Light Element Impurity Annalysis by Spectroscopy Annalysis for Semiinsulating Semiconductor Materials

Abstract

In semiinsulatling (SI) semiconductor materials, light-elements such as carbon act as important role to sustain semiinsulating of electric conduction. They also make electric conduction in SI semiconductor materials. Since there are at least a few elements related to SI electric conduction mechanism, it is difficult for electric conduction measuremenr to reveal the element states in SI semiconductor materials. Therefore, other methods for electric conduction analyses, such as optical method of infrared (IR) absorbance spectroscopy, are required. Since IR spectroscopy can yield different informations from those of electric conduction measurements, gaseous substances of electric conduction in glass ampules and internal states of colligated substances were investigated with optical spectroscopy. [1] Optical spectroscopy can give informations on motions of very small fragment substances in the colligated substances. [2] For example, spectra of impurities such as carbon in solids such as polyethylene film are in a IR range are [3], as well as gas such as ammonia in a KRS-5-window gas-cell or liquid such as ethylalcohol in a KRS-5-window liquid-cell [4] with a Perkin-Elmer double-beam IR spectrometer Model 21 of a sodium chloride crystal prism, a thermocouple IR detector, a Nernst lamp IR source and a synchronized detection amplifier. However, as impurity concentrations in semiinsulating semiconductors are usually not so high, therefore, optical spectroscopy of absorbance as to them requires sensitivity of spectroscopy apparatuses. Moreover, observation range of carbon-related phenomena is in a far IR range. It is difficult to obtain far–IR light sources of high luminosity and high resoultion wavelength dispersion system of far IR. Therefore, cooling of samples is adopted to reduce background noise. Since wavelength of far IR is long (~10 µm—several tens µm) and also it is prefer to eliminate bulk far–IR absorbance in a prism, wavelength dispersion system with a interferometor of resonator frequency-variable mirrors of position scanning is adopted. The author will present examples of relationships between electric parameters and carbon concentartions in SI Gallium Arsenide (GaAs) crystals by Fourier-transform IR (FT–IR) spectroscopy and memos on the way to considering the results.