Si/SiGe electron resonant tunneling diodes with graded spacer wells

Resonant tunneling diodes have been fabricated using graded Si1-xGex (x=0.3 -->0.0) spacer wells and strained Si0.4Ge0.6 barriers on a relaxed Si0.7Ge 0.3 n-type substrate which demonstrates negative differential resistance at up to 100 K. This design is aimed at reducing the voltage at which the pea k current density is achieved. Peak current densities of 0.08 A/cm(2) with peak-to-valley current ratios of 1.67 have been achieved for a low peak vol tage of 40 mV at 77 K. This represents an improvement of over an order of m agnitude compared to previous work. (C) 2001 American Institute of Physics.