Fabrication And Characterisation of Bandgap Tuned Lasers in GaAs/AlGaAs Quantum Well Structures Using Pulsed Laser Irradiation

We report the use of Q-switched Nd:YAG laser irradiation technique to enhance the interdiffusion of Ga-Al, and hence the quantum well intermixing (QWI), in GaAs/AlGaAs double quantum well (DQW) structures. Multiphoton interactions with carriers lead to phonon emission; the phonons interact with lattice thus generating point defects, which diffuse during subsequent annealing stage in a rapid thermal processor (RTP) and cause intermixing. This QWI technique is essentially impurity free and potentially high resolution. 3μm wide ridge waveguide lasers were fabricated from the intermixed and control samples. A differential bandgap shift of up to 40meV have been observed between the intermixed and the as-grown lasers. Parameters, such as threshold current density, internal quantum efficiency, material loss, and transparency current density were extracted from the light-current (L-I) characteristics of the lasers cleaved to different cavity lengths. Compared to as-grown devices, it was found that the bandgap tuned lasers exhibited a small increase in the threshold current density, and negligible change in the slope efficiency. Introduction One of the most powerful technique for fabrication of the photonic integrated circuits (PICs) involve the ability to alter the bandgap of multi-quantum well (MQW) well structure after growth by disordering. Disordering of DQW can also be used to shift the gain envelope of asgrown material, thus allowing laser with a range of tuned wavelengths to be fabricated from a single wafer. technique having a better spatial resolution have been developed in GaInAs-GaInAsP structures. This involves irradiating the MQW material with high energy Q-switched Nd:YAG laser pulses [2]. Measurements of the spatial resolution of this technique show it to be better