The pulse width was 200 ns at 1 kHz. It is certain that with increasing measurement temperature threshold current increases. The temperature dependence of threshold current is shown in Figure 7b . The calculated characteristic temperature was 155K for around room temperature operation and 133K for higher temperature operation. Nakamura et al. suggested that such a kink in the L-I plot for their high power LD was due to the change in emission mode.
More work is necessary to verify the origin of the kink.
The refractive index calculated from the spacing between longitudinal modes was 2.52. T.W. Weeks, H.S. Kong, H.M. Dieringer, J.A. Edmond, J.D. Brown, J.T. Swindell, J.F. Schetzina, Electron. Figure 1 . A schematic of the fabricated LD Figure 2 . Figure 4 .