To lower the power consumption of nanometer devices new materials and novel device structures are required.High mobility channel materials are essential for the low power CMOS.For energy efficient devices steep slope tunnel FETs(TFETs)which employ band to band tunneling transport mechanism and thus provide much steeper subthreshold swing than the thermal limit(60mV/dec at 300K)for MOSFETs are one of the most interesting device structures for ultra low power applications.