The effect of cladding layer thickness on large optical cavity 650-nm lasers

The reduction in penetration of the optical mode into the cladding layers in large optical cavity (LOC) laser structures offers the possibility of reducing the cladding-layer thickness. This could be particularly beneficial in GaInP-AlGaInP high-power devices by reducing the thermal impedance and the electrical series resistance. We have designed and characterized 650-nm LOC lasers by modeling the optical loss due to incomplete confinement of the optical mode by the cladding layers and calculating the thermally activated leakage current. This indicated that the cladding thickness could be reduced to 0.5 μm without adversely affecting performance. We investigated devices with 0.3-, 0.5-, and 1-μm-wide cladding layers. The measured optical mode loss of the 0.3-μm-wide cladding device was 36.2 cm^-1 compared with 12.4 and 11.3 cm^-1 for the 0.5- and 1-μm-wide cladding samples, respectively. The threshold current densities of the 0.5- and 1.0-μm devices were similar over the temperature range investigated (120-320 K), whereas the 0.3-μm devices had significantly higher threshold current density. We show that this can be attributed to the higher optical loss and increased leakage current through the thin cladding layer. The intrinsic gain characteristics were the same in all the devices, irrespective of the cladding-layer thickness. The measured thermal impedance of 2-mm-long devices was reduced from 30.7 to 22.3 K/W by reducing the cladding thickness from 1 to 0.5 μm. Our results show that this can be achieved without detriment to the threshold characteristics