Growth and Fabrication of High‐Quality Single Nanowire Devices with Radial p‐i‐n Junctions

Abstract

Nanowires (NWs) with radial p‐i‐n junction have advantages, such as large junction area and small influence from the surface states, which can lead to highly efficient material use and good device quantum efficiency. However, it is difficult to make high‐quality core–shell NW devices, especially single NW devices. Here, the key factors during the growth and fabrication process that influence the quality of single core–shell p‐i‐n NW devices are studied using GaAs(P) NW photovoltaics as an example. By p‐doping and annealing, good ohmic contact is achieved on NWs with a diameter as small as 50–60 nm. Single NW photovoltaics are subsequently developed and a record fill factor of 80.5% is shown. These results bring valuable information for making single NW devices, which can further benefit the development of high‐density integration circuits.

Toward electrically driven semiconductor nanowire lasers

“…It is relatively easy when we only need to contact the unstructured NWs. For example, Zhang et al [135] optimized the NW doping and the annealing of AuZn contact, and achieved good Ohmic contact on GaAs NWs with a diameter as small as 50~60 nm. However, when it comes to devices, contact fabrication is more challenging.…”

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“…It has been reported that unpassivated GaAs NWs will be seriously depleted when the diameter is below 100 nm, making Ohmic contact formation even more difficult, especially for NWs with a smaller size [90]. Zhang et al optimized the NW doping and the annealing condition of AuZn contact and achieved good Ohmic contact on GaAs NWs with a diameter as small as 50~60 nm [91]. This is the smallest III-V NWs diameter reported so far with Ohmic contacts, which gives valuable information on how small the NWs can be, while still allowing good Ohmic contact.…”

“…When the NWs have stacking faults, it can be even more challenging to achieve uniform shell removal, because the stacking faults can give rise to new surface facets with higher surface energies and hence these regions can be corroded faster. Zhang et al used focused ion beam (FIB) to mill away the surface n-and i-layers and achieved a uniform p-core [91]. After putting on the p-and n-contacts, the single GaAs NW solar cell showed a world-record-high fill factor of 80.5% and a stable photo response (Figure 5a).…”

“…Besides, it needs to be noted that devices with radial junctions have more limitations of fabrication technique because the junction layers are very thin and can easily be damaged by unoptimized fabrication processes, such as annealing. (FIB) to mill away the surface n-and i-layers and achieved a uniform p-core [91]. After putting on the p-and n-contacts, the single GaAs NW solar cell showed a world-record-high fill factor of 80.5% and a stable photo response (Figure 5a).…”

“…The radial p-i-n structure has great advantages in making solar cells, but the device fabrication is still challenging, and the fill factor is commonly lower than 70% [122]. Very recently, a high fill factor of 80.5% from single NWs with radial p-i-n structure has been achieved by Zhang et al [91]. which is a big achievement in single NW device fabrication.…”