The role of Sb in the molecular beam epitaxy growth of 1.30-1.55 mu m wavelength GaInNAs/GaAs quantum well with high indium content

Sb-assisted GaInNAs/GaAs quantum wells (QWs) with high (42.5%) indium content were investigated systematically. Transmission electron microscopy, reflection high-energy electron diffraction and photoluminescence (PL) measurements reveal that Sb acts as a surfactant to suppress three-dimensional growth. The improvement in the 1.55 mu m range is much more apparent than that in the 1.3 mu m range.. which can be attributed to the difference in N composition. The PL intensity and the full-width at half maximum of the 1.55 mu m single-QW were comparable with that of the 1.3 Am QWs. (c) 2006 Elsevier B.V. All rights reserved.

Selectively excited photoluminescence of GaAs1-xNx single quantum wells

GaAsN bulk and GaAsN/GaAs single quantum wells grown by molecular beam epitaxy are studied by selectively excited photoluminescence (PL) measurements. A significant difference is observed in the PL spectra when the excitation energy is set below or above the band gap of GaAs for the GaAsN/GaAs quantum well samples, while the spectral features of GaAsN bulk are not sensitive to the excitation energy. The observed difference in PL of the GaAsN/GaAs quantum well samples is attributed to the exciton localization effect at the GaAsN/GaAs interfaces, which is directly correlated with the transfer and trap processes of the photogenerated carriers from GaAs into GaAsN through the heterointerfaces. This interface-related exciton localization effect can be greatly reduced by a rapid thermal annealing process, making the PL be dominated by the intrinsic delocalized transition in GaAsN/GaAs. (C) 2003 American Institute of Physics.

Study of optical properties in GaAs1-xSbx/GaAs single quantum wells

GaAsSb/GaAs single quantum wells (SQWs) grown by molecular beam epitaxy are studied by selectively-excited photoluminescence (SEPL) measurement. For the first time, we have simultaneously observed the PL, from both type I and type II transitions in GaAsSb/GaAs heterostructure in the SEPL. The two transitions exhibit different PL, behaviours under different excitation energy. As expected, the peak energy of type I emission remains constant in the whole excitation energy range we used, while type U transition shows a significant blue shift with increasing excitation energy. The observed blue shift is well explained in terms of electron-hole charge separation model at the interface. Time-resolved(TR) PL exhibits more type 11 characteristic of GaAsSb/GaAs QW. Moreover, the results of the excitation-power-dependent PL and TRPL provide more direct information on the type-II nature of the band alignment in GaAsSb/GaAs quantum-well structures. By combining the experimental results with some simple calculations, we have obtained the strained and unstrained valence band offsets of Q(v) = 1.145 and Q(v)(0) = 0. 76 in our samples, respectively.

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.

Selectively excited photoluminescence of GaAs1-xSbx/GaAs single quantum wells

GaAsSb/GaAs single quantum wells grown by molecular-beam epitaxy are studied by selectively excited photoluminescence measurements. We have simultaneously observed the photoluminescence (PL) from both type-I and type-II transitions in the samples. The two transitions exhibit different PL behavior under different excitation energies. As expected, the peak energy of the type-I emission remains constant in the entire excitation energy range we used, while the type-II transition shows a significant blueshift with increasing excitation energy. The observed blueshift can be well explained by an electron-hole charge separation model at interface. This result, along with the excitation-power-dependent PL and the measured longer carrier decay time, provides more direct information on the type-II nature of the band alignment in GaAsSb/GaAs quantum well structures. (C) 2002 American Institute of Physics.

GdxSi grown with mass-analyzed low energy dual ion beam epitaxy technique

Semiconducting gadolinium silicide GdxSi samples were prepared by mass-analyzed low-energy dual ion beam epitaxy technique. Auger electron spectroscopy depth profiles indicate that the gadolinium ions are implanted into the single-crystal silicon substrate and formed 20 nm thick GdxSi film. X-ray double-crystal diffraction measurement shows that there is no new phase formed. The XPS spectra show that one type of silicon peaks whose binding energy is between that of silicide and silicon dioxide, and the gadolinium peak of binding energy is between that of metal Gd and Gd2O3. All of these results indicate that an amorphous semiconductor is formed. (C) 2002 Elsevier Science B.V. All rights reserved.

Effect of rapid thermal annealing on electron emission and DX centers in strained InGaAs/GaAs single quantum well laser diodes

Thermal processing of strained In0.2Ga0.8As/GaAs graded-index separate confinement heterostructure single quantum well laser diodes grown by molecular beam epitaxy is investigated. It is found that rapid thermal annealing can improve the 77K photoluminescence efficiency and electron emission from the active layer, due to the removal of nonradiative centers from the InGaAs/GaAs interface. Because of the interdiffusion of Al and Ga atoms, rapid thermal annealing increases simultaneously the density of DX centers in the AlGaAs graded layer. The current stressing experiments of postgrowth and annealed laser diodes are indicative of a corresponding increase in the concentration of DX centers, suggesting that DX centers may be responsible for the degradation of laser diode performance.

Photoluminescence properties of a GaN0.015As0.985/GaAs single quantum well under short pulse excitation

Under short pulse laser excitation, we have observed an extra high-energy photoluminescence (PL) emission from GaNAs/GaAs single quantum wells (QWs). It dominates the PL spectra under high excitation and/or at high temperature. By measuring the PL dependence on both temperature and excitation power and by analyzing the time-resolved PL results, we have attributed the PL peak to the recombination of delocalized excitons in QWs. Furthermore, a competition process between localized and delocalized excitons is observed in the temperature-dependent PL spectra under the short pulse excitation. This competition is believed to be responsible for the temperature-induced S-shaped PL shift often observed in the disordered alloy semiconductor system under continuous-wave excitation. (C) 2001 American Institute of Physics.

MnSi similar to 1.73 grown on silicon with mass-analyzed low energy dual ion beam epitaxy technique

Semiconducting manganese silicide, Mn27Si47 and Mn15Si26, were obtained using mass-analyzed low energy dual ion beam epitaxy technique, Auger electron spectroscopy depth profiles showed that some of the Mn ions were deposited on single-crystal silicon substrate and formed a 37.5 nm thick Mn film, and the other Mn ions were successfully implanted into the Si substrate with the implantation depth of 618 nm. Some samples were annealed in the atmosphere of flowing N-2 at 840 degreesC. X-ray diffraction measurements showed that the annealing was beneficial to the formation of Mn27Si47 and Mn15Si26 (C) 2001 Published by Elsevier Science B.V.

Optical transitions and type-II band lineup of MBE-grown GaNAs/GaAs single-quantum-well structures

We have investigated transitions above and below band edge of GaNAs/GaAs and InGaNAs/GaAs single quantum wells (QWs) by photoluminescence (PL) as well as by absorption spectra via photovoltaic effects. The interband PL peak is observed to be dominant under high excitation intensity and at low temperature. The broad luminescence band below band edge due to the nitrogen-related potential fluctuations can be effectively suppressed by increasing indium incorporation into InGaNAs. In contrast to InGaNAs/GaAs QWs, the measured interband transition energy of GaNAs/GaAs QWs can be well fitted to the theoretical calculations if a type-II band lineup is assumed. (C) 2001 Elsevier Science B.V. All rights reserved.

Multiplicity factor and diffraction geometry factor for single crystal X-ray diffraction analysis and measurement of phase content in cubic GaN/GaAs(001) epilayers

On the basis of integrated intensity of rocking curves, the multiplicity factor and the diffraction geometry factor for single crystal X-ray diffraction (XRD) analysis were proposed and a general formula for calculating the content of mixed phases was obtained. With a multifunction four-circle X-ray double-crystal diffractometer, pole figures of cubic (002), {111} and hexagonal {1010} and reciprocal space mapping were measured to investigate the distributive character of mixed phases and to obtain their multiplicity factors and diffraction geometry factors. The contents of cubic twins and hexagonal inclusions were calculated by the integrated intensities of rocking curves of cubic (002), cubic twin {111}, hexagonal {1010} and {1011}.

Optical properties and band lineup in GaNxAs1-x/GaAs single quantum wells

The optical properties and the band lineup in GaNAs/GaAs single quantum wells (SQWs) grown by molecular beam epitaxy (MBE) using photoluminescence (PL) technique were investigated. It was found that the low-temperature PL is dominated by the intrinsic localized exciton emission. By fitting the experimental datawith a simple calculation, band offset of the GaN0.015As0.985/GaAs heterostructure was estimated. Moreover, DeltaE(c), the discontinuity of the conduction band was found to be a nonlinear function of the nitrogen composition (chi) and the average variation of DeltaE(c) is about 0. 110eV per % N, such smaller than that reported on the literature to (0.156 similar to 0.175 eV/N %). In addition, Qc has little change whtn N composition increares, with an experimential relation of QC approximate tox(0.25). The band bowing coefficient (b) was also studied in this paper. The measured band bowing coefficient shows a strong function of chi, giving an experimental support to the theoretic calculation of Wei Su-Huai and Zunger Alex (1996).

Influence of dual incorporation of In and N on the luminescence of GaInNAs/GaAs single quantum wells

The optical properties of above- and below-band-edge transitions have been investigated by incorporating In atoms into GaNAs/GaAs single quantum wells. The experimental results show that with increasing In concentration the interband luminescence is improved and the luminescence intensity below the band edge in GaInNAs/GaAs decreases significantly. An interpretation is given that N atoms are preferable to form a covalent bond with In than with Ga atoms in a GaInNAs alloy, due to the compensation of the atomic-size difference between In and N atoms on the GaAs substrate. The photoreflectance spectra of the GaInNAs/GaAs single quantum well support the assignment of an intrinsic mechanism to the high-energy luminescence peak. (C) 2000 American Institute of Physics. [S0003- 6951(00)01752-6].

Photoluminescence properties of SiGe/Si single wells with fluctuating structural parameters

Photoluminescence properties of SiGe/Si single wells with fluctuating structural parameters are studied. Four SiGe/Si single wells have been grown on Si(001) at 750 degrees C by disilane and solid Ge molecular beam epitaxy with varied disilane cracking-temperatures. Intense NP and TO-phonon replicas are detected up to 70 K in the photoluminescence spectra and the activation energy of the thermal quenching of the photoluminescence is 28 +/- 4 meV. The high growth temperature and purposeful introduction of fluctuation of structural parameters may be responsible for the improvement of the thermal quenching property.

A study of the interface of CeO2/Si heterostructure grown by ion beam deposition

Epitaxial cerium dioxide films on single-crystal silicon substrates (CeO2/Si) have been grown by a dual mass-analyzed low-energy ion beam deposition (IBD) system. By double-crystal X-ray diffraction (XRD), Full Width at Half Maximum (FWHM) are 23' and 33' in the rocking curves for (222) and (111) faces of the CeO2 film, respectively, and the lattice-mismatch Delta a/a with the substrate is about - 0.123%. The results show that the CeO2/Si grown by IBD is of high crystalline quality. In this work, the CeO2/Si heterostructure were investigated by X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) measurements. Especially, XPS and AES depth profiling was used to analyze the compositions and structures in the interface regions of the as-grown and post-annealed CeO2/Si. It was found that there was no silicon oxide in the interface region of the as-grown sample but silicon oxide in the post-annealed sample. The reason for obtaining such high quality heterostructure mainly depends on the absence of silicon oxide in the surface at the beginning of the deposition. (C) 1998 Elsevier Science Ltd. All rights reserved.