Chapter 1 - Visible-Wavelength Laser Diodes

Abstract

The first visible red InGaA1P laser diodes appeared by the mid-1980s and have shown a marked progress since then, but this field has not yet reached the maturity of the A1GaAs and InGaAsP. Most recently, developments in blue–green laser diodes have shown considerable progress. This progress has taken place mainly in the MgZnSSe system, but the GaAlInN system is coming up strongly. This chapter reviews the present status of visible laser diodes. The magnitude of the threshold current and its temperature dependence are vital in limiting the properties of InGaA1P laser diodes and of visible laser diodes. In the InGaA1P system, the use of strained layer quantum wells reduces the threshold current considerably for both compressive and tensile strains. The field of InGaA1P lasers is now rapidly maturing. In blue–green lasers based on the MgZnSSe system, the use of strained active layers combined with the use of quaternary cladding layers has made c.w. operation at room temperature possible. In red lasers, the use of strained-layer quantum wells together with index-guided structures with a low internal optical loss is expected to shift the c.w. limit at room temperature down to about 600 nm. The use of multiquantum barrier reflectors could help in further reducing the temperature dependence of threshold. In the area of II–VI diode lasers, defect reduction in the growth of the MgZnSSe system is expected to lead to improved lifetimes for c.w. lasing at room temperature and even above for lasers emitting near 500 nm and possibly even at somewhat shorter wavelengths.