Spectral investigation of the radiation emitted by strained InGaAs/GaAlAs quantum-well heterostructures

The spectral-threshold characteristics were determined in the 980 nm range for InGaAs/GaAlAs quantum-well heterostructure injection lasers. These lasers had a GaAs substrate and an anisotropically strained active layer. A systematic study was made of the spectra of subthreshold spontaneous radiation emitted at temperatures in the range 77–300 K. The dependence of the laser photon energy hν on the threshold current density consisted of two sections: the value of hν increased strongly with the current density for low-threshold samples, but above 0.6 kA cm^-2 the value of hν depended weakly on the current density. This behaviour was attributed to the initial filling of the lower quantum states participating in the 1–1h active transition, followed by filling of the second quantum states of the carriers. The lower states ensured a mode gain of 40–50 cm^-1.