Recent research results pertaining to InN, GaN and AlN are reviewed, focusing on the different growth techniques of Group III-nitride crystals and epitaxial films, heterostructures and devices. The chemical and thermal stability of epitaxial nitride films is discussed in relation to the problems of deposition processes and the advantages for applications in high-power and high-temperature devices. The development of growth methods like metalorganic chemical vapour deposition and plasma-induced molecular beam epitaxy has resulted in remarkable improvements in the structural, optical and electrical properties. New developments in precursor chemistry, plasma-based nitrogen sources, substrates, the growth of nucleation layers and selective growth are covered. Deposition conditions and methods used to grow alloys for optical bandgap and lattice engineering are introduced. The review is concluded with a description of recent Group III-nitride semiconductor devices such as bright blue and white light-emitting diodes, the first blue-emitting laser, high-power transistors, and a discussion of further applications in surface acoustic wave devices and sensors.

https://iopscience.iop.org/article/10.1088/0022-3727/31/20/001/pdf

Growth and applications of Group III-nitrides

Low cost photovoltaic modules based on dye sensitized nanocrystalline titanium dioxide and carbon powder

TCO and light trapping in silicon thin film solar cells

A new record conversion efficiency of 24.7% was attained at the research level by using a heterojunction with intrinsic thin-layer structure of practical size (101.8 cm2, total area) at a 98-μm thickness. This is a world height record for any crystalline silicon-based solar cell of practical size (100 cm2 and above). Since we announced our former record of 23.7%, we have continued to reduce recombination losses at the hetero interface between a-Si and c-Si along with cutting down resistive losses by improving the silver paste with lower resistivity and optimization of the thicknesses in a-Si layers. Using a new technology that enables the formation of a-Si layer of even higher quality on the c-Si substrate, while limiting damage to the surface of the substrate, the Voc has been improved from 0.745 to 0.750 V. We also succeeded in improving the fill factor from 0.809 to 0.832.

24.7% Record Efficiency HIT Solar Cell on Thin Silicon Wafer

With a global market share of about 90%, crystalline silicon is by far the most important photovoltaic technology today. This article reviews the dynamic field of crystalline silicon photovoltaics from a device-engineering perspective. First, it discusses key factors responsible for the success of the classic dopant-diffused silicon homojunction solar cell. Next it analyzes two archetypal high-efficiency device architectures – the interdigitated back-contact silicon cell and the silicon heterojunction cell – both of which have demonstrated power conversion efficiencies greater than 25%. Last, it gives an up-to-date summary of promising recent pathways for further efficiency improvements and cost reduction employing novel carrier-selective passivating contact schemes, as well as tandem multi-junction architectures, in particular those that combine silicon absorbers with organic–inorganic perovskite materials.

/pdf/high-efficiency-crystalline-silicon-solar-cells-status-and-47y1w8zg6w.pdf

High-efficiency crystalline silicon solar cells: status and perspectives

A new type of a-Si/c-Si heterojunction solar cell, called the HIT (Heterojunction with Intrinsic Thin-layer) solar cell, has been developed based on ACJ (Artificially Constructed Junction) technology. A conversion efficiency of more than 18% has been achieved, which is the highest ever value for solar cells in which the junction was fabricated at a low temperature (<200°C).

https://iopscience.iop.org/article/10.1143/JJAP.31.3518/pdf

Development of New a-Si/c-Si Heterojunction Solar Cells: ACJ-HIT (Artificially Constructed Junction-Heterojunction with Intrinsic Thin-Layer)

A new method to determine the optical absorption coefficient (α) of thin films is presented. α of hydrogenated amorphous silicon (a-Si:H) based alloys can be accurately determined from transmittance (T) and reflectance (R) by using T/(1-R), which almost completely eliminates disturbance from the optical interference effect. The method is applicable to any thin films, as long as the film is a single layer. Based on the interference-free α, various methods to determine the optical gap (EOPT) of a-Si:H, a-SiC:H, and a-SiGe:H films are discussed. The (nαhν)1/3 plot and the (αhν)1/3 plot are most suitable for characterizing these films. The well-known (αhν)1/2 plot is less suited for detailed discussion of the EOPT than the cube root plot, because the plot includes a large ambiguity in the EOPT. The effect of the optical interference effect on the determination of the EOPT is also discussed.

https://iopscience.iop.org/article/10.1143/JJAP.30.1008/pdf

Interference-Free Determination of the Optical Absorption Coefficient and the Optical Gap of Amorphous Silicon Thin Films

An aperture-area conversion efficiency of 20.0% (intrinsic efficiency: 21.0%) has been achieved for a 1.0 cm/sup 2/ CZ n-type single crystalline silicon (c-Si) solar cell, by using the "HIT (heterojunction with intrinsic thin-layer)" structure on both sides of the cell. This is the world's highest value for a c-Si solar cell in which the junction is fabricated at a low temperature of below 200/spl deg/C. In this paper, the junction fabrication technologies and features of the HIT structure are reviewed. The stability under light and thermal exposure, and the temperature dependence on performance of a high-efficiency HIT solar cell are also reported.

High-efficiency a-Si/c-Si heterojunction solar cell

By both numerical simulation and experimental investigation, we found it possible to enlarge the grain size (?3000 ?) of polycrystalline silicon (poly-Si) films by excimer laser annealing, using a new method to control the solidification process of molten Si - low-temperature (?400?C) substrate heating during laser annealing. Poly-Si thin-film transistors (TFTs) fabricated by this new excimer laser annealing method showed a high field-effect mobility of 230 cm2/V?s, and good uniformity of field-effect mobility (?10%) within the effective laser irradiation area.

https://iopscience.iop.org/article/10.1143/JJAP.30.3700/pdf

Enlargement of Poly-Si Film Grain Size by Excimer Laser Annealing and Its Application to High-Performance Poly-Si Thin Film Transistor

C-axis oriented aluminum nitride (AlN) thin films on (110) silicon were prepared by reactive RF magnetron sputtering in argon and nitrogen atmosphere without substrate heating. We investigated the dependence of some properties for the AlN thin film on sputtering conditions, especially N2 concentration. It was found that c-axis orientation tended to improve gradually with decreasing N2 concentration. The full width of half the maximum intensity (FWHM) of the rocking curve for a (002) plane of hexagonal AlN was 1~2 degrees at a 10% N2 concentration. This was a suitable value for surface acoustic wave (SAW) device. IDT/AlN/(110)Si structure SAW resonators were fabricated. It was confirmed that the insertion loss was 14 dB and phase velocity was 4800 m/s, respectively.

https://iopscience.iop.org/article/10.1143/JJAP.31.3446/pdf

Shoichi Nakano

Papers

Development of New a-Si/c-Si Heterojunction Solar Cells: ACJ-HIT (Artificially Constructed Junction-Heterojunction with Intrinsic Thin-Layer)

Interference-Free Determination of the Optical Absorption Coefficient and the Optical Gap of Amorphous Silicon Thin Films

High-efficiency a-Si/c-Si heterojunction solar cell

Enlargement of Poly-Si Film Grain Size by Excimer Laser Annealing and Its Application to High-Performance Poly-Si Thin Film Transistor

Preparation of c-Axis Oriented AlN Thin Films by Low-Temperature Reactive Sputtering