Asymmetric double barrier resonant tunneling structures with improved   characteristics
  We present a self-consistent calculation, based on the global coherent tunnelling model, and show that structural asymmetry of double barrier resonant tunnelling structures significantly modifies the current-voltage characteristics compared to the symmetric structures. In particular, a suitably designed asymmetric structure can produce much larger peak current and absolute value of the negative differential conductivity than its commonly used symmetric counterpart. 
Jun-jie Shi, Barry C. Sanders, Shao-hua Pan