LASER LIFT-OFF OF GaN THIN FILMS FROM SAPPHIRE SUBSTRATES

Gallium Nitride film was successfully separated from sapphire substrate by laser radiation. The absorption of the 248 nm radiation by the GaN at the interface results in rapid thermal decomposition of interfacial layer, yielding metallic Ga and N2 gas. The substrate can be easily removed by heating above the Ga melting point (29°C). X-ray diffraction, atomic force microscopy and photoluminescence of GaN before and after lift-off process have been performed, which demonstrated that the separation and transfer process do not alter the structural quality of the GaN films. And further discussions on the threshold energy and crack-free strategies of laser lift-off process have also been presented.

Growth Kinetic Studies for MOCVD CdTe and HgCdTe Epilayers on GaAs Substrates

The growth rates of CdTe and CMT on GaAs and on CdTe/GaAs substrates were studied as a function of temperature and gas composition. A Langmuir-Hinshelwood Model for surface reaction control region is suggested. The CdTe/GaAs interface was examined by X-ray double crystal diffraction, laser Raman spectroscopy and transmission electron microscopy (TEM). A defect layer was observed at CdTe/GaAs interface. The relationship between interface qualities and electrical properties of CMT overlayers was discussed.

High power red-light GalnP/AlGalnP laser diodes with nonabsorbing windows based on Zn diffusion-induced quantum well intermixing

The layer structure of GaInP/AlGaInP quantum well laser diodes （LDs） was grown on GaAs substrate using low-pressure metalorganic chemical vapor deposition （LP-MOCVD） technique. In order to improve the catastrophic optical damage （COD） level of devices, a nonabsorbing window （NAW）, which was based on Zn diffusion-induced quantum well intermixing, was fabricated near the both ends of the cavities. Zn diffusions were respectively carried out at 480, 500, 520. 540, and 580 ℃ for 20 minutes. The largest energy blue shift of 189.1 meV was observed in the window regions at 580 ℃. When the blue shift was 24.7 meV at 480 ℃, the COD power for the window LD was 86.7% higher than the conventional LD.

GaInN light-emitting diodes with omni-directional reflector using nanoporous SnO_2 film

Enhancement of light extraction in a GaInN light-emitting diode （LED） employing an omni-directional reflector （ODR） consisting of GaN, SnO2 nanorod and an Ag layer was presented. The ODR comprises a transparent, quarterwave layer of SnO2 nanorod claded by silver and serves as an ohmic contact to p-type GaN. Transparent SnO2 sols were obtained by sol-gel method from SnCl2·2H2O, and SnO2 thin films were prepared by dip-coating technique. The average size of the spherical SnO2 particles obtained is 200 nm. The refractive index of the nanorod SnO2 film layer is 2.01. The GaInN LEDs with GaN/SnO2/Ag ODR show a lower forward voltage. This was attributed to the enhanced reflectivity of the ODR that employs the nanorod SnO2 film layer. Experimental results show that ODR-LEDs have lower optical losses and higher extraction efficiency as compared to conventional LEDs with Ni/Au contacts and conventional LEDs employing a distributed Bragg reflector （DBR）.

High power AlGaInP laser diodes with zinc-diffused window mirror structure

The technology of zinc-diffusion to improve catastrophic optical damage (COD) threshold of compressively strained GaInP/AlGaInP quantum well laser diodes has been introduced. After zinc-diffusion, about 20 μm-long region at each facet of laser diode has been formed to serve as the window of the lasing light. As a result, the COD threshold has been significantly improved due to the enlargement of bandgap by the zinc-diffusion induced quantum well intermixing, compared with that of the conventional non-window structure. 40-mW continuous wave output power with the fundamental transverse mode has been realized under room temperature for the 3.5μm-wide ridge waveguide diode. The operation current is 84 mA and the slope efficiency is 0.74 W/A at 40 mW. The lasing wavelength is 656 nm.

Study on nitridation processes of β-Ga_2O_3 single crystal

Nitridated β-Ga2O3 （100） substrate was investigated as the substrate for GaN epitaxial growth. The effects of nitridation temperature and surface roughness of β-Ga2O3 wafers on the formation of GaN were studied. It was found that the most optimized nitridation temperature was 900 ℃, and hexagonal GaN with preferred orientation was produced on the well-polished wafer. The nitridation mechanism was also discussed.

Compact all-optical switches based on photon-induced suppression of mode interference

An optically activated optical switch based on suppression of mode interference （SMI） is presented. The imaging properties of multi-mode interference （MMI） section in the switch with Y-branch can be modified by a controlling light injection. The switch was simulated by finite difference beam propagation method （FD-BPM） and fabricated on GaAlAs/GaAs epitaxial materials. At the wavelength of 1.31 μm, the primary experiment showed an extinction ratio of about 8 dB with controlling light power density of 73.5 W/mm^2.