Room-temperature single-electron tunneling in highly-doped silicon-on-insulator nanoscale field-effect transistors

Abstract

From the viewpoint of high- (room-) temperature operation of donor-based single-electron transistors, we make a comparative study of nano-scale silicon-on-insulator transistors with phosphorus-doped channels for two dopant concentrations: ND ≈ 1.0×10^18 and 2.0×10^20 cm-3. We experimentally show that the high-ND devices can provide room-temperature single-electron tunneling operation owing to a large tunnel-barrier height, while operation temperature is limited to about 100 K for the low-ND devices. Numerical simulations of random donor-atom distributions indicate that donor clustering plays a dominant role in the formation of quantum dots, and suggests that clusters comprising of more-than-three donors are responsible for room-temperature operation.

Single-Charge Tunneling in Codoped Silicon Nanodevices

“…The results are presented first for nanoscale pn diodes, in which the depletion layers may contain QDs and discrete energy states that can work as stepping-stones for band-to-band tunneling (BTBT) transport [ 38 , 39 , 40 ]. Then, results are presented for codoped SOI-FETs, which function similarly to junctionless transistors [ 5 , 6 , 7 ], with the key difference that codoping may be more effective than single-type doping [ 41 ] for the formation of QDs, thus likely promoting single-electron tunneling (SET).…”

“…It should also be noted that such transistors (i.e., exhibiting SET features) can be found with relatively high yield in this batch of codoped SOI-FETs as compared to n -type SOI-FETs of comparable dimensions [ 41 ]. This suggests a certain impact due to the introduction of B-acceptors on the background of P-donors (for both types of devices, doped at high concentrations, N D ≈ 2.0 × 10 20 cm −3 for the codoped SOI-FETs and, respectively, N D ≈ 1.8 × 10 20 cm −3 for the SOI-FETs doped only with P-donors).…”

“…Therefore, a more reasonable explanation for the formation of the QDs is the random distribution of dopants within the Si nanoscale channel. In our previous work [ 41 ], we illustrated statistically that even highly-doped channels may contain isolated QDs (i.e., with the “metallic” conduction paths cut off) due to the combined effect of the randomness of the dopant distribution and nanoscale dimensionality of the channel. In that case, P-donors were the only dopants introduced in the channel, at a concentration comparable to the one used in the codoped SOI-FETs.…”

Challenges and Progress in the Fabrication of Silicon Nanowire Tunnel Diodes

“…These gap states can be assigned to defects such as dislocations, interface traps or band tails, but a highly likely origin is clusters due to either donors or acceptors, remaining after compensation has also been taken into account. Such clusters can play the role of quantum dots (QDs), although the situation is quite different from that of single-electron tunneling in Si highly-doped nanoscale transistors [23,24,25]. In the case of QDs formed in the depletion layer of a diode, there is a large asymmetry between the barriers on the two sides due to the large electric field naturally present in the depletion layer [19].…”