L. Auvray

Radiative N-localized recombination and confinement in GaAsN/GaAs epilayers and quantum well structures

Abstract The photoluminescence (PL) properties of GaAsN/GaAs epilayers and single quantum wells (QWs) have been investigated as a function of the excitation density and the sample temperature (10–300 K). At low temperatures, the PL spectra were sensitive to the excitation density for epilayers and QWs. For both structures, a blue shift of the PL peak is noted with increasing the excitation power. In contrast, the temperature dependence shows different behaviors for the bulk epilayers and for the quantum wells structures. An S-shape of the PL peak energy versus temperature has been observed for the GaAsN/GaAs epilayer while the QWs peak energy decreases monotically with the sample temperature and could be fitted by conventional Varshni’s law. This behavior is due to the exciton localization effect which is induced by the local fluctuation of nitrogen concentration.

Excitons localization effects in GaAsN/GaAs epilayers grown by MOCVD

Abstract Optical studies of GaAs 1− x N x /GaAs epilayers grown by metal-organic chemical vapour deposition (MOCVD), with low nitrogen concentration (1.65% and 2.2%), have been achieved by a number of optical techniques such as photoluminescence (PL), photoreflectance (PR) spectroscopies and time-resolved PL (TR-PL) measurements in the nanosecond range. It has been shown that the increase of the nitrogen fraction causes a red shift of the PL emission band compared to the GaAs one. TR-PL results at 12 K reveal that the decay time is clearly dependent on the emission energy. It increases for lower emission energy. From the temperature PL decay lifetime study, we suggest that PL emission is dominated by the recombination of localized excitons trapped by potential fluctuations of the near band edge induced by compositional fluctuations in GaAsN epilayer.

Surface morphology of InGaAs and InP materials grown with trimethylarsenic and arsine on vicinal InP substrates

Abstract In this study, we report on an investigation using atomic force microscope (AFM) to study lattice-matched InGaAs surface layers grown by MOVPE with two different sources of group V elements: trimethylarsenic (TMAs) and arsine. The growth was performed with a home made apparatus with a T shaped reactor. The substrate temperature ranged from 570 to 630°C under pure hydrogen or a mixture of hydrogen and nitrogen as carrier gas. After thermal annealing under PH 3 and growth of InP buffer layer, we could clearly observe the step/terrace like feature of the vicinal surface morphology for 0.2° misoriented substrates. For epilayers grown under nitrogen flow, step bunching was observed with terraces as large as 170xa0nm which is twice larger than the nominal value (80xa0nm). Lattice-matched InGaAs/InP epilayers were grown with arsine and TMAs. For TMAs-grown epilayers, we observed that the roughness depends on V/III ratio and growth temperature. The comparison of the surface morphology of TMAs and arsine-based epilayers assessed by AFM characterisation will be presented and discussed in terms of As-carbon adsorbed species.

Surface morphology, electrical and optical properties of In0.53Ga0.47As/InP grown by metalorganic vapor-phase epitaxy using trimethylarsine and arsine

Abstract We report the effect of two sources of arsenic on the surface morphology, optical and electrical properties of InGaAs/InP epilayers grown by metalorganic vapor-phase epitaxy at 600°C. Hydrogen or a mixture of nitrogen and hydrogen was used as a carrier gas. The surface structure varied considerably with the precursor. The detailed surface morphology observed by atomic force microscopy presents the characteristics of the step flow growth mode with monoatomic height steps (0.3xa0nm) for InGaAs/InP (0.2 off substrates) layers grown with arsine. In contrast, islanding growth was observed with trimethylarsine when increasing the V/III ratio. Optical and electrical properties have been studied, the full-width at half-maximum of the luminescence peak at 300xa0K are, respectively, 110xa0nm for arsine and 150–240xa0nm for TMAs-grown epilayers whereas electron mobilities at 77xa0K are 94u2008000xa0cm 2 /Vxa0s (arsine-based samples) and 4000–23u2008000xa0cm 2 /Vxa0s for TMAs-based epilayers. Residual doping level of InGaAs at room temperature varies between 5×10 15 (arsine-based samples) to 2×10 17 xa0cm −3 for TMAs-grown samples under nitrogen flow. The degradation of the optical and electrical properties using TMAs will be interpreted in terms of simultaneous incorporation of C-acceptor impurities and donor impurities. The nature of the donor will be discussed.

N-enrichment at the GaAs1−xNx/GaAs(0 0 1) interface: microstructure and optical properties

Abstract We have investigated the growth, the microstructure and the optical properties of the GaAs0.97N0.03/GaAs interface. Epilayers were grown at 520–550°C using trimethylgallium, dimethylhydrazine and arsine on GaAs(0xa00xa01) vicinal surfaces. A 5–6xa0nm thick layer of GaAsN with N-enrichment is clearly seen by cross-sectional transmission electron microscopy at the interfacial region. The nitrogen composition at the interface is twice that of the bulk epilayer (close to 1.6%) as shown by photoluminescence spectroscopy (PL) and high resolution X-ray diffraction. The PL data of several samples shows two peaks located at 1–1.1 and 1.2–1.3xa0eV associated with the interfacial region and the bulk layer, respectively. We discuss several mechanisms for the nitrogen enrichment by comparing the GaAsN film thickness. The step/terrace surface morphology of GaAs before growth is probably the key parameter.

Optical signature of atomic ordering in In0.53Ga0.47As/InP: photoluminescence properties and IR response

Lattice-matched InGaAs/InP epilayers, grown by metal-organic vapor phase epitaxy, were investigated by PL spectroscopy and FT-IR to analyze the atomic ordering. Owing to the formation of the InGaAs/InP interface it was shown that growth conditions parameters such as growth temperature or arsenic precursor influence the development of atomic ordering. Low temperature optical properties of samples grown at 570-600 °C with trimethylarsenic (TMAs) and arsine are compared. A blue-shift of the PL peak position with increasing the excitation density is observed with a band gap reduction of 70-80 meV for TMAs-grown epilayers. Also a change in the IR absorption spectrum at 600-700 cm 1 is seen. Ordering is enhanced for TMAs-grown epilayers up to 600 °C growth temperature while it is not observed for arsine-grown epitaxial layers at the same growth temperature.