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 Structures (PFS's). These PFS's are observed in the Negative Differential Resistance (NDR) region of double-barrier resonant-tunneling diodes (DBRTD's). DBRTD's were fabricated on MBE material with different well widths and barrier material as well as different device areas and topologies. The voltage periodicity, frequency and the amplitude of the PFS's in 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 periodicity of the PFS's is associated with a reduction in the well width which gives rise to a periodic shift in the resonance conditions in the well. We propose that the narrowing of the well is due to a roughness of the well-barrier junction which is incremental in steps of a fraction of the lattice parameter in the [100] direction of crystal growth. We propose that this two-dimensional disorder is due to random stacking of atomic layers during growth of the diode active layers and it is specifically due to continued growth at the barrier and barrier walls when growth interruption takes place at the barrier and well junctions.