Fabrication and Characterization of Si Substrate-Free InGaN Light-Emitting Diodes and Their Application in Visible Light Communications
Visible light communications with InGaN-based light-emitting diodes (LEDs) grown on large-diameter (6-inch) and cost-effective Si (111) substrates are investigated experimentally. During epitaxial growth, the transition layers consisted of the step-graded AlGaN buffers incorporated with three low-temperature-grown (∼900 °C) AlN interlayers on AlN/Si substrates that are used to compensate for thermally induced tensile stress and to maintain a reasonable crystalline quality of GaN-on-Si LEDs. Strong light absorption from Si can be prevented by fabricating a Si substrate-free InGaN LED with a composite metal coating of Al/Ag/Al multilayer, providing improved adhesive strength and reflectivity comparable to the unitary Ag film. In comparison with GaN-on-Si LEDs, stripping Si substrates combined with the use of a highly reflective bottom mirror (Al/Ag/Al multilayer) reflected a more intense emission pattern corresponding to a 2.2 times (@ 190 mA) increase in light output power in thin-film LEDs. In addition, a 1.8 times (@ 160 mA) increase in optical channel bandwidth is achieved by using thin-film LEDs as optical transmitters. A direct line-of-sight optical link using the proposed thin-film LEDs achieved data transmission rates of up to 100 Mb/s over a distance of 100 cm, indicating that the proposed LEDs have potential for use as optical transmitters in indoor visible light communications.
Transferrable monolithic multicomponent system for near-ultraviolet optoelectronics
A monolithic near-ultraviolet multicomponent system is implemented on a 0.8-mm-diameter suspended membrane by integrating a transmitter, waveguide, and receiver into a single chip. Two identical InGaN/Al0.10Ga0.90N multiple-quantum well (MQW) diodes are fabricated using the same process flow, which separately function as a transmitter and receiver. There is a spectral overlap between the emission and detection spectra of the MQW diodes. Therefore, the receiver can respond to changes in the emission of the transmitter. The multicomponent system is mechanically transferred from silicon, and the wire-bonded transmitter on glass experimentally demonstrates spatial light transmission at 200 Mbps using non-return-to-zero on–off keying modulation.
X‐ray‐diffraction study of quasipseudomorphic ErSi1.7 layers formed by channeled ion‐beam synthesis
ErSi1.7 layers with high crystalline quality (χmin of Er is 1.5%) have been formed by 90 keV Er ion implantation to a dose of 1.6×1017/cm2 at 450 °C using channeled implantation. The perpendicular and parallel elastic strain e⊥=−0.94%±0.02% and e∥=1.24%±0.08% of the heteroepitaxial erbium silicide layers have been measured with symmetric and asymmetric x‐ray reflections using a double‐crystal x‐ray diffractometer. The deduced tetragonal distortion eT(XRD)=e∥−e⊥ =2.18%±0.10%, which is consistent with the value eT(RBS)=2.14±0.17% deduced from the Rutherford backscattering and channeling measurements. The quasipseudomorphic growth of the epilayer and the stiffness along a and c axes of the epilayer deduced from the x‐ray diffraction are discussed.