The gain coeff.and the spectra of gain coeff.are discussed in this paper.The gain coeff.

as one of the important parameters about the emission properties of semiconductor laser

is not only dependent on the transition probability but also dependent on the difference of the density of filled conduction band states and the density of empty valence band states.The transition probability is related to both the factor of energy gap and the factor of the spin orbjt splitting.The spectra of gain coeff.are measured under three different injection conditions:the direct current injection;the pulse current injection;and the direct and pulse current injection.Under the condition of pulse current injection

the thermal effect can be neglected as the width of pulse is shorter than 0.3μs.The peak of gain coeff.is moved towards the shorter wavelength with increasing of injection pulse current.This is due to the fillins of upper conduction band states and the empty of lower valence band states.Under the condition of direct and pulse current injection

the total injection current is kept constant

but the magnitude of components are changed.The peak of gain coeff.is moved towards longer wavelength with increasing of direct current component.That is due to the thermal effect on the active area.Under the direct current injection the peak of gain coeff.is kept constant because of the thermal effect and the filling effect introduce the movement of the peak of gain coeff.in contrary direction.This experimental result is in agreement with the theory.