Monolithic integrated external cavity GaAs/AlGaAs lasers with selectively disordered quantum well passive waveguides

The authors report on selectively disordered integrated external cavity GaAs/AlGaAs lasers, where the passive waveguide length is in the millimeter range. Partial disordering of the single QW (quantum well) was achieved by selective silicon ion implantation and subsequent lamp annealing. Lasers with 2.07-mm-long passive and 0.48-mm-long active sections had threshold currents of 33 mA, compared to 9.8 mA for lasers without passive cavities. Lasing data indicate a residual modal loss of 11 cm/sup 11/ in the passive section, consistent with direct waveguide loss measurements. Control samples of external cavity laser structures in which the QW in the passive section was not disordered showed significantly higher threshold currents and a large red shift (as much as 11.4 nm) of the lasing wavelength compared to lasers without a passive cavity. It is shown that the red shift results from the wavelength-dependent losses in the passive section; the net cavity losses are hence minimized by the red shift to lower threshold currents of the integrated laser structures. Loss measurements inferred from amplified spontaneous emission spectra show that without the red shift, the laser would have to overcome a large absorption of approximately 50 cm/sup -1/. A much smaller red shift (4.2 nm at L/sub p/=2.07 mm) was observed for the implanted samples. The results clearly demonstrate that partial disordering of the QW in the passive section leads to reduced cavity losses and hence to lower threshold currents of the integrated laser structures.