Growth and Fabrication of High External Quantum Efficiency AlGaN-Based Deep Ultraviolet Light-Emitting Diode Grown on Pattern Si Substrate.

Growing III-V semiconductor materials on Si substrates for opto-electronic applications is challenging because their high lattice mismatch and different thermal expansion coefficients cause the epitaxial layers to have low quality. Here we report the growth of a high-quality AlN template on a micro-circle-patterned Si substrate by using NH3 pulsed-flow multilayer AlN growth and epitaxial lateral overgrowth techniques. Then, we fabricated and characterized a deep-ultraviolet light-emitting diode (UV-LED) device using this AlN/patterned Si. By using standard lithography and inductively coupled plasma etching, the Si substrate was prepared with very high pattern density and was made deep enough to grow a thick AlN template with high crystal quality and very few threading dislocations, allowing for further re-growth of the deep UV-LED device. And by combining a transparent p-AlGaN contact layer, an electron blocking layer and using this high quality AlN template: a deep UV-LED device fabricated and showed a strong single sharp electroluminescence (EL) peak at 325 nm and achieved an external quantum efficiency (EQE) of about 0.03%, for a deep UV-LED grown on Si substrate.

Performance Improvement of AlN Crystal Quality Grown on Patterned Si(111) Substrate for Deep UV-LED Applications.

An AlN template layer is required for growth of AlGaN-based deep ultraviolet light-emitting diodes (UV-LEDs). However, the crystal quality of AlN templates grown on both flat and patterned Si substrates has so far been insufficient for replacing templates grown on sapphire substrates. In this work, we grew a high-quality AlN template on 2 in. micro-circle-patterned Si substrate (mPSiS) with two different sizes and shapes through controlling the bias power of inductively coupled plasma (ICP) etching. The experimental results showed that the best AlN template was obtained on a large pattern size with a bow-angle shape and the template had X-ray rocking curves with full widths at half-maximum of 620 and 1141 arcsec for the (002) and (102) reflection planes. The threading dislocation density near surface of AlN template through transmission electron microscopy (TEM) estimation was in the order of 107 cm-2, which is the lowest dislocation density reported for a Si substrate to our knowledge. A strong single electroluminescence (EL) peak was also obtained for an AlGaN-based deep UV-LED grown on this template, means that it can be used for further developing high-efficiency deep UV-LEDs.

Direct Growth and Controlled Coalescence of Thick AlN Template on Micro-circle Patterned Si Substrate.

High-density micro-circle patterned Si substrates were successfully fabricated for the direct overgrowth of thick AlN templates by using NH3 pulsed-flow multilayer AlN growth and epitaxial lateral overgrowth techniques. The experimental results show that an 8-µm-thick AlN template was grown at a very high growth rate on the substrates. The AlN template had full widths at half maximum of 0.23° and 0.37° for the (002) and (102) reflection planes in X-ray diffraction rocking curves. Atomic force microscopy and transmission electron microscopy confirmed that the roughness of the surface was low (3.5 nm) and the dislocation density was very low (1.5 × 10(8) cm(-2) (screw), 3.7 × 10(8) (edge) cm(-2)).

Efficiency improvement of InGaP/GaAs/Ge solar cells by hydrothermal-deposited ZnO nanotube structure.

In this paper, a zinc oxide (ZnO) nanotube, fabricated by the hydrothermal growth method on triple-junction (T-J) solar cell devices to enhance efficiency, is investigated. Compared to those of bare T-J solar cells (without antireflection (AR) coating) and solar cells with Si3N4 AR coatings, the experimental results show that the T-J solar cells, which use a ZnO nanotube as an AR coating, have the lowest reflectance in the short wavelength spectrum. The ZnO nanotube has the lowest light reflection among all experimental samples, especially in the range of 350 to 500 nm from ultraviolet (UV) to visible light. It was found that a ZnO nanotube can enhance the conversion efficiency by 4.9%, compared with a conventional T-J solar cell. The Si3N4 AR coatings also enhance the conversion efficiency by 3.2%.The results show that a cell with ZnO nanotube coating could greatly improve solar cell performances.