tailieunhanh - Nanotechnology and Nanoelectronics - Materials, Devices, Measurement Techniques Part 12

Tham khảo tài liệu 'nanotechnology and nanoelectronics - materials, devices, measurement techniques part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 214 9 Innovative Electronic Devices Based on Nanostructures Fig. Structure and local electron energy distribution of a resonant tunneling diode with applied bias voltage from 303 which is schematically presented in Fig. 303 . The contact layers in the areas I II VI and VII consist of a heavily doped semiconductor with a relatively small band gap for instance GaAs. The layers III and IV are the tunneling barriers implemented with semiconductors of a relatively large gap and in particular with a large conduction band offset relative to the neighboring regions like AlGaAs. The quantum well layer confined by the two tunneling barriers again consists of a material with a relatively small band gap. The operating principle can be explained with the help of Fig. a local distribution of the electron energy is shown when a bias voltage is applied to a DBQW structure. The energy distribution of the electrons in the heavily doped region I must be described by the Fermi-Dirac distribution and the electrons in this region are assumed to be in thermal equilibrium. At the boundary surfaces there are multiple reflections of the electrons due to their wave nature leading to destructive and constructive interferences as a function of the electron energy. Thus the tunneling of those electrons is favored which hit the left barrier with an energy E1 corresponding to the energy E0 in the quantum well. The tunneling probability decreases drastically with both higher and lower electron energies. However since the maximum of the electron energy distribution in the regions I and II can be tuned by changing the applied bias voltage a local maximum peak is found in the current-voltage characteristics of the resonant tunneling diode followed by a local minimum valley . In Fig. this is shown for an InGaAs AlAs based RTD at 300 and 77 K 304 . Even at room temperature a region with a negative differential resistance NDR can be clearly identified with a peak-to-valley ratio better .