Study on in-plane optical anisotropy of semiconductor materials by reflectance difference spectroscopy

In the present review, the measuring principle of reflectance difference spectroscopy (RDS) is given. As a powerful tool in the surface and interface analysis technologies, the application of RDS to the research on semiconductor materials is summarized. along with the origins of the in-plane optical anisotropy of semiconductors. And it is believed that RDS will play an important role in the electrooptic modification of Si-based semiconductor materials.

Large g factors of higher-lying excitons detected with reflectance difference spectroscopy in GaAs-based quantum wells

Exciton g factors in GaAs-based quantum wells (QWs) were evaluated by reflectance difference spectroscopy (RDS) under a weak magnetic field. The well-width dependence of the n=1 heavy-hole exciton (1H1E) g factor agrees well with the reported results, demonstrating RDS as a sensitive tool for detection of g factor. By comparison, the n=1 light-hole exciton g factor increases with the well width, and shows a larger value than that of 1H1E. In a 20-nm-wide Al0.02Ga0.98As/AlAs multiple QW sample, the g factors of up to ten excitons are obtained, and the higher-lying exciton g factors are found to be one order larger than that of the 1H1E exciton.

Evolution of the amount of InAs in wetting layers in an InAs/GaAs quantum-dot system studied by reflectance difference spectroscopy

The wetting layer (WL) in InAs/GaAs quantum-dot systems has been studied by reflectance difference spectroscopy (RDS). Two structures related to the heavy-hole (HH) and light-hole (LH) related transitions in the WL have been observed. On the basis of a calculation model that takes into account the segregation effect and exciton binding energies, the amount of InAs in the WL (t(WL)) and its segregation coefficient ( R) have been determined from the HH and LH transition energies. The evolutions of tWL and R exhibit a close relation to the growth modes. Before the formation of InAs dots, t(WL) increases linearly from similar to 1 to similar to 1.6 monolayer (ML), while R increases almost linearly from similar to 0.8 to similar to 0.85. After the onset of dot formation, t(WL) is saturated at similar to 1.6 ML and R decreases slightly from 0.85 to 0.825. The variation of tWL can be interpreted by using an equilibrium model. Different variations of in-plane optical anisotropy before and after dot formation have been observed.

Evolution of wetting layer of InAs/GaAs quantum dots studied by reflectance difference spectroscopy

For the InAs/GaAs quantum-dot system, the evolution of the wetting layer (WL) with the InAs deposition thickness has been studied by reflectance difference spectroscopy (RDS) in combination with atomic force microscopy and photoluminescence. One transition related to the light hole in the WL has been observed clearly in RDS, from which its transition energy and in-plane optical anisotropy (OA) are determined. The evolution of WL with the InAs dot formation and ripening has been discussed. In addition, the remarkable changes in OA at the onsets of the dot formation and ripening have been observed, implying the mode transitions of atom transport between the WL and the dots.

Study on in-plane optical anisotropy of Si0.75Ge0.25/Si/Si0.5Ge0.5 asymmetric superlattice by reflectance difference spectroscopy - art. no. 071908

Si0.75Ge0.25/Si/Si0.5Ge0.5 trilayer asymmetric superlattices were prepared on Si (001) substrate by ultrahigh vacuum chemical vapor deposition at 500 degrees C. The nonlinear optical response caused by inherent asymmetric interfaces in this structure predicted by theories was verified by in-plane optical anisotropy in (001) plane measured via reflectance difference spectroscopy. The results show Si0.75Ge0.25/Si/Si0.5Ge0.5 asymmetric superlattice is optically biaxial and the two optical eigen axes in (001) plane are along the directions [110] and [-110], respectively. Reflectance difference response between the above two eigen axes can be influenced by the width of the trilayers and reaches as large as similar to 10(-4)-10(-3) in 15-period 2.7 nm-Si0.75Ge0.25/8 nm-Si/1.3 nm-Si0.5Ge0.5 superlattice when the normal incident light wavelength is in the range of 500-1100 nm, which is quite remarkable because the optical anisotropy does not exist in bulk Si.

Interface-related in-plane optical anisotropy in GaAs/AlxGa1-xAs single-quantum-well structures studied by reflectance difference spectroscopy

The in-plane optical anisotropies of a series of GaAs/AlxGa1-xAs single-quantum-well structures have been observed at room temperature by reflectance difference spectroscopy. The measured degree of polarization of the excitonic transitions is inversely proportional to the well width. Numerical calculations based on the envelope function approximation incorporating the effect of C-2v-interface symmetry have been performed to analyze the origin of the optical anisotropy. Good agreement with the experimental data is obtained when the optical anisotropy is attributed to anisotropic-interface structures. The fitted interface potential parameters are consistent with predicted values.

Detection of indium segregation effects in InGaAs/GaAs quantum wells using reflectance-difference spectrometry

The influence of the Indium segregation on the interface asymmetry in InGaAs/GaAs quantum wells have been studied by reflectance-difference spectroscopy (RDS). It is found that the anisotropy of the 2H1E (2HH --> 1E) transition is very sensitive to the degree of the interface asymmetry. Calculations taking into account indium segregation yield good agreement with the observed anisotropy structures. It demonstrates that the anisotropy intensity ratio of the 1L1E (1LH --> 1E) and 2H1E transitions measured by RDS can be used to characterize the interface asymmetry. (C) 2002 Elsevier Science B.V. All rights reserved.

Polishing-related optical anisotropy of semi-insulating GaAs studied by reflectance difference spectroscopy

The strong in-plane optical anisotropy of (001) semi-insulating GaAs, which comes from the submicron region under the surface, has been observed by reflectance difference spectroscopy. The optical anisotropy can be explained by the anisotropic strain that is introduced by the asymmetric distribution of 60 degrees dislocations during surface polishing. The simulated spectra reproduce the line shape of the experimental ones. The simulations show that the anisotropic strain is typically about 2.3x10(-4). (C) 2000 American Institute of Physics. [S0021-8979(00)01315-3].

Interference effects in differential reflectance spectra of the GaAs epilayers grown on Si substrate

We report the observation of oscillating features in differential reflectance spectra from the GaAs epilayer grown on Si substrate in the energy range both below and above the fundamental band gap. It is demonstrated that the oscillating features are due to the difference in the interference between two neighboring areas of the sample. The interference arises from two light beams reflected from different interfaces of the sample. The calculated spectra in the nonabsorption region are in good agreement with measured data. It is shown that the interference effect can be used as a sensitive method to characterize the inhomogeneity of the semiconductor heterostructures. (C) 1998 American Institute of Physics. [S0021-8979(98)08723-4].

Evolution of wetting layers in InAs/GaAs quantum-dot system studied by reflectance difference spectroscopy

The wetting layers (WL) in InAs/GaAs quantum-dot system have been studied by reflectance difference spectroscopy (RDS), in which two structures related to the heavy-hole (HH) and light-hole (LH) transitions in the WL have been observed. The evolution and segregation behaviors of WL during Stranski-Krastanow (SK) growth mode have been studied from the analysis of the WL-related optical transition energies. It has been found that the segregation coefficient of Indium atoms varies linearly with the InAs amount in WL. In addition, the effect of the growth temperature on the critical thickness for InAs island formation has also been studied. The critical thickness defined by the appearance of InAs dots, which is determined by AFM, shows a complex variation with the growth temperature. However, the critical thickness determined by RDS is almost constant in the range of 510-540 degrees C.

In-plane optical anisotropy in GaAsN/GaAs single-quantum well investigated by reflectance-difference spectroscopy

The interface properties of GaNxAs1-x/GaAs single-quantum well is investigated at 80 K by reflectance difference spectroscopy. Strong in-plane optical anisotropies (IPOA) are observed. Numerical calculations based on a 4 band K . P Hamiltonian are performed to analyze the origin of the optical anisotropy. It is found that the IPOA can be mainly attributed to anisotropic strain effect, which increases with the concentration of nitrogen. The origin of the strain component epsilon(xy) is also discussed.

Reflectance-difference spectroscopy study of the Fermi-level position of low-temperature-grown GaAs

The results of a reflectance-difference spectroscopy study of GaAs grown on (100) GaAs substrates by low-temperature molecular-beam epitaxy (LT-GaAs) are presented. In-plane optical anisotropy resonances which come from the linear electro-optic effect produced by the surface electric field are observed. The RDS line shape of the resonances clearly shows that the depletion region of LT-GaAs is indeed extremely narrow (much less than 200 Angstrom). The surface potential is obtained from the RDS resonance amplitude without the knowledge of space-charge density. The change of the surface potential with post-growth annealing temperatures reflects a complicated movement of the Fermi level in LT-GaAs. The Fermi level still moves for samples annealed at above 600 degrees C, instead of being pinned to the As precipitates. This behavior can be explained by the dynamic properties of defects in the annealing process.

Investigation of GaAs/AlGaAs interfaces by reflectance-difference spectroscopy

The in-plane optical anisotropy of several GaAs/AlGaAs quantum well samples with different well widths has been measured at room temperature by reflectance-difference spectroscopy (RDS). The RDS line shapes are found to be similar in all the samples examined here, which dominantly consist of two peak-like signals corresponding to 1HH-->1E and 1LH-->1E transition. As the well width is decreased, or the 1 ML InAs layer is inserted at one interface, the intensity of the anisotropy increases quickly. Our detail analysis shows that the anisotropy mainly arises from the anisotropic interface roughness. The results demonstrate that the RDS technique is sensitive to the interface structures.

Detection of indium segregation effects in InGaAs/GaAs quantum wells using reflectance-difference spectrometry

The influence of the Indium segregation on the interface asymmetry in InGaAs/GaAs quantum wells have been studied by reflectance-difference spectroscopy (RDS). It is found that the anisotropy of the 2H1E (2HH --> 1E) transition is very sensitive to the degree of the interface asymmetry. Calculations taking into account indium segregation yield good agreement with the observed anisotropy structures. It demonstrates that the anisotropy intensity ratio of the 1L1E (1LH --> 1E) and 2H1E transitions measured by RDS can be used to characterize the interface asymmetry. (C) 2002 Elsevier Science B.V. All rights reserved.