broadband infrared photodetectors for wavelengths ranging from NIR, SWIR to MWIR.

Synthesis and characterization of mesoporous vanadium sulfides as environmental catalysts for the cycloaddition of CO2 with 2-(phenoxymethyl)oxirane) and oxidation reactions

Metal sulfide is a vital species of compound semiconductor materials, whose metallic ions are in mono-, bi-, or maybe in multi-form. Considering such materials, layered transition metal sulfide (LTMS) including layered transition metal dichalcogenides (LTMDs) like VS2 and VS4 (also called patronite mineral) has attracted growing interest. Moreover, it can be regarded as graphene analogs due to its large interlayer spacing and high theoretical specific capacity, enabling such materials to be applied in different fields i.e. photoelectric staffs, electro-catalysis phenomena, Li-containing batteries, and energy storage usages. Herein, a practical synthetic protocol is designated to construct mesoporous vanadium sulfides (VS2 and VS4) with controlled morphologies from VS2 (Flower-like), VS4 (Urchin-like), VS4 (Microsphere), and VS2 (Nanosheet assemblies) via adjusting the molar ratio of vanadium acetylacetonate and L-cysteine using a one-step solvothermal method. The catalytic activity of vanadium sulfides as an environmental catalyst has been considered for cycloaddition reaction of CO2 and 2-(phenoxymethyl)oxirane), oxidation of dibenzyl sulfide, and 1-phenylethan-1-ol. The prepared mesoporous vanadium sulfides have a higher surface area than the previously reported ones. The results and analysis revealed that the catalytic behavior of vanadium sulfides significantly depends on physical features such as morphology and specific surface area. The structure of the prepared materials was studied using a variety of characterization techniques: FTIR, XRD, TGA, BET, FE-SEM, EDX, and X-ray mapping

A High‐Detectivity, Fast‐Response, and Radiation‐Resistant TiN/CdZnTe Heterojunction Photodiode

AbstractA novel high‐performance ultraviolet–visible–near‐infrared (300–820 nm) heterojunction photodiode based on radiation‐resistant semiconductor materials is proposed. A titanium nitride (TiN) “window” layer is deposited via magnetron sputtering onto a cadmium zinc telluride (CdZnTe) solid solution single crystal. The TiN/CdZnTe heterojunction photodiodes concurrently reveal an outstanding detectivity, response time, and linear dynamic range outperforming similar heterojunction photodiodes and photodetectors, based on photoactive inorganic compound semiconductor materials. Moreover, the added feature of the proposed heterojunction photodiodes is their excellent radiation resistance, experimentally demonstrated under short impulse proton irradiation (170 keV) with an accumulated fluence of 2 × 1012 proton cm−2. This unusual synergy of high performance and advanced radiation resistance of the TiN/CdZnTe photodiodes provides a unique platform for operation in space or radioactively contaminated environments.

Perspectives on the Development of Metalorganic Vapor Phase Epitaxy for III-V Optoelectronic Devices

The mainstream production of optoelectronic and electronic devices based on epitaxial III-V compound semiconductor materials largely employs metalorganic vapor phase epitaxy, a process first demonstrated for devices in the 1970’s. For this special issue in honor of Prof. P. Daniel Dapkus, this paper first briefly reviews his early contributions that spearheaded the interest of MOVPE as a III-V device epitaxy process. Next, the paper discusses MOVPE reactor development in the 1980’s, which at the time was one of the key challenges in establishing MOVPE technology as a reliable epitaxy manufacturing process. The approach combined physical modeling and numerical simulations of reactor processes followed by materials and device demonstrations. Highly uniform performance metrics of AlGaAs/AlGaAs quantum-well diode lasers and two-dimensional monolithic surface-emitting lasers were demonstrated with excellent run-to-run reproducibility. This foundational approach advanced efforts to standardize reactors and subsequent scaling for high-throughput production.

Influence of Si Doping on Dislocations and Mechanical Properties of GaAs Crystals Grown by Modified Vertical Bridgman Method

AbstractGaAs crystals are important III–V compound semiconductor materials and the bandgap and quantum efficiency can be optimized by doping. However, the doping may bring some problems to the crystal growth. In this paper, Si‐doped GaAs crystals are grown by the modified vertical Bridgman method and the influence of Si doping on dislocations and mechanical properties are discussed. It is found that a proper amount of Si doping significantly reduces the dislocation density of GaAs crystals. The mechanical properties of (100), (110), (111), and (511) planes are measured, and the results show that the mechanical properties of Si‐doped GaAs crystals have obvious anisotropy. The (111) plane has the strongest mechanical properties among them. The Vickers hardness, fracture toughness, nanoindentation hardness, and elastic modulus of the (111) plane are 6.05 GPa, 0.69 MPa m1/2, 10.82 GPa, 138.7 GPa, respectively. Moreover, Si doping can improve the mechanical properties of GaAs crystals.

Catalysis-Free Growth of III-V Core-Shell Nanowires on p-Si for Efficient Heterojunction Solar Cells with Optimized Window Layer

The growth of high-quality compound semiconductor materials on silicon substrates has long been studied to overcome the high price of compound semiconductor substrates. In this study, we successfully fabricated nanowire solar cells by utilizing high-quality hetero p-n junctions formed by growing n-type III-V nanowires on p-silicon substrates. The n-InAs0.75P0.25 nanowire array was grown by the Volmer–Weber mechanism, a three-dimensional island growth mode arising from a lattice mismatch between III-V and silicon. For the surface passivation of n-InAs0.75P0.25 core nanowires, a wide bandgap InP shell was formed. The nanowire solar cell was fabricated by benzocyclobutene (BCB) filling, exposure of nanowire tips by reactive-ion etching, electron-beam deposition of ITO window layer, and finally metal grid electrode process. In particular, the ITO window layer plays a key role in reducing light reflection as well as electrically connecting nanowires that are electrically separated from each other. The deposition angle was adjusted for conformal coating of ITO on the nanowire surface, and as a result, the lowest light reflectance and excellent electrical connectivity between the nanowires were confirmed at an oblique deposition angle of 40°. The solar cell based on the heterojunction between the n-InAs0.75P0.25/InP core-shell nanowire and p-Si exhibited a very high photoelectric conversion efficiency of 9.19% with a current density of 27.10 mA/cm2, an open-circuit voltage of 484 mV, and a fill factor of 70.1%.

Enhancing anisotropy of thermal conductivity based on tandem acoustic Bragg reflectors

Thermal metamaterials have emerged as one of the latest research topics in applied science due to breakthrough advantages in modifying conductive heat flux. An acoustic Bragg reflector (ABR), composed of alternating arrays of two materials with contrasting acoustic impedances, is anticipated to coherently manipulate the transport properties of thermally important phonon branches by attaining interface roughness close to the monoatomic scale. However, there is a lack of research on how a narrow portion of the phononic band of a particular ABR can be extended to cover the entire thermal spectrum. Here, we report a modeling study of thermal transport using ABR, representatively based on GaAs/AlAs, GaN/AlN, or HfO2/SiO2 superlattices. Our calculations show that the anisotropy of thermal conductivity in HfO2/SiO2 can be significantly improved by tandemizing four different ABR layers, thus approaching the theoretically anticipated values based on monolayered materials. This work demonstrates how the tandem ABR can expand forbidden phononic bands beyond that occupied by a single ABR and proposes a practical strategy for realizing spectrally functionalized thermal properties from compound semiconductor materials that can be directly integrated into the existing device fabrication processes.

Geant4 simulation of neutron displacement damage effect in InP

As the second-generation compound semiconductor material, indium phosphide (InP) has strong irradiation resistance and high photoelectric conversion efficiency. It has advantages in the field of photonics and radio frequency. In atmospheric space, high-energy cosmic rays enter into the earth’s atmosphere and interact with nitrogen (N), oxygen (O) and other elements to produce secondary cosmic rays. The irradiation particles in the atmosphere are mainly neutrons because the penetration of charged particles is weak. The InP semiconductor devices are affected by atmospheric neutron irradiation of various energy from all directions, which results in the internal defects in InP crystals, the degradation of device performance and the reduction of device lifetime. In this paper, Monte Carlo simulation software Geant4 is used to simulate the neutron irradiation effect, and the initial state distribution of displacement damage caused by neutrons with different energy is obtained, including the distribution of non-ionized energy loss (NIEL) with depth, the relationship between NIEL and the energy of incident neutrons, and the type, number and energy of primary knock-on atoms (PKA). The results show that 1) the NIEL is uniformly distributed when material thickness is on the order of μm and for the material thickness on the order of cm and more, the NIEL decreases as the depth increases and can be reduced to zero when the target material is thick enough; 2) by analyzing the NIEL produced by 1–20 MeV neutrons incident on 3-μm InP and their distribution with depth, it is found that the NIEL first increases and then decreases with incident neutron energy increasing. This trend is caused mainly by PKA produced through the inelastic scattering reaction; 3) by analyzing the type and the energy of PKA produced by 1–20 MeV neutrons incident on 3 μm InP, it is found that the PKA of In/P accounts for a large proportion, which causes displacement damage mainly, and the higher the neutron energy, the richer the variety of PKA is and the greater the maximum kinetic energy of PKA, but the PKAs mainly distribute in the low energy part. The present research has theoretical and guiding value for the long-term application of InP-based 5G devices in atmospheric neutron irradiation environment.

Spectroscopic measurement of water using an electrostatic transducer with near‐infrared absorber

AbstractThe widespread of near‐infrared spectroscopes in the consumer field is expected to create new demand, such as the detections of fruit and vegetable rot and the easy measurement of the amount of water in the skin. Conventional cooled photodiodes using compound semiconductor materials such as InGaAs have problems with cost reduction and miniaturization. Therefore, we proposed an electrostatic Si microresonator device for the realization of a near‐infrared optical sensor. This device measures the resonance frequency shift caused by the thermal stress generated in the resonator due to light absorption depending on the light intensity. The purpose of this study is to apply the device to near‐infrared spectroscopy of water as a photodetector. We proposed an evaluation method based on a theoretical equation and confirmed that the device could detect the near‐infrared absorption spectrum of water. The measurement results of the developed device matched well with that of the commercially available photodiode intensity sensor. In the future, it is expected that a compact near‐infrared spectrometer with high sensitivity and low cost will be realized by arranging devices that integrate absorbers with different wavelength dependencies.

Piezoelectric properties of substitutionally doped β-Ga2O3

Modern semiconductor materials are increasingly used in multidisciplinary systems demonstrating cross-interactions between mechanical strains and electronic potentials, which gives rise to ubiquitous applications in high sensitivity, self-powered sensor devices. One of the fundamental prerequisites for such semiconductor materials to exhibit piezoelectric properties is the noncentrosymmetry of the crystal structures. β-Ga2O3 has been an emerging compound semiconductor material due to its ultra-wide bandgap. However, pristine β-Ga2O3 has an inversion center, displaying no piezoelectric effect. This work discovered that substitutionally doped β-Ga2O3 possesses piezoelectric property by using the first principles method, while a majority of previous research on its substitutional doping has been focused on the purposes of increasing electrical conductivity and formation of semiconductor heterojunctions. More interestingly, it is unveiled from this work that the formation energy has a clear relation with the piezoelectric coefficient.