Axial p‐n junction design and characterization for InP nanowire array solar cells

Abstract

In this work, InP nanowire (NW) array solar cells with different axial p‐i‐n junction designs were investigated. The optical properties of the different NW structures were characterized through a series of microphotoluminescence measurements to extract important material parameters such as minority carrier lifetimes and internal quantum efficiencies. A glancing angle sputtering deposition technique has been developed to enable a direct visualization of the p‐n junctions in the vertical array of InP NW solar cells (NWSCs) using electron beam‐induced current (EBIC) technique. Based on EBIC and electrical simulation, it is found that the background doping in NWSC significantly affects the junction position. By modifying the junction design, the width and position of the p‐n junction can be varied effectively. By employing a p‐p−‐n structure, a high junction position (>1 μm from the substrate) and wide depletion width have been achieved as confirmed by EBIC measurement. Moreover, the NW growth substrate does not show any influence on the device behavior due to the fully decoupled junction position, indicating a promising structural design for future development of high‐performance, low‐cost flexible NW devices.

Flexible InP–ZnO nanowire heterojunction light emitting diodes

“…Using the depletion width we estimated the p-doping level in the NW to be 6.75 × 10 16 cm −3 which is consistent with previously reported values (Supplementary 3, ESI†). 40 To calculate the carrier concentration of ZnO ( N D ), a planar 30 nm film of n-ZnO deposited under the same conditions on a glass substrate was calculated to be 2 × 10 19 cm −3 using a combination of Drude and Cody–Lorentz models by ellipsometry and is consistent with the reported values in the literature. 41 It is noticed that the EBIC profile is asymmetric, extending more into p-doped NWs.…”

“…It has previously been reported that, for the above-mentioned growth conditions, the NWs have a pure WZ phase irrespective of Zn doping concentration. 40 However, in the EL spectrum, a shoulder at a higher wavelength is observed which will be discussed later.…”

Hot-carrier separation in heterostructure nanowires observed by electron-beam induced current

“…If the sample contains some mechanism whereby electron-hole pairs are separated from each other, a resulting current can be detected without applying any biasing voltage. EBIC has previously been employed to study nanowires containing pn-junctions [16][17][18][19], nanowire-metal Schottky contacts [20], and nanowires containing different types of heterostructures [21,22].…”

Engineering III–V Semiconductor Nanowires for Device Applications

“…Simulations show that the absorption along the vertical NW axis is significantly position‐dependent in contrast to horizontal NWs, with the top 500 nm segment of the NW absorbing light most effectively . Therefore, we investigated InP NW array solar cells with different axial p–i–n junction designs to improve the solar cell efficiency . The p–n junctions in the vertical NWs could also be directly visualized using the EBIC techniques.…”

“…a) Schematic, b) SEM, c) EBIC, d) simulated electric field profile, and e) I – V characteristics under dark (black curve) and 1 Sun@AM1.5G illumination (red curve) conditions of the p–p − –n NW array solar cells. a–e) Reproduced with permission . Copyright 2019, John Wiley & Sons, Ltd.…”