Indium gallium arsenide strained -layer single quantum well lasers

Strained-layer InGaAs-GaAs quantum well structures with interfaces free of misfit dislocations have been grown successfully providing the thickness of InGaAs active layer is less than some composition-dependent critical value. Theoretical calculations indicate that the biaxial compressive strain in these structures induces splitting of the valence band and lowers the density of states in the highest energy valence band permitting lasing to occur at lower threshold current density than for unstrained lasers. Also due to strain the reduction of the in-plane heavy hole effective mass leads to a greater differential gain and increases the fundamental relaxation oscillation frequency. Therefore strained layer lasers should operate at faster modulation frequency. Experimental data has confirmed that for a strained single quantum well, a slightly higher relaxation oscillation frequency results, but only for certain limited ranges of device parameters.;A step separate confinement InGaAs-GaAs-AlGaAs strained single quantum well laser has been fabricated and tested. The key idea for this laser is that a 125 nm thick GaAs is adopted as a waveguiding region on both sides of the InGaAs quantum well. The removal of AlGaAs from the waveguiding region reduces the effects of traps in the AlGaAs wide-bandgap region on the active layer of the device. Also since the active InGaAs layer is far from the AlGaAs layers the quality of AlGaAs is not expected to influence the performance of the laser.;In this work, a quick-turnaround fabrication process for laser diodes have been developed that completely bypasses the usual backside preparation steps. As a result, we are able to rapidly update the MBE growth parameters and test out device concepts more readily. Although the process produces larger area diodes than usual, the low threshold current densities in the devices under development render this consideration unimportant.