Low temperature Al2O3 surface passivation for carrier-injection SiGe optical modulator.

Surface passivation by Al(2)O(3) deposited by atomic layer deposition (ALD) at 200 °C is examined to suppress surface recombination for carrier-injection SiGe optical modulators. We have investigated the interface trap densities at SiO(2)/Si and Al(2)O(3)/Si interfaces formed by plasma enhanced chemical vapor deposition (PECVD) and ALD, respectively. By evaluating metal-oxide-semiconductor (MOS) capacitors formed on Si surfaces after dry etching, we found that the interface trap density of Al(2)O(3) passivated surface is more than one order of magnitude less than that of SiO(2) passivated one. As a result, the modulation efficiency is improved by 1.3 by inserting Al(2)O(3) layer prior to SiO(2) deposition by PECVD owing to superior interface between Al(2)O(3) and Si. The Al(2)O(3) passivated device exhibits comparable modulation efficiency to a thermally-grown SiO(2) passivated one formed by dry oxidation. Hence, the ALD Al(2)O(3) passivation is effective to passivate SiGe optical modulators for which low temperature processes are required.