G. Guillot

Rapid thermal annealing in GaNxAs1-x/GaAs structures: effect of nitrogen reorganization on optical properties

We report on the effect of rapid thermal annealing (RTA) on the photoluminescence (PL) properties of GaNxAs1−x/GaAs structures. In particular, a blueshift of the PL peak energy is observed when annealing the samples. The results are examined as a consequence of a RTA-induced nitrogen diffusion inside the GaNxAs1−x material rather than diffusion out of the alloy, which homogenizes initial nitrogen composition fluctuations. We propose a simple model that describes the RTA-induced blueshift of the low temperature PL peak energy. This model is in good agreement with experimental results and is consistent with recent studies in which lateral composition fluctuations in the GaNAs alloy were reported.We report on the effect of rapid thermal annealing (RTA) on the photoluminescence (PL) properties of GaNxAs1−x/GaAs structures. In particular, a blueshift of the PL peak energy is observed when annealing the samples. The results are examined as a consequence of a RTA-induced nitrogen diffusion inside the GaNxAs1−x material rather than diffusion out of the alloy, which homogenizes initial nitrogen composition fluctuations. We propose a simple model that describes the RTA-induced blueshift of the low temperature PL peak energy. This model is in good agreement with experimental results and is consistent with recent studies in which lateral composition fluctuations in the GaNAs alloy were reported.

Photoluminescence properties of GaN grown on compliant silicon-on-insulator substrates

A compliant substrate approach has been employed to release lattice-mismatch caused strain in GaN epilayers through stress absorption in the substrate. GaN layers have been grown on silicon-on-insulator (SOI) substrates by low-pressure metalorganic chemical vapor deposition. Photoluminescence measurements at 4 K show the spectrum of grown GaN being dominated by UV emission around 3.47 eV related to neutral-donor bound excitons. The much weaker yellow luminescence shows a broad spectrum around 2.16 eV. Peak position of the UV emission changes both with measurement temperature and strain. At room temperature, the UV peak is red shifted by 64 meV corresponding well to the band-gap temperature dependence. Strain-induced blue shift of the peak, compared to unstrained GaN, is much less than for growth on sapphire, indicating strain relief in the GaN by growth on SOI. Further reduction of the blue shift is consistent with increased electron mobility.

The acceptor level of vanadium in III-V compounds

The positions of the acceptor level of vanadium in GaAs, GaP, and InP are estimated. This level is found to be at about Ec−0.14 eV in GaAs and about Ec−0.8 eV in GaP. It is above the conduction band edge in InP. These positions in the three hosts are in agreement with the trends proposed by Ledebo and Ridley. The finding of a very high acceptor level of vanadium in GaAs does not allow to explain the semi‐insulating behavior of GaAs:V. Other possible compensating centers are considered.

Electrical characterization of instabilities in 6H silicon carbide metal‐oxide‐semiconductor capacitors

Capacitance, charge, and current measurements have been performed on p‐type 6H‐SiC metal‐oxide‐semiconductor capacitors in order to study electrical instabilities in the SiO2/6H‐SiC system and the behavior of the inversion layer at different temperatures. The analysis of hysteresis and deformation of capacitance‐voltage curves shows the presence of interface states and oxide traps with a density of approximately 5–7×1010 eV−1u2009cm−2 in the midgap and a peak of 3×1012 eV−1u2009cm−2 at E=Ev+0.53 eV. Ionic contamination of the oxide layer has also been investigated, by thermally stimulated ionic current: A mobile charge concentration in the range of 1012 cm−2 was found. Finally, it is shown, by charge‐voltage measurements, that the minority‐carrier generation is assisted by deep levels during the formation of the inversion layer.

Absolute photoionization cross sections of the acceptor state level of chromium in indium phosphide

We have studied by deep‐level transient spectroscopy and deep‐level optical spectroscopy n‐type chromium‐doped InP. We definitively confirm that the Cr2+/Cr3+ acceptor state is positioned at EC −0.4 eV in InP. We have measured for the first time the absolute values of the photoionization cross sections of Cr2+ in InP by deep‐level optical spectroscopy. The σ0n cross section exhibits both a resonant and a nonresonant character. The former corresponds to the internal transition 5T2→5E of Cr2+, while the latter is attributed to the photoexcitation from the Cr2+ to the conduction band. The threshold of this transition at EC −0.41 eV indicates a very small Franck–Condon shift. The scales of the absolute photoionization values (σ0n) and photoneutralization (σ0p) cross sections towards the conduction and valence bands are the same, which seems to indicate no selection rules.

Photoreflectance studies of lattice‐matched and strained InGaAs/InAlAs single quantum wells

Lattice‐matched and strained InxGa1−xAs/In0.52Al0.48As single quantum wells with x=0.53 and x=0.60 have been studied by the optical modulation technique of photoreflectance (PR) at room temperature. The measurements have allowed the observation of interband transitions from the heavy‐ and light‐hole valence subbands to the conduction subbands. The PR data have been adjusted with a least‐squares fit to the first‐derivative functional form. The energetic positions of the optical transitions deduced from the fit have been compared with theoretical values obtained by an envelope function model calculation including strain effects. The best adjustment allowed the determination of the conduction‐band offset parameter Qc which is found equal to 0.71±0.07 for the lattice‐matched and strained compositions.

A Comprehensive Optimization of InAlAs Molecular Beam Epitaxy for InGaAs / InAlAs HEMT Technology

The effects of the substrate temperature in the molecular beam epitaxy growth of on have been investigated. A strong dependence of the structural, electrical, and optical properties of films on the growth temperature has been found and optimized material can be grown at 530°C. The low substrate temperatures deteriorate the material quality due to insufficient growth kinetics, while the higher temperatures allow the formation of composition inhomogeneities which also deteriorate the structural, optical, and electrical characteristics of . Using buffers grown at 530°C, state‐of‐the‐art high electron mobility transistors were fabricated and showed reduced output conductance and no kink effect in the I(V) characteristics.

A study of deep levels by transient spectroscopy on p‐type liquid‐phase‐epitaxial GaxIn1−xAsyP1−y grown on semi‐insulating InP

p‐type layers of InP, Ga0.28In0.72As0.6P0.4 (λ=1.3 μm) and Ga0.47In0.53As (λ=1.65 μm) grown by liquid ‐phase epitaxy on semi‐insulating InP:Fe substrates have been investigated by deep level transient spectroscopy. In InP, we have found near the surface a majority‐carrier trap which is located at 0.22 eV above the top of the valence band. A very similar trap (capture cross section and energy) appears with about the same concentration in the quaternary layer but is not present in the ternary layer. Thus, we suggest that this trap could be related to the phosphorus sublattice (e.g., a complex, a vacancy, or a substitutional impurity), caused by a phosphorus depletion produced at the end of the epilayer growth. Other traps have been found in quaternary and ternary layers but are not identified.

Alloy broadening in photoluminescence spectra of Ga0.47In0.53As

The low‐temperature photoluminescence of undoped GaxIn1−xAs layers, lattice matched to InP, grown by liquid‐phase epitaxy and molecular‐beam epitaxy has been studied. In this work, we focus mainly on the origin of the line broadening of the two main emissions (excitonic and donor‐acceptor pair transitions) observed. We find that, as it has been recently shown in GaxAl1−xAs, the dominant broadening mechanism is alloy broadening, due to random cation distribution. This model gives linewidths of the bound exciton and the donor‐acceptor pair transitions based on compositional fluctuations within the crystal volumes which are characteristic of the two transitions. Calculated linewidths agree rather well with experimental results, thus demonstrating that alloy broadening leads also in GaxIn1−xAs to a quantitative understanding of the low‐temperature photoluminescence spectra. Careful analysis of the donor‐acceptor pair band yields acceptor activation energies of 15, 22, and 25 meV which are attributed to C, Zn,...

The donor level of vanadium in InP

We have studied p‐type vanadium‐diffused InP by deep‐level transient spectroscopy. A level at 0.21 eV above the valence band is observed at a concentration comparable to that of vanadium. This level is interpreted as the V3+/V4+ donor state of vanadium in agreement with photoluminescence excitation experiments on n‐type InP:V. Measurement of the photoneutralization cross section allows us to observe, for the first time, an excited state of a transition metal ion in resonance with the valence band. This observation confirms the charge state of the level that we have found.