Photoreflectance study of quantum effects on E1 and E1+Δ1 transitions in GaAs/AlAs superlattices

We have systematically investigated the E₁ and E₁ +Δ₁ transitions at the critical point along the [111] direction in (GaAs) _m /(A1As) _m and (GaAs)₁₀/(AIAs) _n superlattices with m = 8-35 and n = 1-14 monolayers by using photoreflectance spectroscopy. In all the superlattices, we have succeeded to detect the E ₁ and E ₁+Δ₁, transitions in addition to the T-point (E ₀) transitions. It is found that the layer-thickness dependence of the energies of the E ₁ and E ₁+Δ₁ transitions is similar to that of the quantized T transitions. The experimental results are explained by the calculation in the framework of an effective-mass approximation.