ABSORPTION-COEFFICIENT AND EXCITON OSCILLATOR-STRENGTHS IN INGAAS/INP MULTIQUANTUM WELLS

The excitonic properties of InGaAs/InP multi-quantum-well systems grown by chemical beam epitaxy have been investigated with absorption measurements in the temperature range 8-300 K and in the spectral region 0.775-1.550 eV. In this region, the excitonic resonances corresponding to n=1, n=2 interband transitions, and the steplike behaviour of the two-dimensional density of states have been clearly observed. By fitting the lineshape of the excitonic features with Gaussian functions the most noteworthy parameters are discussed. The energy position of the peak changes as a function of temperature, according to the relation known for the InGaAs energy gap. Moreover, the full width at half maximum is deduced and is discussed in terms of an intrinsic contribution plus a thermal broadening due to the interaction with LO phonons. The integrated area of the excitonic peak examined seems to be temperature independent. On the other hand, the integrated area decreases when the well width increases, because of the shrinkage of the Is exciton wave function. A ratio of the oscillator strengths related to light, and heavy hole excitons equal to 0.6 has been determined, in accordance with the theoretical prediction.