DIFFUSED DIODES IN SILICON-ON-SAPPHIRE

The forward and reverse I-V characteristics of diffused diodes made in silicon grown epitaxially on sapphire have been measured. Silicon of doping density 4 × 1015 to 6 × 1017/cm3p-type and 2 × 1015 to 1018/cm3 n-type have been used in these experiments. The forward conduction current of all diodes tested varied as exp (qv/>nkT) with n ≈ 1.7. Minority carrier lifetimes of the order 10-10 sec have been inferred from the I-V data. The reverse currents were somewhat larger than predicted on the basis of currents generated in the space charge region but were reproducible from diode to diode. The temperature dependence of the diode currents was measured from room temperature to 200°C and followed the theoretical prediction. The variation of minority carrier lifetime with film thickness was measured, and the lifetime was found to increase as the silicon became thicker. Diodes produced by diffusion through the silicon to the silicon-sapphire interface were found to have minority carrier lifetimes about an order of magnitude lower than diodes not diffused to the bottom interface. © 1968.