Quantum well intermixing for high brightness semiconductor lasers
The research presented in this thesis describes how monolithic opto-electronic integration using quantum well intermixing (QWI) can be applied to improve the high brightness performance of single-mode ridge waveguide GaAs/AlGaAs quantum well (QW) lasers. The sputtered SiO2 QWI technique is explained, and a selective process suitable for device manufacture was demonstrated. This QWI technology was applied to create three distinct devices to address the performance limitations imposed by catastrophic optical damage (COD), spatial mode instability, and overheating. A non absorbing mirror (NAM) laser technology was successfully demonstrated, capable of significantly improving the COD level of high power lasers prone to mirror degradation. Under pulsed test conditions designed to induce COD, the standard ridge laser suffered COD at 230 mW/facet, compared to 600 mW/facet for the NAM laser, demonstrating an improved COD level by a factor of 2.6. Confirmation of the COD failure mechanism was achieved by facet inspection, and removal of the damaged facets. Successful demonstration of a high brightness single lateral mode ridge laser with a self-aligned buried heterostructure defined by QWI was achieved. The device benefits from de-coupling of the optical and electrical confinement, allowing enhanced fundamental lateral mode operation up to higher powers; the buried heterostructure improves the lateral mode discrimination, thus suppressing higher order modes. Comparison of the standard ridge laser and the buried heterostructure ridge laser for ridge widths of 5 mm clearly demonstrated the improvement gained; the standard ridge laser was too wide to operate in the fundamental mode, whereas the buried heterostructure ridge laser showed dominantly single-mode operation up to 130 mW/facet.