ABSORPTION-SPECTROSCOPY ON ROOM-TEMPERATURE EXCITONIC TRANSITIONS IN STRAINED-LAYER INGAAS/INGAALAS MULTI-QUANTUM-WELL STRUCTURES

The physical properties (transition energy, oscillator strength, linewidth, binding energy, and reduced effective mass) of room temperature excitons in compressively strained InGaAs/InGaAlAs multiquantum-well (MQW) structures as a function of the well width have been investigated for the first time by both absorption measurements and photomodulated transmittance measurements. Photomodulated transmittance spectroscopy has been successfully applied to clearly reveal critical transition points. Measured transition energies are in good agreement with a model which includes the heavy hole and light hole splitting due to the strain. For well widths of 2.5-7.5 nm, oscillator strengths are smaller for the strained layer MQWs than for the lattice-matched MQWs by 35%-45%. This is due to the larger exciton radius for the strained MQWs resulting from smaller in-plane reduced effective masses (0.031-0.038m0), which are 65% of those of the lattice-matched MQWs.