Showing papers in "Semiconductor Science and Technology in 2023"

Dawn of nitride ferroelectric semiconductors: from materials to devices

Abstract: III-nitride semiconductors are promising optoelectronic and electronic materials and have been extensively investigated in the past decades. New functionalities, such as ferroelectricity, ferromagnetism, and superconductivity, have been implanted into III-nitrides to expand their capability in next-generation semiconductor and quantum technologies. The recent experimental demonstration of ferroelectricity in nitride materials, including ScAl(Ga)N, boron-substituted AlN, and hexagonal BN, has inspired tremendous research interest. Due to the large remnant polarization, high breakdown field, high Curie temperature, and significantly enhanced piezoelectric, linear and nonlinear optical properties, nitride ferroelectric semiconductors have enabled a wealth of applications in electronic, ferroelectronic, acoustoelectronic, optoelectronic, and quantum devices and systems. In this review, the development of nitride ferroelectric semiconductors from materials to devices is discussed. While expounding on the unique advantages and outstanding achievements of nitride ferroelectrics, the existing challenges and promising prospects have been also discussed.

Optimizing the flatness of 4H-silicon carbide wafers by tuning the sequence of lapping

Abstract: In this letter, we optimize the flatness of 4H silicon carbide (4H-SiC) wafers by tuning the sequence of single-sided lapping, enlightened by the different mechanical properties of the Si face and C face of 4H-SiC. After wire sawing, the coarse lapping and fine lapping are carried out to rapidly remove the surface damage and optimize the flatness of 4H-SiC wafers. From the point of view of controlling the values of the bow and warp of 4H-SiC wafers, the coarse-lapping sequence of the C-face lapping followed by Si-face lapping is beneficial, while the preferred fine-lapping sequence is Si-face lapping followed by C-face lapping. Nanoindentation tests indicate that the C face has higher hardness and lower fracture toughness than the Si face. This gives rise to thicker surface damage at the C face after the wire sawing. After removing the same amount of wire-sawing induced surface damage, the thickness of residual surface damage of the C face is higher than that of the Si face after the coarse lapping. The fine lapping basically removes all the surface damage and creates the near-perfect C face and Si face. The higher amount of surface damage of the C face after the coarse lapping and the higher fracture toughness of the near-perfect Si face after the fine lapping can tolerate more plastic deformations, which gives rise to the superior flatness of the C-face-followed-by-Si-face coarse lapped and the Si-face-followed-by-C-face fine lapped 4H-SiC wafers, respectively.

Using ensemble Monte Carlo methods to evaluate non-equilibrium Green’s functions

Abstract: The use of ensemble Monte Carlo (EMC) methods for the simulation of transport in semiconductor devices has become extensive over the past few decades. This method allows for simulation utilizing particles while addressing the full physics within the device, leaving the computational difficulties to the computer. More recently, the study of quantum mechanical effects within the devices, effects which also strongly affect the carrier transport itself, have become important. While particles have continued to be useful in quantum simulations using Wigner functions, interest in analytical solutions based upon the non-equilibrium Green's functions (NEGF) have become of greater interest in device simulation. While NEGF has been adopted by many commercial semiconductor, there remains considerable computational difficulty in this approach. Here, a particle approach to NEGF is discussed, and preliminary results presented illustrating the computational efficiency that remains with the use of particles. This approach adopts the natural basis functions for use in a high electric field and the preliminary results are obtained for quantum transport in Si at 300 K. This approach appears to offer significant advantages for the use of NEGF.

Influence of swift heavy ion irradiation on electrical characteristics of β-Ga2O3 Schottky barrier diode

Abstract: The radiation effect of swift heavy ions (16 MeV 181Ta) on the Au/Ni/β-Ga2O3 vertical Schottky barrier diodes (SBDs) were investigated at the fluence of 1 × 108, 3 × 108 and 3 × 109 cm−2. The SBDs were characterized by current density–voltage (J–V) and capacitance–voltage (C–V) measurements. It was found that Schottky barrier height φ decreased from 1.11 eV to 0.94 eV, the ideality factor n increased from 1.01 to 1.29, turn-on voltage V on increased from 0.52 V to 0.80 V after radiation of 3 × 109 cm−2. The reverse breakdown voltage was decreased from −405 V to −375 V, −350 V and −255 V after radiation of 1 × 108, 3 × 108 and 3 × 109 cm−2, respectively. In addition, the carrier concentration calculated from the capacitance–voltage curves was decreased significantly. Based on the G/ω–ω measurement results, the trap density at the Ni/β-Ga2O3 interface was extracted to be 2.89 × 1015–2.49 × 1016 cm−2 eV−1 and 2.18 × 1015–4.98 × 1016 cm−2 eV−1 with the energy level of 0.85–0.87 eV below the conduction band edge.

Terahertz quantum-cascade lasers for high-resolution absorption spectroscopy of atoms and ions in plasmas

Abstract: We report on terahertz (THz) quantum-cascade lasers (QCLs) based on GaAs/AlAs heterostructures, which exhibit single-mode emission at 3.360, 3.921, and 4.745 THz. These frequencies are in close correspondence to fine-structure transitions of Al atoms, N+ ions, and O atoms, respectively. Due to the low electrical pump power of these THz QCLs, they can be operated in a mechanical cryocooler in continuous-wave mode, while a sufficient intrinsic tuning range of more than 5 GHz is maintained. The single-mode operation and the intrinsic tuning range of these THz QCLs allow for the application of these lasers as radiation sources for high-resolution absorption spectroscopy to determine the absolute densities of Al atoms, N+ ions, and O atoms in plasmas.

Design of step-graded AlGaN buffers for GaN-on-Si heterostructures grown by MOCVD

Abstract: For the growth of low-defect crack-free GaN heterostructures on large-area silicon substrates, compositional grading of AlGaN is a widely adapted buffer technique to restrict the propagation of lattice-mismatch induced defects and balance the thermal expansion mismatch-induced tensile stress. So far, a consolidation of the design strategy of such step-graded buffers has been impaired by the incomplete understanding of the effect of individual buffer design parameters on the mechanical and microstructural properties of the epilayers. Herein, we have analyzed a series of metal-organic chemical vapor deposition grown GaN/graded-AlGaN/AlN/Si heterostructures through in situ curvature measurements and post-growth x-ray diffraction (XRD). Our results reveal that in such epi structures, the GaN layer itself induces more compressive stress than the AlGaN buffer, but the underlying AlGaN layers dictate the magnitude of this stress. Furthermore, for a fixed AlGaN buffer thickness, the mean-stress accumulated during the GaN growth is found to be correlated with its structural properties. Specifically, one µm thick GaN layers that acquire 1.50 GPa or higher compressive mean-stress are seen to possess 202ˉ1 XRD ω-FWHM values less than 650 arc-sec. Also, the evolution of instantaneous stresses during the growth of the AlGaN layers is found to be a valuable indicator for buffer optimization, and composition difference between successive layers is established as a crucial criterion. The results also show that increasing the total buffer thickness (for a fixed number of steps) or increasing the number of steps (for a fixed total buffer thickness) may not always be beneficial. Irrespective of the buffer thickness, optimized high electron mobility transistor structures show similarly low sheet-resistance (∼350 Ω □)−1 and high mobility (∼2000 cm2 V−1 s −1) at room temperature.

Growth modification via indium surfactant for InGaN/GaN green LED

Abstract: In this work, indium (In) was introduced as a surfactant during growth of high temperature GaN quantum barriers (QBs) and GaN interlayer of InGaN/GaN green LEDs. A reference LED grown without In-surfactant was also included for comparison. Results suggested that the LED growth was improved by introducing the In-surfactant, especially during the growth of the GaN interlayer. The In-surfactant improved the morphology of the interlayer, hence allowed it to serve as a good surface growth for the LED. Moreover, the LED showed the lowest full width at half maximum of each x-ray diffraction satellite peak when the In-surfactant was introduced in the GaN interlayer, suggesting an effective way to improve the multi-quantum wells. The introduction of the In-surfactant in the GaN interlayer and GaN QBs growths shifted the emission wavelength of the corresponding LEDs towards red (λ emission = 534 nm) with respect to the reference LED where λ emission = 526 nm. Furthermore, the In-surfactant introduction reduced the forward voltage, V f of the corresponding LEDs down to 4.56 V, compared to the reference LED with V f of 5.33 V. It also allowed the LEDs to show faster carrier decay lifetime, and hence higher radiative recombination, particularly when it was introduced in the GaN interlayer growth.

Hyperdoped silicon materials: from basic materials properties to sub-bandgap infrared photodetectors

Abstract: Hyperdoping silicon, which introduces deep-level dopants into Si at concentrations near one atomic percent, drastically changes its optoelectronic properties. We review recent progress in the fundamental understanding of the material properties and state of the art sub-bandgap infrared photodetectors. Different hyperdoping techniques are reviewed and compared, namely ion implantation followed by pulsed laser melting (PLM) or other fast annealing methods and PLM of Si with a dopant precursor. We review data available in the literature for material properties related to the success of optoelectronic devices such as the charge carrier lifetime, mobility, and sub-bandgap light absorption of hyperdoped Si with different dopants. To maximize carrier generation and collection efficiency in a sub-bandgap photodetector, charge carrier lifetimes must be long enough to be transported through the hyperdoped layer, which should be on the order of light absorption depth. Lastly, the charge transport properties and photodetector responsivities of hyperdoped Si based photodiodes at room temperature and at cryogenic temperatures are compared. The charge carrier transport mechanisms at different temperature ranges and in different dopant systems are discussed. At room temperature, despite different dopant energetics and hyperdoped thicknesses, light detection exhibits similar spectral responsivities with a common cutoff around 0.5 eV, and at low temperatures, it extends further into the infrared range. The roles of the dopant energetics and process-induced defects are discussed. We highlight future material development directions for enhancing device performance.

Estimation of performance degradation due to interface traps in the gate and spacer stack of NC-FinFET

Abstract: Device reliability issues originating from interface traps or bias temperature instability has been of great concern in emerging devices such as negative capacitance (NC)-fin field effect transistor (FinFET), gate-all-around field-effect transistor etc. Exploration of the interface traps at the different interfaces of these three-dimensional devices is of much importance in predicting the reliability of device behavior. In the proposed analysis, for the first time, we have demonstrated the individual and the overall impact of trap densities at the various practical interfaces present in the gate and spacer stack of the ferroelectric (FE)-dielectric spacer based NC-FinFET. The trap states in the proposed device alter the polarization dynamics and improve sub-threshold characteristics especially the off-state current (I OFF), thus revealing excellent short-channel characteristics. We have further evaluated the degree of performance degradation occurring due to interface traps by means of optimized capacitance matching (FE parameters), hysteretic window, output transconductance (gds) and voltage gain (AV ). Furthermore, we have also studied the impact of trap states on the mixed-mode characteristics of the spacer-based NC-FinFET inverter design.

Tunable Schottky barrier in a graphene/AlP van der Waals heterostructure

Abstract: The controllable modulation of the electronic properties of two-dimensional van der Waals (vdW) heterostructures is crucial for their applications in the future nanoelectronic and optoelectronic devices. In this paper, the electronic properties of a graphene/AlP heterostructure are theoretically studied by first-principles calculation. The results show that due to the weak vdW interaction between graphene and the AlP monolayer, both the Dirac semi-metallic properties of graphene and the semiconductivity properties of monolayer AlP are well retained. The graphene/AlP heterostructure forms a 0.41 eV p-type Schottky contact, and the barrier height and contact type can be successively controlled by the applied external electric field and vertical stress. When the applied electric field exceeds −0.5 V Å−1, the heterostructure interface changes from a p-type Schottky contact to an n-type Schottky contact. When the applied electric field exceeds 0.4 V Å−1 or the interlayer spacing is less than 3.1 Å, the interface contact type changes to Ohmic contact. These results indicate that the graphene/AlP heterostucture behaves as tunable Schottky barrier for potential applications in nano-devices.

Strain relaxation and self-heating effects of fin AlGaN/GaN HEMTs

Abstract: In this paper, we present a methodology of 3D electro-thermo-mechanical simulation to analyze the strain relaxation and self-heating effects of fin AlGaN/GaN high electron mobility transistors (HEMTs). The free boundaries of narrow fins cause strain relaxation of the AlGaN barrier and a non-uniform strain distribution near the AlGaN/GaN interface. The strain relaxation not only reduces the surface piezoelectric polarization charges (PPCs), but also introduces space PPCs in AlGaN/GaN, leading to a reduction of two-dimensional electron gas density and a positive shift of threshold voltage (V th). The simulated V th shift with fin width agrees well with experimental results from literature. In addition, the inter-fin trenches facilitate more efficient lateral heat spreading and suppress the self-heating effect compared with the planar HEMTs with the same effective gate width.

The thermo-E.M.F. of an n-type silicon: assessment of the contribution due to the presence of minority carriers

Abstract: In the common thermoelectric theory, minority charge carriers are assumed to be absent in n- or p-type thermoelectric materials. This study considers their presence and evaluates the effects of that presence on the thermo-electromotive force (Thermo-E.M.F.) of a non-degenerate n-type semiconductor. The calculations are done in the case of silicon. The contribution due to the presence of the minority holes to the total Thermo-E.M.F. depends on the thermopower of minority carriers, their electrical and thermal conductivities. It also depends on their bulk and surface recombinations and depends on the majority carriers only through their thermal and electrical conductivities. In the case of silicon, that contribution remains generally very low although it can increase or decrease the total Thermo-E.M.F. depending on the concentration of the doping elements, the bulk and surface recombination rates, and the length of the sample.

Epitaxial lift-off method for GaAs solar cells with high Al content AlGaAs window layer

Abstract: The epitaxial GaAs substrate lift-off (ELO) technique is widely used to produce thin film III–V semiconductor optoelectronic devices. However, the hydrofluoric (HF) acid used in the process forbids the incorporation of active AlGaAs device layers with high Al content due to its selective etching. In this work, a new ELO method is presented, which allows for the protection of AlGaAs layers against the HF acid attack. The method is used here to prepare and analyse thin film GaAs solar cells containing Al0.85Ga0.15As window layer. We employ a sacrificial GaAs buffer and device perimeter pre-processing that covers the exposed edges with back contact metals and electroplated Cu. A comparison of the epitaxially lifted GaAs solar cells with identical cells prepared by substrate etching demonstrates identical photovoltaic figures of merit and confirms the viability of the AlGaAs protection approach. In addition to applications in thin film photovoltaics, this ELO method can be applied to solid-state lasers and single-photon emitters employing AlGaAs-based Bragg reflectors, among other III–V semiconductor optoelectronic devices.

Investigation of trap characteristics under the inverse piezoelectric effect in AlGaN/GaN HEMT devices at room temperature and low temperature

Abstract: Changes in the electrical properties and the trap characteristics of AlGaN/GaN high electron mobility transistors under the application of reverse bias stress at both room temperature and low temperature were investigated. When the critical stress voltage was reached, the gate current, which complied with the Poole–Frenkel conduction conditions, showed an abrupt increase. Furthermore, the magnitude of the critical stress voltage for occurrence of the inverse piezoelectric effect can be increased at 83 K. The transient current method was used to establish that the detrapping peak amplitudes of the traps increased, but the trap activation energy remained unchanged. The changes observed in both the time constant spectra and the pulsed current–voltage curves confirmed that the trap densities in the AlGaN barrier layer increased as a result of the inverse piezoelectric effect. However, the different degrees to which the numbers of traps increased at room temperature and at 83 K contributed to the occurrence of different degradations in the device.

Modified photodiode equivalent circuit model considering coplanar waveguide electrodes

Abstract: Accurate equivalent circuit models can assist in better analyzing the performance of photodetectors. This study proposes a modified photodiode (PD) equivalent circuit model that considers coplanar waveguide (CPW) electrodes. First, the CPW electrodes of the PD are analyzed using high-frequency structure simulation software and advanced design simulation software. Skin effect occurs inside the electrode at high frequencies, increasing the PD loss and reducing the bandwidth. Subsequently, the extraction formula for the proposed model is derived, and the proposed model is compared with two conventional CPW electrode models. The proposed model effectively eliminates the frequency-dependency issue in the parameter extraction process of previous models, thereby demonstrating its accuracy. Furthermore, simulation and experimental results validate the reliability of the proposed model. Among the entire frequency band, the proposed model has good stability and a low error rate and can achieve excellent fitting with the measured results. Compared with previous studies, the average error rate is reduced by over 10%, demonstrating a significant improvement. Finally, the influence of the skin effect and high-impedance transmission lines on PD performance is analyzed and a viable approach to improve the bandwidth of PDs is proposed. The proposed model provides a viable approach to model and optimize CPW structures and is significant for the design of high-performance PDs.

A novel double RESURF SOI-LIGBT with dynamic avalanche immunity and low losses

Abstract: A novel, trench gates, double reduced surface field, lateral insulated gate bipolar transistor based on silicon-on-insulator (SOI-LIGBT) is proposed and investigated. A p-top layer connected to the emitter via two series diodes and n-rings surrounding the bottom of trench gates are used to reduce the on-state voltage drop (V CE(sat)) and turn-off loss (E off). A deep trench with a p-ring is introduced to form a gate-drain shorted positive channel metal oxide semiconductor, which can automatically raise the potential of the p-ring during turn-off so as to enhance the dynamic avalanche immunity. Besides, the deep trench with a p-ring can shield the high electric field from n-rings at the blocking state, which avoids the breakdown of n-rings. Simulation results indicate that the proposed LIGBT can be safely turned off even under a bus voltage equal to the breakdown voltage (V B), and V CE(sat) under E off = 1 mJ cm−2 can be 24% lower than that of the conventional LIGBT.

Regulating the rectifying effect of zigzag germanium selenide nanoribbons by selective edge decoration

Abstract: Germanium selenide (GeSe) nanoribbons as quasi-one-dimensional materials are expected to host fascinating tunable electronic properties due to the edge state and quantum confinement effect. Herein, the effect on the electronic structures and transport properties of zigzag GeSe nanoribbon (ZGeSeNR) of different functional passivation groups is systematically studied using a combination of density functional theory and the non-equilibrium Green’s function. The N-, P-, and S-passivated ZGeSeNRs are metallic, while the F-, Cl-, OH-, and H-passivated ones exhibit semiconductor properties. The rectification behavior is found in lateral ZGeSeNR heterojunctions composed of a metal–semiconductor contact, and the rectification performance can be modulated by changing the edge passivation group, the ribbon width, and the length of the scattering region. Especially, the highest rectification ratio (RR) reaches 9.2 × 106 in the S–H–ZGeSeNR heterojunctions, in which the left and right half-edge atoms are passivated by the S and H groups, respectively. These results are useful for the design of nanoscale rectifiers based on ZGeSeNRs.

Negative capacitance gate-all-around PZT silicon nanowire with high-K/metal gate MFIS structure for low SS and high I on/I off

Abstract: In the present work, a high-k dielectric hafnium dioxide and lead zirconate titanate (PZT) have been incorporated as a ferroelectric (FE) layer in the gate stack. The Ion/Ioff ratio obtained of the order of 1013, and the subthreshold swing 49.7 mV dec−1 are the most captivating findings of the device which outshines earlier findings. There is a significant improvement in the on-state current (I on) and off-state current (I off). Furthermore, comparatively high value of transconductance (g m) and transconductance generation factor (g m/I d), due to the incorporation of 20 nm PZT NC FE layer, insinuates that the device could be used in low power applications. These enticing findings of the proposed PZT GAA-NCFET nanowire could pave the way for low power devices.

Combined experimental and theoretical investigation on SONOS pFLASH switch

Abstract: In this paper, a new push–pull pFLASH switch is designed and fabricated based on a 110 nm eFLASH process, which includes two 2 T-pFLASH transistors and one signal transmission transistor. The pFLASH transistors are programmed and erased by band-to-band tunneling-induced hot electron and Fowler–Nordheim tunneling to realize its ‘on/off’ function, and the current of the signal transmission transistor can be effectively tuned by the drain voltage of the 2 T-pFLASH. In order to clarify the degradation mechanism of the electronic properties, first principles calculations are performed from the atomic scale. Nitrogen vacancies have been proven to play a crucial role in nitrides. In addition, the effects of vacancies on the charge retention are investigated in terms of electronic structure. The nitrogen vacancies have proven to be detrimental to the electron storage by the simulated localization energies. Therefore, this study will provide a newly designed field-programmable gate array configuration unit, whose electrical mechanisms are revealed by theoretical simulations, which can also become the design foundation for future FLASH switches.

Paralleled multi-GaN MIS–HEMTs integrated cascode switch for power electronic applications

Abstract: A cascode gallium nitride (GaN) switch integrating four paralleled GaN depletion-mode metal–insulator–semiconductor–high-electron-mobility transistors (MIS–HEMT) and a silicon MOSFET (Si-MOSFET) is presented. Each GaN chip is wire-bonded into a multi-chip power module to scale up the power rating. An optimized symmetric configuration and wire bonding of an integral package are used in the cascode switch. By utilizing an optimized packaging approach, the performance of the multi-GaN-chip cascode switch was evaluated through both static and dynamic characterizations. The constructed cascode switch provides a low-static on-state resistance of 72 mΩ and an off-state blocking capability of 400 V with a positive threshold voltage of 2 V. Analysis of dynamic switching characteristics are discussed and demonstrates stable dynamic on-state resistance (R DS-ON) in inductive load circuits with switching dependencies of voltage, frequency, time, and temperature. The extended defects from buffer caused a minimal decrease in dynamic and static R DS-ON with respect to hard switching conditions. However, there was no noticeable degradation in R DS-ON under harsh switching conditions. This study provides a complete analysis of the multi-GaN-chip cascode switch, including MIS–HEMT manufacturing, cascode packaging and static and dynamic characterizations.

The development and applications of nanoporous gallium nitride in optoelectronics: a review

Abstract: The development of nanoporous gallium nitride (NP-GaN) has widened the material properties and applications in third-generation semiconductor areas. NP-GaN has been used in laser emitters, light-emitting diodes, optical sensors, and optical energy storage devices. In this paper, we reviewed the most recent progress in the NP-GaN field by electrochemical etching. The etched GaN has many superior properties compared with original GaN templates, such as stronger photoluminescence intensity, thermal conductivity, piezo-electricity, more accessible area, stress relief, and refractive index. These advantages will make GaN more widely used in the field of optics and optoelectronics. Pore formation can be controlled by adjusting the applied potential and etching time. The NP-GaN makes the material of GaN have broader application prospects. We introduced in detail the application prospects of different GaN based processes and subsequent application methods in optoelectronics, sensors, and materials themselves. This review will help to improve further development of NP-GaN applications.

Optically excited artificial synapse based on α-In2Se3 FETs on Ta2O5

Abstract: Materials and devices for artificial synapse are being increasingly investigated owing to their promise for brain-inspired computing. Here, we demonstrate an optoelectronic synapse with light-modulated memory capability in back-gated ferroelectric channel field-effect transistors made of multi-layered 2D α-In2Se3 on Ta2O5. The optical tunability is achieved by exploiting the frequency of the optical signal in vertically stacked layers of In2Se3, which generate a unique persistent photoresponse due to trapping at the In2Se3/Ta2O5 interface. For the 527nm source wavelength at intensities of 15 mW/cm2, the In2Se3-FET exhibits a high photoresponsivity at 850 AW1. These devices can replicate synaptic functions such as photo-induced short-term memory and long-term memory, paired-pulse facilitation – all via optical modulation. We have also demonstrated common memory effects that occur in the brain such as memory loss, memory transitions that depend upon the stimulation rate (i.e., the interval between stimulation pulses). These demonstrations provide a simple and effective strategy for fabricating light-stimulated synaptic transistors with memory and learning ability which are attractive for building vision-inspired neuromorphic systems.

Enhanced photodetector performance of SnO2/NiO heterojunction via Au incorporation

Abstract: Heterojunctions are known to have trap states and defects that are detrimental to the light responses, especially slowing down the rise and decay time. To address these issues in the charge transfer process, SnO2/NiO heterojunction was modified by incorporating Au at the surface and interface of different devices. The rectifying SnO2/NiO diode showed self-powered photodetector (SPD) characteristics when illuminated by 365 nm light and the responsivity obtained was 3 µA W−1. The 5 nm Au surface decorated SnO2/NiO diode showed the highest rectification ratio, 42.8 and the 2 nm Au decorated device showed 10.6 µA photocurrent generation. The 2 and 5 nm thick Au surface decoration resulted in the formation of nano-Schottky junctions with NiO. The embedding of Au at the interface of the SnO2/NiO diode showed a decrease in diode rectification. Two methods are used for Au incorporation at the interface; glancing angle deposition and electron beam evaporation followed by annealing. Unlike the glancing angle deposited Au film, the larger Au nanoparticles(NPs) formed by electron beam evaporation and annealing, and when embedded at SnO2/NiO interface, generated 9.6 µA of photocurrent and dark currents were lowered by one order. The modified diode characteristics were studied using impedance spectroscopy. The junction capacitance and time constant of Au incorporated devices were found to be much lower than that of bare SnO2/NiO heterojunction, leading to an improved response time and SPD performance. The responsivity, rise time, detectivity, and ON/Off ratio calculated for the device SnO2/NiO with Au NPs at the interface were 3.1 mA W−1, 1.6 s, 1.8 × 1010 Jones, and 2.6 × 103 respectively, best among all the devices. The heterojunction PDs with Au incorporation are a potential way to address the surface and interface effects at the nanoscale, thereby improving the device performance.

Micro-Raman analysis of HVPE grown etched GaN epilayer with porous formation

Abstract: The GaN epilayer grown by hydride vapor phase epitaxy was wet etched by phosphoric acid as the etchant. X-ray diffraction confirms that the GaN has a wurtzite structure. Scanning electron microscopy shows various sizes of hexagonal pits for different times of etchant reactions. Atomic force microscopy shows increase in surface roughness with different etchant rate. The photoluminescence gives a 3.4 eV luminescence for the pristine GaN epilayer. In the etched films, the deep-level defect belonging to yellow and green luminescence was found. The deconvoluted Ga 3d peaks of etched samples show Ga-rich epilayers. Micro-Raman spectroscopy is a non-destructive method for measuring carrier concentration, phonon lifetime and strain using A 1 (LO) spectra of Raman vibration mode was utilized via the Lorentz fitting method. The carrier concentration increases while the phonon lifetime decreases with etching rate. Overall, in the 9 min reaction, the epilayer was etched heavily with a perfect hexagonal etch pit structure.

Investigation of multi-fingers drain field plate in dual-threshold coupling AlGaN/GaN HEMTs for optimizing linearity at high electrical field in Ka-bands

Abstract: GaN-High-electron-mobility transistors (GaN-HEMTs) were fabricated and investigated in detail to improve the linearity at high operation voltage. The scheme of dual-threshold coupling was adopted to mitigate the transconductance (Gm) non-linearity, and multi-finger drain field plate was employed to alleviate the high electric field. The proposed devices yielded Gm plateau of 5.5 V, 10 dB improvement in output third order intercept power. The load-pull measurements at 30 GHz delivered peak power-added-efficiency of 52.5 %, and saturation output-power-density of 5.5 W/mm, whose 2.4 dB improvement in gain compression, and 2 dB enhancement in 1-dB compression point, respectively.

Proton irradiation influence on gate-channel low-field carrier mobility of AlGaN/GaN HEMTs

Abstract: AlGaN/GaN high electron mobility transistors (HEMTs) with different device sizes were prepared and exposed to 0.4 MeV proton irradiation. The low-field carrier transport characteristics of the gate channel are obtained from the capacitance-voltage curves and current-voltage curves. For the device with a longer gate-drain distance (30 μm), after 0.4 MeV proton irradiation, the gate-channel low-field carrier mobility increases by 14.3% on average. For the device with a shorter gate-drain distance (15 μm), the carrier mobility decreases by 13.4% on average after proton irradiation. This phenomenon is studied with regard to the polarization scattering effect. It is found that the polarization distribution in the AlGaN/GaN HEMTs changes after proton irradiation and different gate-drain distances correspond to different polarization distributions.

Optical FOMs of extended-source DG–TFET photodetector in the visible range of the spectrum

Abstract: In this paper, the optical characteristics of an extended-source double-gate tunnel field-effect transistor (ESDG–TFET)–based photodetector in the visible range of the spectrum at wavelength λ = (300–700) nm are investigated. The optical characteristics are examined at three specific wavelengths λ= 300, 500, and 700 nm at an intensity of 0.7 W cm−2. The optical characteristics of photosensors, such as absorption rate, generation rate, energy band profiles, transfer characteristics, sensitivity (S n), quantum efficiency (η), signal-to-noise ratio (SNR), and detectivity, are extracted according to the incident wavelength of light. The results reveal that the ESDG–TFET-based photosensor exhibits better optical characteristics at λ = 300 nm compared to at λ = 500 and 700 nm. Moreover, the proposed photosensor provides sensitivity, SNR, and responsivity in the order of 91.2, 79 (dB), and 0.74 (A Watt−1), respectively, at λ = 300 nm. Due to the high incident optical energy (E g) at 300 nm, the absorption and emission rates of this photosensor are significantly larger; consequently, it reports better optical characteristics. Finally, a comparative study of the proposed TFET-based photosensor with photosensors cited in the literature is summarized in tabular form. A comparison study in terms of spectral sensitivity between single-gate and double-gate ESDG–TFET is also reported. Moreover, an inverter circuit based on ESDG–TFET is designed, and the corresponding transient analysis is highlighted under both dark and light states.

Hydrothermal synthesis and solar cell application studies of Nickel doped Zinc Oxide nanocomposites

Abstract: Nickel doped Zinc Oxide nanoparticles are synthesised via hydrothermal technique at three different temperatures. XRD analysis shows a decrease in grain size with doping at low temperature and an increase in crystallite size at high temperature. Nano flowers and a mixture of rods and sheets are observed in SEM images. Zinc Oxide nanorods wrapped with Nickel Oxide nano thread and spider web like structures are clearly visible in TEM micrographs. Doping introduced defects in composites which enhanced UV and visible absorption. Composite with an excellent photo absorption property and a noted thermal stability is chosen for fabricating solar cell devices by spin coating and doctor blade techniques which delivered a power conversion efficiency of 3.96% and 2.32% respectively.

Using ensemble Monte Carlo methods to evaluate non-equilibrium Green’s functions, II. Polar-optical phonons

Abstract: In semi-classical transport, it has become common practice over the past few decades to use ensemble Monte Carlo methods for the simulation of transport in semiconductor devices. This method utilizes particles while still addressing the full physics within the device, leaving the computational difficulties to the computer. More recently, the study of quantum mechanical effects within the devices, have become important, and have been addressed in semiconductor devices using non-equilibrium Green’s functions (NEGF). In using NEGF, one faces considerable computational difficulties. Recently, a particle approach to NEGF has been suggested and preliminary results presented for non-polar optical phonons in Si, which are very localized scattering centers. Here, the problems with long-range polar-optical phonons are discussed and results of the particle-based simulation are used to examine quantum transport in InN at 300 K.

Dual gate AlGaN/GaN MOS-HEMT biosensor for electrical detection of biomolecules-analytical model

Abstract: This paper proposes an analytical model for a dual gate AlGaN/GaN Metal oxide semiconductor-high-electron-mobility transistor (MOS-HEMT) biosensor for electrical detection of neutral species such as Biotin, Keratin, ChOx, and Zein. When only one subband is occupied and the AlGaN layer is assumed to have been fully ionized, the Fermi–Dirac statistic and 2D state density are used to produce a self-consistent calculation of the carrier density in the quantum well at the interface. It is done by analyzing the impact of biomolecule concentration by inserting a biomolecule of appropriate dielectric permittivity in the cavity area beneath the gate region. The impact of cavity length has been analyzed on the sensor’s performance. The proposed device significantly changes the channel potential, transconductance, drain current, and threshold voltage. Dual gate structures offer superior resistance to short channel effects. Due to enhanced transport characteristics, high carrier mobility, drain current, and a variety of other factors, double gate MOS HEMT outperforms single-gate MOS HEMT. The maximal transconductance, drain on sensitivity, and the maximal drain current that has been attained in this work is 0.017 s, 0.22 and 0.129 mA, respectively, for biomolecule concentration, N b = 3 × 1012. Among all the biomolecules used in this study, Keratin has achieved the maximum shift in threshold voltage and transconductance of 0.4 V and 0.016 s. The increase in current for Keratin, Biotin, Zein, and ChOx is 0.67%, 78%, 17%, and 42%, respectively, from single to dual gate AlGaN/GaN MOS-HEMT. SiO2, Al2O3, and HfO2 oxides have been compared by filling them in the left side of the cavity. Dual gate AlGaN/GaN MOS-HEMT biosensor presents an opportunity to develop robust, low-cost, specific detection and analysis of neutral biomolecule. The analytical model provides good results for drain current according to the comparison of simulation and analytical model findings.