N-type Substrates Research Articles

Influence of Temperature on the Growth of Vertically Aligned ZnO Nanowires in Wet Oxygen Environment

The nanowires (NWs) of zinc oxide (ZnO) are developed effectively on an n-type silicon substrate through a seed zinc (Zn) layer by a wet oxidation technique. The growth is performed at different temperatures, 650, 750, and 850 °C, in a wet and rich oxygen environment under a flow of oxygen in the presence of water vapor at atmospheric pressure with a heating rate of 100 °C in 30 min. At 415 °C, the oxygen gas is introduced for the oxidation process. The Zn seed layer is deposited by the thermal evaporation technique. The structural, morphological, and optical properties are investigated. The temperature effect on NWs of ZnO growth intensity and their direction are explored. The nanowires are grown vertically oriented at a temperature of T = 750 °C. The ultraviolet (UV) analysis has been exposed in the visible region ranging from 10 nm to 700 nm at UV to visible intensity ratio of 2.22. In addition, X-ray diffraction analysis (XRD) is employed to research the structural properties of NWs of ZnO, and the characterization is verified by a scanning electron microscope (SEM) to investigate the morphology.

Influence of buffer layer on nitrogen doped AZO relative humidity sensor with p-n heterojunction structure

A nitrogen doped AlZnO (N-doped AZO) relative humidity (RH) sensing p-n heterojunction structure on n-type silicon substrate using DC sputtering system and lift-off technique has been proposed in this research. N-doped AZO RH sensing film was adopted to enhance photocatalyst effect and realize the heterojunction structure in humidity sensing device. The carrier properties of N-doped AZO RH sensing film were evaluated in the carrier type, carrier mobility, carrier concentration, and carrier conductivity using Hall effect measurement. The N-doped AZO RH sensors were designed with a p-n heterojunction structure and embedded a buffer layer structure. The sensing properties of N-doped AZO RH sensors both with polymer buffer layer and without polymer buffer layer were respectively explored and evaluated in the hysteresis effect, sensitivity, linearity, sensing response and recover response characteristics using environment measurement system and measurement firmware. The research results revealed the carrier type, carrier mobility, carrier concentration, and carrier resistivity of the N-doped AZO RH sensing film deposited on p-n heterojunction structure with buffer layer respectively reached as p-type, 9.6✕101 cm2/Vs, 3.3✕1017 cm−3, and 5.0✕100 Ω-cm. The RH sensing hysteresis error of N-doped AZO RH sensor with buffer layer is approximately 4.57% at 60 %RH which is less than those at other relative humidity values. The sensitivity of N-doped AZO RH sensor with buffer layer reaches as more than 15.7 kΩ/%RH at desorption process which is better than that of sensor without buffer layer either at relative humidity value from 30 %RH to 90 %RH and from 30 %RH to 75 %RH. The adsorption linearity and desorption linearity of N-doped AZO RH sensor with buffer layer are respectively 0.31 and 0.27 between 30 %RH and 75 %RH which are better than those without buffer layer. The adsorption time and desorption time responses of N-doped AZO RH sensor with buffer layer measured during the measurement time of 2000 s with two measuring cycles were estimated about 235 s and 295 s at first cycle respectively less than those of the RH sensor without buffer layer. The design of polymer buffer layer embedded between N-doped AZO RH sensing p-n heterojunction structure and use of n-type silicon substrate revealed the better sensing characteristics and electrical properties both the molecular adsorption/desorption effects in chemical property and the carrier transport phenomena in physical property respectively.

Thermoelectric performance of Fe2V0.9W0.1Al thin films deposited on n-type Si substrates

Fe2V0.9W0.1Al thin films are prepared on n-type Si substrates by means of rf magnetron sputtering with varied substrate temperatures from 743–1043 K, then subsequently annealed for one hour in a vacuum at 1043 K. The thin films deposited at 1043 K are chemically degraded, exhibiting a low Seebeck coefficient, –65 μV K–1, at 330 K. On the other hand, the films deposited at 943 K possess –100 μV K–1 in a Seebeck coefficient at around 330–350 K, which is very similar to the Seebeck coefficient of the bulk W-substituted Fe2VAl that possesses a well-ordered L21 structure. The maximum power factor of 1.6 mWm–1 K–2 was obtained for the sample deposited at 943 K. Accordingly, with the thermal conductivity of 3.5 Wm−1 K−1, the figure of merit reached up to ZT = 0.16, which is comparable with Fe2V0.9W0.1Al of bulks and two times larger than that of the thin films of Si-substituted Fe2VAl.

Facile method for fabricating the MXenes-Si based Schottky-junction solar cells

Owing to their tunable properties, 2D materials including MXenes are widely used in different optoelectronic devices due to their inherent conductivity and transparency. MXenes are a class of 2D materials that can be synthesized in the form of a colloidal solution, and these are hydrophilic in nature. Due to their hydrophilicity, MXenes can be easily coated on different substrates, making them suitable in applications like solar cells. Like other materials, MXenes-based solar cell fabrication doesn't require a growth process or a transfer process, hence, solar cells fabrication using MXenes is comparatively a simplified process. In this study, a facile technique was adopted to fabricate the metal-semiconductor (MXenes-Si) junction simply by spin-coating Ti3C2Tx-MXenes on an n-type Si substrate. The electrical properties of the coated MXenes films were investigated at different MXenes to DI water ratios to obtain the optimized concentration for the highest solar cell efficiency. To stabilize the interface between MXenes and Si, Al2O3 was deposited, and the thickness-dependent tunneling effect was also optimized at a 2 nm thick Al2O3 layer. To improve the solar cell efficiency, AuCl3 doping, and texturing of silicon substrate were performed. With these two additional treatments, the efficiency of the solar cell was increased from 2.87% to 3.36%, exhibiting an increase of ∼17% as compared to that without treatment.

Self-powered photodetectors with high detectivity based on MoSe2/Si heterojunction using ITO as the transparent electrode and highlight trapping structures

Due to the remarkable light absorption effect and electrical properties, transition metal dichalcogenide-based heterojunction allows for the realization of a highly sensitive photodetector. A self-powered photodetector with high detectivity (355–980 nm) was reported based on the MoSe2 that was prepared by the MoO3 films as the precursor layer which reduced the reaction temperature. The n-type silicon substrates with optical trapping structures were prepared by wet chemistry, which can enhance the performance of photodetectors. The as-grown MoSe2 nanosheet was applied in the self-powered ITO/MoSe2/Si photodetector. The self-powered device can detect faint light with a power density below 200 μW/cm2 which shows high responsivity (18.13 mA/W), normalized detectivity (2.80 × 1012 cm·HZ1/2W−1) and a fast response time of 43 ms under 980 nm (1.5 mW/cm2) illumination at zero bias. The ITO/MoSe2/ Si heterojunction with outstanding properties has promising potential for application in self-powered, sensitive, and broadband photodetectors.

Core-level photoelectron spectroscopy study on the buffer-layer formed in approximately atmospheric pressure argon on n-type and semi-insulating SiC(0001)

Using core-level photoelectron spectroscopy, we studied the surface of SiC(0001)-6√3 × 6√3R30° (buffer layer surface) formed on n-type and semi-insulating substrates via the approximately-atmospheric-pressure graphitization method. When the surface was exposed to air after buffer layer formation, hydrocarbons were adsorbed and oxygen atoms were chemically bonded to the carbon atoms comprising the buffer layer. Subsequently, annealing in ultra-high vacuum and an ethylene ambient allowed the removal of these oxygen atoms and hydrocarbons, and a clean buffer layer surface was obtained. Furthermore, using the peak position of Si 2p, band bending of the buffer layer on the n-type and semi-insulating substrates was estimated. A reasonable value of −0.05 eV was obtained for the n-type substrate. However, for the semi-insulating substrate, the Fermi level (Ef) was located at 0.05 eV below the conduction band minimum (CBM) on the surface. This is anomalous if we interpret the change in the CBM position over Ef from the bulk to the surface to be solely induced by band bending. To interpret this situation, we propose a mechanism in which the n-type region appears near the surface of the SiC bulk under the buffer layer.

Richardson constant and characteristics of pentacene organic planar Schottky diode

Planar organic Schottky diodes were fabricated using undoped pentacene as an active layer with both palladium and aluminum as contacts. Pentacene organic thin films were deposited on n-type silicon substrates with 100 (n-Si<100>) and 111 (n-Si<111>) orientations. X-ray diffraction (XRD) measurements revealed that the pentacene films’ XRD patterns exhibit several peaks with various orientations. The energy-dispersive X-ray technique was used for chemical analysis of the pentacene, and scanning electron microscopy was used to characterize the surface morphology. A structural and morphological study of the deposited pentacene indicates a polycrystalline triclinic (anorthic) nature. A current–voltage curve was experimentally constructed at temperatures (T) ranging from 300 K to 360 K with a step of 15 K. The diode parameters, such as saturation current, ideality factor (n), and barrier height (ΦB), were systematically analyzed using thermionic emission theory. The fabricated devices exhibit decreasing n and increasing ΦB values with increasing T. Richardson's constant for pentacene was calculated, which indicated that the conventionally calculated value from the temperature-dependent characteristic curve is much lower than the calculated theoretical value. It was also observed that the device deposited over the n-Si<111> substrate exhibited larger forward and lower reverse currents than the n-Si<100> substrate device.

All-Monolithically Integrated Self-Scanning Addressable VCSEL Array for 3D Sensing

We propose an all-monolithically integrated self-scanning addressable vertical-cavity surface-emitting laser array for time-of-flight measurement. Some advantages of addressable VCSELs for ToF measurement applications include large reductions in power consumption, heat generation, multi-pass noise, and flare noise. In this paper, we discuss the characteristics of the proposed self-scanning addressable VCSEL array. All layers in the epilayer structure of the proposed VCSEL array were formed at once by metal-organic chemical vapor deposition. The device consists of an (Al)GaAs-based thyristor and a conventional top-emitting 940-nm oxide-confined VCSEL on an n-type GaAs substrate. The array contained 12 blocks (4 × 3) that have more than 40 emitters each. The device required only four signals from a field-programmable gate array to select the emitting blocks and one emission signal from a conventional VCSEL driver, even for arrays containing hundreds of blocks. The proposed module is capable of one-block sequential emission, parallel emission from several blocks, and emission from all blocks. The rise and fall times of the fabricated VCSEL array were observed to be 200 and 400 ps, respectively, for each emission mode. The influence of flare noise from an obstacle in front of the camera was dramatically reduced by avoiding emission to the obstacle.

Annealing effect on structural and optical properties of glad synthesized Gd2O3 nanorod

Gadolinium oxide nanorod (Gd2O3 NR) was fabricated on an n-type silicon substrate by catalyst-free glancing angle deposition (GLAD) technique. The as-grown sample was annealed at 500 °C to investigate the impact of annealing on structure and optical properties. XRD analysis reveals an improvement in the crystal structure after annealing. Field emission scanning electron microscope (FE-SEM) and energy dispersive X-ray (EDX) confirm the successful growth of vertically aligned Gd2O3 NR with the presence of Gd, O, and Si. Transmission electron microscope (TEM) showed the crystalline nature of the grown Gd2O3 NR. Finally, UV–vis spectroscopy was performed to study the optical properties. A significant enhancement in the photon absorption (200–300 nm) was observed, which can be attributed to increased grain size, improved crystallinity, and large generation of electron–hole pairs. In addition, the Tauc plot showed a decrease in the bandgap from 5.05 eV to 4.98 eV after annealing at 500 °C.

Improvement in the Performance of P-Type Tunnel Oxide Passivated Contact Solar Cell With Selective Tunneling Junctions Underneath the Contacts on Front Side

Industrial silicon solar cells are now moving further from passivated emitter and rear contact (PERC) toward Tunnel Oxide Passivated contact (TOPCon) technology. The efficiency of the PERC solar cell is improved by TOPCon technology, in which the rear side is fully passivated by an oxide/poly-Si tunneling junction. The performance of a TOPCon solar cell may further be improved by the incorporation of selective tunneling junctions underneath the front contacts. Some fabrications have been reported on a similar structure for an n-type Si substrate but they have not achieved the expected results. Also, a detailed study has not been done yet. Using 3-D sentaurus technology computer aided design (TCAD) simulation software, a detailed analysis has been done on the modified structure through the optimization of the tunnel oxides, the interfaces, the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</sup> poly-Si layer, the selective (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</sup> -poly-Si) tunneling junctions underneath the front contacts, etc., which has not been done earlier. It is seen that a thick n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</sup> poly-Si layer causes parasitic absorption of light, whereas a very thin poly-Si layer cannot provide sufficient field for tunneling of carriers. A thicker tunnel oxide produces a high series resistance, whereas a very thin tunnel oxide cannot restrict the minority carriers to reach to the contacts. Therefore, an optimization is required and the optimization is done based on a fabricated bifacial p-TOPCon solar cell reported in the literature with an efficiency of 21.2% and bulk lifetime of 200 μs. After performing all the modifications in the fabricated reference cell and optimizing different parameters, the efficiency is improved by 3.5% in absolute. The efficiency is further improved to 25.4% with the bulk lifetime of 1 ms.

Multilayer α′-4H-borophene growth on gallium arsenide towards high-performance near-infrared photodetector

Multilayer borophene was predicted to have a similar semiconductor property to its monolayer arise from the weak van der Waals interactions between the layers. Besides, multilayer borophene has a higher carrier mobility than monolayer ones, so it is placed great hopes in applications of photoelectric and photovoltaic devices. However, its preparation and application in experiments of multilayer borophene are still lacking. Here, multilayer α′-4H-borophene was synthesized on semiconducting n-type GaAs substrates using NaBH4 source as precursor and hydrogen as the carrier gas under controlled temperature and pressure conditions. The experimental results of the borophene are in good agreement with those of its theoretical prediction. The borophene is a semiconductor with a bandgap of 2.48 eV. To demonstrate the device application potential of the borophene, a near-infrared photodetector composed of p-type borophene and n-type GaAs was fabricated. The photodetector shows a high photoresponsivity of 0.31 mA·W−1, a high specific detectivity of 108 Jones, and a fast response or recovery speed of 117 or 109 ms under the irradiation with the wavelength of 940 nm at zero bias. The results prove that the α′-4H-borophene/GaAs photodetector can show high sensitivity and zero consumption, which is of great value in meeting the appeal of sustainable development of society.

Surface Photovoltage Study of Metal Halide Perovskites Deposited Directly on Crystalline Silicon.

Perovskite (PVK) films deposited directly on n-type crystalline Si substrates were investigated by two operating modes of the surface photovoltage (SPV) method: (i) the metal-insulator-semiconductor (MIS) mode and (ii) the Kelvin probe force microscopy (KPFM). By scanning from 900 to 600 nm in the MIS mode, we consecutively studied the relatively fast processes of carrier generation, transport, and recombination first in Si, then on both sides of the PVK/Si interface, and finally in the PVK layer and its surface. The PVK optical absorption edge was observed in the range of 1.61-1.65 eV in good agreement with the band gap of 1.63 eV found from photoluminescence spectra. Both SPV methods evidenced an upward energy band bending at the PVK/n-Si interface generating positive SPV. Drift-diffusion modeling allowed us to analyze the shape of the wavelength dependence of the SPV. It was also observed that the intense illumination in the KPFM measurements induces slow SPV transients which were explained by the creation and migration of negative ions and their trapping at the PVK surface. Finally, aging effects were studied by measuring again SPV spectra after one-year storage in air, and an increase in the concentration of shallow defect states at the PVK/n-Si interface was found.

Spatially Resolved Photo-Response of a Carbon Nanotube/Si Photodetector

Photodetectors based on vertical multi-walled carbon nanotube (MWCNT) film-Si heterojunctions are realized by growing MWCNTs on n-type Si substrates with a top surface covered by Si3N4 layers. Spatially resolved photocurrent measurements reveal that higher photo detection is achieved in regions with thinner MWCNT film, where nearly 100% external quantum efficiency is achieved. Hence, we propose a simple method based on the use of scotch tape with which to tune the thickness and density of as-grown MWCNT film and enhance device photo-response.

Growth and characterization of Cu2ZnxFe1-xSnS4 thin films deposited on n-type silicon substrates

Cu2FeSnS4 and Cu2ZnSnS4 ingots were successfully grown by direct melting of their high-purity constituent elements from stoichiometric compositions (copper, iron, zinc, tin and sulfide). Subsequently, thin films of CFTS and CZTS were deposited on unheated n-type silicon substrates through the vacuum evaporation method. These deposited films were sulfided for 30 min at a sulfidation treatment temperature Ts = 400 °C. The structural properties of the C (Z, F)TS thin films were studied by X-ray diffraction (XRD), Raman spectroscopy and electron backscatter diffraction (EBSD).The resulting studies suggest the existence of polycrystalline phases where CZTS has a kesterite structure and CFTS a stannite structure. Composition analysis also indicates that the synthesized C (Z,F)TS powders are close to the expected stoichiometry.A good crystallinity of CZTS followed by an increase in the average roughness value of this film is highlighted in the thin film micrographs of C (Z,F)TS. Furthermore, the Hall effect indicates that the prepared C (Z,F)TS films exhibit a manifest p-type semiconductor, and the conductivity, mobility and carrier charge concentration are higher for the CZTS thin film. The electrical conductivity of the CFTS and CZTS thin films were investigated using the impedance spectroscopy technique in the frequency range 5 Hz–13 MH. Values of activation energy are indicative of thermal activation of the conduction mechanism by jumping between localized states. Further, the analysis of the frequency and temperature dependence of the AC conductivity supports the correlated barrier hopping (CBH) model.

LiF film enhanced high brightness blue electroluminescence of diamond /CeF3 composite film

Diamond/CeF3 composite film (DCCF) and diamond/CeF3/LiF composite film (DCLCF) electroluminescent(EL)devices were deposited on n-type heavy-doped silicon substrates by using microwave plasma chemical vapor deposition system (MPCVD) and vacuum electron beam vapor deposition system (EBVD). A series of corresponding tests characterized the composition, microstructure, and EL characteristics of the devices. The experimental results show that the LiF layer can effectively enhance the blue light emission intensity of the composite film device. Blue light emission can be observed in the two types of devices when the forward bias is applied, and the EL spectra of both devices show a strong wide peak at 440 nm. Meanwhile there is no significant difference in the maximum luminous intensity between them. However, when the reverse bias voltage is applied to the two devices, it is found that DCCF device hardly observes visible light emission, while the blue light emission of DCLCF device is very strong. And the EL spectrum of DCLCF device still shows a strong wide peak at 440 nm, and the blue light emission can reach the maximum at 350 V reverse bias voltage. Its maximum luminous intensity is 3.5 times that of DCCF devices, and its brightness can reach 35 cd/m2.

Packaging design and thermal analysis for 1 mm2 high power VCSEL

PurposeVertical-cavity surface-emitting laser (VCSEL) is a high-performance semiconductor device made of unique epitaxial layers grown on n-type GaAs or InP substrates. The VCSEL’s thermal resistance, Rth, is an essential metric that reflects its thermal properties and dependability. The purpose of this paper is to develop packaging for 1 mm2 VCSEL chips made of a variety of materials, such as ceramic, lead frame and printed circuit board (PCB)-based packaging, as well as provide an idea or design that can withstand and perform well in terms of Rth and heat dissipation during operation. SolidWorks 2017 and AutoCAD Mechanical 2017 software were used to publish all thoughts and ideas, including the size dimensions (x, y and z) and material choices for each package.Design/methodology/approachFollowing the modelling and material selection, the next step is to use the Ansys Mechanical Structural FEA Analysis software to simulate all packaging for Rth and determine which packaging produced the best result, therefore, determining the heat dissipation for each packing. All parameters were used based on the standard cleanroom requirement for the industrial manufacturing backend process, where the cleanroom classification is 10,000 particles (ISO 7). The results demonstrated that the ceramic and lead frame provided good Rth values of 7.3 and 7.0 K/W, respectively, when compared to the PCB, which provided more than 80 K/W; thus, the heat dissipation for PCB packaging also increased.FindingsAs a result of the research, it was determined that ceramic and lead frame packaging are appropriate and capable of delivering good Rth and heat dissipation values when compared to PCB. In comparison to PCB, which requires numerous modifications, such as adding via holes and a thermal bar in an attempt to lower the Rth value, neither packaging requires improvement. Ceramic was chosen for development based on Rth's highest performance, with the actual device consisting of a lead frame and PCB. The Zth measurement test was carried out on a ceramic package, and the Rth result was comparable to the simulation result of 7.6 K/W, indicating that simulation was already proved for research and development.Originality/valueThe purpose of this study is to determine which proposed packaging design would give the highest Rth performance of a 1 mm2 chip as well as the best heat dissipation. In comparison to other studies, VCSEL packaging used the header and window cap as package components with a wavelength of 850 nm, and other VCSEL packaging developments used the sub mount on ceramic package with an output power ranging from 500 mW to 2 W, whereas this study used a huge wavelength and an output power of 4 W.

Change of the elastic strain in SiC films growing on Si substrates by the method of consistent atomic substitution

Sequential stages of synthesis of SiC epitaxial films on n- and p-type Si(111) substrates in a mixture of carbon monoxide and silane are studied by X-ray diffraction (XRD) and Raman scattering methods. It was found that the elastic strain in SiC films grown on n-type Si(111) is absent in contrast to SiC films grown on p-type Si(111), where the deformations are formed and completely relaxed by the 40 min of synthesis. A dramatic change in the SiC film structure is observed on the third minute of the growth, which is associated with the formation and growth of pores in the SiC layer. Differences in the lattice constants of SiC films grown on p- and n-type Si substrates are determined and verified via analysis of the change in the curvature of SiC/Si wafers. Keywords: Silicon carbide on silicon, elastic strain, nanostructures, microstructure evolution.

Synthesis of arrays nanostructured porous silicon wires in electron conductivity type silicon with crystallographic orientation (111)

The method of modified metal-assisted electrochemical etching was proposed and arrays of nanostructured porous silicon wires on n-type monocrystalline silicon substrate with crystallographic orientation (111) were obtained. The influence of the electrolyte composition at the second stage of obtaining on the morphology of silicon wires by scanning electron microscopy methods was revealed. The phase composition of porous silicon wires was controlled by Raman spectroscopy. Keywords: Porous silicon,porous Silicon nanowires, MACE, Nanomaterials, Raman spectroscopy.

Изменение упругих деформаций в пленках SiC в процессе роста методом согласованного замещения атомов на подложках Si

Sequential stages of synthesis of SiC epitaxial films on n- and p-type Si(111) substrates in a mixture of carbon monoxide and silane are studied by X-ray diffraction (XRD) and Raman scattering methods. It was found that the elastic strain in SiC films grown on n-type Si(111) is absent in contrast to SiC films grown on p-type Si(111), where the deformations are formed and completely relaxed by the 40th minute of synthesis. A dramatic change in the SiC film structure is observed on the third minute of the growth, which is associated with the formation and growth of pores in the SiC layer. Differences in the lattice constants of SiC films grown on p- and n-type Si substrates are determined and verified via analysis of the change in the curvature of SiC/Si wafers.

Синтез массивов наноструктурированных пористых кремниевых стержней в кремнии электронного типа электропроводности с кристаллографической ориентацией (111)

The method of modified metal-assisted electrochemical etching was proposed and arrays of nanostructured porous silicon wires on n-type monocrystalline silicon substrate with crystallographic orientation (111) were obtained. The influence of the electrolyte composition at the second stage of obtaining on the morphology of silicon wires by scanning electron microscopy methods was revealed. The phase composition of porous silicon wires was controlled by Raman spectroscopy.