Search

We investigate the laser actions of 5at.% Yb:Gd2xY2(1-x)SiO5 (Yb:GYSO; x = 0.1) crystals with different cutting directions, parallel and vertical to the growth axis. Our results show that the cutting direction of the sample plays an astonished role in the laser operation. The sample cut vertically to the growth axis possesses the favourable lasing characteristics. Its output power reaches 3.13W at 1060nm with a slope efficiency of 44.68% when the absorbed pump power is 8.9 W. In contrast, the sample cut parallel reaches only 1.65 W at 1044 nm with a slope elLiciency of 33.76% with absorbed pump power of 7.99 W. The absorption and emission spectra of the two samples are examined and the merit factor M is calculated. Our analysis is in agreement well with the experimental results. The wavelength tuning range of the superior sample covers from 1013.68 nm to 1084.82 nm.

Direct-current transfer characteristics of (InGaN)/AlGaN/AlN/GaN heterojunction field effect transistors (HFETs) are presented. A drain current plateau (IDS = 32.0 mA/mm) for VGS swept from +0.7 V to −0.6 V is present in the transfer characteristics of InGaN/AlGaN/AlN/GaN HFETs. The theoretical calculation shows the coexistence of two-dimensional electron gas (2DEG) and two-dimensional hole gas (2DHG) in InGaN/AlGaN/AlN/GaN heterostructures, and the screening effect of 2DHG to the 2DEG in the conduction channel can explain this current plateau. Moreover, the current plateau shows the time-dependent behavior when IDS−VGS scans repeated are conducted. The obtained insight provides indication for the design in the fabrication of GaN-based super HFETs.

A homemade 7 × 2 inch MOCVD system is presented. With this system, high quality GaN epitaxial layers, InGaN/GaN multi-quantum wells and blue LED structural epitaxial layers have been successfully grown. The non-uniformity of undoped GaN epitaxial layers is as low as 2.86%. Using the LED structural epitaxial layers, blue LED chips with area of 350 × 350 μm2 were fabricated. Under 20 mA injection current, the optical output power of the blue LED is 8.62 mW.

An InxGa1−xN/InN quantum-dot intermediate-band solar cell is calculated by means of solving the Schrodinger equation according to the Kronig—Penney model. Based on particular assumptions, the power conversion efficiency is worked out. The results reveal that the InxGa1−xN/InN quantum-dot intermediate-band solar cell manifests much larger power conversion efficiency than that of p-n junction solar cells, and the power conversion efficiency strongly depends on the size of the quantum dot and the interdot distance.