Wide Bandgap Semiconductor Materials Research Articles

Diamond/GaN HEMTs: Where from and Where to?

Gallium nitride is a wide bandgap semiconductor material with high electric field strength and electron mobility that translate in a tremendous potential for radio-frequency communications and renewable energy generation, amongst other areas. However, due to the particular architecture of GaN high electron mobility transistors, the relatively low thermal conductivity of the material induces the appearance of localized hotspots that degrade the devices performance and compromise their long term reliability. On the search of effective thermal management solutions, the integration of GaN and synthetic diamond with high thermal conductivity and electric breakdown strength shows a tremendous potential. A significant effort has been made in the past few years by both academic and industrial players in the search of a technological process that allows the integration of both materials and the fabrication of high performance and high reliability hybrid devices. Different approaches have been proposed, such as the development of diamond/GaN wafers for further device fabrication or the capping of passivated GaN devices with diamond films. This paper describes in detail the potential and technical challenges of each approach and presents and discusses their advantages and disadvantages.

Designing sp3 networks of two novel carbon allotropes in the P4/mmm phase

Two novel carbon allotropes in the P4/mmm phase with sp3 hybridization, denoted as P4/mmm C40 and P4/mmm C60, are predicted using the density functional theory. Both the carbon allotropes are dynamically, mechanically, and thermodynamically stable. The shear modulus G, Young's modulus E, and bulk modulus B of both P4/mmm C40 and P4/mmm C60 are larger than those of any other carbon allotropes in the P4/mmm phase in the present, with the G, E, and B of P4/mmm C40 being all larger than those of P4/mmm C60. Three empirical hardness models (the Lyakhov–Oganov model, Chen's model, and the Mazhnik–Oganov model) show that only P4/mmm C40 is a superhard material. Both P4/mmm C40 and P4/mmm C60 are indirect, wide band gap semiconductor materials. By studying the mechanical anisotropies of the elastic moduli (such as E and Poisson's ratio v, G, and B) along with some mechanical anisotropy factors (such as the universal elastic anisotropy index AU, the linear bulk modulus, the percentage of mechanical anisotropy for G and B, and shear anisotropic factors) and sound wave velocity, it is proved that P4/mmm C40 and P4/mmm C60 are mechanically anisotropic materials.

Pushing Power to New Levels

Wide-bandgap semiconductor materials are helping to push power to new levels.

CuI/Nylon Membrane Hybrid Film with Large Seebeck EffectSupported by the International Scientific and Technological Innovation Cooperation Project between the Governments of Key National R&D Program of China (Grant No. 2018YFE0111500), and the National Natural Science Foundation of China (Grant No. 51972234).

Room-temperature thermoelectric materials are important for converting heat into electrical energy. As a wide-bandgap semiconductor material, CuI has the characteristics of non-toxicity, low cost, and environmental friendliness. In this work, CuI powder was synthesized by a wet chemical method, then CuI film was formed by vacuum assisted filtration of the CuI powder on a porous nylon membrane, followed by hot pressing. The film exhibits a large Seebeck coefficient of 600 μV · K−1 at room temperature. In addition, the film also shows good flexibility (∼95% retention of the electrical conductivity after being bent along a rod with a radius of 4 mm for 1000 times). A finger touch test on a single-leg TE module indicates that a voltage of 0.9 mV was immediately generated within 0.5 s from a temperature difference of 4 K between a finger and the environment, suggesting the potential application in wearable thermal sensors.

Study of In x Ga1-x N/GaN Homotype Heterojunction IMPATT Diodes

In this work, a novel n-In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-<i>x</i></sub> N/N-gallium nitride (GaN) homotype heterostructure is proposed instead of P-GaN/N-GaN homostructure to produce impact-ionization-avalanche-transit-time (IMPATT) diode. Conventional GaN IMPATT device will lose its working ability due to the immature p-type GaN, so this work predicts that the n-In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-<i>x</i></sub> N/N-GaN IMPATT diode can be an alternative to the GaN p-n IMPATT diode; thus, the difficulty of the p-type doping process is avoided. The dc and RF large-signal output characteristics with different compositions are investigated in detail. The simulation results show that the power and efficiency of the novel structure device increase when the In composition increases. When the In composition is greater than 0.4, the performance of the homotype heterojunction IMPATT is better than that of p-n IMPATT. Moreover, homotype heterojunction IMPATT is better in frequency bandwidth, and it can hold greater bias current density than p-n IMPATT. Meanwhile, the performance of homotype heterojunction IMPATT does not depend on the thickness of the InGaN layer, but it decreases as the thickness of the p-type region in p-n IMPATT increases. As it has greater potential in the application, this work brings a reference for the design and manufacture of IMPATT devices based on wide bandgap semiconductor materials, especially GaN materials.

A Novel BN Polymorph in P4/mbm Phase with a (4,4) Nanotube

Herein, based on density functional theory, a new boron nitride structure derived from diamond is designed, and its stability is also proved. The new boron nitride structure is denoted as P4/mbm BN. The elastic moduli (bulk modulus, shear modulus, and Young's modulus) of P4/mbm BN are slightly greater than those of C72 and T carbon, and the shear modulus and Young's modulus are larger than those of P‐4m2 B7N7, B11N11, and B15N15. The shear modulus and Young's modulus of P4/mbm BN exhibit a smaller mechanical anisotropy than that of P‐4m2 B7N7, B11N11, and B15N15, where P‐4m2 B15N15 exhibits the greatest mechanical anisotropy of shear modulus and Young's modulus. The anisotropy of shear modulus in the (100), (010) plane of P‐4m2 B15N15 is 26.5 times that of P4/mbm BN, and the mechanical anisotropy of Young's modulus in (110) plane of P‐4m2 B15N15 is 35.6 times that of P4/mbm BN. P4/mbm BN is a wide and indirect bandgap semiconductor material with bandgap of 4.8 eV. Compared with silicon carbide and gallium nitride, P4/mbm BN has a wider bandgap, it might be more suitable for making high temperature, high frequency, radiation resistance, and high‐power devices.

Microstructure Analysis of GaN Epitaxial Layers During Ion Implantation Using Synchrotron X-Ray Topography

Power electronic devices based on wide band-gap semiconductor materials such as GaN and SiC are rapidly being developed to replace traditional silicon-based devices whose performance has nearly reached their material limits. In the fabrication of GaN vertical power devices, selective area doping (SAD) processes are essential [1]. Several SAD techniques have been developed, including ion implantation [2], etching and regrowth method [3, 4], diffusion doping and neutron transmutation [5]. However, the influences of these procedures on the microstructures of GaN epitaxial layers is one of the key factors to determine the performance of the devices.In this study, ion-implanted GaN epitaxial layers from different stages including ammonothermal grown substrate material, metal organic chemical vapor deposition (MOCVD) epitaxial growth, ion implantation and subsequent annealing was characterized by synchrotron monochromatic beam X-ray topography (SMBXT) [6], synchrotron X-ray rocking curve topography (SXRCT) [7], and high-resolution X-ray diffraction (HRXRD). The change of distribution of threading dislocations (TDs) is characterized. The comparison of lattice strain of the material from each processing stage is conducted by both HRXRD and SXRCT.Enlarged contrast of screw and edge types of threading dislocations (TDs) on X-ray topographs after homoepitaxial growth is observed and likely due to interaction with point defects. X-ray topographs reveal ion implantation does not change the distribution of dislocations in the wafer. Strain and tilt maps derived from X-ray rocking curve topographs also show that annealing leads to an improvement in lattice bending levels. These results will be discussed with their implications for further processing into devices.

(Invited) Materials Integration, Interlayers, and Interactions for Thermal Management of Wide Bandgap Device Structures

Wide bandgap semiconductor materials provide opportunities for high power device structures and circuits to perform more efficiently than is achievable with silicon. To optimize such performance, however, management of heat dissipation from the device-active regions of the structure is necessary. This presentation will focus on materials integration schemes and on interfacial materials reactions in order to understand thermal transport across interfaces to improve thermal management and hence device performance.Bonding a wide bandgap material to a high thermal conductivity substrate has often been touted as a means to improve thermal conductivity. We will discuss different bonding methods for a variety of materials combinations, including GaN / Si and b-Ga2O3 / SiC and how these results point to opportunities with other materials combinations. As was the case with the development of silicon-on-insulator, these bonding schemes also require the ability to produce structures that include a thin layer of the wide bandgap material on the high thermal conductivity substrate, through a combination of wafer removal and surface polishing. We will demonstrate stock wafer removal or exfoliation combined with chemical-mechanical polishing to achieve such structures. Bonding also requires high quality substrates and our efforts to assess wafer quality prior to bonding using x-ray diffraction and x-ray topography will be described.Interfacial layers and metal contacts can either enhance or degrade thermal transport across interfaces. We will highlight a case where such interlayers improve performance and will also address interactions between deposited metals and the wide bandgap materials and the impact of such interactions on thermal management.

(Invited) Nanoscale Investigation of Extended Defects in Wide Bandgap Semiconductors By Exploiting Phonon-Resonant Near-Field Interaction

The use of wide-bandgap semiconductor materials like SiC and GaN can dramatically improve the performance of electronic devices at high powers and temperatures. However, the propensity of extended defects in these materials does challenge their implementation in commercial electronic and optical applications. Spectroscopic and microscopic tools for identifying and characterizing these defects typically offer either spectroscopic or microscopic information exclusively and/or may be destructive. Here, we show how extended defects within 4H-SiC manifest in the nanoscale infrared phonon response probed by scattering-type scanning near-field optical microscopy (s-SNOM), a nondestructive method capable of simultaneously collecting topographic and spectroscopic information with frequency-independent nanoscale spatial resolution (≈20 nm).We correlate the s-SNOM response of various defects in 4H-SiC with UV-photoluminescence, secondary electron and electron channeling contrast imaging, and transmission electron microscopy. We identify evidence of step-bunching, recombination-induced stacking faults, and threading screw dislocations, and also demonstrate the interaction of surface phonon polaritons with extended defects. Phonon-enhanced infrared nanospectroscopy and spatial mapping via s-SNOM thus offer significant insights into extended defects within emerging semiconductor materials and devices. It thus serves as an important diagnostic tool to help advance material growth efforts for electronic, photonic, phononic, and quantum optical applications.[1] B. Hauer, C. E. Marvinney, et al. Advanced Functional Materials 30, 1907357 (2020).

Induction Heating in Domestic Cooking and Industrial Melting Applications: A Systematic Review on Modelling, Converter Topologies and Control Schemes

In the current scenario, power electronic device-based induction heating (IH) technologies are widely employed in domestic cooking, industrial melting and medical applications. These IH applications are designed using different converter topologies, modulation and control techniques. This review article mainly focuses on the modelling of half-bridge series resonant inverter, electrical and thermal model of IH load. This review also analyses the performance of the converter topologies based on the power conversion stages, switching frequency, power rating, power density, control range, modulation techniques, load handling capacity and efficiency. Moreover, this paper provides insight into the future of IH application, with respect to the adaptation of wide band-gap power semiconductor materials, multi-output topologies, variable-frequency control schemes with minimum losses and filters designed to improve source-side power factor. With the identified research gap in the literature, an attempt has also been made to develop a new hybrid modulation technique, to achieve a wide range of power control with high efficiency. A 100 W full-bridge inverter prototype is realised both in simulation and hardware, with various modulation schemes using a PIC16F877A microcontroller. The results are compared with existing techniques and the comparisons reveal that the proposed scheme is highly viable and effective for the rendered applications.

Spray Pyrolysed Nanostructured Gold-Doped Tin Oxide (Auto) Thin Films

Nanostructured SnO2 thin films were grown by the chemical spray pyrolysis (CSP) method. Homemade spray pyrolysis technique is employed to prepare thin films. SnO2 is wide band gap semiconductor material whose film is deposited on glass substrate. A gold nanoparticle-doped tin oxide thin film (AuTO) was also prepared. UV-VIS (ultraviolet visible) spectroscopy and four-point probe analysis are done for optical and electrical analysis. UV-Visible absorption spectra show that the band gap of SnO2 thin film is 3.78 eV and 3.82 eV for AuTO. Band gap of SnO2 thin film can be tuned that it can be used in optical devices. The films have transmittance increases (to about 60%) and the absorbance decreases in the visible region of the electromagnetic spectrum. The electrical conductivity of the Tin Oxide is enhanced by functionalizing with the Gold nanoparticles. It is higher than that of the Tin oxide only; 0.77 x 10-2 (Ohm cm)-1 and 3.55 x 10-2 (Ohm cm)-1 for SnO2 and AuTO respectively. These properties reveal that Tin Oxide doped with gold can actually be a good material for a transparent conducting oxide to be used in photovoltaic fabrication and in electronics.

Higher-performance Fabry-Perot microlaser enabled by a quadrilateral microwire via Ag nanowires decoration

In this work, ultraviolet Fabry-Perot (FP) microlaser, made of an individual rectangular-shaped ZnO microwire, was achieved. The bilateral smooth facets and single-crystalline specificity of as-grown ZnO microwires can enable the realizing of lateral FP microresonators. By incorporating Ag nanowires (AgNWs), plasmon-enhanced FP lasing performances of an individual ZnO microwire, specifically for the sharply reduced threshold, increased lasing intensity and increased Q-factor, were achieved. Accordingly, the enhanced working principle was implemented, and is resorting to the confinement and enhancement of localized electromagnetic-field produced by AgNWs, which can make up the metal loss and accelerate more radiative recombination. Thereby, the incorporation of a rectangular-shaped microwire and AgNWs via desired ultraviolet plasmons can be used to exploit the modulation of metal nanostructures on lasing characteristics of wide bandgap semiconductors. Further, this study also suggestes that AgNWs with excellent ultraviolet plasmons can be generally utilized to modulate the optoelectronic characteristics of wide bandgap semiconductor materials and devices, indicating its underlying applications in fabricating high-performance light-emitting diodes and lasers, photodetectors and so on, working in the ultraviolet wavelengths.

The first foreseen of structural, mechanical, electronic and optical properties of novel alkali metal tetrafluoridobromate ABrF4 (A=Na, K and Rb)

This study deals with the first theoretical investigation of structural, mechanical, electronic, and optical properties of ABrF4 (A = Na, K, and Rb) ternary compounds using ab-initio calculations within the framework of the density functional theory (DFT) using the pseudo-potential plane-wave method. The structural parameters are in agreement with the experimental values stated in the literature. The elastic constants indicate that these compounds are ductile. For a better and in-depth confirming the anisotropic character of the mechanical properties, several indexes such as the universal anisotropic, and the percentage elastic anisotropy for compression and shear have been investigated. The electronic properties indicate that these compounds are wide-band gap semiconductor materials. The optical properties including the dielectric function, the absorption and extinction coefficients, the optical reflectivity and conductivity, the refractive index, and the energy loss function have been studied in detail. The wide optical absorption range in the ultraviolet (UV) region suggests that these materials could be useful for specific implementations in UV optoelectronic devices; therefore, this theoretical investigation is probable to motivate future experimental works.

Effects of gate width variation on the performance of Normally‐OFF dual‐recessed gate MIS AlGaN/GaN HEMT

AbstractDiscovery of wideband gap semiconductor materials has boosted the field of power electronics. Fabrication of HEMT has overcome the drawback of lower mobility and ON‐state current of wide bandgap materials. However, due to lower ON‐state current earlier proposed devices suffer from poor ON‐state resistance; hence, in this work dual gate technique has been proposed. To further switch the device characteristics from Normally‐ON to Normally‐OFF state, recessed gate technique is used. Device physics, analog parameters of Normally‐OFF dual‐recessed gate metal insulator semiconductor AlGaN/GaN HEMT (DRG‐MIS‐HEMT) are analyzed and compared with conventional DG‐MIS‐HEMT. To solidify the analysis, width of recessed gate has been varied from 2 nm to 28 nm. At recessed gate width (=28 nm), proposed device resulted RON = 1.98 Ω‐cm2, threshold voltage 1.25 V, IDS of 1100 mA/mm, ION/IOFF = 1014 and ft = 10 GHz. Proposed device also resulted in improved linearity characteristics over single gate structure. In future, the proposed device can be used for RF applications.

Study on Electric Field Modulation and Avalanche Enhancement of SiC/GaN IMPATT Diode

This paper proposes a 6H-materials silicon carbide (SiC)/gallium nitride (GaN) heterogeneous p-n structure to replace the GaN homogenous p-n junction to manufacture an impact-ionization-avalanche-transit-time (IMPATT) diode, and the performance of this 6H-SiC/GaN heterojunction single-drift-region (SDR) IMPATT diode is simulated at frequencies above 100 GHz. The performance parameters of the studied device were simulated and compared with the conventional GaN p-n IMPATT diode. The results show that the p-SiC/n-GaN IMPATT performance is significantly improved, and this is reflected in the enhanced characteristics in terms of operating frequency, rf power, and dc-rf conversion efficiency by the two mechanisms. One such characteristic that the new structure has an excessive avalanche injection of electrons in the p-type SiC region owing to the ionization characteristics of the SiC material, while another is a lower electric field distribution in the drift region, which can induce a higher electron velocity and larger current in the structure. The work provides a reference to obtain a deeper understanding of the mechanism and design of IMPATT devices based on wide-bandgap semiconductor materials.

A Memristor‐Based Silicon Carbide for Artificial Nociceptor and Neuromorphic Computing

AbstractWith the advancement of artificial intelligence technology, more and more biological functions need to be imitated to complete more complex tasks and adapt to a complex external work environment. Memristors, as an excellent candidate for neuromorphic artificial electronic devices with many biological functions, have inspired the interest of researchers because of the advantages of scalability, good retention, and high operating speed. In this work, wide band gap semiconductor materials silicon carbide (SiC) films are prepared as a memristor medium. By adjusting the current compliance, both threshold character and bipolar resistive switching phenomenon are realized in one device with both lower powers for set operation. For the threshold characteristic, this device has mimicked the “threshold,” “inadaptation,” and “relaxation” features of a nociceptor, which will protect the artificial intelligence system to have stronger adaptability to the external environment. For the bipolar resistive switching characteristics, this device demonstrates good stability and retention time, with a switching speed of 18 ns. These bipolar resistance switching characteristics have simulated many synaptic functions. Pulses with hundreds of nanosecond time scale widths are conducive to fast learning and calculation. This device‐based third‐generation SiC semiconductor material will find a broad application in neuromorphic chip systems.

Modifying Precursor Solutions to Obtain Screen-Printable Inks for Tungsten Oxides Electrochromic Film Preparation

Tungsten trioxide (WO3) is used to prepare the important electrochromic layer of the electrochromic device as a wide bandgap semiconductor material. In this study, WO3 electrochromic film was successfully prepared by screen printing. To modify the thixotropy and wettability of the ink, polyvinyl alcohol (PVA) and 2-perfluoroalkyl ethanol (FSO) were added in the ammonium meta-tungstate (AMT) solution. We found that the PVA additive could improve the dynamic viscosity of the solution and modify the uniformity of the film. 2-Perfluoroalkyl ethanol (FSO) could lower the surface tension and increase the wettability of the AMT solution on the substrate. By observing the morphology of the printed films, the ink formulas for screen printing were selected. We found the annealing process could help remove PVA. Through characterization of electrochromic performance, it was found that the best performing device had 42.57% modulation and 93.25 cm2·C−1 coloration efficiency (CE) for 600 nm light. This study showed great potential in the preparation of WO3 electrochromic devices by a low-cost screen-printing method.

Novel BCN2 and CN compounds in C2/m phase: First-principle calculations

A novel superhard CN (the stoichiometric ratio of carbon to nitrogen is 1:1) and BCN2 compound in C2/m phase are proposed and predicted according to density functional theory in this work. The physical properties, such as crystal structure, electronic properties, elastic properties, mechanical anisotropy properties and the stable of CN and BCN2 are investigated. The shear modulus G, Young's modulus E, and bulk modulus B of BCN2 and CN are 253 and 310 GPa; 448 and 719 GPa; and 186 and 323 GPa with GGA functional, respectively. Utilizing the Lyakhov-Oganov's model, CN and BCN2 are superhard materials, the hardness of CN and BCN2 is 60.99 GPa and 53.38 GPa, respectively. Compared with diamond and c-BN, although the hardness of CN and BCN2 is not as great as that of diamond, while they are both greater than that of c-BN. Using the Chen's model, CN also is a super-hard material with hardness is 58.63 GPa, while the hardness of BCN2 is only 26.67 GPa. C2/m CN is an indirect and wide band gap semiconductor material, while BCN2 is a metallic material. In addition, mechanical anisotropy of shear modulus G, Young's modulus E, and bulk modulus B of CN and BCN2 are also studied in detail.

A New Wide Bandgap Semiconductor: Carbyne Nanocrystals

AbstractDeep ultraviolet (DUV) photodetectors (PDs) always and inevitably face a drastic working environment such as high temperature. However, DUV PDs based on the reported wide bandgap semiconductor materials cannot simultaneously possess high stability and high performance at high temperatures. Here, for the first time, a new wide bandgap semiconductor material, carbyne nanocrystals (CNCs), is reported. The constructed DUV PD made from CNCs demonstrates high‐performance and high stability at the temperature of 300 °C, which is the highest working temperature reported to date for DUV PDs. Under 266 nm light at room temperature, the CNCs‐based PD exhibits a low dark current of less than 10 pA and a high signal‐to‐noise ratio of greater than 106 at a bias voltage of 2 V. It can work at the temperature up to 300 °C, exhibiting a current on‐off ratio of 2.1, and accompanied by a fast response/recovery speed of less than 0.06 s. The excellent transport properties of CNCs would be of great benefit to enhance the performance of devices. These findings open the door to the applications of CNCs as a new wide bandgap semiconductor material.

From Amorphous to β-Gallium Oxide: Practical Implementation of Energetics Considerations in Process Design and Optimization

Gallium oxide (Ga2O3) is a wide bandgap material (bandgap ~4.0 eV – 5.2 eV) with a large breakdown field that has considerably high figures of merit (FOM) in power handling compared to other wide bandgap semiconductor materials in use today (such as GaN and SiC) [1, 2]. Gallium oxide is also expected to expand the operating spectral range of optoelectronic devices to deep UV.Properties of gallium oxide depend on its crystal structure; amorphous [3, 4] as well as different crystalline forms [5] of this material have been used in electronic and optoelectronic devices. Among gallium oxide crystalline polymorphs, β-Ga2O3 has attracted the most attention because it is the most stable gallium oxide polymorph and, therefore, can ultimately be obtained by heating other gallium oxide polymorphs (and even amorphous gallium oxide) at sufficiently high temperatures (ca. 550°C and above); this polymorph can also be obtained from the melt at high temperatures (ca. 1800°C) using bulk crystal growth techniques [1, 6]. In the thin film form, growing high quality β-Ga2O3 is only possible on very limited substrates (e.g., β-Ga2O3 native substrate and sapphire) while having to carefully choose very specific process conditions based on each process and the instrument being used.In this work, we present strategies and guidelines, based on energetics considerations, that make it possible to design epitaxial deposition processes that achieve β-Ga2O3 thin films at low temperatures (< 300°C). We use the atomic layer deposition (ALD) technique to achieve dense and pinhole-free films of amorphous gallium oxide. Then, we revise the deposition process conditions step-by-step so that the energetics of the process can lead us to obtain high quality epitaxial β-Ga2O3 at low temperatures while not being limited to β-Ga2O3 native substrates or very specific (or instrument-dependent) process conditions. The results presented in this work facilitate the implementation of Ga2O3 in next generation wide bandgap electronic devices.