Novel Experimental Techniques for Semiconductor Laser Characterisation and Optimisation

This paper discusses novel experimental characterisation techniques that have been used to gain fundamental information about recombination mechanisms in semiconductor lasers. Applying high pressure to semiconductor lasers increases the direct band gap whilst simultaneously decreasing the indirect X-minima gap. From measurements of the threshold current and lasing wavelength as a function of pressure, it is shown that Auger recombination and carrier leakage into indirect X-minima dominate the characteristics of near infra-red (1.3µm and 1.5µm) and visible semiconductor lasers, respectively. It is also demonstrated that measuring the spontaneous emission from semiconductor lasers can reveal quantitative information about the important current paths present in the devices. From such measurements further evidence of the importance of Auger recombination in 1.3µm and 1.5µm lasers is shown. It is demonstrated that GaInNAs/GaAs-based 1.3µm lasers are dominated by defect related recombination and that if this is removed, the threshold current of such devices would be halved, at the expense of an increased temperature sensitivity. These techniques are shown to be invaluable tools in the design and assessment of semiconductor lasers that can be applied to study other new and interesting material systems for improved semiconductor laser performance.