ANALYSIS OF VOLTAGE PERIODIC STRUCTURES IN THE NEGATIVE DIFFERENTIAL RESISTANCE REGION OF DOUBLE-BARRIER RESONANT-TUNNELING DIODES

We present a comprehensive investigation of the Periodic Fine Structur es (PFS's). These PFS's are observed in the Negative Differential Resi stance (NDR) region of double-barrier resonant-tunneling diodes (DBRTD 's). DBRTD's were fabricated on MBE material with different well width s and barrier material as well as different device areas and topologie s. The voltage periodicity, frequency and the amplitude of the PFS's i n the NDR region were studied as a function of these materials and the device parameters. The effect of self-oscillations of the DBRTD's on the PFS's was also investigated. The results indicate that the periodi city of the PFS's is associated with a reduction in the well width whi ch gives rise to a periodic shift in the resonance conditions in the w ell. We propose that the narrowing of the well is due to a roughness o f the well-barrier junction which is incremental in steps of a fractio n of the lattice parameter in the [100] direction of crystal growth. W e propose that this two-dimensional disorder is due to random stacking of atomic layers during growth of the diode active layers and it is s pecifically due to continued growth at the barrier and barrier walls w hen growth interruption takes place at the barrier and well junctions.