2.2 Indium phosphide (InP) laser diodes

To extend the emission wavelength from λ 1.55–2.1 μm in the InxGa1-xAs material system compressive strain is applied by increasing the indium (In) composition. Figure 6 shows the calculated bandgap wavelength (λ<sup>g</sup> (μm) = 1.2407/Eg (eV)) for a bulk InxGa1-xAs layer on InP as a function of In composition. As shown

#### Figure 2.

(a) Cross-section scanning-electron micrograph of a 3-μm-wide laser ridge topped with a titanium-platinumgold contact layer. (b) Top view of the LC-DFB laser structure, with a cross section of the grating (inset) [18].

in Figure 2, a compressive strain larger than 1% is required to obtain a bandgap wavelength longer than 2 μm. Also shown in Figure 4 is the experimentally measured quantum well photoluminescence peak wavelength for four separate active regions with the In composition varied. When a quantum well structure is used instead of a bulk layer, the bandgap wavelength becomes smaller because of the quantum size effect on the bandgap energy. Therefore larger strain is required for InxGa1-xAs quantum wells (QWs) to obtain the same bandgap wavelength as bulk InxGa1-xAs [14].
