Important loss mechanisms in visible lasers revealed by hydrostatic pressure

It is found that above 10 kbar, the effect of pressure on the threshold current of visible lasers is to increase losses to the X minima in the barriers. Below 10 kbar the threshold current remains relatively constant with pressure. By monitoring the lasing wavelength, the pressure dependence of the direct band gap of ordered GaInP has been measured to be 7 meV/kbar. Considerations of the effect of strain in the active region of a laser suggest that increases in I_th for tensile strained visible lasers as a function of increasing strain are due to losses from the Γ minimum to X minima in the well. Similar increases in I_th observed at high compressive strains can be explained by the reduction in well width, and hence optical confinement factor, which is necessary to maintain the same operating wavelength as the strain is increased