High Sensitive Gas Analyzer Research Articles

Characterization of high-purity arsine and gallium arsenide epilayers grown by MOCVD

Impurities present in the metal organic chemical vapor deposition (MOCVD) process gases and precursors can have a significant effect on the performance of III–V compound semiconductor devices. High-purity arsine purified using chemical, adsorption and distillation techniques, has been characterized for impurities by using high sensitivity gas analysis methods and low temperature photoluminescence (PL) of GaAs epilayers. Permanent gas, hydrocarbon and dopant impurities can all be removed using these purification methods to below the detection limit of instrumentation (low nmol mol −1–pmol mol −1, depending on method). Capability to remove water vapor to single digit nmol mol −1 levels is also demonstrated and cylinder depletion studies show that gas-phase arsine, with consistently low H 2O, can be delivered from the cylinder, even well after phase break. Low temperature PL measurements are made on 10 μm GaAs/GaAs grown with three different arsine sources. Well-resolved near-band emission characteristics of high-purity n-type GaAs is obtained with high-purity distilled arsine. PL of epilayers grown with less pure arsine show the presence of Ge as well as elevated levels of Mg and Zn, incorporated from the trimethylgallium. The incorporation of O from an arsine cylinder containing H 2O at 200 nmol mol −1 results in reduced full width at half maximum (FWHM) of the near-band emission and decreased ( D 0, X) and ( F, X) intensity, highlighting the importance of minimizing H 2O impurity.

GaSb-based mid-infrared 2–5 μm laser diodes

Laser diodes emitting at room temperature in continuous wave regime (CW) in the mid-infrared (2–5 μm spectral domain) are needed for applications such as high sensitivity gas analysis by tunable diode laser absorption spectroscopy (TDLAS) and environmental monitoring. Such semiconductor devices do not exist today, with the exception of type-I GaInAsSb/AlGaAsSb quantum well laser diodes which show excellent room temperature performance, but only in the 2.0–2.6 μm wavelength range. Beyond 2.6 μm, type-II GaInAsSb/GaSb QW lasers, type-III ‘W’ InAs/GaInSb lasers, and interband quantum cascade lasers employing the InAs/Ga(In)Sb/AlSb system, all based on GaSb substrate, are competitive technologies to reach the goal of room temperature CW operation. These different technologies are discussed in this paper. To cite this article: A. Joullié, P. Christol, C. R. Physique 4 (2003).

High sensitivity methane analyzer based on tuned near infrared diode laser

A portable automatized high sensitive gas analyzer was developed for the detection of trace gas concentration measurements in the atmosphere. Methane was chosen as an example gas for demonstration of the possibilities of the device. Main features of the instrument are long path Chernin optical multipass cell (50 cm base and up to 100 m optical path length) and original data processing. A near infrared (IR) tunable diode laser (DL) operating at wavelength 1.65 μm at room temperature allowed the avoidance of coolants. The measurements can be produced in open atmosphere as well as with gas mixture samples at various pressures. Short term sensitivity of methane detection in the open atmosphere was found to be 30 ppb, long term stability—100 ppb, which is enough for methane concentration monitoring in the open atmosphere.