A.S. Barrière

Electrical characterization of InGaN/GaN light emitting diodes grown by molecular beam epitaxy

We studied the electrical behavior of multiple InGaN/GaN quantum well based light emitting diodes grown by molecular beam epitaxy and we determined three different domains of current-voltage dependence. We then described the charge carrier transport mechanisms for these three domains. The first domain, corresponding to leakage currents (V 3.5 V), the current is limited by the p-GaN zone. In this zone, the...

Intra‐4f‐shell transitions at room temperature of Er3+ ions in Ca1−xErxF2+x thin films grown on Si(100)

Intra‐4f‐shell transitions of Er3+ ions in Ca1−xErxF2+x thin films were studied by means of photoluminescence (PL) and cathodoluminescence (CL) measurements at room temperature. The samples, with x varying from 0.01 to 0.2, were epitaxially grown on Si(100) substrates by sublimation of solid solution powders. Using the 488‐nm line of an Ar+‐ion laser as the excitation source, it is shown that the films present strong PL lines corresponding to the internal transitions between the 4S3/2,4F9/2,4I11/2, and 4I13/2 excited levels and the 4I15/2 fundamental state of Er3+ (4f11) ions. Their centers of gravity were pointed out at λ=533, 650, 980, and 1530 nm, respectively. These electronic transitions were also evidenced by means of the CL technique. Moreover, this technique showed that the luminescence is uniform in all points of the layers. The PL intensities vary considerably as a function of the erbium substitution rate. In the visible range the strongest luminescence was found for x less than 0.01, while for ...

Physico-chemical characterization of thin films obtained by fluorination of GaAs under 5 bar of fluorine

Abstract Fluoride-GaAs(100) structures have been prepared by fluorination under 5 bar of fluorine for different temperatures and times. This paper deals with the preparation method and with the physico-chemical characterization of the samples obtained. The bulk of the fluoride layers has been investigated by Rutherford backscattering, IR absorption and Auger electron spectroscopy measurements. It has been demonstrated that for fluorine at this pressure, the best oxidation temperature is close to 200°C. The bulk composition of the films formed at the surface of GaAs substrates is GaF3. The semiconductor-fluoride interface has been studied using the X-ray photoelectron spectroscopy technique, and arsenic has been found to be bound to fluorine.

Heteroepitaxial growth and characterization of SrF2/(100)InP

The composition of SrF2 thin films deposited on carbon plates by sublimation under ultrahigh vacuum has been investigated mainly by Rutherford backscattering (RBS) of α particles as a function of the substrate temperature during the condensation phase and of the thickness of the layers. It is shown that for TS = 270 °C the obtained films are stoichiometric, homogeneous, and quasi‐insensitive to air exposure. The structure of such layers grown on (100)InP single crystals has been deduced from the study of channeling phenomenon. It is demonstrated that the RBS minimum yield χmin, measured on SrF2, decreases with increasing thin‐film thickness, varying from 100 to 400 nm. For a 400‐nm‐thick SrF2 thin film at 350 nm from the interface χmin=0.05 showing that the layer is well crystallized and presents the same orientation as the substrate.

A study of the chemical oxide/InP interface by deep-level transient spectroscopy

Metal‐insulator‐semiconductor structures prepared by chemical oxidation of the InP surface in HNO3 solutions are studied before and after aging and annealing. One interfacial deep level with an activation energy ΔE=0.4 eV and a capture cross section σ=3.7×10−14 cm2 is observed on a freshly oxidized structure. After aging in air the characteristics of the deep level are ΔE=0.2 eV and σ=6×10−20 cm−2. Annealed aged structures exhibit two interfacial deep levels, one with ΔE=0.4 eV and σ=10−14 cm2 and the other with ΔE=0.2 eV and σ=2.1×10−19 cm2; this latter is located further in the bulk of InP. Some hypotheses are proposed to explain the instability phenomena observed in these devices.

Study of a chemical cleaning of InP(100) substrates by infrared absorption and nuclear reaction analysis

Abstract A standard chemical cleaning of InP(100), which allows a thermal desorption of oxidized surface phases under vacuum at relatively low annealing temperature (350°C), has been studied by infrared absorption (IR) spectroscopy and nuclear reaction analysis (NRA). It consists, after a degreasing and chemical etching of the substrate using a H 2 SO 4 /H 2 O 2 /H 2 O (2:1:1) mixture, in a de-oxidation of the surface by a HF-ethanol (10%) solution, performed on a spinner operated in a nitrogen box. At different stages of the process IR measurements allowed a description of the different atomic groups present at the surface of InP. Traces of oxygen have been evidenced from NRA studies.

Characterization of Ca1−xErxF2+x solid solution thin films grown on Si(100) substrates

Erbium‐substituted Ca1−xErxF2+x calcium trifluoride layers were grown on Si(100) substrates by sublimation under ultrahigh vacuum of high purity solid solution powders. X‐ray diffraction and scanning electron microscopy techniques were performed to study the texture and the structure of the layers. Their composition was mainly deduced from Rutherford backscattering of α particles and particle induced x‐ray emission. For an erbium substitution rate, x, lower than 0.2, it has been shown that the film compositions are analogous with that of the sintered material and quite homogeneous. A Rutherford backscattering study in channeling conditions showed that heteroepitaxial Ca1−xErxF2+x/Si(100) structures can be grown for a substrate temperature of 550 °C.

Low temperature luminescence studies of Ca1−xErxF2+x thin films epitaxially grown on silicon substrates

Room temperature photoluminescence studies of Ca1−xErxF2+x thin films epitaxially grown on silicon substrates exhibit strong light emissions in both the visible range and the infrared domain. With an Ar+‐ion laser as an excitation source, the maximum of the 4I13/2→4I15/2 infrared (1530 nm) luminescence of Er3+ (4f11) ions was found for x=0.16. It is assumed that a particular Er3+ ion environment exists in the layers to explain why the quenching phenomena do not dominate at these very high erbium concentrations. To describe this environment, a photoluminescence study at low temperature (2 K) has been performed which shows that only one Er3+ ion site (having C4v symmetry) predominates for an erbium substitution rate x≤0.02. At higher Er3+ concentrations, however, a clustering process of erbium ions is observed. In thin films, however the clustering appears only at concentrations two orders of magnitude higher than in bulk single cystals.Room temperature photoluminescence studies of Ca1−xErxF2+x thin films epitaxially grown on silicon substrates exhibit strong light emissions in both the visible range and the infrared domain. With an Ar+‐ion laser as an excitation source, the maximum of the 4I13/2→4I15/2 infrared (1530 nm) luminescence of Er3+ (4f11) ions was found for x=0.16. It is assumed that a particular Er3+ ion environment exists in the layers to explain why the quenching phenomena do not dominate at these very high erbium concentrations. To describe this environment, a photoluminescence study at low temperature (2 K) has been performed which shows that only one Er3+ ion site (having C4v symmetry) predominates for an erbium substitution rate x≤0.02. At higher Er3+ concentrations, however, a clustering process of erbium ions is observed. In thin films, however the clustering appears only at concentrations two orders of magnitude higher than in bulk single cystals.

Characterization of SrF2 thin films and of SrF2/InP structures

Abstract The composition of SrF2 thin films deposited on carbon substrates by sublimation under vacuum has been investigated by Rutherford backscattering of α particles. It is shown that, for a substrate temperature TS = 573 K during the condensation of the vapour, the bulk composition of the layers is quasi-stoichiometric. Only a slight lack of fluorine, correlated with the presence of oxygen, is observed near their external surface. Coating with a very thin film of gold prevents air contamination. The interactions of such compounds with InP(100) single crystal have been deduced from X-ray diffraction and X-ray photoelectron spectroscopy studies. On the one hand, thin SrF2 films have been found to be polycrystalline, a part of the polycrystals being oriented like the InP crystal, and, on the other hand, chemical bonds between phosphorus and fluorine have been observed at the insulator-semiconductor interface.

Interface GaAs - gallium fluoride thin film grown by fluorination: Electrical behaviour of the obtained MIS fluorinated GaAs structures

Abstract Fluoride-GaAs(100) structures have been prepared by fluorination of the semiconductor under 1 bar of fluorine at different temperatures ( T f ) and times ( t f ). The physico-chemical characterizations of the obtained samples have been deduced mainly from RBS, XPS and STEM experiments. It has been demonstrated that the bulk composition of the films formed at the surface of GaAs substrates is GaF 3 . At the fluoride-semiconductor interface, arsenic has been found to be bound with fluorine. In the case of thick films, it has been shown that the fluorine diffusion becomes inhomogeneous. Consequently, the thickness of the fluoride layers changes at different points on the structures. For T f ≥300°C, the capacitance voltage ( C-V ) characteristics of the obtained MIS fluorinated GaAs structures show that, using this passivation technique, an important modulation of the surface potential of the GaAs is obtained without hysteresis for a sweep frequency down to 10 -2 Hz. The surface state density in the gap of GaAs is very low ( N ss about 10 11 eV -1 cm -2 ) To minimize the inhomogeneous fluorine diffusion effect, very thin layers of fluorine were grown by fluorination at the surface of GaAs and these structures were coated with a GaF 3 thin film deposited by sublimation under vacuum. This process, which allows us to predict the thickness of the insulator, keeps the insulator-semiconductor interface in the state previously described.