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Herein, aluminum nitride (AlN) powder is thermally treated via a thermocycle process for use in PVT growth.

Background: Although a rapid response system (RRS) can reduce the incidence of cardiopulmonary resuscitation (CPR) in general wards, avoidable CPR cases still occur. This study aimed to investigate the incidence and causes of avoidable CPR. Methods: We retrospectively reviewed the medical records of all adult patients who received CPR between April 2013 and March 2016 (35 months) at a tertiary teaching hospital where a part-time RRS was introduced in October 2012. Four experts reviewed all of the CPR cases and determined whether each event was avoidable. Results: A total of 192 CPR cases were identified, and the incidence of CPR was 0.190 per 1,000 patient admissions. Of these, 56 (29.2%) were considered potentially avoidable, with the most common cause being doctor error (n=32, 57.1%), followed by delayed do-not-resuscitate (DNR) placement (n=12, 21.4%) and procedural complications (n=5, 8.9%). The percentage of avoidable CPR was significantly lower in the RRS operating time group than in the RRS non-operating time group (20.7% vs. 35.5%; P=0.026). Among 44 avoidable CPR events (excluding cases related to DNR issues), the rapid response team intervened in only three cases (6.8%), and most of the avoidable CPR cases (65.9%) occurred during the non-operating time. Conclusions: A significant number of avoidable CPR events occurred with a well-functioning, part-time RRS in place. However, RRS operation does appear to lower the occurrence of avoidable CPR. Thus, it is necessary to extend RRS operation time and modify RRS activation criteria. Moreover, policy and cultural changes are needed prior to implementing a full-time RRS.

Epitaxial growth using graphene (GR), weakly bonded by van der Waals force, is a subject of interest for fabricating technologically important semiconductor membranes. Such membranes can potentially offer effective cooling and dimensional scale-down for high voltage power devices and deep ultraviolet optoelectronics at a fraction of the bulk-device cost. Here, we report on a large-area β-Ga2O3 nanomembrane spontaneous-exfoliation (1 cm × 1 cm) from layers of compressive-strained epitaxial graphene (EG) grown on SiC, and demonstrated high-responsivity flexible solar-blind photodetectors. The EG was favorably influenced by lattice arrangement of SiC, and thus enabled β-Ga2O3 direct-epitaxy on the EG. The β-Ga2O3 layer was spontaneously exfoliated at the interface of GR owing to its low interfacial toughness by controlling the energy release rate through electroplated Ni layers. The use of GR templates contributes to the seamless exfoliation of the nanomembranes, and the technique is relevant to eventual nanomembrane-based integrated device technology.

Single-crystal gallium nitride (GaN) thin films were grown using a graphene mask via multiple epitaxial lateral overgrowth (multiple-ELOG). During the growth process, the graphene mask self-decomposed to enable the emergence of a GaN film with a thickness of several hundred nanometres. This is in contrast to selective area growth of GaN using an SiO2 mask leading to the well known hexagonal-pyramid shape under the same growth conditions. The multiple-ELOG GaN had a single-crystalline wurtzite structure corresponding to the crystallinity of the GaN template, which was confirmed with electron backscatter diffraction measurements. An X-ray diffraction rocking curve of the asymmetric 102 reflection showed that the FWHM for the multiple-ELOG GaN decreased to 405 from 540′′ for the underlying GaN template. From these results, the self-decomposition of the graphene mask during ELOG was experimentally proven to be affected by the GaN decomposition rather than the high-temperature/H2 growth conditions.

Cu2ZnSn(S,Se)4 (CZTSSe) solar cells with low cost and eco-friendly characteristics are attractive as future sources of electricity generation, but low conversion efficiency remains an issue. To improve conversion efficiency, a method of inserting intermediate layers between the CZTSSe absorber film and the Mo back contact is used to suppress the formation of MoSe2 and decomposition of CZTSSe. Among the candidates for the intermediate layer, graphene oxide (GO) and reduced GO have excellent properties, including high-charge mobility and low processing cost. Depending on the type of GO, the solar cell parameters, such as fill factor (FF), were enhanced. Thus, the conversion efficiency of 6.3% was achieved using the chemically reduced GO intermediate layer with significantly improved FF.

This Letter describes the impact of shape on micro light-emitting diodes (µLEDs), analyzing 400 µm2 area µLEDs with various mesa shapes (circular, square, and stripes). Appropriate external quantum efficiency (EQE) can yield internal quantum efficiency (IQE) which decreases with increasing peripheral length of the mesas. However, light extraction efficiency (ηe) increased with increasing mesa periphery. We introduce analysis of Jpeak (the current at peak EQE) since it is proportional to the non-radiative recombination. Etching the sidewalls using tetramethylammonium hydroxide (TMAH) increased the peak EQE and decreased the sidewall dependency of Jpeak. Quantitatively, the TMAH etching reduced non-radiative surface recombination by a factor of four. Hence, shrinking µLEDs needs an understanding of the relationship between non-radiative recombination and ηe, where analyzing Jpeak can offer new insights.

Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells are showing great promise due to using earth-abundant and nontoxic materials and tuning the band gap through the amount of S and Se. Flexible high-effi...

The effect of a graphene oxide (GO) intermediate layer on the performance of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells was studied. The formation of dielectric MoSe2, which can be induced by a reaction between CZTSSe and Mo, was successfully suppressed. The GO layer prevented the decomposition of CZTSSe along with the formation of binary chalcogenides. Furthermore, the interference effect generated between the incident light and the light reflected by Mo was effectively alleviated, thereby reducing photon loss to effectively absorb light. The incorporation of the GO layer resulted in a stronger electric field in the absorber, as determined by the transfer matrix method, and accordingly, a higher absorption spectrum was observed in absorption measurements. Consequently, the series resistance was reduced because MoSe2 formation was inhibited, and a significant improvement in the Jsc value was confirmed via the mitigation of the interference effect and an improved series resistance. The CZTSSe solar cell exhibited a notable power conversion efficiency of 11.2%, which represented an improvement over a conventional reference cell that was fabricated with a GO layer.

The unique degradation behavior of a tunneling field-effect transistor (TFET) under hot-carrier injection (HCI) stress has been previously investigated. However, while the source side (p+/p junction) of degradation (due to HCI stress) has been extensively studied, the drain side (p/n+ junction) has not been investigated yet. Our study revealed that both bulk oxide and interfacial layer degradation occurred at the drain side, while an interfacial layer degradation was dominant at the source side at 300 K. This evidences a unique degradation mechanism of the tunneling FET.

ZnO is of great interest for large-area optoelectronic devices, e.g., flat panel displays, light-emitting diodes, transparent semiconductors, and transparent conductive oxides (TCOs) etc., owing to its good optical properties. In the present study, quaternary ZnO thin films are deposited on a soda lime glass substrate using Mg and group III elements, such as Al, Ga, and In, to enhance the optical and electrical properties. The structural, optical, and electrical properties of quaternary ZnO TCO materials are investigated for improved thin film solar cell performance. All of the films show a uniform microstructure without any void and crack and have a transmittance over 75% in the visible region. They possess comparable band gap differences. Especially, as for the optical properties, a Mg and Ga co-doped ZnO, MgGaZnO (MGZO) thin film shows a high optical band gap of 3.87 eV with a transmittance of about 90% in the visible region. In addition, the MGZO thin film shows improved electrical properties with the lowest resistivity of 3.97 × 10−4 Ωcm, higher carrier concentration of 1.11 × 1021cm−3, high mobility of 14.07 cm2V−1s−1 and lower sheet resistance of 7.39Ω/sq. Moreover, a wide band gap of 3.87 eV is obtained for MGZO thin films, and the performance of a Cu2ZnSn(S, Se)4 (CZTSSe) photovoltaic device fabricated with a MGZO TCO layer is improved owing to higher band gap and outstanding electronic properties. The improved short circuit current results in a device with a MGZO thin film with a power conversion efficiency of 8.79%.

The doping of Mg and Ga into ZnO is a method for obtaining excellent optical and electrical properties for a window layer in an inorganic solar cell. Because a tradeoff exists between the electrical and optical properties in the window layer, balancing them is important for enhancing the performance of the solar cells. From this viewpoint, the thickness change of the window layer affects the transmittance and the conductivity. In particular, it affects the transmittance in the NIR-IR region significantly, which can enhance the current collection but lead to poor conductivity when the transmittance of the window layer is increased. We examine the thickness effect of MGZO films for CZTSSe solar cells in order to determine the optimal conversion efficiency. The enhanced transmittance in the NIR-IR region with a thin MGZO layer contributed to a high current density, although the electrical resistivity was relatively high. An enhanced conversion efficiency of 7.54% was eventually recorded for an optimal thickness of the MGZO layer with an improved current density over 7 mA/cm2.

Light-emitting diodes (LEDs), which emit efficient and bright light ranging from infrared to ultraviolet, have been adopted in various fields to improve quality of life. In particular, micro-LEDs, which are III–V inorganic-based micro-miniaturized light sources, which can form clear and vivid displays for smart portable devices and can be used with artificial intelligence, are drawing great attention. The micro-LEDs can be used in applications where it is difficult to use existing inorganic LEDs, such as in medicine, clothing, and miniature electronics. Research on developing micro-LEDs is underway around the world as the demand for micro-miniaturized light sources increases, especially for display applications. However, problems are also emerging that hinder the mass production of micro-LED displays. Herein, we introduce the current research trends and issues involved in overcoming various problems associated with using micro-LEDs as full-color light sources in display applications. We also briefly review newly presented research and development strategies and technologies for micro-LEDs by research institutes and companies, including their patents and products.

Recently, microLED-based displays have been steadily developing and one of the technologies, the “RGB LED array monolithic integration” technology, has considerable prospects. This chapter introduces device manufacturing methods using only semiconductor patterning processes after bonding of red, green, and blue LEDs. These technologies are suitable for high-resolution applications such as AR/VR where it is hard to use a pick-and-place method. Here, various bonding technologies for color integration are reported: substrate bonding for two colors by wafer stacking, a method that realizes full color by combining a selective area growth method and a bonding technology, and a method that realizes full color using only a bonding technology. We also propose integration technologies using a monolithic 3D(M3D)-like process for high-resolution displays. We demonstrate ultra-high-resolution stacked LEDs exceeding 60,000 PPI estimated from their pattern size. Furthermore, we demonstrate one transistor-one photodiode M3D integration that has a clear readout operation without any degradation of the bottom Si devices after the integration process.

It is well‐known that the alkali doping of polycrystalline Cu2ZnSn(S,Se)4 (CZTSSe) and Cu(In,Ga)(Se,S)2 has a beneficial influence on the device performance and there are various hypotheses about the principles of performance improvement. This work clearly explains the effect of Na doping on the fill factor (FF) rather than on all of the solar cell parameters (open‐circuit voltage, FF, and sometimes short circuit current) for overall performance improvement. When doping is optimized, the fabricated device shows sufficient built‐in potential and selects a better carrier transport path by the high potential difference between the intragrains and the grain boundaries. On the other hand, when doping is excessive, the device shows low contact potential difference and FF and selects a worse carrier transport path even though the built‐in potential becomes stronger. The fabricated CZTSSe solar cell on a flexible metal foil optimized with a 25 nm thick NaF doping layer achieves an FF of 62.63%, thereby clearly showing the enhancing effect of Na doping.

In this study, we proposed a strategy to fabricate vertically stacked subpixel (VSS) micro-light-emitting diodes (μ-LEDs) for future ultrahigh-resolution microdisplays. At first, to vertically stack the LED with different colors, we successfully adopted a bonding-interface-engineered monolithic integration method using SiO2/SiNx distributed Bragg reflectors (DBRs). It was found that an intermediate DBR structure could be used as the bonding layer and color filter, which could reflect and transmit desired wavelengths through the bonding interface. Furthermore, the optically pumped μ-LED array with a pitch of 0.4 μm corresponding to the ultrahigh-resolution of 63 500 PPI could be successfully fabricated using a typical semiconductor process, including electron-beam lithography. Compared with the pick-and-place strategy (limited by machine alignment accuracy), the proposed strategy leads to the fabrication of significantly improved high-density μ-LEDs. Finally, we systematically investigated the effects of surface traps using time-resolved photoluminescence (TRPL) and two-dimensional simulations. The obtained results clearly demonstrated that performance improvements could be possible by employing optimal passivation techniques by diminishing the pixel size for fabricating low-power and highly efficient microdisplays.

Recently, researches on the micro-displays using inorganic LEDs have stirred much attentions due to its various advantages such as reduced power consumption, long life time and short response time. In this study, we achieved a full-color integration of LEDs for display applications by combining growth and bonding technologies with two different approaches. First method was integrating inorganic red, green, and blue LEDs on a single substrate using metalorganic chemical vapor deposition and thin film bonding techniques. Second method was fabricating inorganic red, green, and blue LEDs by using GaN-on-Si-based blue LEDs and adhesive bonding.

Deep ultraviolet light-emitting diodes (DUV LEDs) (

As the size of micro light-emitting diodes ( μLEDs) decreases, μLEDs encounter etching damage especially at the sidewalls that critically affects their properties. In this study, we investigated the influence of etching bias power ( Pbias) on the performance of μLEDs and found that the current–voltage and light output–current characteristics of μLEDs were enhanced when Pbias was reduced. It was shown that at low Pbias, the chemical reaction between etching gas and gallium nitride, rather than ion sputtering, dominated the etching process, leading to low plasma damage and rough surface morphology. Additionally, to understand the etching-induced surface roughening behaviors, various substrates with different threading dislocation densities were treated at low Pbias. It was found that for the sample (with p-contact size of 10 × 10 μm2), the efficiency droop was approximately 20%, although the current reached 10 mA due most probably to the suppressed polarization effect in the quantum well. It was further observed that the external quantum efficiency (EQE) was dependent on Pbias, where the lowest Pbias yielded the highest maximum EQE, indicating that the plasma damage was mitigated by reducing Pbias. Optimization of dry etching and polarization-suppression conditions could pave the way for realizing high-performance and brightness μLEDs for next-generation displays.

In recent years, research into implementing microdisplays for use in virtual reality and augmented reality has been actively conducted worldwide. Specifically, inorganic light-emitting diodes (LED)...

Rapid response systems (RRSs) have been introduced into hospitals to help reduce the incidence of sudden cardiopulmonary arrest (CPA). This study evaluated whether an RRS reduces the incidence of in-hospital postoperative CPA. This retrospective before-and-after analysis evaluated data collected from electronic medical records during a pre-intervention (January 2008 to September 2012) and post-intervention (implementation of an RRS) interval (October 2012 to December 2016) at a single tertiary care institution. The primary outcome was a change in the rate of CPA in surgical patients recovering in a general ward. A Poisson regression analysis adjusted for the Charlson Comorbidity Index (CCI) was used to compare CPA rates during these two intervals. Of the 207,054 surgical procedures performed during the study period, mean (95% confidence interval [CI]) CPA events per 10,000 cases of 7.46 (5.72 to 9.19) and 5.19 (3.85 to 6.52) were recorded before and after RRS intervention, respectively (relative risk [RR], 0.73; 97.5% CI, 0.48 to 1.13; P = 0.103). Cardiopulmonary arrest incidence was reduced during RRS operational hours of 07:00–22:00 Monday-Friday and 07:00–12:00 Saturday (RR, 0.56; 97.5% CI, 0.31 to 1.02; P = 0.027) but was unchanged when the RRS was not operational (RR, 0.86; 97.5% CI, 0.52 to 1.40; P = 0.534). The CCI-adjusted RR of CPA after RRS implementation was lower than before RRS intervention (0.63; 97.5% CI, 0.41 to 0.98; P = 0.018) but this reduction was still only apparent during RRS operational hours (RR, 0.48; 97.5% CI, 0.27 to 0.89; P = 0.008 vs RR, 0.85; 97.5% CI, 0.45 to 1.58; P = 0.55). Implementation of an RRS reduced the incidence of postoperative CPA in patients recovering in a general ward. Furthermore, this reduction was observed only during RRS operational hours.

Background The purpose of a rapid response system (RRS) is to reduce the incidence of preventable cardiopulmonary arrests (CPAs) and patient deterioration in general wards. The objective of this study is to investigate the incidence and temporal trends of preventable CPAs and determine factors associated with preventable CPAs in a hospital with a mature RRS. Methods This was a single-center prospective cohort study of all CPAs occurring in the general ward between March 2017 and June 2020. The RRS operates from 07:00 to 23:00 on weekdays and from 07:00 to 12:00 on Saturdays. All CPAs were reviewed upon biweekly conference, and a panel of intensivists judged their preventability. Trends of preventable CPAs were analyzed using Poisson regression models and factors associated with preventable CPAs were analyzed using multivariable logistic regression. Results There were 253 CPAs over 40 months, and 64 (25.3%) of these were preventable. The incidence rate of CPAs was 1.07 per 1000 admissions and that of preventable CPAs was 0.27 per 1000 admissions. The number of preventable CPAs decreased by 24% each year (incidence rate ratio = 0.76; p = 0.039) without a change in the total CPA incidence. The most common contributor to the preventability was delayed response from physicians (n = 41, 64.1%). A predictable CPA with a pre-alarm sign had increased odds in the occurrence of preventable CPAs, while a cardiac cause of CPAs and RRS operating hours had decreased odds in terms of occurrence of preventable CPA. Conclusion Our study showed that one-fourth of all CPAs occurring in the general wards were preventable, and these arrests decreased each year. A mature RRS can evolve to reduce preventable CPAs with regular self-evaluation. Efforts should be directed at improving physicians’ response time since a delay in their response was the most common cause of preventable CPAs.

Monolithic 3-D integration has emerged as a promising technological solution for traditional transistor scaling limitations and interconnection bottleneck. The challenge we must overcome is a processing temperature limit for top side devices in order to ensure proper performance of bottom side devices. To solve this problem, we developed a low temperature III-V and Ge layer stacking process using wafer bonding and epitaxial lift-off, since these materials can be processed at a low temperature and provide extended opportunity/functionality (sensor, display, analog, RF, etc.) via heterogeneous integration. In this paper, we discuss technology for integrating III-V and Ge materials and its applicability to CMOS, thin film photodiodes, mid-infrared photonics platforms, and MicroLED display integration for creating the ultimate 3-D chip of the future.

Ge alloyed Cu 2 SnS 3 (CTGS) thin films were prepared by annealing the sputtered deposited Cu-Ge-Sn precursor films under sulfur atmosphere at different annealing temperatures. The influence of different annealing temperatures on morphological, compositional, crystal structure of CTGS thin films were investigated. It was found that the annealing temperature of 550 °C provides a favorable sulfurization environment to promote grain growth leading to a compact thin film formation. Improved performance is ascribed to high Ge contents as evidenced from X-ray fluorescence (XRF) studies. Well incorporated Ge atoms into CTS thin film can be confirmed by X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) study provides an evidence of existence of Ge atoms where its binding energy located at 25.78 and 26.78 eV, respectively. However, the decreased performance was found at unsuitable annealing temperatures such as 500 °C, 520 °C, 580 °C and 600 °C. Finally, with annealing temperatures of 550 °C, the best power conversion efficiency (PCE) of 2.14% was attained with an open circuit voltage ( V oc ) of 220 mV, a short circuit current density ( J sc ) of 23.74 mA/cm 2 and a fill factor ( FF ) of 41%.

Monolithic 3-D integration has emerged as a promising technological solution for traditional transistor scaling limitations and interconnection bottleneck. The challenge we must overcome is a processing temperature limit for top side devices in order to ensure proper performance of bottom side devices. To solve this problem, we developed a low temperature III–V and Ge layer stacking process using wafer bonding and epitaxial lift-off, since these materials can be processed at a low temperature and provide extended opportunity/functionality (sensor, display, analog, RF, etc.) via heterogeneous integration. In this paper, we discuss technology for integrating III–V and Ge materials and its applicability to CMOS, thin film photodiodes, mid-infrared photonics platforms, and MicroLED display integration for creating the ultimate 3-D chip of the future.

Cu2ZnSn(S,Se)4 (CZTSSe) has attracted much attention as the absorption layer of photovoltaic devices because of its appropriate bandgap energy and low cost. However, CZTSSe solar cells have so far shown low power conversion efficiency compared to other solar cells and studies are being conducted to improve it. In this study, we achieved an improvement in the shunt resistance and power conversion efficiency (PCE) of CZTSSe solar cells with quantification of the effective thermal conductivity. A CZTSSe solar cell fabricated using a graphite box designed with high thermal conductivity exhibited a high shunt resistance of 413 Ω cm2 and a fill factor of 63.8%, and additionally, secondary phases such as Cu2S/Se and CuS/Se were not detected. On the other hand, a CZTSSe solar cell fabricated using a graphite box with low thermal conductivity showed a rougher surface and low shunt resistance mainly related to secondary phase formation. As a result, a PCE of 9.72% was achieved using a graphite box designed with high thermal conductivity.

In this study, highly efficient and flexible Na-doped kesterite Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells with an efficiency of over 8% were developed. A CZTSSe thin film was deposited on a flexible Mo foil using metal precursors with varying thickness of the NaF layers on the CZTSSe thin film. The sample maintained 92.2% of its performance after 1000 bending cycles with a bending radius of 12 mm. To investigate defect passivation effect of Na doping through the electrical properties of Na-passivated grain boundaries (GBs), the cells were examined by scanning probe microscopy. Downward band bending was observed at GBs in the Na-sufficient CZTSSe absorber layers; that is, Na enhanced the potential barrier at the CZTSSe GBs in the solar cells and the separation of carriers. The carrier separation increased under illuminated condition. Moreover, the surface photovoltage (SPV) of the cells was measured at laser wavelengths of 405, 532, and 640 nm using photo-assisted Kelvin probe force microscopy to investigate the photogenerated carrier transport in Na-passivated CZTSSe solar cells. The Na content strongly affected the photo-induced changes in the carrier behavior. A cell with a sufficiently Na-doped CZTSSe absorber layer exhibited a large SPV with a maximum value of 46 meV under illumination, whereas Na-deficient samples showed a lower SPV, indicating that Na passivates defects that act as recombination sites. A photo-induced defect passivation effect was observed in a cell with optimal Na content under 405 nm wavelength illuminated condition, which resulted in charge accumulation at the absorber surface.

We report the effects of precursor uniformity on the efficiency of Cu 2 ZnSnS x Se 4 − x (CZTSSe) solar cells using sputtered precursors. The reduction of Sn cluster agglomeration in the Cu/Sn/Zn stacked precursor created synthesis of more uniformly distributed CZTSSe absorbers during the annealing process. The secondary phase difference between the 80 W and 40 W sputtered CZTSSe absorbers was confirmed with Raman analysis at 178 cm − 1 and 259 cm − 1 . The 40 W sputtered CZTSSe cell produced blue region enhancement of external quantum efficiency results due to improvement of the pn-junction properties. The CZTSSe 40 W cells achieved a maximum power conversion efficiency of 5.7% and short-circuit current of 32.4 mA/cm 2 .

Severe melt-back etching has forced the epitaxy of GaN on Si to use an AlN buffer layer for growing high-quality two-dimensional layers, despite its high resistivity. Herein, we report a metal-based pre-orienting layer (POL) for growing GaN nanostructures (NSs) to replace the traditional AlN buffer layer. Two metals, titanium (Ti) and hafnium (Hf), were evaluated as POLs. We succeeded in fabricating arrays of GaN NSs with highly preferred orientation using selective-area growth. The crystallographic phase of the POLs critically affected the evolved orientation of the crystals. Photoluminescence measurements revealed that GaN NSs with Hf-based POLs were of reasonably high quality. We believe that this result will facilitate broader III-V semiconductor applications using alternative substrates moving beyond conventional Si-based optoelectronics.

As an alternative to Cu(In,Ga)(S,Se)2 (CIGS) and Cu2ZnSn(S,Se)4 (CZTS)-based thin film solar cells (TFSCs), the ternary chalcogenide semiconductor Cu2SnS3 (CTS) is an emerging material with suitable optical band gap energy ranging from 0.93 to 1.77 eV and high absorption coefficients (>104 cm−1). In this study, we report the preparation of high-quality CTS thin films by the annealing of the sputtered Cu-Sn metallic precursor under S vapor atmosphere in a graphite box using the RTA process. Furthermore, the influence of different S vapor partial pressures in the graphite box during annealing on the properties of the CTS thin films has been investigated systematically. It is observed that the properties and photovoltaic performance of the CTS thin films are strongly dependent on the S vapor partial pressure during annealing. The monoclinic crystal structure is observed from X-ray diffraction (XRD) of the (1 1 2), (2 2 0), and (3 1 2) planes, and it is further confirmed using Raman spectroscopy by the presence of Raman peaks at 295 and 354 cm−1. The direct band gap energy is found to be 0.91 eV by extrapolation from external quantum efficiency (EQE) measurement of a CTS thin film annealed using 60 mg of S powder. The preliminary best power conversion efficiency (PCE) of 2.21% with a short circuit current density of 29.7 mA/cm2, an open circuit voltage of 179.5 mV, and a fill factor of 41% have been obtained for a CTS thin film annealed using 60 mg of S powder, although the processing parameters have not been optimized.

The effect of magnetic fields on the optical output power of flip-chip light-emitting diodes (LEDs) with InGaN/GaN multiple quantum wells (MQWs) was investigated. Films and circular disks comprising ferromagnetic cobalt/platinum (Co/Pt) multilayers were deposited on a p-ohmic reflector to apply magnetic fields in the direction perpendicular to the MQWs of the LEDs. At an injection current of 20 mA, the ferromagnetic Co/Pt multilayer film increased the optical output power of the LED by 20% compared to an LED without a ferromagnetic Co/Pt multilayer. Furthermore, the optical output power of the LED with circular disks was 40% higher at 20 mA than the output of the LED with a film. The increase of the optical output power of the LEDs featuring ferromagnetic Co/Pt multilayers is attributed to the magnetic field gradient in the MQWs, which increases the carrier path in the MQWs. The time-resolved photoluminescence measurement indicates that the improvement of optical output power is owing to an enhanced radiative recombination rate of the carriers in the MQWs as a result of the magnetic field gradient from the ferromagnetic Co/Pt multilayer.

It is well‐known that the alkali doping of polycrystalline Cu2ZnSn(S,Se)4 (CZTSSe) and Cu(In,Ga)(Se,S)2 has a beneficial influence on the device performance and there are various hypotheses about the principles of performance improvement. This work clearly explains the effect of Na doping on the fill factor (FF) rather than on all of the solar cell parameters (open‐circuit voltage, FF, and sometimes short circuit current) for overall performance improvement. When doping is optimized, the fabricated device shows sufficient built‐in potential and selects a better carrier transport path by the high potential difference between the intragrains and the grain boundaries. On the other hand, when doping is excessive, the device shows low contact potential difference and FF and selects a worse carrier transport path even though the built‐in potential becomes stronger. The fabricated CZTSSe solar cell on a flexible metal foil optimized with a 25 nm thick NaF doping layer achieves an FF of 62.63%, thereby clearly showing the enhancing effect of Na doping., The effects of Na doping on polycrystalline flexible Cu2ZnSn(S,Se)4 (CZTSSe) solar cells are analyzed. When doping is excessive, the device shows low contact potential difference and fill factor and selects a worse carrier transport path even though the built‐in potential becomes stronger. On the other hand, the optimized CZTSSe solar cell clearly shows the enhancing effect of Na doping.

Transparent electrodes are often regarded as a trade-off between transmittance and sheet resistance, although the effect of thin-film interference on the performance of an optoelectronic device is significant. In this paper, we report the effect of optical thin-film interference of an Al-doped ZnO (AZO) transparent electrode on the performance of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. First, we distinguished the transmittance in the overall wavelength region (450–800 nm) of the AZO transparent electrode from the transmittance in the maximum absorption region for CZTSSe solar cells (550–700 nm). From the results, a thicker AZO transparent electrode showed higher transmittance (87.1%) than that of a thinner AZO transparent electrode (82.9%) in the maximum absorption region. These electrodes were applied in CZTSSe solar cells, which showed a difference of up to 26% in power conversion efficiency. In addition, the colors generated by the optical interference between the AZO transparent electrodes. We anticipate that our results will be useful for improving the performance and/or color tuning of thin-film solar cells for application in building-integrated photovoltaics.

We report on a method for controlling the polarity of gallium nitride (GaN) using an E-beam evaporated aluminum (Al) layer on a sapphire substrate. A high-temperature nitridation process was designed to enable the amorphous Al layer to serve as a nucleation layer for single-crystal Ga-polar GaN growth. The Al layer also acts as a mask that prevents N-polar GaN growth. As a result, Ga-polar and N-polar GaN can be grown on the Al layer and sapphire surface, respectively. This method is not only advantageous for the selective polarity control but also to simplify the fabrication process of lateral polarity structures.

Highly crystallized Cu 2 SnS 3 (CTS) thin films are synthesized by sputtering based deposition route. Further, Influence of different annealing temperatures on crystallographic, electrical and optical properties of CTS thin films have been investigated. The synthesized CTS thin films are grown as a monoclinic structure observed from X-ray diffraction (XRD) of (112), (220), and (312) plane and it is further confirmed using Raman spectroscopy by the presence of Raman peaks at 295 and 354 cm −1 . The direct band gap energy of CTS thin film annealed at 580 °C is found to be 1.03 eV by extrapolation from external quantum efficiency (EQE) measurement. An X-ray photoelectron spectroscopy (XPS) study suggests that the ionic states of Cu, Sn, and S are Cu + ,Sn 4+ , and S 2− , respectively. The CTS based thin film solar cells (TFSCs) are fabricated with a structure of Mo/CTS/CdS/i-ZnO/AZO/Al. The preliminary power conversion efficiency of 1.35% with a short circuit current density of 28.3 mA/cm 2 , an open circuit voltage of 147.5 mV, and a fill factor of 32% were obtained, although the processing parameters have not yet been optimized.

We have demonstrated the effect of p-GaN hole concentration on a graphene current spreading layer (CSL) for stabilization and improved performance of a near-ultraviolet light-emitting diode (NUV LED). While NUV LEDs with a more lightly-doped p-GaN showed poor electrical and optical properties and unstable performance, NUV LEDs with more heavily-doped p-GaN (∼2 × 1017 cm−3) showed very stable, outstanding performance. The main factor of the improvement was the enhanced contact property between the graphene CSLs and the p-GaN that resulted from the increase of the hole concentration, which led to a thinner barrier and an enhanced current injection. From our results, we were able to determine that hole concentration as heavy as 2 × 1017 cm−3 in p-GaN layers is a primary condition in NUV LEDs with graphene-based CSLs.