D. Golmayo

A New Hydrogen Sensor Based on a Pt / GaAs Schottky Diode

A new hydrogen-sensitive detector based oii a PffGaAs Scliottlry diode has been fabricated. The dcvices have been characterized sy dark current-voltage aiid capacitance-voltage measurtrnents, as a function of temperature and gas phase composition. At 150°C, the detection limit for liydrogen is 6 ppm iil a nitrogeii environment and 200 ppm in air.

Different catalytic metals (Pt, Pd and Ir) for GaAs Schottky barrier sensors

Abstract The effect of using different catalytic metals in GaAs Schottky diode sensors is evaluated for hydrogen and ammonia. Both thick and porous metal films are tested and optimized in view of the application.

Hydrogen sensor based on a Pt/GaAs Schottky diode

Abstract A new sensitive hydrogen detector based on a Pt/GaAs Schottky barrier diode has been fabricated. When the device is implemented with an organic layer (polyetherimide), the diode sensitivity increases. The effects of temperature, hydrogen concentration and ambient atmosphere on the device responses are examined.

The ammonia sensitivity of Pt/GaAs Schottky barrier diodes

In this work a new ammonia gas sensor is presented. Schottky barrier devices, Pt/n‐GaAs, with discontinuous platinum films are sensitive detectors of ammonia gas in a wide temperature range (from room temperature to 150 °C). The effect of parameters such as operation temperature, thickness of the catalytic metal film, background atmosphere, and applied voltage bias on the device sensitivity are investigated. In addition, significant characteristics have been examined including sensitivity limits, linearity of response, and adsorption and desorption kinetics.In this work a new ammonia gas sensor is presented. Schottky barrier devices, Pt/n‐GaAs, with discontinuous platinum films are sensitive detectors of ammonia gas in a wide temperature range (from room temperature to 150 °C). The effect of parameters such as operation temperature, thickness of the catalytic metal film, background atmosphere, and applied voltage bias on the device sensitivity are investigated. In addition, significant characteristics have been examined including sensitivity limits, linearity of response, and adsorption and desorption kinetics.

Photoluminescence characterization of GaAs quantum well laser structure with AlAs/GaAs superlattices waveguide

Dependence on the excitation power and temperature of the photoluminescence emission of GaAs quantum well laser structures using GaAs/AlAs superlattices in the waveguide is reported. The effects related to a quality reduction due to the presence of a thick ternary AlGaAs cladding layer in the bottom of the laser structure were elucidated by comparing to the photoluminescence of a similar waveguide structure, except for the AlGaAs bottom layer. The excitation power dependence shows the strong excitonic origin of the light emission in the temperature range 4–300 K in both structures. Carrier transport mechanisms through the superlattices is analyzed from the evolution of the photoluminescence of the quantum well and the superlattice confining layers; a structure dependent transparency temperature is defined, at which transport changes from tunneling assisted to extended minibands regime. The value of this parameter depends on the localized states in the superlattice minibands, caused by interface roughness.

(Ga0.22In0.78As)m⧸(Ga0.22In0.78P)m superlattices grown by atomic-layer molecular beam epitaxy on InP

Strained-layer superlattices (SLSs) made up of alternated GaxIn1-xAs and GaxIn1-xP, with x=0.22 is an alternative to the quaternary GaxIn1-xAsyP1-y. Strain is near symmetrized when grown on InP substrates. Lattice mismatch to InP (-1.57% GaInP, 1.71% GaInAs) being compensated, the net value of strain in the SLS is expected to be negligible. Using low temperature atomic-layer MBE (Ts = 350°C), P2 and As4 are supplied in successive pulses to group III terminated intermediate surfaces, minimizing competition, by using specially designed, fast operating valved solid source cells. A set of (Ga0.22In0.78 As)m/(Ga0.22In0.78P)m superlattices have been grown, with m ranging from 1 to 10 monolayers. The samples were characterized by X-ray diffraction. Photoluminescence measurements were performed, at 98 and 300 K, the emission wavelength ranging from 1.27 to 1.52 μm at room temperature. These superlattices have been used as pseudoquaternary material in InP/GaInAsP/GaInAs structures emitting at 1.5 μm.

Ga0.47In0.53As multiquantum well heterostructures, confined by pseudoquaternary (InP)n/(Ga0.47In0.53As)m short period superlattices lattice‐matched to InP

(InP)n/(Ga0.47In0.53As)m lattice‐matched short‐period superlattices have been used as pseudoquaternary material to confine Ga0.47In0.53As multiquantum wells in a GaxIn1−xAs/GaxIn1−xAsyP1−y/InP heterostructure. The samples have been grown by low‐temperature atomic layer molecular beam epitaxy, using fast operating valved solid sources to generate P2 and As4 beams. X‐ray diffraction was used to assess the structural quality of the samples. The effect of the superlattice period on the pseudoquaternary band gap is reported. Room‐temperature photoluminescence wavelength of the multiquantum well structure is close to 1.55 μm. Growing short‐period superlattices results in a much easier method to control band‐gap energy than growing alternative quaternary material.

Ammonia sensitivity of Pt/GaAs Schottky barrier diodes. Improvement of the sensor with an organic layer

Abstract Schottky barrier devices, Pt/ n -GaAs, with discontinuous platinum films are sensitive detectors of ammonia gas over a wide temperature range. When an organic layer of polyetherimide is combined with the device, the diode sensitivity increases. The characteristic parameters of these devices, such as sensitivity limits, linearity of response, and interfering gases, are examined.

Urea biosensor based on ammonia gas-sensitive Pt/GaAs Schottky diode

Abstract Pt/n-GaAs Schottky diodes with discontinuous catalytic metal are sensitive detectors of ammonia gas in a wide temperature range including room temperature. The combination of such devices with immobilized urease allows sensitive biosensors to be developed, which determine the urea concentration by means of the ammonia release in the enzyme-catalysed reaction. In this paper we report urea determinations in the concentration range 0.4–10 mM.

Electrical and optical properties of Be-doped InP grown at low temperature by solid source atomic layer molecular beam epitaxy

Beryllium-doped InP layers have been grown by solid source atomic layer molecular beam epitaxy at low substrate temperature. The residual n-type doping was reduced by controlling both the amplitude and the length of the phosphorus pulse. We have shown a well controlled p-type doping and obtained a hole concentration in the range 4×1017–3×1019 cm−3 at room temperature. The electrical and optical properties of InP layers grown at low temperatures were investigated by Hall effect and photoluminescence (PL) measurements. PL spectra for lightly doped samples have a near band emission at 1.41 eV and Be-related emissions around 1.38 eV.