Abstract
Many doses of ions have been implanted through near-surface AlGaAs/GaAs double-barrier diodes. The first objective of this work was the creation of a resistive layer beneath the diodes in selected areas of the wafer. It is shown that if the damage within the double-barrier diodes could be annealed without removing the resistive layer, the three-dimensional integration of the diodes with a second level of devices beneath the resistive layer could be attained. Implantation-and-annealing to create either a damaged or a chemically-compensated resistive layer has been attempted, where, during both types of process, the damage within the doublebarrier diodes was much less than that below them. After implantation of 5.0x1018 2.0MeV B+ ions cm-2, and anneals at 600° C, near-surface Al0.4Ga0.6As/GaAs double-barrier diodes still had good quality negative differential-resistance. It is shown that if (the smaller and less damaging) 1.2MeV Be+ ions were implanted instead of the 2.0MeV B+ ions, an n+-doped layer beneath the diodes can, in principle, be chemically compensated without destroying the diodes irreparably. This work was the first to successfully carry out the anneal-induced recovery of an ion-implanted electronic device having quantum-length-scale layers. The second objective of this work was the elucidation of the electronic and structural characteristics of the same implanted-and-annealed double-barrier diodes. Before annealing, electron conduction through the ion-implanted diodes was limited primarily by field-enhanced emission of electrons from defect states within the lightly-doped spacer layers. The current of ballistic electrons through the as-grown double-barrier structures was suppressed by implantation-and-annealing; this was probably caused by scattering of these electrons by the remaining defect states. The suppression of the ballistic-electron current within implanted-and- annealed double-barrier diodes is proposed to be the primary cause of their larger-than-as-grown 5K and 77K peak-to-valley current ratios. Multi-stage annealing of defects within the double-barrier diodes has been investigated by electrical measurements. The anneal-induced creation of defect clusters within the device mesas was confirmed by both DC and AC measurements, where these clusters were surrounded by percolation paths of as-grown material. Single-electron switching and resonant tunnelling through donor states have been observed within the percolation paths at 4.2K; these observations indicate that the typical diameter of the paths was probably less than five microns, and possibly less than one micron.