We consider the performance and leakage issues in 80-to-20 nm Ge, Si, and InGaAs bulk, SOI and Double-gate (DG) devices. The performance is studied with DAMOCLES, band-to-band tunneling processes with a nonlocal band-to-band model as a post-processor in DAMOCLES, and gate tunneling by a Green's function method accounting also for image force effects, so far ignored at 'internal' interfaces. The performance is affected by the bottleneck effect in III-Vs, especially for thin channels, but InGaAs and Ge still may be optimized to outperform Si. Zener leakage is high for Ge and tolerable for InGaAs. The effect of image forces led to an order of magnitude increase in gate tunneling currents.