Table of contents

The electron transport layer (ETL) plays a fundamental role in perovskite solar cells (PSCs), where ETL extracts and transports photogenerated carriers and influences the photoelectric conversion efficiency. In this context, this paper develops a novel design for the titanium–tin alloy-based ETL. Experimental results show that the efficiency of power conversion efficiency (PCE) can be maximized (i.e. 16.42%) when the molar ratio of titanium dioxide (TiO₂) to tin oxide (SnO₂) doping reaches 7:1. Moreover, in this case, the PSC device can maintain the 81.5% of the maximum efficiency over 42 d. Therefore, the proposed scheme can significantly improve the electron mobility and surface morphology in ETL, thereby achieving superior performance compared with prior schemes.

This paper provides a comprehensive review of multi-stage infrared detectors, including interband cascade infrared photodetectors (ICIPs) and quantum cascade detectors (QCDs). These detectors exhibit low dark current, high detectivity, and high 3 dB bandwidth positioning them as promising candidates in infrared (IR) detector technology. The review covers the history of multi-stage IR detectors, the corresponding device physics, materials systems, DC and RF performance, and recent advancements. Additionally, a comparative analysis of ICIPs and QCDs is provided, along with discussions on optimization strategies. This review is intended to be a valuable resource for researchers and engineers in the field of IR detector technology, offering a detailed insight into the most advanced multi-stage IR detector technology and providing guidance for future development.

Gallium nitride (GaN) has gained traction in replacing silicon for power electronics applications, due to its high breakdown field, high mobility 2D electron gas, and effective n/p-type doping. This paper reviews three important topics of GaN power devices. One is the voltage-blocking structures needed to operate at high voltage while minimizing conduction loss and switching loss. Another one is the structure used to achieve normally-off operation, which is often required for power electronics. The third topic is the monolithic integration of gate drivers and power switches to achieve the ultimate switching speed at a low cost.

Construction of a p-doping free HgCdTe-based laser diode is proposed. Hole injection in the active region is done by carrier tunneling from the valence band to the conduction band through the resonance state formed in a series of quantum wells in an external electric field. The charge carriers are localized in the active region by barrier layers with selective resonant tunneling: for holes on one side and for electrons on the other. Calculations of the resonance state providing interband tunneling are carried out.

Nanomaterials have facilitated the development of innovative technologies in various industries. However, most research has been limited to nanoscale phenomena, and the effects of nanomaterials on microscale crystal growth remain obscure. In this study, we demonstrated a straight 2H–Si microneedle with a longitudinal growth rate of 6.7 × 10⁴ Å·s⁻¹, which could not be explained by conventional crystal growth mechanisms, through AlN nanowires. The AlN nanowires were grown using the hydride vapor-phase epitaxy method, which induced the formation of Al membranes when NH₃ supply was ceased. At this time, an elliptical Al membrane was created within 0.166 s, in accordance with the principle of Plateau–Rayleigh instability. The average spacing of the Al membrane was 4 μm, and approximately 10 000 elliptical Al membranes absorbed SiCl almost simultaneously to form a 40 mm 2H–Si microneedle within 100 min of growth time. Therefore, we realized straight 2H–Si microneedles with a growth rate of 6.7 × 10⁴ Å·s⁻¹. Differing from the conventional growth mechanism, this new growth method sheds light on the mechanism by which nanoscale phenomena contribute to the growth of microscale crystals.

Ge-doped (1.4 at. %) β-Ga₂O₃ nanostructures are successfully synthesized using the hydrothermal method followed by annealing at 1000 °C in an O₂ atmosphere. The crystal structures and morphologies of both intrinsic and Ge-doped β-Ga₂O₃ nanostructures are analyzed using high-resolution x-ray diffraction, field-emission scanning electron microscopy, transmission electron microscope, and energy dispersive spectroscopy. Photoluminescence measurements are also performed to investigate defect-related energy levels within the bandgap. The photocatalytic activity is evaluated through the degradation of methylene blue in an aqueous solution. Ge-based precipitates form when the Ge concentration exceeds 1.4 atomic percent in the β-Ga₂O₃ nanostructures. As with other dopants such as Sn, Al, and Cr, this controlled incorporation of Ge significantly enhances the photocatalytic properties and potentially improves the electronic and optical properties of Ga₂O₃-based devices.

This study aims at exploring the potential of inorganic wide-bandgap mixed-halide aluminum-containing perovskites of Cs₃AlI_xBr_6−x for solar harvesting, by investigating their structural, electronic and optical properties through density functional theory using the augmented plane wave plus local orbital method. The structural properties were calculated with the PBE-GGA potential. Volume optimization and negative formation energies confirm the structural and thermal stability of the compounds. The electronic and optical properties were calculated using Tran–Blaha modified Becke–Johnson (TB-mBJ) potential. The TB-mBJ corrected band gaps revealed that these materials belong to the wide-bandgap (WBG) perovskite family, displaying band gaps in the range of 3–5 eV. The electronic properties confirm their direct bandgap nature, with the I-p and Br-p states mainly contributing to the formation of the valence band and the Al-s, Al-p and Cs-d states to the conduction band. Absorption coefficients range from 10 to140 × 10⁴ per cm in the UV region, thus making these WBG perovskites suitable for applications in this region. Optical properties show absorption of light beyond 3 eV and validate the calculated electronic band gaps. Absorption coefficients, optical conductivity and dielectric function (real and imaginary) were calculated and revealed a peak shift from higher to lower energies with increasing I concentration. The above results suggest that these materials can be highly considered for use in photovoltaics, optoelectronic devices (light-emitting diodes, photodiodes), to power small batteries in the Internet of Things, in agrivoltaics and in fabrication of semi-transparent solar cells.

We designed and fabricated a nonplanar metal–semiconductor–metal (MSM) ultraviolet photodetector (PD), incorporating a 30-pair Al_0.5Ga_0.5N/AlN superlattice (SL) absorption layer on GaN-on-sapphire templates. In contrast to conventional PDs featuring a 100 nm-thick Al_0.25Ga_0.75N epilayer, our proposed PDs with the higher Al content of Al_0.5Ga_0.5N/AlN SLs did not exhibit degradation in epiwafer quality. With the incorporation of Al_0.5Ga_0.5N/AlN SLs, proposed MSM PDs with a top Ti/Al-based metal stack and a bottom Ni/Au electrode configuration showcased an enhanced photoresponsivity of 1129.8 A W⁻¹ at ‒5 V in comparison to unitary Al_0.25Ga_0.75N epilayer made PDs. Moreover, by utilizing the Al_0.5Ga_0.5N/AlN SL absorption layer, we achieved an increased light-to-dark current ratio, reaching 3.66 × 10⁵ biasing at a ‒7 V. The improvement in PD's output performance could be attributed to the low metal/semiconductor Schottky barrier and strong electric field intensity within the SL absorption layer as the Ti/Al-based metal stack was used as the top electrode (the bottom electrode is Ni/Au). Finally, a 3 dB cut-off frequency of ∼1.2 MHz is achieved by using a homemade LED-based optical link with the proposed MSM PDs as the optical receiver.

Modifying the back contact interface plays a key role in improving the efficiency of Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells. Aiming at the phase decomposition and carrier recombination issues in the CZTSSe/Mo back contact interface, an ultra-thin Mg(OH)₂ intermediate layer was introduced between the Mo substrate and the CZTSSe absorber layer. The Mg(OH)₂ intermediate layer effectively suppressed the interface phase decomposition reactions and inhibited the generation of interface secondary phases. Meanwhile, during the high-temperature selenization process, the Mg²⁺ doped into CZTSSe at the back contact interface, reducing the defects and band offset at the CZTSSe/Mo interface. The performance of the device was improved, with a significant increase in efficiency compared to the control device. This work highlights the modification effect of Mg(OH)₂ for improving back contact and also provides an easy-handling method to achieve high-performance CZTSSe solar cells.

Technologically relevant narrow-gap Hg_1−xCd_xTe is known to contain a considerable amount of mercury vacancies that supposedly degrade carrier lifetimes. Using a semiclassical approach with no adjustable parameters, we calculate the capture coefficients for acceptor states with different binding energies. Resulting Shockley–Read–Hall recombination times agree well with the experimental data and suggest that the operating temperature of Hg_1−xCd_xTe detectors with ∼20 µm cutoff can be elevated above 77 K.

In this paper, we use Silvaco-ATLAS two-dimensional numerical simulation to calculate the performance of two different circular-gate AlGaN/GaN HEMT device models. The influence of the special circular-gate structure on the DC characteristics of the AlGaN/GaN HEMT device is studied and compared with that of conventional devices. Compared with conventional, the threshold voltage of the drain-center and source-center circular-gate devices increased from 1.1 V to 1.5 V, while the transconductance improved from 245 mS mm⁻¹ to 328 mS mm⁻¹ and 285 mS mm⁻¹ respectively. In the on-state of devices, the maximum saturation output current increased from 536 mA mm⁻¹ to 620 mA mm⁻¹ and 650 mA mm⁻¹ . Furthermore, the breakdown voltage of the source-center circular-gate device rose from 765 V to 870 V compared to conventional devices; however, for the drain-center circular-gate device it was only at 685 V due to concentrated electric fields outside the drain region—this limitation can be effectively addressed by increasing the drain area. Simulation results demonstrate that circular-gate AlGaN/GaN HEMT devices can avoid edge effects, improve electric field distribution, and alleviate self-heating effects.

With the rapid development of semiconductor technology, silicon carbide has been widely used in various power electronic device. However, the material has an extremely high hardness ranking second only to diamond, which makes processing difficult. In this work, the two methods of laser cutting and dicing saw are utilized to test the cutting process of silicon carbide respectively, then the appropriate through-cutting process parameters are obtained. The two methods are combined to compare the cutting quality of the three approaches. As a result, the laser cutting is affected by heat with through-cutting 0.5 mm-thick silicon carbide, which results in the rough front-surface edge and much residue, and the cutting groove of the back surface is irregular. The dicing saw having more mechanical stress, resulting in serious tool wear, prone to chipping and micro-cracks and other phenomena, the back surface chipping is as high as 171.6 µm. The hybrid processing method not only reduces the degree of thermal damage, but also reduces tool wear, and the front surface is flat and clean after cutting, without a chipping phenomenon, and the back surface chipping is only 7.9 µm, which is 20 times lower than the dicing saw method.

This study compares the effects of ultrathin Y₂O₃ and Al₂O₃ interfacial layers on the electrical properties of ZrO₂ and HfO₂ dielectrics deposited on Ge substrates, specifically examining the ZrO₂/Y₂O₃, ZrO₂/Al₂O₃, HfO₂/Y₂O₃, and HfO₂/Al₂O₃ stacked structures. Reductions in both interface trap density (D_it) and leakage current were observed after five cycles of the atomic layer deposition (ALD) process for Y₂O₃ and Al₂O₃ interfacial layers. Compared with Y₂O₃, the Al₂O₃ interfacial layer was more effective in reducing the leakage current and decreasing the effective bulk trap density (N_trap). However, this also leads to an increase in the capacitance-equivalent oxide thickness, which could be a potential drawback. The observed electrical properties are closely linked to the distinct interfacial reactions of Y₂O₃ and Al₂O₃ with Ge during ALD, resulting in similar reductions in D_it. However, the formation of a thick Al₂O₃ interfacial layer was more efficient in suppressing Ge out-diffusion than Y₂O₃, which contributed to the reduction in both the leakage current and N_trap.

Ammonia (NH₃) is a corrosive and toxic gas to which exposure can cause serious health problems and even death. Elevated levels of it in exhaled breath can serve as a biomarker for various diseases. Consequently, monitoring NH₃ in the ambient air and for medical diagnostics is important for public health and safety. However, developing NH₃ gas sensors that function effectively in high humidity conditions, such as those found in human breath, has proven challenging. In this study, we present a simple and cost-effective NH₃ gas-sensor based on a structure of interconnected silicon nanwires (SiNWs), fabricated with metal-assisted chemical etching. Two different versions were made and compared; SiNWs, with and without germanium nanoparticles. The sensing mechanism is attributed to the formation of a hole accumulation layer in the air, whose width decreases upon exposure to NH₃. It was also observed that bundling of individual nanowires enhances the sensor's response time, down to approximately 70 s, which is an order of magnitude faster response than that of similar SiNW structures reported in the literature.

Because of its environmental protection, pollution free, renewable and other advantages, photovoltaic energy has become one of the most potential for research and development. Among them, the Tunnel Oxide Passivated Contact (TOPCon) solar cells solar cells with its excellent passivation structure is highly competitive in efficiency and cost. To mitigate the optical limitations of the emitter and enhance the overall efficiency of TOPCon solar cells, through numerical simulation analysis, the structural parameters of the emitter region of the CuO₂-based TOPCon solar cells were optimized, and the conversion efficiency of the optimized solar cells reached 21.82%. Then, by comparing and analyzing the performance of the TOPCon solar cells based on CuO₂ and the TOPCon solar cells based on polysilicon with the change of the emitter structure parameters, the influence mechanism of the change of material's band gap width on the relationship between solar cells structure parameters and performance is further explored. Comparing the optimal structural parameters of TOPCon solar cells based on CuO₂ and polycrystalline silicon, it was found that an increase in bandgap width leads to a decrease in the optimal emitter thickness of the solar cells, reducing production costs.

Germanium (Ge) is a promising candidate in the field of Si-based optoelectronic integration. The introduction of C may modify the energy band of Ge and thus has scientific and technical significance. In this work, we performed first-principles calculations to investigate the C aggregation behavior in Ge and its effect on the electronic properties. Our results show that for a single C impurity, the substitutional site is more energetically favorable than the interstitial site. The formation energy per C atom decreases with the number of C atoms, indicating the tendency of C clustering in Ge. In particular, the C quadruplet in regular tetrahedral shape is found to be the most stable configuration in Ge. Formation energy calculations of C-related defects with various charge states demonstrate that, for single C doping, the (0/−1) and (−1/−2) transition levels are respectively located at 0.41 and 0.64 eV above VBM, displaying the potential acceptor characteristic. The band structure calculations show the vanishing of the direct band gap characteristic with the aggregation of C atoms in Ge.

Vertical germanium-on-silicon (Ge/Si) avalanche photodiodes (APDs) offer the advantages of being low-cost, CMOS-compatible and demonstrating high performance for the development of short-wave infrared sensors for telecommunications. Nevertheless, the origins of dark current and noise in Ge-on-Si APDs still need to be clearly identified to improve their performance. In this paper, we report the study of the electro-optical characteristics of fabricated Ge-on-Si Avalanche Photo Diodes. A maximum gain of 95 was achieved at −33 V on these devices (λ = 1550 nm and P = 0.4 mW). Technology Computer-Aided Design simulations were compared with measurements to extract the parameters of the ionization model. Through dark current measurements at various temperatures, we extracted the activation energy at different bias voltages. The dark current is governed by generation-recombination Shockley–Read–Hall (SRH) mechanisms in silicon and germanium below and above the punch-through bias, respectively. Low frequency noise measurements performed on a 10 µm diameter Ge/Si APD device under dark current conditions showed the presence of a 1/f noise prior to multiplication, confirming a dominant SRH mechanism.

In wireless energy harvesting (WEH) systems, the performance of rectifier diodes directly determines the upper limit of rectification efficiency. Schottky diodes and MOSFETs are currently the most widely used rectifier devices, but their performance is unsatisfactory in micro-power density input environments. To address this, this paper proposes and designs a high rectification efficiency Fin Field-Effect Transistors (FinFET) model for 2.45 GHz micro-power microwave WEH using Sentaurus TCAD software simulation. When selecting 16 nm gate length, 6 nm fin width, and 53 nm fin height as the basic structural parameters of the FinFET device, the device's subthreshold swing approaches the ideal value of 60 mV dec⁻¹, significantly enhancing the switching speed. Furthermore, a dual-fin structure is adopted to maintain excellent subthreshold swing characteristics and achieve a substantial increase in drive current strength. Finally, a dual-fin strained Si quantum well channel SiGe-OI FinFET structure is proposed to reduce the adverse effects of interfacial scattering on carrier mobility while introducing stress into the channel region to further enhance carrier mobility. The improvement in rectification efficiency is verified by constructing a half-wave rectifier circuit with filter capacitors via the Mixmode module. The rectification efficiencies reach 4.94% and 21.41% when the input power is −20 dBm and −10 dBm, respectively, which are 7 times and 3.4 times higher than conventional near-zero-threshold-voltage Si-based MOS devices under the same conditions.

Compared to conventional (0001)-oriented GaN-based devices, which suffer from performance-degrading polarization effects at the heterojunction interfaces, semipolar (11–22) GaN and nonpolar (11–20) GaN have demonstrated significant potential for reducing or eliminating these polarization effects, thus offering possibilities for enhancing device performance. Here, we have fabricated ReSe₂/(0001) GaN, ReSe₂/(11–22) GaN, and ReSe₂/(11–20) GaN heterostructures to investigate the impact of different GaN crystal orientations on the band alignment of ReSe₂/GaN heterostructures. Band alignments were characterized using x-ray photoelectron spectroscopy. The measured VBOs for the three ReSe₂/GaN heterostructures (polar, semipolar, nonpolar) were determined to be 3.08 ± 0.15 eV, 2.62 ± 0.15 eV, and 2.24 ± 0.15 eV, respectively, while the calculated conduction band offsets were 1.51 ± 0.15 eV, 1.05 ± 0.15 eV, and 0.67 ± 0.15 eV, respectively, indicating type II band alignment for all three heterostructures. The significant influence of different GaN surface orientations on heterostructure performance revealed herein provides an important reference for the design and optimization of high-performance devices based on these materials in the future.

This study investigates the influence of interface trap charges (ITCs) on the performance parameters of the proposed lateral hetero-stacked source with pocket n-type tunneling field-effect transistor (HSSP-nTFET). The influence of different concentrations of donor and acceptor trap charges on the device's DC performance metrics is thoroughly examined. It is observed that the presence of interface traps in the device leads to variations in both the threshold voltage (V_th) and subthreshold swing (SS). To evaluate the impact of various ITCs on analog/RF performance, critical parameters including electric field characteristics, Transconductance (g_m), parasitic capacitance, cut-off frequency (f_T), gain-bandwidth product, transit delay, TFP, R_out and device efficiency have been comprehensively analyzed for the HSSP-nTFET. Additionally, this work investigates the reliability of the proposed device by analyzing its susceptibility to interface trap conditions, temperature variations (280 to 480 k), and also, positive biased temperature instability induced degradation, as inspected in this study, poses significant reliability concerns for analog/digital circuit design, necessitating careful consideration and mitigation strategies. Vital statistics yielded in this 3D simulation research are on-current (I_ON= 8.18E⁻⁵ A μm⁻¹), off-current (I_OFF = 1.33E⁻¹⁹ A μm⁻¹), V_th = 0.18 V, SS_avg = 14 mV dec⁻¹, g_m = 1.86E⁻⁴ S and f_T = 0.384 THz which can serve as a strong contender for energy-efficient and high-performance applications.

In this paper, AlGaN/GaN high-electron-mobility transistors (HEMTs) and metal–insulator–semiconductor HEMT (MIS-HEMTs) with 5 nm Al₂O₃ gate dielectric grown by thermal atomic layer deposition (TALD) and plasma-enhanced ALD (PEALD) were investigated. Polarization Coulomb field scattering intensity was reduced and electron mobility was improved due to low additional polarization charges and a high two-dimensional electron gas density (n_2d) in MIS-HEMTs. PEALD MIS-HEMT has a lower threshold voltage (V_th) and more significant gate leakage current (I_G) suppression than TALD MIS-HEMT. Compared with HEMT, a lower I_G (∼4 orders), a higher on/off current ratio (I_on/I_off) (∼4 orders) and a higher transconductance peak (g_m.peak) (∼26%) are recorded in PEALD MIS-HEMT. Moreover, the breakdown voltage (V_BR) of PEALD MIS-HEMT and TALD MIS-HEMT is improved by ∼53% and ∼33% respectively, due to the effective suppression of the electric field at the gate edge.

Spin-transfer torque magnetic random access memory (STT-MRAM) shows promising prospects for the next generation of embedded non-volatile memory. In this paper, an improved model for calculation of the power consumption of STT-MRAM is proposed and verified. In the proposed model, the unique asymmetry properties of magnetic tunnel junction (MTJ) devices during STT-MRAM read and write operations are taken into account. To more comprehensively calculate the energy consumption, the impact of temperature variation on the switching property of the MTJ device is considered. A comparison with NVSim on the power calculation is presented. The results indicate that the proposed model can provide energy consumption simulation results with higher accuracy. The results of the read/write delay and the leakage power can be simultaneously provided. An analysis of the results based on the proposed model is conducted. The proposed model shows potential applications for architectural design of power grids in STT-MRAM with large scale storage capacity.