Quantum well intermixing in GaInAs/GaInAsP and GaAs/AlGaAs structures using pulsed laser irradiation

An essentially impurity free, direct write and potentially high spatial resolution quantum well intermixing technique using pulsed laser irradiation is reported. This technique uses a Q-switched Nd:YAG laser emitting at 1.06 μm with a pulse length of approximately 20 ns and repetition rate of 10 Hz. The typical energy densities used for both GaInAs/GaInAsP and GaAs/AlGaAs structures were approximately 5 mJ mm^-2. Multiphoton interactions with carriers lead to phonon emission, the phonons interact with the lattice thus generating point defects which diffuse during a subsequent annealing stage in a rapid thermal annealer and cause intermixing. Photoluminescence measurements have demonstrated that the spatial resolution of the process is better than the resolution of the PL measurement (ie better than 25 μm) and the technique has been used to write directly a grating of period 1.25 μm into a GaInAs/GaInAsP quantum well structure. This was achieved using a grating of period 2.5 μm etched into the surface of the substrate; when illuminated by the Q-switched pulses this grating generated a volume hologram of point defects within the sample at half the etched period. A clear dip in the transmission spectrum of the waveguide which had been processed in this way was observed at 1.525 μm. Differential bandgap shifts of up to 40 meV have been observed in GaAs/AlGaAs double quantum well samples. 3 μm wide ridge waveguide lasers were fabricated from the intermixed and control samples. The threshold currents of the intermixed and the control lasers were comparable. The slope efficiency of the intermixed lasers showed insignificant changes when compared to the as-grown lasers.