We have studied the cyclotron-resonance absorption and photoluminescence properties of the modulation n-doped ZnSe/BeTe/ZnSe type-II quantum wells. It is shown that only the doped sample shows electron cyclotron-resonance absorption. Also, the undoped sample shows two distinctive peaks in the spatially indirect photoluminescence spectra, and the doped one shows only one peak. The results reveal that the high concentration electrons accumulated in ZnSe quantum well layers from n-doped layers can tunnel through BeTe barrier from one well layer to the other. The electron concentration difference between these two well layers originating from the tunneling results in a new additional electric field, and can cancel out a built-in electric field as observed in the undoped structures.
The results are reported of the spatially indirect photoluminescence (PL) spectrum measurements performed on undoped ZnSe/BeTe type-Ⅱ quantum wells with special interface structures at low temperatures (5—10 K). The PL spectra have two main peaks that show a weak PL intensity and a low linear polarization degree and that their linear polarizations are contrary to each other, And the PL spectra are strikingly dependent on an applied external electric field perpendicular to the layers. The results show that the special interface structures reduce spatially indirect radiative recombination efficiency and linear polarization degree, and that a weak built-in electric field exists in the heterostructure. With the increase of excitation intensity, the PL peak on high energy side shows a rapid increase. This is explained by the formation of high charge density on both sides of the high energy side interface.
Optical band gap or band gap is an important characteristic parameter of semiconductor materials. In this study, several representative InGaN/GaN multiple quantum well structures are taken as the research objects, and the test conditions that need to be met for the luminescence measurement of the optical band gap of the InGaN well layer at a certain target temperature are discussed in depth. Since the InGaN well layer is a multi-element alloy and is subject to stress from the GaN barrier layer, there are not only impurity/defect-related non-radiation centers in the well layer, but also localized potential fluctuation induced by composition fluctuation and quantum confinement Stark effect (QCSE) induced by polarization field. Therefore, in order to obtain a more accurate optical band gap of the InGaN well layer, we propose the following test conditions that the luminescence measurement should meet at least, that is, the influence of the non-radiation centers, the localized centers and the QCSE on the emission process at the target temperature must be eliminated. Although these test conditions need to be further improved, it is expected that this test method can provide valuable guidance or ideas for semiconductor optical band gap measurement.
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