N-type Layer Research Articles

Simple thermal vapor deposition process for and characterization of n-type indium oxysulfide thin films

The search continues for alternative nontoxic n-type electron transport layers in optoelectronic thin-film devices. Indium oxysulfide, In2(O,S)3, represents one promising material for this application, especially when paired with chalcogenide absorber layers. The ternary nature of the composition allows for electrical conductivity and optical bandgap tuning by tailoring the sulfur to oxygen ratio in the oxysulfide alloy. However, thin films of In2(O,S)3 are typically deposited only by chemical bath deposition or plasma-enhanced atomic layer deposition. We report deposition of thin films of In2(O,S)3 in a custom-built thermal reactor using only water vapor and hydrogen sulfide as the coreactants. This advance is enabled by the use of a recently reported, highly reactive indium formamidinate precursor. As shown by x-ray photoelectron spectroscopy, the composition can be tuned from pure In2O3 to pure In2S3 by varying the ratio of cycles employing water or hydrogen sulfide. The oxygen to the sulfur ratio in the film can be controlled by altering the dose sequence, although films typically contain more sulfur than would be expected naively from the percentage of hydrogen sulfide doses in the deposition recipe. Rutherford backscattering spectrometry confirms the composition is sulfur-rich relative to the dosing ratio. Structural characterization indicates films are relatively amorphous in nature. Electrically, these films offer reasonably constant electron mobility at different O:S ratios, with an electron concentration tunable over 4 orders of magnitude. These oxysulfide films possess a higher indirect bandgap than their oxygen-free indium sulfide counterparts, indicating higher transmittance to blue light. These indium oxysulfide films may be suitable candidates for electron transport layers in thin-film solar cells where their wider bandgap might result in higher optical transparency and thus short circuit current density, while the tunability of their conduction band offset with an absorber layer may result in higher open circuit voltage.

Fluorinated Alcohol-Processed N-Type Organic Electrochemical Transistor with High Performance and Enhanced Stability.

Tuning the film morphology and aggregated structure is a vital means to improve the performance of the mixed ionic-electronic conductors in organic electrochemical transistors (OECTs). Herein, three fluorinated alcohols (FAs), including 2,2,2-trifluoroethanol (TFE), 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), and perfluoro-tert-butanol (PFTB), were employed as the alternative solvents for engineering the n-type small-molecule active layer gNR. Remarkedly, an impressive μC* of 5.12 F V-1 cm-1 s-1 and a normalized transconductance of 1.216 S cm-1 are achieved from the HFIP-fabricated gNR OECTs, which is three times higher than that of chloroform. The operational stability has been significantly enhanced by the FA-fabricated devices. Such enhancements can be ascribed to the aggregation-induced structural ordering by FAs during spin coating, which optimizes the microstructure of the films for a better mixed ion and electron transport. These results prove the huge research potential of FAs to improve OECT materials' processability, device performance, and stability, therefore promoting practical bio-applications.

Synthesis, Crystal Structures, and Nonlinear Optical Properties of Chalcone Doped by Titanium Dioxide Nanoparticles for Solar Cell Application

In this work, we investigate the effects of titanium dioxide (TiO2) nanoparticle percentages on the optical and electrical properties of 3-(4-(dimethyl-amino)phenyl)-1-phenyl-(2E)-propen-1-one (DAAP). In order to achieve thin films, DAAP was dissolved in acetone and doped with different ratios of TiO2. The pure and composite mixtures were spin-coated onto a glass substrate. We investigated the influence of TiO2 on XRD patterns, absorption, energy band gaps, refractive indices, sheet resistance, resistivity, and Hall coefficients. We used the XRD technique to study the structure of DAAP pre- and post-doping with TiO2 nanoparticles. It was evident from the XRD patterns that the composite transformed from an amorphous to a polycrystalline nature and behaved similarly to titanium oxide crystals. The pure sample exhibited an absorption band of 409 nm. With the addition of TiO2, the whole absorption spectrum shifted to the blue region. For example, with a dopant percentage of 15%, the spectrum shifted to a wavelength of 368 nm. The energy band gap values increased with a dopant concentration from 2.65 eV of pure DAAP to 2.91 eV of maximum dopant percentage (15%). The refractive index decreased to its lowest value of 2.47 with the increase in TiO2 concentration. The impact of increasing TiO2 percentage highly improved electrical characteristics by reducing the sheet resistance and resistivity to 905 k(Ω/sq) and 230 k on the (Ω · cm), respectively. An optimized DAAP doped with 15% TiO2 has been used as an n-type layer on a p-type monocrystalline silicon wafer (Si (111)) to fabricate η = 0.23% efficient solar cells. On the other hand, the amplified spontaneous emission (ASE) of the DAAP and dopant mixture was excited by the third harmonic generation (λex = 355 nm). The pure DAAP exhibits an ASE peak at 535 nm. The intensity decreased rapidly with increased dopant concentration, whereas the full width at half-maximum (FWHM) increased slightly.

A Novel 4H-SiC JBS-Integrated MOSFET With Self-Pinching Structure for Improved Short-Circuit Capability

Monolithic integration of junction barrier-controlled Schottky (JBS) diode with SiC MOSFET (termed JMOS) offers unique advantages. However, the short-circuit (SC) ruggedness issue stands in the way of the development of the conventional JMOS. The purpose of this numerical study is to investigate a new 4H-SiC JMOS with a self-pinching (SP) structure formed in the JFET region (termed SP-JMOS). The SP structure features that an N-type current spread layer is sandwiched between the P+ layer and the buried P-shield layer, forming a lateral JFET channel. In the forward conduction state, the lateral JFET channel self-pinches off and clamps the potential, thus limiting the saturation current of the device. In the blocking state, both the P+ layer and the buried P-shield layer collaboratively shield the Schottky contact and the SiC/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interface from a high electric field for long-term reliable operation. Numerical simulation results show that the proposed SP-JMOS not only withstands a roughly <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.6\times $ </tex-math></inline-formula> longer SC withstanding time than that of the conventional JMOS, but also shows an ultralow oxide electric field in the SP-JMOS.

Simulation Study of Single-Event Burnout Reliability for 1.7-kV 4H-SiC VDMOSFET

A single-event burnout (SEB) reliability and hardening method for 1.7-kV 4H-SiC power VDMOSFET under high liner energy transfer (LET) value range is proposed and researched by the 2-D numerical simulation. Compared with the conventional VDMOSFET with N-type multi-buffer layers, the hardened VDMOSFET not only ensures that the forward conduction capability does not deteriorate, but also reduces the peak electric field under breakdown voltage from 3.62 MV/cm to 2.98 MV/cm. The advantage of the hardened structure is providing a hole leakage path and increasing the contact area between the source metal and the N+ source, eliminating the effect of electron-hole pairs generated by heavy ion strike on the device, thus improving the SEB performance significantly. In addition, this fabricating technology is compatible with the current technological processes. This hardened structure provides a great potential in aerospace application.

Temperature-Dependent Self-Powered Solar-Blind Photodetector Based on Ag2O/β-Ga2O3 Heterojunction.

In this study, a high-photoresponsivity self-powered deep ultraviolet (DUV) photodetector based on an Ag2O/β-Ga2O3 heterojunction was fabricated by depositing a p-type Ag2O thin film onto an n-type β-Ga2O3 layer. The device characteristics after post-annealing at temperatures ranging from 0 to 400 °C were investigated. Our DUV devices exhibited typical rectification characteristics. At a post-annealing temperature of 300 °C, the as-fabricated device had a low leakage current of 4.24 × 10−11 A, ideality factor of 2.08, and a barrier height of 1.12 eV. Moreover, a high photo-responsivity of 12.87 mA/W was obtained at a 100 μW/cm2 light intensity at a 254 nm wavelength at zero bias voltage, the detectivity was 2.70 × 1011 Jones, and the rise and fall time were 29.76, 46.73 ms, respectively. Based on these results, the Ag2O/β-Ga2O3 heterojunction photodetector operates without an externally applied voltage and has high responsivity, which will help in the performance improvement of ultraviolet sensing systems.

Role of Metallic Adlayer in Limiting Ge Incorporation into GaN.

Atomically thin metal adlayers are used as surfactants in semiconductor crystal growth. The role of the adlayer in the incorporation of dopants in GaN is completely unexplored, probably because n-type doping of GaN with Si is relatively straightforward and can be scaled up with available Si atomic flux in a wide range of dopant concentrations. However, a surprisingly different behavior of the Ge dopant is observed, and the presence of atomically thin gallium or an indium layer dramatically affects Ge incorporation, hindering the fabrication of GaN:Ge structures with abrupt doping profiles. Here, we show an experimental study presenting a striking improvement in sharpness of the Ge doping profile obtained for indium as compared to the gallium surfactant layer during GaN-plasma-assisted molecular beam epitaxy. We show that the atomically thin indium surfactant layer promotes the incorporation of Ge in contrast to the gallium surfactant layer, which promotes segregation of Ge to the surface and Ge crystallite formation. Understanding the role of the surfactant is essential to control GaN doping and to obtain extremely high n-type doped III-nitride layers using Ge, because doping levels >1020 cm−3 are not easily available with Si.

Photoconductivity buildup and decay kinetics in unintentionally doped β-Ga2O3

Photoconductivity transients in an unintentionally doped (UID) n-type β-Ga2O3 layer are investigated at temperatures ranging from 90 to 210 K. Illumination of the β-Ga2O3 layer with a 600 nm light pulse induces photoconductivity, which persists after the light is turned off. The origin of persistent photoconductivity (PPC) is probed using the temperature dependencies of the photoconductivity buildup and decay kinetics. Upon excitation by 600 nm light, the photoconductivity in the UID β-Ga2O3 sample is related to the photoionization of two distinct deep levels with thermal ionization energies of 1.76 ± 0.07 eV (Franck–Condon energy D FC: 0.78 ± 0.24 eV) and 2 ± 0.08 eV (D FC: 0.52 ± 0.15 eV). When the light is turned off, PPC is observed due to thermal capture barriers preventing the photo-generated electrons from relaxing back to deep levels. Capture barriers of 35 meV and 165 meV have been estimated using the temperature dependence of the PPC decay time constant. The experimentally detected deep levels are ascribed to deep donors, such as oxygen vacancies.

Current Transient Spectroscopic Study of Vacancy Complexes in Diamond Schottky p-i-n Diode

The present state-of-the-art of junction-based diamond electronic devices is limited by the challenges inherent to the synthesis of n-type layers, where the dopant itself forms defect complexes that are donor compensating centers. Recently, the fabrication of diamond Schottky p-i-n diodes (SPINDs) by chemical vapor deposition (CVD) of intrinsic diamond films followed by an n-type layer on p-type diamond substrates has been reported to demonstrate excellent diode-like behavior with high rectification factors and surface barrier height at elevated temperatures. However, due to the ultrawide bandgap of diamond and small contact area of the devices, it is challenging to characterize the defect centers that limit the performance of the SPINDs using conventional capacitance transient spectroscopy. In this article, we report the characterization of defect centers in the diamond SPINDs with a contact area of 280 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}\,\,\times \,\,280\,\,\mu \text{m}$ </tex-math></inline-formula> using current transient spectroscopy (CTS), which measures thermally induced emission rates from trap centers through change in device current instead of junction capacitance. The CTS scans in the temperature range 80–800 K revealed the presence of five trap-related peaks. Results from density functional theory (DFT) calculations were used to identify the nature of the traps. While most of the detected traps were identified to be vacancy complexes coupled to phosphorus and hydrogen impurities, one trap has been identified as single carbon vacancy. Most of the phosphorus-related defect complexes were observed to be in neutral and/or negative charge states and were identified as acceptor-like states.

Performance-Improved Vertical Ni/SiO₂/4H-SiC Metal–Oxide–Semiconductor Capacitors for High-Resolution Radiation Detection

We report the fabrication of vertical metal–oxide–semiconductor (MOS) detectors with the highest energy resolution ever reported. The MOS detectors have been fabricated on 50- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> -thick n-type 4H-SiC epitaxial layers by growing a silicon dioxide (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) layer thermally prior to contact deposition. The MOS detectors exhibited leakage currents two orders of magnitude lower than that observed in a Schottky barrier detector (SBD) fabricated on similar 4H-SiC epilayers. The MOS detectors exhibited a much higher energy resolution of 0.4% compared to 0.8% observed in an SBD for 5486-keV alpha particles although both the devices showed a high charge collection efficiency (CCE) of 96% when exposed to the alpha particles. Capacitance mode deep-level transient spectroscopy (C-DLTS) revealed the presence of “lifetime killer” <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{Z}_{\mathrm {1/2}}$ </tex-math></inline-formula> defects in similar concentrations in both the devices, and however, the corresponding capture cross section in the SBD has been observed to be one order of magnitude higher compared to the MOS detector, and instead of EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6/7</sub> center seen in the SBD, the MOS device showed the presence of EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> center. The higher resolution of the MOS device is attributed to the lower leakage current and difference in defect configurations observed between the two devices. The MOS detector showed a positive polarity C-DLTS peak with an activation energy of 1.22 eV, which is likely due to the nonnegligible impedance of the back contact because of the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer. The present study opens the great potential of other wide bandgap semiconductor-based vertical MOS detectors, which can be fully depleted for high-resolution X-/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula> -ray detection.

Normally-off β-Ga2O3 MOSFET with an Epitaxial Drift Layer.

A normally-off β-Ga2O3 metal-oxide-semiconductor field-effect transistor (MOSFET) is proposed using a technology computer-aided design (TCAD) device simulation, which employs an epitaxial drift layer grown on an n-type low-doped body layer. The low-doped body layer under the MOS gate enabled normally-off operation, whereas the epitaxial drift layer determined the on-resistance and breakdown characteristics. The effects of the doping concentration of each layer and thickness of the drift channel layer on the device characteristics were investigated to design a device with a breakdown voltage of 1 kV. A threshold voltage of 1.5 V and a breakdown voltage of 1 kV were achieved by an n-type body layer with a doping concentration of 1 × 1015 cm−3 and an n-type drift layer with a doping concentration of 3 × 1017 cm−3, a thickness of 150 nm, and a gate-to-drain distance of 9.5 μm; resulting in an on-resistance of 25 mΩ·cm2.

Improving the photovoltaic performance for PbS QD thin film solar cells through interface engineering

Interfaces exist between functional layers inside thin film optoelectronic devices, and it is very important to minimize the energy loss when electrons move across the interfaces to improve the photovoltaic performance. For PbS quantum dots (QDs) solar cells with the classical n-i-p device architecture, it is particularly challenging to tune the electron transfer process due to limited material choices for each functional layer. Here, we introduce materials to tune the electron transfer across the three interfaces inside the PbS-QD solar cell: (1) the interface between the ZnO electron transport layer and the n-type iodide capped PbS QD layer (PbS-I QD layer), (2) the interface between the n-type PbS-I layer and the p-type 1,2-ethanedithiol (EDT) treated PbS QD layer (PbS-EDT QD layer), (3) the interface between the PbS-EDT layer and the Au electrode. After passivating the ZnO layer through APTES treating; tuning the band alignment through varying the QD size of PbS -EDT QD layer and a carbazole layer to tune the hole transport process, a power conversion efficiency of 9.23% (Voc of 0.62 V) under simulated AM1.5 sunlight is demonstrated for PbS QD solar cells. Our results highlights the profound influence of interface engineering on the electron transfer inside the PbS QD solar cells, exemplified by its impact on the photovoltaic performance of PbS QD devices.

Modified divacancies in 4H-SiC

Divacancies near or at lattice defects in SiC, the PL5–PL7 photoluminescence centers, are known to have more favorable optical and spin properties for applications in quantum technology compared to the usual divacancies. These centers were previously predicted to be divacancies near stacking faults. Using electron paramagnetic resonance, we observe PL5, PL6, and four other divacancy-like centers, labeled PLa–PLd, in electron-irradiated high-purity semi-insulating (HPSI) 4H-SiC. From the observed fine-structure D-tensors, we show that these centers including PL6, which has so far been believed to be an axial center, all have C1h symmetry. Among these, PLa, PLc, and PLd are basal divacancies and PL5 and PL6 are slightly deviated from axial symmetry, while PLb is different from others with the principal Dzz axis of the D-tensor aligning at ∼34° off the c-axis. We show that these modified divacancies are only detected in one type of HPSI materials but not in commercial n- and p-type substrates or n-type pure epitaxial layers irradiated by electrons regardless of surface treatments which are known to create stacking faults.

(Digital Presentation) Study on the Electrical Characteristics and Band Diagrams of Ga2O3 MOS Gate Stacks

β-Ga2O3 is expected as one of the candidate materials for high-efficient and cost-effective power devices for high-voltage applications [1]. For the fabrication of MOSFETs the understanding of band diagrams of MOS structure is inevitably important. However, the previous reports on band alignments of β-Ga2O3 and various dielectrics including Al2O3 and SiO2 are controversial with significant inconsistencies in their values [2]. Since the ideal band diagram referring to the vacuum level is not clarified we cannot tell the Fermi level of β-Ga2O3 and the flat-band voltage (Vfb) shift of MOS capacitors. In this study we fabricated MOS structures and its band diagram was investigated from photoelectron spectroscopy.We employed SiO2 as the gate dielectric. Single crystalline β-Ga2O3 (001) wafers with ~2×1016 cm-3 n-type doped epitaxial layers were cleaned in diluted HF solution. Then SiO2 films were deposited by electron-beam evaporation of Si in O2 ambient of ~1×10-2 Pa, followed by post-deposition annealing (PDA) in 1 atm-O2 at various temperatures. Au was evaporated as gate electrode to form MOS capacitors. Ultraviolet photoelectron spectroscopy (UPS) was conducted to determine the energy level of the valence band edge on the surface of β-Ga2O3 epitaxial layer referring to the vacuum level. The valence band spectrum of ~4nm-thick SiO2/β-Ga2O3 was also investigated by x-ray photoelectron spectroscopy to determine the valence band offset at the interface.From C-V characteristics of MOS capacitors with different PDA conditions, the higher PDA temperature was found to be beneficial to achieve nearly-ideal C-V characteristics. A negligibly-small hysteresis was obtained for the one fabricated with O2-PDA at 1000℃ [3]. The energy profiles of interface state density (Dit) were determined by conductance method for the samples of different PDA conditions. The values of Dit decreased for higher PDA temperature down to ~1010 cm-3 at the energy level of EC−0.2 eV [3]. These values are significantly lower than typically reported ones for ALD-Al2O3 MOS structures on β-Ga2O3 [4]. The additional annealing at low temperature at 400℃ works for the further reduction of hysteresis to less than 1 mV/nm.Next the band diagrams of the MOS structures were investigated. From the UPS spectra we could deduce the energy level of valence band edge referring to the vacuum level, from the difference between minimum (cut-off) and maximum edges of the obtained kinetic energy spectra of photoelectrons. We also evaluated the valence band offset from the deconvolution of the valence band XPS of thin SiO2/β-Ga2O3 stack. From the energy edge difference between the deconvoluted spectra corresponding to SiO2 and Ga2O3, respectively, the valence band offset ~1.1 eV was deduced, which is not conflicting with the estimated valence band edge energy of Ga2O3 and the well-reported valence band edge energy of SiO2. The conduction band edge energy was also estimated assuming the bandgap of β-Ga2O3 (4.7eV) [1]. Considering the Fermi-level of β-Ga2O3 with n-type doping of ~2×1016 cm-3 was approximated to be ~0.1 eV from the conduction band edge, the Fermi-level on the surface of β-Ga2O3 epitaxial layer after 1000℃ O2 annealing was estimated to be 3.6-3.7eV below the vacuum level [5]. Note that this value would be significantly smaller than the one simply estimated from the previously reported electron affinity of Ga2O3 [6].Finally the Vfb shifts were investigated for the MOS capacitors fabricated with O2 annealing at 1000℃ with various thicknesses, referring to the ideal flat-band voltage determined with the Fermi-level of β-Ga2O3 as discussed above and the work function of Au electrode which was also determined with UPS measurement. As a result, we found the most of the Vfb values were around the ideal flat-band voltage irrespective of the film thickness from 20 to 60 nm, which indicates a small density of fixed charges <2×1011 cm-2 [5].In conclusion, we found that SiO2/β-Ga2O3 (001) MOS capacitors showed nearly-ideal electrical characteristics with small fixed charge density by applying O2-PDA at 1000℃. The band diagram for the MOS stacks referring to the vacuum level was clarified by photoelectron spectroscopy, which enables us to understand the β-Ga2O3 MOS interface properties correctly.

Relationship of carbon concentration and slow decays of photoluminescence in homoepitaxial n-type GaN layers

In this study, we analyzed the slow decay in time-resolved photoluminescence (TR-PL) of n-type GaN homoepitaxial layers with carbon concentrations of (0.26–4.0) × 1016 cm−3. The relative signal intensities of the slow decays to the TR-PL signals at t = 0 s increased almost linearly with increased carbon concentration, suggesting that the carrier recombination process is subjected to the deep level formed by the carbon atoms in GaN. Slow decay curves were calculated based on the rate equations for trapping and emission at the deep level. The experimental carbon concentration dependence of the time constants and the relative signal intensities was reproduced by calculation. TR-PL is a technique used to estimate carbon concentrations in GaN homoepitaxial layers.

β-(AlxGa1−x)2O3/Ga2O3 heterostructure Schottky diodes for improved VBR2/RON

We propose and demonstrate the use of a β-(AlxGa1–x)2O3 capping layer to achieve increased breakdown voltage, VBR, and VBR2/RON figure of merit in β-Ga2O3 Schottky diodes, where RON is the on-state resistance. We demonstrate that the addition of a 30 nm-thick β-(Al0.22Ga0.78)2O3 cap to an n-type β-Ga2O3 layer grown by metal organic chemical vapor deposition increases the breakdown voltage from 246 to 387 V in diodes with Pt contacts and 3 × 1016 cm−3 n-type doping. The cap increases the surface Schottky barrier with Pt, resulting in reduced carrier injection under reverse bias. The results are in good agreement with simulations which show that the addition of the capping layer enables the peak electric field at breakdown to increase from 2.5 to 3.6 MV/cm. Simulations further show that RON penalty associated with the (AlxGa1–x)2O3 cap can be almost completely eliminated by grading the capping layer. Thus, by raising the barrier height beyond the limit imposed by the metal work function and Fermi level pinning, the proposed heterojunction helps to improve VBR by reducing the reverse leakage current in ultrawide bandgap semiconductor diodes where bipolar doping remains a challenge.

Increase in net donor concentration due to introduction of donor-like defects by ultra-low-dose Si-ion implantation and subsequent annealing in homoepitaxial n-type GaN

Si ions were implanted at a dose of 1 × 1010 cm−2 into a homoepitaxial n-type GaN layer with a net donor concentration (N D) of 3–8 × 1015 cm−3. The N D in the implanted region increased by 1–3 × 1015 cm−3 after annealing at a temperature greater than 900 °C compared with that for the as-grown homoepitaxial layer. The increase in N D was considerably larger than the peak concentration of implanted Si ions (3 × 1014 cm−3). No increase in N D was observed for an as-grown sample after annealing. These results clearly suggest that donor-like defects were introduced by implantation of Si ions and a subsequent annealing process.

Minority carrier lifetime extraction methodology based on parallel pn diodes with a field plate

A method for using device simulation to extract the hole lifetime (τ p) of a thin n-type SiC epitaxial layer on the basis of the characteristics of parallel diodes is proposed. The voltage drop (ΔV) across a forward-biased pn diode (single-setup) and parallel pn diodes (multi-setup) at the same current density (J) is correlated with the defined τ p. A severe error in the extraction of ΔV was found and attributed to surface recombination. The extraction error was recovered by the introduction of a field-plate between the anodes, where the field-plate was biased to accumulate the surface of the n-base region. An extraction accuracy of 99% was achieved even with a surface recombination velocity of 105 cm s−1.

Atomically Thin Delta-Doping of Self-Assembled Molecular Monolayers by Flash Lamp Annealing for Si-Based Deep UV Photodiodes.

Delta doping (δ-doping) can find a wide range of applications in advanced metal oxide semiconductor field effect transistors, deep UV photodetectors, quantum devices, and others. In this work, we formed a δ-doping layer in silicon by employing flash lamp annealing to treat the PCl3 monolayers grafted on silicon surfaces. The δ-doping layer is atomically thin (<1 nm). Low-temperature Hall measurements show that the δ-doping layer is in a metallic state and exhibits a weak localization phenomenon, implying that a two-dimensional electron gas is formed. When we form such an n-type δ-doping layer on a highly doped p-type Si substrate, a highly sensitive solar-blind UV photodetector is created, which traditionally was only possible by using wide band gap semiconductors such as gallium nitride (GaN) or silicon carbide (SiC).

Lead-Tin Laminated All-Perovskite Solar Cells: Verification of Feasibility from the Perspective of Device Simulation

Although conventional lead-based perovskite solar cells have good power conversion efficiency, their toxic drawbacks seriously affect the environment and commercialization. This work introduces lead-tin laminated all-perovskite solar cells, and the addition of a tin-based perovskite layer can reduce this, while effectively compensating for the absorption of light in different wavelength ranges by the lead-based perovskite layer. The SACPS-1D (Solar Cell Capacitance Simulator) was used to study the intrinsic factors affecting each performance parameter of the device and optimize the parameters to maximize the overall performance of the device. We have obtained power conversion efficiency (PCE) of 17.59% and 6.14% lead-based and tin-based single-section perovskite solar cells, which are close to the experimental results. The simulation results show that the n-type doped n-CH3NH3SnI3 layer (electron transport layer ETL) and the p-type doped p-CH3NH3PbI3 layer (hole transport layer HTL) of the lead-tin laminated all-perovskite solar cell have a significant impact on the overall performance of the device. The optimized ETL and HTL are 1000 nm and 200 nm, respectively, which are consistent with the purpose of lead reduction. Accurate control of the n-MASnI3 or p-MAPbI3 to the top region doping concentration is very important process and has a great impact on the open circuit voltage VOC. The optimized ETL and HTL are optimal at 1017 cm−3 and 1014 cm−3, respectively. We also found that in all-perovskite solar cells, the ETL defect density near the light source dominates the overall device effect, and the larger the defect density the worse the device performance. This shows that to improve the performance of laminated all-perovskite solar cells, we need to pay more attention to the quality of the absorber layer close to the light source. Taking these factors into account, we optimized the device performance parameters as VOC = 1.07 V, JSC =19.56 mA cm−2, FF = 70.55% and PCE = 17.29%.