Gain spectra measurement of InGaAsP/AlGaAs laser structures for wavelengths near 800 nm using a new variable stripe length method

Gain spectra are determined by a new variable stripe length method using current injection. The amplified spontaneous emission of laser structures with contact stripes of different length is measured in dependence on the current density. From these spectra "resolved in TE and TM polarization" the corresponding gain spectra are extracted and the maximum modal net gain, the transparency current density and the internal losses are determined. Laser structures for wavelengths near 800 nm with InGaAsP active regions of different thicknesses and compositions are analyzed. With decreasing thickness and increasing compressive strain in the Al-free quantum well, the transparency current density is reduced and the TM gain is suppressed compared to the TE gain. Under high excitation conditions the gain from the first subband transition saturates and the wavelength of the gain maximum shifts to smaller values due to the additional occupation of higher subbands.