Short wavelength limitation in high power AlGaInP laser diodes

In wavelength region of red color, luminous efficacy rapidly increases as wavelength shortens. In that sense, red laser diode (LD) with shorter wavelength is required for display applications. Experimental results for short wavelength limitation in AlGaInP LDs are shown and discussed in this paper. Broad area LDs with 625, 630, and 638 nm are successfully fabricated. Operation current versus output power (P-I) characteristics and its temperature dependence of 625 nm LD are inferior to that of 630 and 638 nm ones. The main reason might be carrier leakage, and the results indicate that additional countermeasures to carrier leakage should be adopted to realize a 625 nm LD with the same temperature characteristics as 630 and 638 nm LDs. Conversion efficiencies from input electrical power to luminous flux output of the LDs are also studied. 625 nm LD has low efficiency, though brightness of 625 nm light is 1.7 times of 638nm one with the same output power. And 630 nm LD shows better conversion efficiency at high luminous flux region than 638 nm one, though the P-I characteristics of 630 nm is worse than that of 638 nm one. The tendency is inverted at low flux region, indicating that the lasing wavelength of red LD for laser display should be chosen carefully.