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Gallium nitride (GaN) layers grown on sapphire substrate wafers have been successfully separated using a novel line beam laser lift-off (LLO) approach. The absorption of the 248 nm excimer laser radiation by the GaN through the sapphire wafer results in the formation ofmetallic gallium and nitrogen gas. The sapphire wafer was easily removable by heating above the gallium melting point. The metallic gallium phase has been inspected via diverse microscopic surface analysis techniques after line beam LLO processing. The measurements indicate that the sapphire separation process using line beam laser scanning has only a marginal impact on the structural quality of the GaN layer. Line beam LLO processing has inherent upscaling advantages over conventional square field LLO. Processing results are evaluated in view of aptness for mass production of high brightness light emitting diodes (HB-LEDs). Differential interference contrast image of GaN film after 248-nm LLO with line beam (A) and square beam (B)

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In recent years, optically pumped semiconductor disk lasers (OPSDLs) have attracted increasing interest due to their capability of delivering simultaneously high output power and excellent beam quality. Here we report on group-III-Sbbased OPSDLs allowing to cover the wavelength range around and above 2 µm. First the current state-of-the-art and recent progress for OPSDLs emitting in the 2.0-to-2.3 µm spectral range is presented, which includes power scaling through the use of multiple gain elements and as well as spectral tuning and line width narrowing, exploiting in both cases the versatility of the external cavity concept. Then, results on III-Sb-based OPSDLs emitting at 2.8 µm with a cw output power of up to 0.12 W and a peak output power in pulsed mode of >0.5 W, both data referring to roomtemperature operation, are presented. In both cases, the active region of the OPSDL chip consists of compressively strained GaInAsSb quantum well (QW) layers embedded between AlGaAsSb barrier and pump-light-absorbing layers. The emission wavelength is controlled by adjusting the composition of the quaternary QW material. The active region is grown on top of an epitaxial GaSb/AlAsSb Bragg mirror. For efficient heat extraction, SiC intra-cavity heat spreaders were bonded to the surface of the cleaved laser chips. An N-shaped resonator with one OPSDL chip acting as an end mirror and the second OPSDL chip as a folding mirror was used for power scaling, while a V-shaped resonator configuration with a birefringent tuner inserted into the collimated beam path of the resonator was employed for wavelength tuning. Optical pumping was achieved by standard fiber-coupled diode laser modules emitting at 980 nm.