Study of GaAs and AlGaAs buried structures by differential photoreflectance spectroscopy

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Abstract
Application of the newly developed differential photoreflectance (DPR) technique to study layered GaAs/AlGaAs structures is presented and discussed. We show that in most instances DPR can provide selective photoreflectance (PR) response from layers buried within thin multilayer structures, where such responses may be superimposed on one another in ordinary PR technique. DPR measurement is achieved through alternative modulations from two laser pumps with different penetration depths, so that the modulation has a gradient with respect to the depth within the sample. The application of this technique is demonstrated for a buried heterojunction and buried multiple quantum wells. Comparison is made with ordinary PR. In one case the heterojunction of interest was buried under two highly doped 40-nm-thick GaAs and AlGaAs layers. We show that this heterojunction is barely distinguishable in an ordinary PR measurement. Nevertheless, at room temperature DPR shows distinct peaked signals which correspond to the previously reported PR from a two-dimensional electron gas.

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