Gain spectra in GaAs double−heterostructure injection lasers

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Abstract
Gain spectra for GaAs double−heterostructure junction lasers have been obtained with high resolution. This is accomplished by using an automated data aquisition system to analyze the Fabry−Perot resonance modulation in the spontaneous emission spectra. For active regions doped with Ge at a level of 4×1017 cm−3, the gain in the TE polarization at a fixed wavelength increases linearly with current, below lasing threshold. However, the peak gain (at a variable wavelength) increases slightly faster than linearly with current. The photon energy at which gain is a maximum increases logarithmically with current. Gain in the TM polarization depicts the same general behavior as that for the TE case, except that it is slightly less than the TE gain. It is concluded that for this particular doping the spectral gain characteristics are intermediate between those for undoped and heavily doped active regions. Above the threshold for lasing in the TE mode the TE gain spectra are well saturated, with new fine details revealed in the saturated spectra. On the other hand, gain in the nonlasing TM polarization is not well saturated above threshold, with marked differences in gain between high and low photon energies relative to the TE lasing energy.