Search

A new approach was proposed and its role in improvement of the beam quality of high-power broad-area diode lasers was demonstrated, in which a composite arrow array and trench microstructure was used to suppress the beam waist and tailor the high order lateral modes. The beam waist shows a special shrinkage with increasing injection current resulting from the combined effect of mode tailoring and the thermal lens effect. A 58% improvement in lateral beam parameter product was realized compared with conventional broad-area diode lasers.

Porous templates were fabricated by hydrogen-etching metal organic chemical vapor deposited gallium nitride (GaN); these templates were used as substrates for the growth of GaN via hydride vapor phase epitaxy. The influence of annealing porous templates on GaN growth behavior was investigated. GaN epitaxied on the unannealing porous template followed the Volmer–Weber mode with the void preserved at the growth plane, whereas the GaN film on the annealed porous templates exhibited a layer-by-layer growth and filled the porous material. The GaN crystal quality was characterized by high-resolution XRD and CL, the results indicated that GaN grown with pores preserved at the template interface had a lower dislocation density than that grown with pores filled, and the best GaN film had a TD density of 10 4 cm −2 .

A self-separated GaN layer was prepared by hydride vapor phase epitaxy on a large-period square network template. The morphology of the surface formed was consistent with the substrate patterning that comprised terrace and concave. The mixed polarity of the surface was studied by wet etching and micro-Raman scattering. Micro-Raman scattering was performed to investigate the strain distribution of the surface on the front and backside, as well as the cross-section. Differences were observed in the Raman phonon peaks such as the A1(LO), E1(TO), E2(high) phonon, and LO phonon–plasmon mode (LPP−)/A1(TO) peaks between the terrace and concave. The strain distribution varied regularly, which was interpreted based on the facet growth mode.

A self-separated GaN layer was prepared by hydride vapor phase epitaxy (HVPE) on a square-patterned template with large periodicity. Self-separation was completed by breakage of the fragile layer because of the thermal stresses generated during the cooling process after HVPE growth. The GaN layer exhibited graphical surface comprising the terrace and the concave, the shapes of which were corresponding with the mask pattern. The terrace came from the growth on window openings, and had Ga-polarity by wet etching and micro-Raman measurement. The concave over the mask was composed of large inclined facets, and was demonstrated to have N-polarity. The growth on large square-patterned template was considered to be facet growth. The polarity inversion was related to dislocation accumulation. The strain distribution regularly varied, which was interpreted based on the facet growth mode.

Broad-area diode lasers usually supply high output power but low lateral beam quality. In this Letter, an on-chip combined angled cavity is proposed to realize narrow lateral far field patterns and high brightness. The influence of included angles, emitting facets on output power, and beam quality are investigated. It demonstrates that this V-junction laser is able to achieve a single-lobe far field at optimal cavity length with a 3.4 times improvement in brightness compared with Fabry–Perot (F-P) cavity lasers. The excited high-order modes at a high injection level reduce the brightness, but it is still 107% higher than that of F-P lasers.

Far-field blooming, a serious far-field dependence on driving current, affects the stability of beam quality and applications of broad-area (BA) diode lasers. In this Letter, the lateral ridge waveguide (LRW) is introduced to BA lasers by a simple and cost-effective approach to control the far-field stability and beam divergence. The influences of LRW length on output power, near- and far-field, are investigated and it is found that the optimized LRW length is able to improve both the far-field blooming and output power. The mechanism behind this is analyzed and a 0.13°/A dependence of lateral divergence angle on the injection current is achieved.

The La212 type compounds substituted by silver or praseodymium are prepared by solid state reaction method. It is found that compounds La 2-x Sr x Ca 0.5 Pr 0.5 Cu 2 O 6 , La 1.6 Pr 0.4 Ca 1-x Sr x Cu 2 O 6 and La 2-x Pr x Ca 0.5 Sr 0.5 Cu 2 O 6 can be formed for x=0.4-1.1, 0-0.5 and 0-1.5, respectively. A new member of La212 type compounds, La 2-x Ag x CaCu 2 O 6 is also prepared. Their structures are verified by Rietveld structure refinement to belong to the structure type of La212 cuprate oxide with space group I4/mmm. Their electrical properties are investigated. La 1.65 Ag 0.35 CaCu 2 O 6 displays metal-like behavior and its resistivity decreases with the decrease of temperature from 300K to 4.2K.

The effects of preparation condition on structure and superconductivity of LaBa2Cu3Oy (LaBCO) system have been investigated, and the optimum preparation condition and superconductivity of Tc(0)=97 K and Tc(onset)=101 K, which are the best results at present, have been achieved. The optimum preparation condition is A-B-C3-D-E. Investigations show that keeping LaBa2Cu3Oy, being of tetragonal structure before oxygenation, at 305°C is a key procedure to obtain a single phase LaBa2Cu3Oy sample with the best superconductivity.