Deposition of polycrystalline Si (poly-Si) on oxidized Si and silicon-on-sapphire (SOS) substrates in an ASM Epsilon-2000 reactor with a SiC-coated graphite susceptor is studied. A simple model for the poly-Si growth rate, taking into account effects of wafer emissivity and absorptivity on instantaneous wafer temperature, is used to assist assessment of the depositions. The success of poly-Si deposition on SOS in the lamp-heated single-wafer reactor with a SiC-coated graphite susceptor confirms that the substrate wafer is mainly heated by thermal conduction from the underlying susceptor. However, the poor ability for the SOS wafers to absorb radiative energies from the heating lamps results in a 6-12% reduction of growth rates of poly-Si, as compared to identical depositions on Si substrates. Hence, thermal radiation from the lamps as well as from the susceptor contributes to detail regulations of the wafer temperature. Calculation of wafer emissivity and absorptivity and measurement of susceptor temperature indicate that in response to variations in the wafer absorptivity during deposition, the lamp radiation is regulated. Since the wafer emissivity varies simultaneously during deposition, the true wafer temperature can deviate from the set-point temperature measured at the thermocouple encapsulated in the susceptor under the wafer. Our modeling of growth rates for poly-Si deposition on oxidized Si substrates qualitatively agrees with the experimentally measured data.