Invited Paper EM-MoA6
Surface Passivation of III-V Antimonides and Ge Based MOSFETs

Monday, October 28, 2013, 3:40 pm, Room 101 B

Si CMOS scaling is reaching practical and fundamental limits. Currently, use of strain engineering to boost mobility is the dominant technology for high performance Si MOSFETs. However, mobility boosting by straining Si will also saturate with future scaling. Therefore, looking into future it becomes important to look at higher mobility materials like Ge and III-Vs to continue scaling of MOSFETs. For these materials to become main-stream several problems need to be solved, including surface passivation. In this talk we will present our recent results on passivation of Ge, GeSn and III-V antimonides.

Ge and GeSn have recently emerged as promising candidates not only for high performance CMOS but also for optoelectronics. Ge PMOS with several different high-k dielectrics have been demonstrated with excellent performance. Ge surface passivation with GeO₂ shows low D_it near valance band (E_v). However, Ge NMOS have so far exhibited poor drive current. This is partially attributed to high D_it near the conduction band (E_c). In recent work we have achieved low and symmetric D_it through sulfur passivation followed by ALD of Al₂O₃ and then annealing in ozone. With these two treatments, a record-low D_it (<1E11/cm²eV) at both band edges is achieved

In GeSn with increasing Sn content G valley comes down with respect to the indirect valleys, increasing population of electrons in this low electron mass valley which boosts mobility. A novel surface passivation scheme using ozone oxidation of thin Ge cap has been demonstrated with record low D_it of 3E10¹¹/cm²eV at high-ĸ/GeSn interface.

While there have been many demonstrations on n-channel MOS in III-V semiconductors showing excellent electron mobility and high drive currents, hole mobility in III-V p-channel MOS has traditionally lagged in comparison to Si. GaSb is an attractive candidate for high-performance III-V pMOS due to its high hole mobility. Performance degradation due to interfacial traps is generally considered one of the main challenges for III-V MOSFETs. We have demonstrated passivation of GaSb with an ALD Al₂O₃ gate dielectric with a midband-gap D_it of 3E10¹¹/cm²eV and demonstrated excellent pMOSFETs.

We have further investigated the suppression of interface state response using band engineering in III-V quantum well MOSFETs and experimentally verified the concept in antimonide compounds system using a gate-stack consisting of Al₂O₃/GaSb/InAlSb. It is shown that if the thickness of the interfacial layer of GaSb is scaled down to a few monolayers, the effective bandgap of the interfacial layer increases dramatically due to quantum confinement, which leads to the suppression of interface-trap response.