CdSeTe solar-cell performance with different dopant types

Effect of device geometry on the performance of TiO2 nanotube array-organic semiconductor double heterojunction solar cells

Study on dynamic properties of the photoexcited charge carriers at anatase TiO2 nanowires/fluorine doped tin oxide interface

In recent years, Ga2O3/GaN heterojunction ultraviolet photodetectors (PDs) have garnered considerable interest for ultraviolet (UV) communication, high-resolution imaging, and multiband photodetection. However, commercialization has been constrained by high wafer costs and simplistic device designs. This study investigates the growth of high-quality β-Ga2O3 films on silicon-based GaN substrates using RF magnetron sputtering by varying the growth temperatures and annealing conditions. Three device structures with ring-type, standard, and composite interdigitated electrodes were developed. The utilization of small interdigitated electrode spacing combined with an extended carrier collection length provides distinct advantages in terms of responsivity, detectivity, and response speed under self-powered conditions. Under 254 nm frontside illumination, the PDs exhibited a high responsivity of 9.18 mA/W and a detectivity of 7.71 × 1010 Jones, while 365 nm illumination yielded a responsivity of -2.99 mA/W and a detectivity of 2.51 × 1010 Jones. To further enhance detection capabilities, we removed the backside Si substrate, producing suspended membrane p-n junction PDs, enabling dual-sided detection and current polarity reversal under different UV wavelengths. After elucidating the relevant carrier transport mechanisms, a UV communication system was established using the ring-type interdigitated electrode PD. This system achieved a maximum transmission rate of 40 kbps for on-off keying modulated pseudorandom binary sequence signals under 254 nm frontside illumination and 30 kbps under 365 nm backside illumination. These results demonstrate the significant potential of Ga2O3/GaN p-n junction PDs for UV communication applications.

A step forward on NETmix reactor for heterogeneous photocatalysis: Kinetic modeling of As(III) oxidation

This paper presents the optical response of the DC and the RF (C-Band) performance of a 1 /spl mu/m gate length epitaxial lift-off PHEMT device under backside illumination. The device when biased near pinch off exhibited an increase of S/sub 21/, G/sub max/, and g/sub m/ of 1.2 dB, 2 dB, and 56%, respectively. The measured responsivity was as high as 13.4 A/W with a quantum efficiency of 2300 percent. These results far exceeded previously reported performances for devices under frontside illumination. >

Single-photon avalanche diodes (SPADs), integrated in CMOS technology, offer high-gain detection of low-intensity optical signals. SPADs are widely adopted in imaging systems, including both 2D and 3D depth sensing. As SPAD arrays scale to higher resolutions, backside illumination (BSI) is one approach to improving fill factor (FF) and routing, though it increases fabrication complexity. Alternatively, in frontside illumination (FSI), the integration of circuitry within the pixel area results in a significant reduction of the FF. Thus, this brief proposes an external counter architecture with a photon event summing and coincidence detection scheme. Unlike conventional FSI designs, it preserves FF and improves routing efficiency, which facilitates scalability. This architecture is well suited for SPAD-based imaging and 3D sensing, which require high pixel resolution and compact signal integration.

The present work describes the study and improvement of the Epitaxial Lift‐Off (ELO) technique, which is used to separate III/V device structures from their GaAs substrates. As a result the ELO method, initially able to separate millimetre sized GaAs layers with a lateral etch rate of about 0.3 mm/h, has been developed to a process capable to free entire 2″ epitaxial structures from their substrates with etch rates up to 30 mm/h. It is shown that with the right deposition and ELO strategy, the thin‐film III/V structures can be adequately processed on both sides. In this way semi‐transparent, bifacial solar cells on glass were produced with a total area efficiency in excess of 20% upon front side illumination and more than 15% upon back side illumination. The cell characteristics indicate that, once the thin film processing has been optimized, ELO cells require a significantly thinner base layer than regular III/V cells on a GaAs substrate and at the same time have the potential to reach a higher efficiency. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work, TiO2 nanotube was prepared by rapid breakdown electrooxidation of Ti foil in electrolyte containing 0.15 M HClO4. The obtained TiO2 nanotube bundling powder was calcinated at 450°C for 3 hours, then characterized by SEM, XRD, UV-Vis DRS, and BET. Zinc-porphyrin-imide dyes was deposited into TiO2 nanotube by immersion of TiO2 nanotube in zinc-porphyrin-imide solution for 24 hours. Free zinc-porphyrin-imide dyes shows characteristics of absorption spectra in visible region at 439 nm and 620 nm. Meanwhile, when it was immobilized to TiO2-nanotube, the absorption peak shifted to 421 nm and 640 nm. The zinc-porphyrin-imide/TiO2 electrode showed an excellent response toward the visible light with the typical photocurrent density of 1.1 mA/cm2. When the fabricated photoelectrode was assembled in a typical Dyes Sensitize Solar Cell (DSSC), the I-V curve showed photoconversion efficiency of the assembled zinc-porphyrin-imide/TiO2 DSSC was 1.914% (front side illumination) and 1.147% (backside illumination), respectively.

This paper presents N-well Schottky diodes for high speed optical detection in 28nm CMOS technology. These diodes enable fully integrated CMOS optical receivers suited for the 850, 1310 and 1550nm telecommunication bands. The measured 1310 and 1550nm DC responsivity is 0.71mA/W and 0.16mA/W respectively at 1.5V reverse bias when backside illumination is performed while the 850nm responsivity is 0.27mA/W at the same biasing when frontside illumination is done. This is the first reported CMOS photodetector demonstrated at these three wavelengths. The measured capacitance-to-area ratio at zero bias is 1.7mF/m2.

Image sensors have become ubiquitous, appearing in cellular phones, car sensors, notebook webcams, digital cameras, video camcorders, and security & surveillance systems. CMOS image sensors gave birth to the low-cost, high-volume camera phone market and are being adopted for various high-end applications. The backside illumination technique has significant advantages over the front-side illumination on account of separating the optical path from the high density metal interconnects. Wafer bonding plays a key role in manufacturing backside illuminated sensors. The cost-effective integration of miniaturized cameras in various handheld devices becomes a reality through the introduction of CMOS image sensor modules manufactured with wafer-level processing and integration techniques. In order to realize cost-effective manufacturing of CMOS image sensor modules or camera modules, we developed various technologies enabling wafer-level processing and integration, such as (a) wafer-to-wafer permanent bonding with oxide or polymer layers for manufacturing backside illuminated sensor wafers, (b) wafer-level lens molding and stacking based on UV imprint lithography for making wafer-level optics, (c) conformal coating of various photoresists within high aspect ratio through-silicon vias, and (d) backside lithography for various metallization processes in wafer-level packaging. Those techniques improve the electrical and optical aspects of devices as well as the module manufacturability, and thus pave the way to the future growth of the digital imaging industry.

Herein, ultrathin Al2O3 is investigated as a rear interface passivation layer for kesterite solar cells with F:SnO2 (FTO) back contact for potential performance improvement. On the passivation layer, a thin Mo layer is deposited to improve the FTO's ohmicity. Further, NaF is evaporated on the copper zinc tin sulfide (CZTS) precursors to create openings at the passivation layer and achieve Na‐induced benefits in the absorber. The CZTS absorbers deposited directly on the Al2O3‐coated FTO peel off, while those with Mo interlayer do not. For pure sulfide kesterite devices, the Al2O3 layer reduces the short‐circuit current density (JSC), resulting in poor device efficiency. On the other hand, significantly higher JSC is realized for mixed sulfide and selenide kesterite devices with Al2O3 passivation layer, with the current density–voltage curve suggesting a reduced barrier height at the rear interface. As a result, the efficiency is improved from 1.5% for devices without Al2O3 to 4.6% for those with Al2O3. Likewise, improved external quantum efficiency response is observed in the devices with passivation layer for backside and frontside illumination. Therefore, contribution of Al2O3 passivation layer to the performance of kesterite‐based solar cells is evident from the results of this study.

A non-contact lifetime screening technique for measuring excess carrier lifetime in HgCdTe (MCT) using transient millimetre-wave reflectance (TMR) is presented. The TMR system described is capable of measuring lifetimes ranging from <or approximately=10 ns found in high-doped (>or approximately=1*1016 cm-3) p-type material to >1 mu s found in low-doped (<or approximately=1*1015 cm-3) n-type material. In TMR the reflected 90 GHz millimetre-wave (mm-wave) signal is proportional to a transient change in photoconductivity induced by a short (1.06 mu m) YAG laser pulse. The details of the TMR test system including the mm-wave circuit design are described. The system uses a computer controller for 80-300 K temperature control, x-y wafer translation and data acquisition and analysis. The TMR technique is shown to be equivalent to standard photoconductive decay. Applications of the technique, including MCT epilayer characterization by both frontside and backside illumination and in-process wafer characterization, are discussed. Spatial mapping of lifetime over an MCT wafer is demonstrated.

Toward improving the performance of Cu2ZnSnS4-based solar cells with Zr, W or sulfurized layers at the SnO2:F/Cu2ZnSnS4 rear interface

High-efficiency CdTe-based thin-film solar cells with unltrathin CdS:O window layer and processes with post annealing

Isotype bifacial silicon solar cells obtained by ITO spray pyrolysis