[en] Cu₂ZnSnS₄ (CZTS) thin films with kesterite structures were prepared by directly sol-gel synthesizing spin-coated precursors on soda-lime-glass (SLG) substrates. The CZTS precursors were prepared by using solutions of copper (II) chloride, zinc (II) chloride, tin (IV) chloride, and thiourea. The ratio of SnCl₄ in the precursors was found to play a critical role in the synthesization of CZTS. CZTS phases of SnS and SnS₂ were observed in the synthesized films as prepared using precursors with a close to stoichiometric ratio of CuCl₂:ZnCl₂:SnCl₄:CH₄N₂S = 4:1:1:8, where SnCl₄ was 1 mol/l. The amounts of the educed SnS and SnS₂ phases observed in the SEM images could be readily reduced by decreasing the volume of SnCl₄ in the mixed solution. With decreasing amount of SnCl₄ from 1 mol/l, the as prepared CZTS reveals a significant improvement in its crystalline properties. In this work, CZTS with an average absorption coefficient and an optical energy gap of over 10⁴ cm^-1 and ∼1.5 eV, respectively, was obtained using precursors of copper (II) chloride, zinc (II) chloride, tin (IV) chloride, and thiourea mixed in a ratio of 2:1:0.25:8, and it had good crystallinity revealing a Cu-poor composition.

[en] Metal induced crystallization (MIC) can be generated by using a silver nanoparticles (AgNPs) solution spin coated on amorphous silicon (a-Si) film, and annealing the sample in a furnace under vacuum. Because nanoscale metal has a large specific surface area, its catalytic effect is enhanced, resulting in a low processing temperature. Thus, a poly-Si thin film with a high crystalline fraction can be obtained by using AgNPs induced crystallization. In this study, the size and annealing time of AgNPs are discussed. According to the results, the grain size of the poly-Si thin film produced using AgNPs induced crystallization was more uniform than that of the film obtained by employing traditional thermally evaporated Ag induced crystallization. Smaller AgNPs size and long annealing time enhance the crystallization of poly-Si thin film. Applying an annealing temperature of 550 °C for 480 min with 10 nm of AgNPs yielded a crystalline fraction of 75%. (paper)

[en] Flip-chip (FC) aluminum gallium indium phosphide (AlGaInP) mini light-emitting diodes (mLEDs) with p and n lateral electrode structures and a larger light-emitting area have significant potential for integrating red, green, and blue mLEDs of locally dimmable zones for developing new-generation LED-backlit liquid crystal displays. Herein, an FC AlGaInP mLED having 9 × 6 mil dimensions is fabricated using wafer bonding and transfer technology methods. We propose a patterned n-gallium-arsenide (GaAs) epilayer by etching for ohmic contact and optimizing the specific contact resistance of an FC mLED. The light-output intensity images demonstrated that this etching process improved the uniformity of current distribution and matched the simulation results. Compared with conventional FC mLEDs, the output powers of FC mLEDs with a patterned n-GaAs layer increased from 3.4% to 4.5% and the wall-plug efficiency improved by 1.04%. Moreover, Ag was applied as a reflector on patterned n-GaAs rather than AuGe. The output power of FC mLEDs with an Ag reflector showed a 3.5%–8.2% improvement over FC mLEDs with an AuGe reflector. Finally, FC mLEDs that were encapsulated with epoxy and far-field radiation patterns indicated that packaged FC mLEDs had a smaller divergence angle and narrower viewing angle. (paper)

[en] An n-side up-type AlGaInP multiple-quantum-well light-emitting diode (LED) has been developed by texturing the current spreading layer utilizing photolithography followed by an anisotropic etching process over n-AlGaInP grown by metalorganic chemical vapor deposition. The GaP-ITO-Ag omni-directional reflective LEDs with the wavelike textured surfaces provide a reasonable improvement in light output power and efficiency over the corresponding conventional structures. The luminous intensity of the surface-textured LED is 1.46 times greater than that of the conventional LED in the normal direction. The output power (at 350 mA) of the surface-textured LED is increased approximately 40% as compared with that of the conventional LED. Additionally, the optical simulation also presents a tendency towards the ray extraction ratio as the size of the wavelike hole changes, confirming a proper formation of pattern size associated with the fabrication process

[en] In this article, Ga-doped Al-zinc-oxide (GAZO)/titanium-doped indium-tin-oxide (ITIO) bi-layer films were deposited onto glass substrates by direct current (dc) magnetron sputtering. The bottom ITIO film, with a thickness of 200 nm, was sputtered onto the glass substrate. The ITIO film was post-annealed at 350 deg. C for 10-120 min as a seed layer. The effect of post-annealing conditions on the morphologies, electrical, and optical properties of ITIO films was investigated. A GAZO layer with a thickness of 1200 nm was continuously sputtered onto the ITIO bottom layer. The results show that the properties of the GAZO/ITIO films were strongly dependent on the post-annealed conditions. The spectral haze (T_diffuse/T_total) of the GAZO/ITIO bi-layer films increases upon increasing the post-annealing time. The haze and resistivity of the GAZO/ITIO bi-layer films were improved with the post-annealed process. After optimizing the deposition and annealing parameters, the GAZO/ITIO bi-layer film has an average transmittance of 83.20% at the 400-800 nm wavelengths, a maximum haze of 16%, and the lowest resistivity of 1.04 x 10^-3Ω cm. Finally, the GAZO/ITIO bi-layer films, as a front electrode for silicon-based thin film solar cells, obtained a maximum efficiency of 7.10%. These encouraging experimental results have potential applications in GAZO/ITIO bi-layer film deposition by in-line sputtering without the wet-etching process and enable the production of highly efficient, low-cost thin film solar cells.

[en] Highlights: • Al-doped ZnGa₂O₄ (ZGO) films were successfully prepared by co-sputtering. • High crystallinity along with excellent optical properties was achieved. • Deep-ultraviolet photodetectors (PD) fabricated with Al-doped ZGO films have been studied. • Al-doped ZGO PD exhibited remarkably high responsivity of 3.01 A/W at low bias of 3 V under the incident light of 220 nm. Al-doped ZnGa₂O₄ (ZGO) films were deposited on c-plane sapphire substrates by co-sputtering of Al and ZGO targets at a substrate temperature of 400 ℃ and thermally annealed at 800 ℃ to enhance their crystalline quality. In this investigation, the DC power for metallic Al target was varied from 0 to 50 W and its effect on structural, optical, and optoelectronic properties of these films were investigated. After annealing, all films exhibited the crystalline nature with the ZGO phase. Further, this investigation revealed that the 800 ℃ annealed Al-doped ZGO film deposited with the 20 W DC power possessed the highest crystalline quality among other films along with the wide-bandgap of 5.18 eV. The X-ray photoemission spectrum measurements revealed from the Ga 2p_3/2 and Al 2p core-level spectra that the Al atoms occupy the octahedral sites, which makes Al–O–Ga bonding in the ZGO network. The metal–semiconductor-metal photodetector with this annealed 20 W Al-doped ZGO film exhibited the photocurrent to the dark current ratio of 3.35 × 10⁴ and high responsivity of 3.01 A/W (at 3 V and 220 nm), which shows the enhancement in device performance about 12 times when compared with that of annealed 0 W Al-doped ZGO photodetector.

[en] High-frequency plasma-enhanced chemical vapor deposition (HF-PECVD) is a widely applicable method of deposition over a large area at a high rate for fabricating silicon thin-film solar cells. This investigation presents the properties of hydrogenated amorphous silicon (a-Si:H) films and the preparation of highly-efficient p-i-n solar cells using an RF (27.1 MHz) excitation frequency. The influence of the power (10-40 W) and pressure (20-50 Pa) used during the deposition of absorber layers in p-i-n solar cells on the properties and mechanism of growth of the a-Si:H thin films and the solar cells is studied. The a-Si:H thin films prepared under various deposition conditions have widely varying deposition rates, optical-electronic properties and microstructures. When the deposition parameters were optimized, amorphous silicon-based thin-film silicon solar cells with efficiency of 7.6% were fabricated by HF-PECVD. These results are very encouraging for the future fabrication of highly-efficient thin-film solar cells by HF-PECVD.

[en] A barrier structure consisting of silicon oxide and silicon nitride films was deposited via plasma-enhanced chemical vapor deposition (PECVD) for the encapsulation of polymer solar cells (PSCs). The total concentration of the solution and the ratio of P3HT and PCBM on the performance of polymer solar cells were studied by UV-Vis absorption spectroscopy, atomic force microscopy and photocurrent measurement. Base on these measurements, there is a compromise between light absorption and phase separation with increasing blend concentration. The PSCs were annealed at 80, 100, 120 and 140 ^oC for 10-60 min to investigate the thermal effects and to estimate the best deposition temperature of the barrier layers. Nevertheless, the devices with the encapsulation of barrier layers had relatively low power conversion efficiencies (PCE) of 0.98% comparing to the devices heated in the PECVD system (1.57%) at the same condition of 80 ^oC for 45 min due to the plasma damage during the film deposition process. After inserting a 5-nm TiO_x layer between Al/barrier structure and active layer against the plasma damage, the annealed devices presented an average PCE of 2.26% and demonstrated over 50% of their initial value after constant exposure to ambient atmosphere and sunlight for 1500 h.

[en] GaN-based resonant-cavity light-emitting diodes (RCLEDs) have been fabricated on Si substrates with a current confinement by hydrogen (H) implantation. In order to ascertain the optimum implantation concentration for the current confinement layer of RCLEDs, the effects of implantation concentration (as-grown, 10¹³, 10¹⁴ and 10¹⁵ ions cm⁻²) on the characteristics of a p-GaN cladding layer were investigated in terms of Hall measurements, photoluminescence (PL) spectra and x-ray (XRD) diffraction. The properties of PL, XRD and contact resistance of the epi-LED wafers with different implantation concentrations were also analyzed. An optimum H-implantation concentration of 10¹⁴ ions cm⁻² has been determined based on the current confinement performance. Under this condition, the 10¹⁴ ions cm⁻² implanted RCLED sample shows the higher electroluminescence intensity than that of the SiO₂-insulated RCLED one. Furthermore, the light emission pattern of the 10¹⁴ ions cm⁻² implanted RCLED also shows a superior directionality. The improved results could be attributed to the better current and photon confinements laterally in the light aperture

[en] The 120-nm-thick cobalt-doped ZnO (Co-doped ZnO, CZO) dilute magnetic films deposited by pulsed laser deposition were employed as the n-electrodes for both lateral-type blue (450 nm) and green (520 nm) InGaN light emitters. In comparison to the conventional blue and green emitters, there were 15.9% and 17.7% enhancements in the output power (@350 mA) after fabricating the CZO n-electrode on the n-GaN layer. Observations on the role of CZO n-electrodes in efficiency improvement of InGaN light emitters were performed. Based on the results of Hall measurements, the carrier mobilities were 176 and 141 cm"2/V s when the electrons passed through the n-GaN and the patterned-CZO/n-GaN, respectively. By incorporating the CZO n-electrode into the InGaN light emitters, the electrons would be scattered because of the collisions between the magnetic atoms and the electrons as the device is driven, leading to the reduction of the electron mobility. Therefore, the excessively large mobility difference between electron and hole carriers occurred in the conventional InGaN light emitter can be efficiently decreased after preparing the CZO n-electrode on the n-GaN layer, resulting in the increment of carrier recombination rate and the improvement of light output power.