Abstract

In semiconductor lasers dramatic improvements in threshold current and high-temperature operation can be obtained if the valence-band density of states (and corresponding hole mass) is reduced.^1-5 In most semiconductors (bulk and quantum wells) the hole density of states is fairly large; hence, under high-level injection the hole quasi-Fermi level is fairly close to the band edge, which makes the photon emission process somewhat inefficient. However, in coherently strained quantum wells (e.g. In_xGa_1-xAs/AlGaAs grown on GaAs or In_0.53+xGa_0.47-xAs/InP grown on InP) the hole band structure can be tailored to give a much lower density of states, resulting in a much more efficient photon emission for a given carrier injection. Using a 4 x 4 Hamiltonian to describe the valence-band structure, we calculate the modification of the hole dispersion relations in a variety of quantum-well structures. As can be seen in Fig. 1, a biaxial strain causes the hole masses (inverse curvature) to fall rapidly, which reduces the hole density of states by up to a factor of 3 near the band edges. Next we calculate the gain spectra for lattice-matched and strained quantum-well structures as a function of temperature. Typical results for the TE and TM mode material gain are shown as a function of carrier injection (for an example see Fig. 1) in Figs. 2 and 3.

© 1990 Optical Society of America