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Ridge microstructures were prepared by etching through samples consisting of a series of stacked InAs x P 1 − x quantum wells (QWs) with step graded composition grown on InP by molecular beam epitaxy. Different etching techniques were used: wet etching with HCl/H 2 O and reactive ion etching with CH 4 /H 2. These microstructures were characterized by low-temperature micro-photoluminescence. The photoluminescence (PL) emission associated with each QW was clearly identified. The PL was measured in detail across etched ridge stripes of various widths. Variations of the integrated PL intensities across the etched stripes were observed. The PL intensities for all QWs increase gradually from the edge to the center of the ridge microstructures. The PL intensity measured at the ridge center is systematically reduced for ridges which are 10 or 20 μ m wide as compared to ridges which are 30 μ m wide or larger. On the other hand, the spectral peak position of the PL lines remained constant with high accuracy (0.2–0.4 meV) across the microstructures. These observations are discussed in terms of the different possible mechanisms which determine the PL intensity variations, namely, non-radiative recombination at the etched walls and effects of stray electric fields which result from the etching process. Based on this discussion, we compare quantitatively the different etching processes which we have used. Altogether, this study illustrates the contribution that specially designed test structures, coupled with advanced spectroscopic characterization, can provide to the development of semiconductor photonic devices (e.g., lasers or waveguides) involving etching processes. [ABSTRACT FROM AUTHOR]

We demonstrate what we believe is the first nonmechanical tunable vertical-cavity surface-emitting laser operating in the C band. This was achieved as a result of the combination of an InGaAs quantum well structure with a 6[lambda] thickness tunable index nano-polymer-dispersed liquid-crystal material. Experimental results exhibited a potential tunable range close to 10 nm, in the preliminary version, and excellent single mode locking due to the side-mode suppression ratio (more than 20 dB) over the whole spectral range. Another decisive advantage, compared to mechanical solutions, was the tuning response time of a few tens of microseconds (>30 [micro]s) to scan the full spectral range (10 nm), making this device appropriate for some access network functions, as well as being robust and low cost. The voltage values are the main limitation to wavelength range extension. We present a first version of the device optically pumped. The next version will be electrically pumped as required for the access network applications targeted here.

We compare the potentiality of bulk InGaPN and GaAsPN materials quasi-lattice-matched to silicon (Si), for multi-junction solar cells application. Bandgaps of both bulk alloys are first studied by a tight-binding model modified for nitrogen incorporation in diluted regimes. The critical thicknesses of those alloys are then calculated for various compositions. For the same lattice-mismatch and nitrogen amount, the bandgap of bulk GaAsPN is found to be closer to the targeted gap value of 1.7 eV for high efficiency tandem solar cell. GaPN and GaAsPN epilayers are then grown by molecular beam epitaxy on GaP substrate and studied by photoluminescence and X-ray diffraction. A GaAsPN bulk alloy emitting light at 1.77 eV at room temperature is obtained, demonstrating promising properties for further use in III-V/Si photovoltaic multijunction solar cells. [ABSTRACT FROM AUTHOR]

Amorphous silicon (a-Si) and amorphous silicon nitride (a-SiNx) layers deposited by magnetron sputtering have been analyzed in order to determine their optical and surface properties. A large value of ∼1.9 of index difference is found between these materials. Distributed Bragg reflectors (DBRs) based on these dielectric material quarter wave layers have been studied by optical measurements and confronted to theoretical calculations based on the transfer matrix method. A good agreement has been obtained between the experimental and expected reflectivities. A maximum reflectivity of 99.5% at 1.55 μm and a large spectral bandwidth of 800 nm are reached with only four and a half periods of a-Si/a-SiNx. No variation of the DBR reflectivity has been observed with the time nor when annealed above 240 °C and stored during few months. This result allows us to use this DBR in a metallic bonding process to realize a vertical cavity surface emitting laser (VCSEL) with two dielectric a-Si/a-SiNx DBRs. This bonding method using AuIn2 as the bonding medium and Si substrate can be performed at a low temperature of 240 °C without damaging the optical properties of the microcavity. The active region used for this VCSEL is based on lattice-matched InGaAs/InGaAsP quantum wells and a laser emission has been obtained at room temperature on an optically pumped device. [ABSTRACT FROM AUTHOR]

Amorphous silicon (a-Si) and amorphous silicon nitride (a-SiN(sub x)) layers deposited by magnetron sputtering was analyzed in order to determine their optical and surface properties. Distributed Bragg reflectors (DBRs) based on these dielectric material quarter wave layers was studied by optical measurements and confronted to theoretical calculations based on the transfer matrix method and the DBr is used in a metallic bonding process to realize a vertical cavity surface emitting laser with two dielectric (a-Si)/ a-SiN(sub x) DBRs.

The best solar conversion efficiencies have been reached thanks to multijunction solar based on III-V semiconductors on GaAs or Ge substrates. While displaying high conversion efficiencies, these solar cells suffer from the high cost of such substrates. To benefit from both the low cost and technological maturity of silicon cells, III-V tandem cells on silicon seem a good compromise to overpass the theoretical efficiency limit of the Si single cells. To study the GaP/Si interface effect on the solar cell characteristic, a GaP n-i-p solar cell has been grown on silicon substrate. Two types of electrical contacts configurations have been processed: a top-top configuration in which the current does not see the GaP/Si interface and the top-bottom configuration where the electric current crosses the interface. A comparison of dark I-V, I-V under solar illumination, and EQE measurements on both configurations is performed. The top-bottom contacts configuration shows an EQE a little bit lower than the top-top contact one, likely due to lower carrier diffusion length or recombination at the lower interface. However, the result on the EQE of the top-bottom configuration is encouraging for the future development of the GaP-based/Si tandem solar cells, and any other tandem cell on silicon using GaP as an intermediate selective contact.