Mixed crystals including Ga, As, and P (GaPxAs1-x) are interesting since the emission wavelength can be shorter than for GaAs, reaching the visible range while the bandgap is direct for x below 0.45. N. Holonyak Jr. and co-workers at the General Electric laboratory in the USA, began to work with GaPxAs1-x in the late 1950s, and succeeded in making p-n junctions and observing LED emission. Laser diode emission at 710 nm (red) was reported in 1962 [15].