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5 pages, 7 figures., SnTe-doped InP layers were grown at low temperature by solid-source atomic layer molecular beam epitaxy. The samples were characterized by Hall measurements versus temperature, low temperature photoluminescence, x-ray diffraction, and secondary ion mass spectroscopy. The temperature of the SnTe effusion cell was varied from 320 to 440 °C, and the free electron concentration measured at room temperature ranged between 2.0×1016 cm−3 and 5.6×1018 cm−3 with the corresponding Hall mobility varying from 2320 to 1042 cm2/V s., The authors would like to thank Dr. A. J. Springthorpe, from Nortel Networks, for SIMS measurements, and the Spanish CICYT for financially supporting this research under Contract No. TIC-99-0645-C05-05.

A novel monolithically integrated optoelectronic microsensor is fabricated on GaAs substrates by means of a single epitaxial process step (atomic layer molecular beam epitaxy, ALMBE), conventional lithography and selective chemical etching techniques. The microsensor integrates an IR (0.86-1.1 μm) lateral emitting diode linked through a leaky optical waveguide to a photodiode. © 1993.

Room temperature laser emission near 1.55µm is obtained in compressive strained multiquantum well separate confinement heterostructure grown at 340°C by all-solid source Atomic Layer Molecular Beam Epitaxy , where (lnP)5/(Ga0.47 In0.53 As)5, lattice-matched short period superlattices have been used as pseudoquaternary barrier to confine Ga0.27 In0.73 As wells . These preliminary results show that solid source Atomic Layer Molecular Beam Epitaxy is well adapted to fabricate advanced optoelectronic components including pseudoquaternary material.

5 páginas, 6 figuras, 1 tabla., 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.

4 páginas, 7 figuras, 1 tabla.-- PACS: 82.45.Jn; 07.07.Df; 85.30.Hi., A new hydrogen-sensitive detector based on a Pt/GaAs Schottky diode has been fabricated. The devices have beencharacterized by dark current-voltage and capacitance-voltage measurements, as a function of temperature and gas phasecomposition. At 150°C, the detection limit for hydrogen is 6 ppm in a nitrogen environment and 200 ppm in air.

Undoped InP layers grown at low temperature by atomic layer molecular beam epitaxy have been studied by Hall measurements and deep level transient spectroscopy. The free carrier concentration at room temperature increases linearly with phosphorus pressure and it has been possible to obtain layers with a free carrier concentration of 1 × 1016 cm−3 and an electron mobility of about 3000 cm2 V−1s−1, which are similar to values for samples grown at high temperatures. Deep level transient spectroscopy shows the presence, in all the samples, of five electron traps with emission energies of 0·60, 0·40, 0·25, 0·16, and 0·11 eV from the conduction band, with concentrations independent of the free carrier concentration with the exception of the 0·40 eV trap concentration, which increases slightly with free carrier concentration.MST/3332

Photoplethysmography and pulse oximetry are widely used techniques for noninvasive monitoring of heart rate and peripheral oxygen saturation. Over the last years we have been working onto the application of near infrared range wavelengths to replace those of the classical pulse oximeters. The development of laser diodes based sensors, processing algorithms, a calibration procedure, and the comparison with a commercial pulse oximeter, have been followed by a set of experimental studies. The results exposed here demonstrate the applicability of transmittance photoplethysmography and pulse oximetry using laser diodes emitting at specific wavelengths for a wide range of situations.

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., This work was supported by Project No. TIC95-0563-C05-05 of the Spanish Government.

6 páginas, 3 figuras., p++/n++ InP tunnel diodes have been fabricated for the first time on InP and Si substrates by solid source Atomic Layer Molecular Beam Epitaxy (ALMBE) at low temperature. The high peak current density exceeding 200 A/cm2 and the low specific resistance exhibited in these diodes indicate that they are appropriate to use as optically transparent interconnects in InP/Ga0.47In0.53As tandem solar cells. This is a very promising result for the use of solid source ALMBE for fabricating these tandem solar cells with a technological process compatible with low temperature technologies, as the conventional silicon technologies.

The electrical and optical properties of undoped InP layers grown at low temperatures by solid source atomic layer molecular beam epitaxy are investigated. Phosphorus surface coverage during epitaxy is controlled by monitoring the evolution of reflection high-energy electron diffraction pattern during growth. An accurate phosphorus supply by means of a valved cracking phosphorus cell is employed. The relation between phosphorus incorporation and the electronic properties of the epilayers is examined, and it is found that, at a substrate temperature of 340°C, residual electron concentration increases linearly with phosphorus flux. Residual doping of InP layers grown at 340°C has been reduced down to 1×1016 cm-3, and Hall mobilities of 3260 cm2/V s at 300 K and 14 830 cm2/V s at 65 K are reported. Low-temperature photoluminescence of low background doping layers is dominated by near band transitions. © 1995 American Institute of Physics.

4 páginas, 6 figuras., 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.

3 páginas, 2 figuras., InP layers have been grown on Si(001) substrates by using a low temperature process, both for the Si surface preparation (400°C, The authors wish to thank the CEC for their support under ESPRIT III project 6854 'BLES' (buffer layer engineering in semiconductors).

(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-xAs yP1-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.

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.

4 páginas, 7 figuras., 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.

3 páginas, 2 figuras., Electroreflectance spectra of Pt/GaAs Schottky diodes are obtained and analysed as a function of the device exposure to a hydrogen-containing atmosphere at different temperatures. The observed changes in the spectra can be related to a reduction of the diode barrier height by about 0.2 eV as a consequence of saturation of the interface states.

A single monolayer thick InAs quantum well laser structure has been grown at low substrate temperature by atomic layer molecular beam epitaxy (ALMBE). The laser has an emission wavelength of approximately 884 nm and a threshold current density of 1.97 kA/cm2 at room temperature. This value is lower than values obtained for other monolayer thick quantum well lasers, and it demonstrates the device quality of epitaxial layers grown at 350°C by ALMBE.

7 páginas, 12 figuras., 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.

4 páginas, 4 figuras., 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.

Residual doping of InP layers grown at low temperature by atomic layer molecular beam epitaxy (ALMBE) has been reduced down to approximately 10/sup 16/ cm/sup -3/ by control of phosphorus pulses, and then, p-type InP layers doped with Be have been grown at substrate temperatures of 305-340 degrees C. Epilayers show low compensation and mobilities that are comparable to bulk p-type InP. >

Monocrystalline, textured and polycrystalline films of n-type PbSe were obtained by vacuum sublimation onto different types of substrates under otherwise identical experimental conditions. The effect of introducing oxygen to a certain partial pressure into the vacuum system during deposition and of the further sensitization of the films by a thermal treatment in air was studied by transmission electron microscopy and by mobility and carrier concentration measurements. A model for photoconductivity is advanced in which localized deep level centres are introduced into the grains by oxygen doping during the evaporation and become minority carrier traps when an air or selenium heat treatment lowers the Fermi level to achieve p-type conduction. © 1981., This work was partly supported by a fund from CONIE, Spain.

At room temperature the Hall coefficient is a linear function of the intrinsic resistivity of gold films. This linearity can be explained in terms of the Volger-Bube mosaic theory with some modifications. Theoretical predictions of the temperature dependence of the phonon contribution to the Hall coefficient in thin films explain the observed variation of the latter with temperature in the range 50–300 K. In conclusion, combination of the mosaic theory and the size effect theory of Sondheimer allows a fair interpretation of the resistivity and Hall coefficient of polycrystalline gold films.