Large Band Gap Materials Research Articles

Strain tunability of the properties of Fe-doped lithium niobate for optoelectronic applications: Theoretical insights

This work elucidates the impact of strain on the optical and electronic properties of Fe-doped lithium niobate using density functional theory. The Fe-doped lithium niobate is applied with the tensile and compressive strain (10% and 20%) and optical properties are analyzed. Lithium niobate, a large bandgap material (bandgap 3.56 eV), has absorption limited to the UV region of the optical spectrum only. For the Fe-doped lithium niobate, the bandgap is 1.38 eV, with low absorption in the visible region. The computed results show that the tensile and compressive strains have significantly narrowed down the bandgap of Fe-doped lithium niobate in compression to the unstrained structures. The decrease in the bandgap is largest for the tensile strain of 20% among all the applied strains. Further, visible light absorption is also improved due to the application of strain. The improvement in visible light absorption is highest for the tensile strain of 20% with absorption completely shifted in the desired visible region. The improved visible absorption due to the applied strain makes Fe-doped lithium niobate a potential candidate for optoelectronics and solar applications.

Single-Layer Organic Light-Emitting Diode with Trap-Free Host Beats Power Efficiency and Lifetime of Multilayer Devices.

Organic light-emitting diodes (OLEDs) employing a single active layer potentially offer a number of benefits compared to multilayer devices; reduced number of materials and deposition steps, potential for solution processing, and reduced operating voltage due to the absence of heterojunctions. However, for single-layer OLEDs to achieve efficiencies approaching those of multilayer devices, balanced charge transport is a prerequisite. This requirement excludes many efficient emitters based on thermally activated delayed fluorescence (TADF) that exhibit electron trapping, such as the green-emitting bis(4-(9,9-dimethylacridin-10(9H)-yl)phenyl)methanone (DMAC-BP). By employing a recently developed trap-free large band gap material as a host for DMAC-BP, nearly balanced charge transport is achieved. The single-layer OLED reaches an external quantum efficiency (EQE) of 19.6%, which is comparable to the reported EQEs of 18.9-21% for multilayer devices, but achieves a record power efficiency for DMAC-BP OLEDs of 82lmW-1, clearly surpassing the reported multilayer power efficiencies of 52.9-59lmW-1. In addition, the operational stability is greatly improved compared to multilayer devices and the use of conventional host materials in combination with DMAC-BP as an emitter. Next to the obvious reduction in production costs, single-layer OLEDs therefore also offer the advantage of reduced energy consumption and enhanced stability.

To study the effect of strain engineering on the band gap of BaI2 monolayer: a first principle approach

Inspired by the recent proposal of improving materials performance by strain engineering, first principles calculations are performed to investigate the consequences of compressive and tensile strain on the band gap of BaI2 monolayer. Pristine monolayer is discovered to be a large band gap material with a band gap of 4.06 eV. The dynamical stability of material has been confirmed by the phonon dispersion curve which includes only real phonon mode. Calculations show that the application of strain decrease the band gap of monolayer. The effect of strain has been observed at the 4%, 8%, 12% compressive and tensile strain. The band gap has been reduced from 4.06 eV to 3.52 eV and 3.63 eV under the application of 12 % compressive and tensile strain respectively. In our knowledge the effect of strain on BaI2 monolayer has been studied for the first time and it opens new avenue to modify the properties of monolayer.

Ultrahigh current and ultralow power dissipation of Janus monolayer IIIA-VIA Ga2XY MOSFETs

With the advances of two-dimensional semiconductors, it is promising for the miniaturization of highly integrated circuits. However, the high leakage current, small on-state current and unnecessary power consumption hinder the development of high-performance nanodevices. Here, we design sub-5-nm double-gate monolayer Ga2XY (X, Y = S, Se and Te) metal–oxidesemiconductor field-effect transistors. For all the designed devices, the on-state current, intrinsic delay time and power delay product can meet the standard of the International Technology Roadmap for Semiconductor in 2028. Additionally, the devices based on large bandgap materials have strong inhibition effect on leakage current. In particular, the Ga2SSe device has optimized subthreshold swing as low as 60.7 mV/dec and Ion of 5082 μA/μm (about 6 times higher than the high-performance requirements). The extremely low energy-delay product of 3.64 × 10−31 Js/μm is obtained for the Ga2SeTe device. Therefore, monolayer Ga2XY can be expected for the application of next-generation high-performance electronic nanodevices.

Enhancement of second-order optical nonlinearities and nanoscale periodic domain patterning in ferroelectric boron-substituted aluminum nitride thin films

The discovery and development of CMOS-compatible, nonlinear optical materials is essential to produce integrated photonic devices with advanced functionalities. AlN is a strong candidate for on-chip device demonstration due to its intrinsic second-order optical nonlinearities, large bandgap, and well-established fabrication techniques. However, AlN is not easily phase matched for the largest coefficient d33; the coefficients that could potentially be dispersion phase-matched, d31 and d15, have weak nonlinearities. This work investigates ferroelectric Al1-xBxN (x = 0 to 0.11) for viability as a large bandgap nonlinear optical material with unique suitability towards ultraviolet light generation using second harmonic generation. The linear and nonlinear optical properties are characterized accounting for material anisotropy. With increasing B concentration, a large enhancement from near negligible values to d31 = 0.9 ± 0.1 pm/V and d15= 1.2 ± 0.1 pm/V is observed. This compares favorably to other large bandgap materials like β-Ba(BO2)2, where the largest nonlinear coefficient is d22 ∼ 2.3 pm/V at 800 nm. This is accompanied by a change in the bandgap from 6.1 eV to 5.8 eV as B substitution goes from 0 to 11%. A periodically poled, quasi-phase-matched ferroelectric domain pattern with 400 nm domain size and a wall roughness of <16 nm is demonstrated.

Sequential coating of Sb-doped SnO2 nanowire for photoelectrochemical cells of panchromatic light absorption and low thermalization loss

A photoelectrochemical (PEC) cell is a device of enormous potential in producing hydrogen via water splitting using solar energy. However, the low charge collection efficiency and thermalization loss of a photoelectrode limit the performance of the PEC cell. In this study, these problems are addressed by sequentially coating CdS and CdSe along the longitudinal direction of antimony-doped tin oxide and tin oxide nanowire (NW) arrays. Because of the vertical alignment of CdS and CdSe, larger band gap material (CdS) and smaller band gap material (CdSe) absorb blue and red light, respectively. Such selective absorption reduces the thermalization loss and increases the photocurrent density. In addition, antimony-doped tin oxide NWs increase the collection efficiency of photogenerated carriers and decrease the onset voltage by increasing the electric conductivity and decreasing the mismatch in the Fermi energy level. The photocurrent of the vertically aligned CdS and CdSe on antimony-doped tin oxide NWs is 17.6 mA cm−2, which is 50% higher than that of the traditional cascade-type CdSe/CdS photoelectrode.

Topological nature of large bulk band gap materials Sr3Bi2 and Ca3Bi2

Topological materials are an emerging class of materials attracting the attention of the scientific community due to their potential applications in the fields of spintronics and quantum computing. Using first-principles calculations, the structural, electronic, and topological properties of Sr3Bi2 and Ca3Bi2 compounds without and with spin–orbit coupling are investigated. In the absence of spin–orbit coupling, the projected bulk band structure revealed that the Sr3Bi2 compound host a type-I Dirac point along the F-Γ direction. Since the compound possesses time-reversal and space-inversion symmetries, this Dirac point is associated with the nodal line. The existence of a type-I nodal ring around the Γ-point in the kz = 0 planes, as well as a drumhead-like surface state within the nodal ring, suggested that Sr3Bi2 is a type-I nodal-line semimetal with no spin–orbit coupling. The inclusion of spin–orbit coupling introduced an energy gap of 0.36 eV between the valence band and conduction band at Dirac point. The topological surface states forming a Dirac cone between the bulk bandgap for (001) surface of Sr3Bi2 compound is calculated with spin–orbit coupling. The Z2 topological invariants (1;000), as calculated by using parity product criteria, suggested that Sr3Bi2 is a strong topological insulator. Ca3Bi2, another compound with a similar crystal structure, is also predicted to behave similarly to Sr3Bi2 compound without and with spin–orbit coupling. This research broadens the application of topological insulators and existing platforms for developing novel spintronic devices.

Ab-Initio Study of Calcium Fluoride Doped with Heavy Isotopes

Precision laser spectroscopy of the 229-thorium nuclear isomer transition in a solid-state environment would represent a significant milestone in the field of metrology, opening the door to the realization of a nuclear clock. Working toward this goal, experimental methods require knowledge of various properties of a large band-gap material, such as calcium fluoride doped with specific isotopes of the heavy elements thorium, actinium, cerium, neptunium, and uranium. By accurately determining the atomic structure of potential charge compensation schemes by using a generalized gradient approximation within the ab-initio framework of density functional theory, calculations of electric field gradients on the dopants become accessible, which cause a quadrupole splitting of the nuclear-level structure that can be probed experimentally. Band gaps and absorption coefficients in the range of the 229-thorium nuclear transition are estimated by using the G0W0 method and by solving the Bethe–Salpeter equation.

Investigation of the signal amplitude decrease in subsequent detection in irradiated silicon sensors

Upcoming high energy physics experiments like the High-Luminosity LHC require unprecedented radiation hardness of the detectors, as well as short readout time due to high luminosity and occupancy. Silicon has proven to be extremely radiation hard, sufficient signals can be recorded at fluences above 1×1016neq/cm2. The signal formation was studied in silicon strip sensors, which have been irradiated and annealed until the phenomenon of charge multiplication occurred. In previous studies it was observed that the detection of subsequent signals separated up to several microseconds is altered by the charge trapped during the proceeding pulses. In this paper, the investigation of the effects due to previously created charge in subsequent pulse detection is investigated. A decrease of signal pulse amplitude, which originates from effects of the flowing charges on the electric field configuration, is observed using irradiated diodes measured with top-TCT. The decrease can be explained by polarization, which is caused by trapped charges and is well known in larger band-gap materials like diamond, but often neglected for silicon at this relatively high temperature. The polarization mechanisms happening in the sensor are described by a theoretical model and additionally supported by simulations. The initial electric field and therefore the bias voltage, the time delay between subsequent pulses and the amount of initially created charge have a large impact on this phenomenon.

High photocatalytic activity of aerogel tetragonal and monoclinic ZrO2 samples

ZrO2 nanoparticles have been investigated in the photodegradation of formic acid under UV irradiation. ZrO2 photocatalysts were prepared using a ‘one-pot’ sol-gel method followed by drying under supercritical conditions of solvent and calcination at temperatures varying between 400 °C and 800 °C. Samples were characterized by adsorption-desorption isotherms, XRD, Thermal analysis, Raman spectroscopy, HRTEM, DRS, PL and XPS. The aerogel preparation allows the creation of intermediate band gap states making it active under UV irradiation. The photoactivity of ZrO2 samples follow the order; ZrO2 400 ≥ ZrO2 800 > ZrO2 700 > ZrO2 500 > ZrO2 600 in agreement with their optical properties. The lower the value of mid band gap, the higher the photocatalytic activity. The value of mid band gap depends on the nature of the ZrO2 phase (tetragonal or monoclinic), surface oxygen defects and the tendency to lattice distortion for samples treated at high temperature. This study therefore shows for the first time that adequate preparation of oxide materials (here ZrO2) allows finely tuning the creation of intermediary band gap sites through thermal post-treatments making ZrO2, a large band gap material, able to photocatalytically work under UV irradiation.

Optimizing spectral and morphological match of nonfullerene acceptors toward efficient indoor organic photovoltaics with enhanced light source adaptability

High-performance indoor organic photovoltaics (IOPV) require large-bandgap material systems to absorb visible light efficiently and reduce energy loss. However, state-of-the-art non-fullerene acceptors (NFAs) have absorptions in the near-infrared region and are thus not suitable for IOPV applications. Herein, we report a series of large-bandgap (>1.70 eV) NFAs named FCC-Cl-C8, FCC-Cl-4Ph and FCC-Cl-6Ph by modifying the alkyl side chains with alkylphenyl chains partially or completely. Results show that the bulky alkylphenyl side chains can finely tune the absorption properties of the NFAs and also affect their morphological properties. Interestingly, the best-performing NFA is the one (named FCC-Cl-4Ph) with partial alkyl and alkylphenyl substitutions, which blue-shift the absorption of the NFAs while minimizing the negative morphological effect of the bulky alkylphenyl chains. As a result, FCC-Cl-4Ph can achieve excellent indoor efficiencies over 29% under a 3000 K LED lamp at 1000 lux and show better solution processability over FCC-Cl-C8. More importantly, FCC-Cl-4Ph can maintain high indoor performance (29.7–26.8% at 1000 lux) under a wide range of indoor lighting spectra (2600, 3000, 4000, and 6500 K LED lamps), which should be due to the blue-shifted spectra of FCC-Cl-4Ph and better matching with various indoor conditions. This work reveals an interesting structure-property relationship and offers useful strategies for the further design of NFAs toward efficient IOPV devices.

A Systematic Study of Laser‐Engineered Fluorescence in Carbon Black

The feasibility of laser-engineered fluorescence emission from carbon black (CB) with three laser sources of different wavelengths—660 nm (red), 532 nm (green), and 405 nm (blue) is demonstrated. From which the 660 nm focused laser beam produces the most intense fluorescence. Detailed systematic studies on how the laser-engineered fluorescence emission from CB depends on laser power, laser patterning speed, and environmental control during the laser modification process are carried out. From the systematic studies, the CB samples in ambience undergo most noticeable modifications with a laser power of ≈7 mW and patterning speed of ≈12 μms−1. The fluorescence emission is attributed to the creation of complex defects states into the oxidized form of the pristine system by the formation of 1) C60 fullerene and fullerites; 2) ZnO; 3) Zn2SiO4, and more complex hybrid such as 4) carbon-induced mid-gap states in Zn2SiO4, and 5) Ca-induced defects in ZnO. Such incorporations resulted in the formation of intermediate states in the large bandgap materials. As a result, distinct multicolored fluorescence is emitted by these laser-quenched material systems. Accordingly, multicolored fluorescence designs can be created with elaborative control of focused laser treatment in an ambient and helium environment.

Dilute magnetic semiconductor electrode based all semiconductor magnetic tunnel junction for high-temperature applications

In this paper, the spin-transport properties of Gallium Nitride/Indium Phosphide/Gallium Nitride (GaN/InP/GaN) all semiconductor magnetic tunnel junction (MTJ) has been investigated. To induce ferromagnetic properties in the electrodes made of GaN, the electrodes are doped with Manganese (Mn). The central region is made of InP, which is a large bandgap material, thereby improving the zero-bias magnetoresistance. The electrodes used in the proposed device show ferromagnetic behavior beyond room temperature without the conductivity mismatch problem. Finally, a comparison based on the proposed device's performance parameters with the devices reported in the open literature is carried out in this work. The comparison clearly shows the pre-eminence of the proposed device over the previously reported devices as it has high TMR (1.97 × 104%) and works over a wide range of temperature.

X-Ray Photoemission Investigation of the Beryllium Oxide Band Alignment with Magnesium Oxide and Estimates for Other Insulating and Conducting Oxides

Beryllium oxide (BeO) is a wurtzite structured, large bandgap (E g > 8 eV) material of significant interest as an alloying agent and cladding dielectric in various wide band gap oxide based optoelectronic devices. The success of such devices is highly reliant on bandgap and band alignment engineering to achieve sufficient charge carrier and optical confinement for device operation. In this regard, we have utilized x-ray photoemission spectroscopy (XPS) to determine the valence band offset (VBO) between atomic layer deposited (ALD) BeO and a magnesium oxide (MgO) substrate with (001) orientation. The BeO VBO with MgO (001) was determined to be 0.1 ± 0.15 eV. Applying the rules of commutativity and transitivity for band alignment, we additionally predict the BeO VBO with other wide bandgap conductive oxides such as ZnO, Ga2O3, and InGaZnO4, to be 1.15 ± 0.3 eV, 0.3 ± 0.2 eV, and 0.9 ± 0.2 eV, respectively. Utilizing the reported bandgaps for ALD BeO and the conductive oxides, we find a Type I band alignment with CBOs > 1 eV in all cases. BeO is therefore a promising dielectric for oxide based optoelectronic and high-frequency, -power, and -temperature device applications

X-Ray Photoemission Investigation of the Beryllium Oxide Band Alignment with Magnesium Oxide and Estimates for Other Insulating and Conducting Oxides

Beryllium oxide (BeO) is a wurtzite structured, large bandgap (E g > 8 eV) material of significant interest as an alloying agent and cladding dielectric in various oxide based optoelectronic devices. The success of such devices is highly reliant on bandgap and band alignment engineering to achieve sufficient charge carrier and optical confinement for device operation. In this regard, we have utilized x-ray photoemission spectroscopy (XPS) to determine the valence band offset (VBO) between atomic layer deposited (ALD) BeO and a (001) oriented magnesium oxide (MgO) substrate. The BeO VBO with MgO (001) was determined to be 0.1 ± 0.15 eV. Applying the rules of commutativity and transitivity for band alignment, we additionally predict the BeO VBO with other conductive oxides such as ZnO, Ga2O3, and InGaZnO4, to be 1.15 ± 0.3 eV, 0.3 ± 0.2 eV, and 0.9 ± 0.2 eV, respectively.

A Proposed All ZnO Based Thin Film Transistor For UV-B Detection

This article demonstrates that ZnO can be used both as the insulating dielectric and the channel by appropriately mixing with lithium and indium, respectively. The ion-conducting lithium zinc oxide (Li2ZnO2) as the dielectric and indium zinc oxide (IZO) as the channel used to fabricate thin-film transistors operating in accumulation mode are derived using the solution-processable method. The novelty of the structure is that both dielectric and channel are made up of ZnO, which provide the possibility of least interface trap states with very high capacitive coupling (318 nF/cm2) makes the device more attractive for low power electronics. The fabricated devices exhibit low operational voltage (≤2V) with high carrier mobility. Indium doped-ZnO is a large-bandgap material that can be utilized for narrowband UV-B (310 nm) detection, for narrowband phototherapy to treat certain skin diseases.

Formation of Intermediate SiO2 nano-Layer As Effective Passivation at Si/TiO2 Interface By Zone Heating Recrystallization Toward Perovskite/Silicon Tandem Solar Cell

A monolithic perovskite/c-Si tandem solar cell has attracted a lot of attention in the field of photovoltaic for its high theoretical energy conversion efficiency and cost-effectiveness. For this technology to reach its potential, optimization and compromised for both perovskite top cell and silicon bottom cell has to be investigated.In a single-junction perovskite solar cell, the hybrid organic-inorganic perovskite light-absorbing layer is sandwiched with electron and hole transporting layers (ETL and HTL). For optimal carrier extraction, the bandgap of the transporting layers has to match the perovskite material such that electron can be selectively transported to the ETL while only hole moves through HTL. In the majority of perovskite solar cells, titanium dioxide (TiO2) is used as ETL, for its high bandgap alignment, ease of fabrication, and low cost. For this reason, a tandem solar cell with c-Si/ETL(TiO2)/Perovskite/HTL structure has the potential to be highly efficient and low in cost [1].In a single-junction c-Si solar cell, surface passivation of silicon using large bandgap materials such as Al2O3, SiO2 or SiNx is widely known to reduce the velocity of carrier recombination and thus increase the carrier lifetime at silicon surface. This approach, however, is not applicable in tandem solar cells with c-Si/ETL/Perovskite/HTL structure, as the utilization of large bandgap materials in between c-Si and ETL causes bandgap misalignment and prevents interlayer exchange of carriers between perovskite and silicon cells. For this reason, a new approach that accommodates both interlayer exchange of carriers and passivate silicon surface effectively is required.In most of Si-Oxides (Al2O3, TiO2, ZnO, etc.) interface, the existence of SiOx layer is unavoidable and widely known due to high reactivity of silicon surface under oxidizing atmosphere [2]. Furthermore, while the improvement of perovskite solar cell efficiency by controlling spray pyrolysis of TiO2 and the thermal annealing procedure has been reported [3], prolonged exposure to heat during TiO2 fabrication might negatively affect the performance of silicon bottom cell, and thus requires further studies. Due to the high surface passivation effect of thermally grown SiO2 layer, we hypothesized that a proper crystallization of SiOx layer might be able to increase the lifetime of carrier at Si/TiO2 interface and mitigate the surface passivation problem in tandem solar cells with c-Si/ETL/Perovskite/HTL structure.Zone Heating Recrystallization (ZHR) is a process developed by our research group in which the surface of samples was selectively heated by the scanning of highly focus line lamp heater with elliptical mirror. Previously, we reported the utilization of ZHR to obtain smooth seed layers for thin-film silicon solar cell applications [4, 5] among other functionalities. The use of high-intensity lamp heater in ZHR process combines with high transparency of TiO2 layer makes ZHR a suitable process to selectively treat the Si/TiO2 interface and test our hypothesis on SiOx crystallization.With the introduction of ZHR, the minority carrier lifetime of Si/TiO2 interface was increased from less than 5 µs to more than 250 µs. Different scanning rates of lamp heater in ZHR process lead to different carrier lifetime, with higher scanning rates lead to higher carrier lifetime. To explain this phenomenon, cross-sectional TEM images of Si/TiO2 treated with different scanning rate was taken and analyzed. Here, we found that samples treated with higher scanning rates of ZHR have thinner SiOx layer and higher carrier lifetime. The relationship between SiOx thickness and carrier lifetime might be explained with the interface trap density of SiOx layer in which thinner layer shows lower interface trap density. This leads to lower carrier recombination velocity and therefore higher carrier lifetime at Si/TiO2 interface.References Mailoa J. P. et al., A 2-terminal perovskite/silicon multijunction solar cell enabled by a silicon tunnel junction. Appl. Phys. Lett. 106, 121105 (2015).Black L. E. et al., Explorative studies of novel silicon surface passivation materials: Considerations and lessons learned. Solar Energy Materials and Solar Cells 188, 182- 189 (2018).Nukunudompanich M., Ihara M. et al., Dominant effect of the grain size of the MAPbI3 perovskite controlled by the surface roughness of TiO2 on the performance of perovskite solar cell. CrysEngComm 22, 2718-2727 (2020).Ihara M. et al., Fabrication of silicon thin films with defects below detection limit of electron spin resonance for solar cells by high-speed zone-melting crystallization of amorphous silicon. Appl. Phys. Lett. 79, 3809 (2001).Lukianov A., Ihara M. et al., Formation of the seed layers for layer-transfer process silicon solar cells by zone-heating recrystallization of porous silicon structures. Appl. Phys. Lett. 108, 213904 (2016). Figure 1

High-speed ultraviolet photodetectors based on 2D layered CuInP2S6 nanoflakes

Although a lot of promising two-dimensional (2D) semiconductors with various bandgaps, represented by black phosphorus (0.3 eV), transition metal dichalcogenides (< 2 eV), and boron nitride (5 − 6 eV), have been extensively researched in photoelectronic and electronic devices, the spectrum of large bandgap materials is still very narrow, which limits the potential device applications in ultraviolet photodetection. The broad family of layered thio- and seleno-phosphates with wide and tunable bandgaps (1.3 − 3.5 eV) can complement the intermediate bandgaps from 1.6 to 4 eV, which can fill the gap between transition metal dichalcogenides and boron nitride. In this work, a high-performance ultraviolet photodetector based on multilayered CuInP2S6 was fabricated. It exhibits fast response times shorter than 0.5 ms, i.e., rise time ∼ 0.36 ms and fall time ∼ 0.44 ms for ultraviolet illumination (280 nm, 50 nW), which is superior than previously reported 2D layered-based UV detectors. Significantly, this photodetector also shows ultralow dark current (∼ 100 fA), a high on/off ratio (∼103), and a specific detectivity of 7.38 × 1010 Jones. Our results provide an excellent candidate for low power consumption and high-speed photodetection.

Enabling High-Performance Tandem Organic Photovoltaic Cells by Balancing the Front and Rear Subcells.

In tandem organic photovoltaics, the front subcell is based on large-bandgap materials, whereas the case of the rear subcell is more complicated. The rear subcell is generally composed of a narrow-bandgap acceptor for infrared absorption but a large-bandgap donor to realize a high open-circuit voltage. Unfortunately, most of the ultraviolet-visible part of the photons are absorbed by the front subcell; as a result, in the rear subcell, the number of excitons generated on large-bandgap donors will be reduced significantly. This reduces the (photo) conductivity and finally limits the hole-transporting property of the rear subcell. In this work, a simple and effective way is proposed to resolve this critical issue. To ensure sufficient photogenerated holes in the rear subcell, a small amount of an infrared-absorbing polymer donor as a third component is introduced, which provides a second hole-generation and transporting mechanism to minimize the aforementioned detrimental effects. Finally, the short-circuit current density of the two-terminal tandem organic photovoltaic is significantly enhanced from 10.3 to 11.7mAcm-2 (while retaining the open-circuit voltage and fill factor) to result in an enhanced power conversion efficiency of 15.1%.

Ultraviolet optoelectronic devices based on AlGaN-SiC platform: Towards monolithic photonics integration system

Rapid advancement of wide-bandgap AlGaN semiconductor materials offers tremendous opportunities in the field of ultraviolet (UV) optoelectronics for a wide range of advanced applications. Additionally, SiC has large bandgap and excellent material properties, also making itself a suitable material for UV photodetection. More importantly, high-quality AlGaN alloys can be epitaxially grown on SiC substrates because of the very small lattice mismatch between them (less than 1%), which enables a possible monolithic integration of those two materials and allows us to take advantage of their material and physical properties to realize high-performance UV optoelectronics and eventually the integrated UV photonics systems. Herein, we review the recent progress in the development of UV optoelectronics based on AlGaN-SiC platform, mainly focusing on: (1) the growth strategies and material characterizations of AlGaN epilayers on SiC; (2) the fabrication and performance evaluation of UV optoelectronic devices built on the platform, including UV LEDs/lasers and UV photodetectors. Thereafter, we briefly discuss the initial efforts in the pursuit of monolithic integration of those UV optoelectronic devices. Finally, the challenges and potential advances associated with individual UV optoelectronic components as well as UV integrated photonics system on the prosperous AlGaN-SiC platform are outlined, providing insights and perspectives for possible device- and system-level innovation in future. The recent advances in the development of ultraviolet light emitters (LED, lasers) and photodetectors on the AlGaN-SiC platform are reviewed. By taking advantage of the extreme small lattice mismatch between the two wide bandgap semiconductors - AlGaN and SiC, together with their compatible physical and material properties, a monolithic ultraviolet photonics integration system can be built on the AlGaN-SiC platform. • AlGaN and SiC are recognized as two most promising wide bandgap semiconductors for UV optoelectronics applications. • AlGaN and SiC can be integrated to form AlGaN-SiC platform for the monolithic UV photonics integration system. • This review provides a comprehensive summary of the recent advancement of UV optoelectronics based on the AlGaN-SiC platform. • The outlooks and challenges in device- and system-level innovation of UV optoelectronics on AlGaN-SiC platform are discussed.