Y. Cuminal

Observation of room-temperature laser emission from type III InAs/GaSb multiple quantum well structures

Multiple quantum well InAs/GaSb laser heterostructures with type III (type II broken gap) band alignment in the active region have been grown by molecular beam epitaxy. Intense electroluminescence was observed at room temperature (RT) with peak emission wavelengths in the range 1.95–3.4 μm. RT lasing has been achieved at 1.98 and 2.32 μm for the structures with 6 and 12 A thick InAs quantum wells, respectively.

Physical properties of Cu2ZnSnS4 thin films deposited by spray pyrolysis technique

Thin films of Cu2ZnSnS4 (CZTS) were deposited on Pyrex substrates at various temperatures by spray pyrolysis technique from aqueous solution containing an economic stannous chloride (SnCl2) precursor for the tin and the effect of substrate temperature on the structural and opto-electronic properties was investigated. X-ray diffraction patterns and Raman spectroscopy reveal that all the CZTS films exhibited kesterite structure with preferential orientation along the (1 1 2) direction and some secondary phases. Also, they possessed different band gaps, which were found to lie between 1.52 and 1.81 eV, indicating that CZTS compound has absorbing properties favorable for applications in solar cell devices. Van der Pauw technique and Hall effect measurements were used to determine the electrical properties of CZTS films and the resistivity was of about 0.12 Ω cm for film grown at 280 °C.

Long-wavelength (Ga, In)Sb/GaSb strained quantum well lasers grown by molecular beam epitaxy

The molecular beam epitaxy growth of strained (Ga, In)Sb/GaSb quantum wells is investigated. In a narrow range of growth conditions, (Ga, In)Sb quantum well structures exhibiting excellent structural properties as well as intense and narrow photoluminescence transitions are obtained. Stimulated emission at 1.98 m is observed at room temperature from laser diodes with strained quantum wells as the active zone. The lasers exhibit threshold current densities as low as 280 A and a characteristic temperature of 75 K.

Electroluminescence of GaInSb/GaSb strained single quantum well structures grown by molecular beam epitaxy

GaSb-based heterostructures with strained-layer (x = 0.26 or x = 0.35) single quantum wells and cladding layers were grown by molecular beam epitaxy. The thickness of the GaInSb well was varied from 3.0 to 14.5 nm. Intense room-temperature electroluminescence was observed from mesa diodes with peak emission wavelengths in the spectral range. The dependence of emission energy on well thickness is consistent with the predictions obtained by an effective mass treatment assuming a rectangular type I quantum well and a conduction band offset .

Spontaneous emission from InAs/GaSb quantum wells grown by molecular beam epitaxy

We have investigated the spontaneous emission from InAs/GaSb quantum wells grown by molecular beam epitaxy. A strong photoluminescence signal was observed only from samples grown in a narrow substrate temperature range around 400 °C with InSb-like interfaces. From an analysis of the photoluminescence energy with the excitation density, we demonstrated the formation of triangular quantum wells for holes in the GaSb barriers close to the interfaces. Finally, the temperature dependence of the photoluminescence peak energy showed a deviation from the InAs band gap evolution at low temperature, which could be related to the type II broken gap band alignment.

Room-temperature GaInAsSb/GaSb strained quantum-well laser diodes

Diode lasers operating at room temperature with an emission wavelength of have been fabricated from compressively strained multiple-quantum-well structures grown by molecular beam epitaxy. Ridge waveguide lasers long exhibited an RT current threshold of 500 mA, optical power efficiency of /facet and a differential quantum efficiency of 14.5%. A pulsed threshold current density less than with a characteristic temperature have been achieved for broad mesa devices. The laser structure, which has a type-II band alignment at the well-barrier interface, showed an internal efficiency , controlled by the electron-hole wavefunction overlap at the interface.

The post-growth effect on the properties of Cu2ZnSnS4 thin films

Cu2ZnSnS4 (CZTS) thin film was deposited on glass substrate by spray pyrolysis technique using a methanolic solution. This film was annealed under nitrogen atmosphere for an hour at different annealing temperatures. The effect of the annealing temperature on composition, structure, morphology, electrical, and optical properties of CZTS films was investigated. Energy dispersive x-ray analysis showed that after the annealing process, the atomic ratio values tend to their stoichiometric values. Moreover, the X-ray diffraction (XRD) and Raman spectroscopy revealed a kesterite structure with (112) preferential orientation for both as-deposited and annealed CZTS films. Moreover, they exhibited an improvement in crystallinity after annealing which was confirmed by SEM analysis. The conductivity of the heated CZTS films showed also an important increase in crystallinity. The absorption edge shifted toward lower wavelengths leading to an increase in band gap energy for the annealed CZTS films.

Continuous-wave operation of GaInAsSb-GaSb type-II quantum-well ridge-lasers

Ridge-waveguide laser diodes emitting near 2.38 /spl mu/m have been fabricated from GaInAsSb-GaSb type-II quantum-well (QW) structures grown by molecular beam epitaxy. These devices operated continuous-wave (CW) at room temperature, what is obtained for the first time from a type-II QW laser. At 23/spl deg/C threshold currents in the range 60-140 mA and CW output powers exceeding 1 mW/facet were obtained. These lasers showed a tendency to operate in a single longitudinal mode with a temperature red shift of 0.1 nm//spl deg/C and a current red shift of 0.06 nm/mA.

Oxidation pathways towards Si amorphous layers or nanocrystalline powders as Li-ion batteries anodes

Silicon nanomaterials are obtained by an original approach based on the direct solution phase oxidation of a solid state Zintl phase NaSi used as silicon precursor. Alcohols with different alkyl chains are chosen as oxidizing agents. The materials are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The most relevant parameter lies in the amorphous character of the silicon nanoparticles produced by this route. Amorphous nature of silicon is one of the key features for succeeding in the improvement of anodes for Li-ion batteries. The Si nanostructures have been tested as anodic materials for lithium ion batteries.

Modeling of the Boron Emitter Formation Process from BCl3 Diffusion for N-Type Silicon Solar Cells Processing

This work is devoted to the study of boron doping diffusion process for n-type silicon solar cells applications. Deposition temperature is an important parameter in the diffusion process. In this paper we investigate its influence using an industrial scale furnace [1] (LYDOPTM Boron), which is developed by Semco Engineering. We especially used a numerical model (Sentaurus) in order to further understand the boron diffusion mechanism mainly with respect of the diffusion temperature. The model calibration is based on boron concentration profiles obtained by SIMS (Secondary Ion Mass Spectrometry) analysis. We observed that the boron profiles could be correctly simulated by a single fitting parameter. This parameter, noted kBoron which is connected to the chemical reaction kinetics developed at the interface between the boron silicon glass (BSG) and the silicon substrate