The Importance of Schottky Barrier Height in Plasmonically Enhanced Hot‐Electron Devices

Abstract

Plasmonically enhanced hot‐electron (PEH) photodiodes are a new class of optoelectronic device with the potential to be selective to spectral position, polarization, and bandwidth. Reported solid‐state PEH devices based on metal nanoparticles generally have low performance, in part, due to low collection efficiency of photogenerated hot electrons. A correlation is found between the measured external quantum efficiency (EQE) and the temperature at which the ALD‐TiO2 is deposited by atomic layer deposition (ALD) in Au–TiO2‐based PEH photodiodes. By investigating the material properties of the TiO2, it is demonstrated that the change in EQE is driven by a change in the energy levels in the semiconductor. The results show that lowering the implied Schottky barrier height increases the collection efficiency of hot electrons over the junction, in agreement with existing analytical models. This work demonstrates the crucial role that barrier height plays in hot electron devices in general, and indicates that this is an important design consideration for the improvement of PEH photodetectors.

Plasmonic Charge Transfers in Large‐Scale Metallic and Colloidal Photonic Crystal Slabs

“…Since the Schottky barrier height plays an important role in the charge transfer, several strategies have been considered recently in modifying the TiO 2 layer and lowering the barrier to enhance the photocurrent yield. [ 62 ] For the current case of Au/TiO2 heterostructure with a typical barrier height (≈1 eV [ 15,22 ] ), the excited hot‐electrons with sufficient kinetic energy can overcome the Au–TiO 2 interface and get injected into the conduction band of TiO 2 , as shown for the mPhC slab case in Figure 7c‐i. The Schottky barrier height at the interface between Au and TiO 2 can be considered as ≈1.0 eV, according to the difference between electron affinity of TiO 2 (≈−4.0 eV) and work function of Au (≈−5.0 eV).…”

“…Since the property of the metal-semiconductor interface (e.g., defects or nonuniformity [63] ) affects the characteristics of the junction, the junction height has been reported in the range of 0.9-1.2 eV experimentally. [62,64,65] In contrast, the existence of the insulating layer in cPhCs with even 2 nm thickness provides hindrance in the electron transfer process (Figure 7c-ii). Since the polymer ligand comprising this thin-insulating layer is polyethylene glycol (PEG), there may be a presence of defects due to its semi-crystalline nature in a dry environment.…”

Investigation of the mechanisms of plasmon-mediated photocatalysis: synergistic contribution of near-field and charge transfer effects

“…The latter happens in timescales of 1 to ∼100 fs and results in the generation of a non-thermal distribution of electron–hole pairs with energies higher than the Fermi level, commonly referred to as ‘hot electrons’ and ‘hot holes’. Despite their short lifetime, these hot-carriers can be injected over a Schottky barrier formed at a metal–semiconductor interface 33 or into acceptor electronic states of adjacent molecular adsorbates, starting or enhancing chemical reactions 34 (Hot Carrier transfer in Fig. 1(a)).…”

Recent Progress and Future Opportunities for Hot Carrier Photodetectors: From Ultraviolet to Infrared Bands

“…[ 73,74 ] In addition, the responsivity can also be improved with a low‐energy Schottky barrier, which allows more hot electrons to accomplish the interfacial electron transfer process. [ 75 ] However, the dark current could be increased in this case and the tradeoff between the responsivity and detectivity must be considered. The limiting external quantum efficiency (EQE) spectra of the planar hot‐electron devices under thick‐film single‐barrier, thin‐film single‐barrier, and thin‐film double‐barrier configurations are shown in Figure 12B, where the barrier and resistive losses are noted.…”

“…[73,74] In addition, the responsivity can also be improved with a lowenergy Schottky barrier, which allows more hot electrons to accomplish the interfacial electron transfer process. [75] However, the dark current could be increased in this case and the tradeoff between the responsivity and detectivity must be considered. The limiting external quantum efficiency (EQE) spectra of the Figure 13.…”