Abstract
The temperature dependences of the spectral and total hemispherical emissivities of silicon have been experimentally determined, by using a technique which combines isothermal electron beam heating with in situ optical measurements. Emission spectra were used to deduce the absorption coefficient for phosphorus‐doped silicon samples for wavelengths between 1.1 and 1.6 μm, in the temperature range from 330 to 800 °C. For lightly doped samples, the data show good agreement with a model which includes the effects of the various phonon‐assisted processes involved in interband transitions in silicon, as well as the free‐carrier absorption. For heavily doped samples the agreement was less satisfactory, possibly because of inadequacies in the model for free‐carrier absorption. It was shown that reflection spectra can also be used to determine the absorption spectrum, for the range where the absorption coefficient lies between 1 and ∼70 cm−1. By fitting the theoretical model to the absorption coefficients derived from the reflection spectrum, it is possible to deduce the temperature of a sample, which is especially useful for temperatures less than 300 °C, where the thermal emission is very weak. The total hemispherical emissivity of the specimens was determined from the input electron‐beam power densities and the measured temperatures. The total emissivity of a 390‐μm‐thick specimen of lightly doped silicon rises from 0.12 at 280 °C to a limiting value of 0.7 at 650 °C. This behavior is a consequence of the increase in the free‐carrier concentration with the temperature. For heavily doped specimens the total emissivity remains approximately constant at ∼0.7 between 200 and 800 °C because the carrier concentration is high even at room temperature, and the additional thermal generation of carriers produces an insignificant change in the total emissivity.