Application

Nitride semiconductors are candidate materials for high-power transistors. To achieve high breakdown voltage performance, the GaN drift layer must be grown with the lowest amount of impurities possible. To improve device performance, several researchers have focused on reducing the carbon, silicon, and oxygen impurities in GaN. Reducing the carbon concentration is especially difficult under conventional growth conditions, because using trimethyl gallium (TMG), which provides a methyl group needed in the production process, also results in carbon impurities. Metal-organic halide-vapor phase epitaxy (MOHVPE) can effectively reduce carbon incorporation by replacing the carbon-based methyl groups with chlorine using HCl. Previous reports on GaN growth by MOHVPE have focused on high growth rate of the GaN bulk crystal without considering the effects of impurity incorporation. However, Amano et al. reported on the impurity concentration in GaN grown by MOHVPE and concluded that chlorine replacement cannot sufficiently reduce the carbon concentration and that the direct reactions must be monitored in the vapor phase.

In this application note, we present the in-situ monitoring of the reaction of TMG with HCl in a conventional horizontal MOVPE reactor using “infiTOF-Pro”.

In the field of gas monitoring, the concentration of multiple species of gas components must be continuously and stably monitored in real time at intervals on the order of a few seconds. Moreover, if any unexpected impurities are detected during the monitoring interval, these must be identified with a high degree of certainty. Real-time monitoring of the concentration of multiple gas components at few-second intervals is difficult with typical GC or GC-MS measurement systems. In some cases, gaseous emissions have been injected directly into a quadrupole mass spectrometer (QMS) for measurements at few-second intervals; however, if any unexpected impurities are present during
this process, the limited mass resolution and mass accuracy of QMS measurements make it difficult to reliably identify them.
In this application note, we report the use of MSI.Tokyo's infiTOF system for real-time, stable, continuous monitoring of multiple gas components at few-second intervals, with sufficient mass resolution and mass accuracy to allow identification of unexpected impurities.

In general, GC and GC-MS are used for trace impurity analysis of gaseous samples. However, using standard GC to measure trace levels of Ne impurities in gaseous samples is difficult.
In this application note, we report on the use of our smartGC-infiTOF for measuring trace amounts of Ne (18.18 ppm), Kr (1.14 ppm), and Xe (0.087 ppm) in the air.

For trace impurity analysis of gas samples, we typically use GC and GC-MS. For some applications, high throughput, automatic measurement of several sampling lines by a single instrument is desirable.
In this application note, we present a method for measuring CH4 (approximately 1.8 ppm) in air samples from seven sampling lines with automatic switching using our “smartGC-infiTOF” GC-MS system.

For trace impurity analysis of gas samples, conventional detection methods use GC and GC-MS. When unknown impurities are detected, identification is usually attempted in the following manner:
1) Search for a matching retention time in a database that compares parameters such as column type and length, flow rate, and temperature.
2) Measure a standard gas sample of the suspected substance under the same conditions and compare the retention time and mass spectrum against the unknown substance.
3) Estimate the identity using the mass spectral fragment pattern.
Here, we report on using the high-resolution/high mass accuracy of the infiTOF to identify the unknown impurity measured in an air sample by our smartGC-infiTOF system.