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•ZnO/ZnMgO quantum wells are analyzed by polarized reflectance spectroscopy.•Sharp dips are observed in the spectra: interface phonon polariton modes.•Frequency of these modes depends ...on phonon frequency of the ZnMgO layers.•The phonon frequencies of the ZnMgO depend on Mg content.•Compositional analysis of the ZnMgO layers is performed by reflectance spectroscopy.
A method based on infrared reflectance spectroscopy is presented by which the Mg content in ZnO/(Zn,Mg)O multiple quantum wells with very thin barriers can be determined. The method relies on the observation of interface phonon-polaritons which appear as sharp dips in the p-polarized reflectance spectra at oblique incidence near the longitudinal optical (LO)-phonon frequencies of both QW and barrier materials. By fitting the reflectance spectra to a dielectric function model, the LO phonon frequency of the (Zn,Mg)O barrier layers can be determined. The LO phonon frequency depends on the Mg content. Comparing to Mg content calibration via cathodoluminescence, a linear relationship between the reflectance dip frequency and the Mg content is obtained. The presented method serves as a rapid means to determine the Mg content on final structures with very thin (Zn,Mg)O layers -such as device structures- where alternative, destructive methods cannot be used.
We report on spatially- and time-resolved emission measurements and observation of transport of indirect excitons in ZnO/MgZnO wide single quantum wells.
Ternary semiconductor alloys based on the A y B1–y C stoichiometry are widely employed in electronic devices, and their composition plays a key role in band gap engineering of heterostructures. We ...have studied the crucial issue of accuracy in composition measurements of Al y Ga1–y N and Mg y Zn1–y O alloys using atom probe tomography (APT). The results indicate a similar behavior for both nitride and oxide systems. A correct site fraction y is measured at low field conditions, while Ga and Zn preferentially evaporate at high field, yielding an overestimation of y. Furthermore, APT data sets exhibit local biases depending on the distribution of the electrostatic field at the specimen surface. We estimate the detection efficiencies for each species and interpret the results through a model describing preferential evaporation in simple terms.
The growth of GaN based structures on Si(1
1
0) substrates by molecular beam epitaxy using ammonia as the nitrogen precursor is reported. The structural, optical and electrical properties of such ...structures are assessed and are quite similar to the ones obtained on Si(1
1
1) in-spite of the very different substrate surface symmetry. A threading dislocation density of 3.7×10
9
cm
−2 is evaluated by transmission electron microscopy, which is in the low range of typical densities obtained on up to 2
μm thick GaN structures grown on Si(1
1
1). To assess the potential of such structure for device realization, AlGaN/GaN high electron mobility transistor and InGaN/GaN light emitting diode heterostructures were grown and their properties are compared with the ones obtained on Si(1
1
1).
Gallium nitride (GaN) epitaxial layers have been grown on O face (0001¯) zinc oxide (ZnO) substrates by ammonia source molecular beam epitaxy. By adjusting the growth temperature and the III/V ratio ...during the nucleation stage, GaN layers with Ga (0001) or N (0001¯) polarities have been obtained. We show that low growth temperatures (<550°C) and Ga-rich conditions lead to Ga-polar layers, whereas higher growth temperatures (>600°C) and N-rich conditions lead to N-polar layers. Furthermore, the formation of a zinc gallate (ZnGa2O4) interfacial layer between GaN and ZnO has been evidenced, which is responsible for the growth of Ga-polar GaN layers. The structural and optical properties of Ga- and N-polar GaN layers have been characterized and Ga-polar GaN layers exhibit higher crystal quality.
•GaN layers of Ga- and N-polarities have been grown on O face ZnO substrates.•Low temperature growth and Ga-rich conditions of GaN nucleation layers lead to the formation of a continuous ZnGa2O4 interfacial layer.•The ZnGa2O4 interfacial layer is responsible for the growth of Ga-polar GaN layers.•The direct growth of GaN on the bare ZnO surface leads to the growth of N-polar GaN layers.•Ga-polar GaN layers exhibit lower densities of defects and impurities than N-polar layers.
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