A highly orientated cubic indium tin oxide (c‐ITO)/native SiOx/n‐Si Schottky photodiode with negligible electronic noise is demonstrated. This extraordinary property is achieved via simple interface engineering, which combines native SiOx, facile air‐annealing, and the resulting ITO‐lattice‐strain‐assisted oxidation of proximal underlying Si atoms. An exceptionally well‐passivated ITO/n‐Si interface is realized, which leads to a heretofore unreported single‐atom‐thin inversion layer observed via transmission electron microscopy imaging. The device exhibits a record‐low dark current density of ≈3 × 10–8 A cm–2 at −5 V, a tenfold reduction over the lowest reported value. Additional excellent optoelectronic properties achieved include self‐powered operation, high quantum efficiency, fast time response, and ultra‐high sensitivity for low illumination signals. Interface characterization reveals that ITO‐lattice relaxation and oxygen diffusion during annealing create a highly ordered c‐ITO crystal and an extended ≈2.2 nm SiOx interlayer formed via atomic oxidation of the underlying pristine Si, thus rendering a high‐quality interface. Moreover, the Schottky barrier is further enhanced by the presence of negatively charged sub‐stoichiometric silicon oxide interlayer. These results bring forth new insights in the surface atomic oxidation process and the significance of natively grown SiOx which together contribute to the realization of economic highly sensitive photodetectors.

The usage of ultrathin flexible silicon foil can further extend the functionality of silicon and emerging silicon-based tandem solar cells particularly in building and vehicle-integrated photovoltaics where high-efficiency, lightweight, and flexible solar panels are highly desired. However, silicon's relatively weak optical absorption coefficient especially in the near infrared (NIR) region limits its optoelectronic applications with a reduced wafer thickness. Herein, we seek to overcome this limitation by exploring the wave interference phenomenon for effective absorption of NIR light in ultrathin silicon. Particularly, inverted pyramid photonic crystals (PhCs) with nano−micrometer-scale feature sizes are carved directly on silicon. Detailed experimental and theoretical studies are presented by systematically examining the optical properties of PhC-integrated thin silicon substrates (down to a 10 μm thickness). The corresponding maximum photocurrent density for a thin absorber is projected and compared with that predicted by Lambertian's limit. In contrast to traditionally configured microscale inverse pyramids, we show that a small mesa width is critical to achieving high optical performance for a wave-interference-based absorption enhancement. Mesa widths as small as 35 nm are realized over a large wafer-scale fabrication using facile techniques. The optical performance of 10 μm silicon indicates that an ideal photocurrent density approaching 40 mA/cm 2 is feasible. This study indicates that photonic crystals provide strong wave interference in ultrathin silicon, and in particular, we observe high optical absorption even after removing more than 90% of the silicon from conventional "thick" Si wafers.

Photodiodes are fundamental components in modern optoelectronics. Heterojunction photodiodes, simply configured by two different contact materials, have been a hot research topic for many years. Currently reported self‐biased heterojunction photodiodes routinely have external quantum efficiency (EQE) significantly below 100% due to optical and electrical losses. Herein, an approach that virtually overcomes this 100% EQE challenge via low‐aspect‐ratio nanostructures and drift‐dominated photocarrier transport in a heterojunction photodiode is proposed. Broadband near‐ideal EQE is achieved in nanocrystal indium tin oxide/black silicon (nc‐ITO/b‐Si) Schottky photodiodes. The b‐Si comprises nanostalagmites which balance the antireflection effect and surface morphology. The built‐in electric field is explored to match the optical generation profile, realizing enhanced photocarrier transport over a broadband of photogeneration. The devices exhibit unprecedented EQE among the reported leading‐edge heterojunction photodiodes: average EQE surpasses ≈98% for wavelengths of 570–925 nm, while overall EQE is greater than ≈95% from 500 to 960 nm. Further, only elementary fabrication techniques are explored to achieve these excellent device properties. A heart rate sensor driven by nanowatt faint light is demonstrated, indicating the enormous potential of this near‐ideal b‐Si photodiode for low power consuming applications.

Photocarriers predominantly recombine at semiconductor surfaces and interfaces, assuming high bulk carrier lifetime. Consequently, understanding the extraction of photocarriers via surfaces is critical to optoelectronics. Here, we propose Haynes-Shockley experiment analogs to investigate photocarrier surface extraction. A Schottky junction is used to tune the silicon near-surface electric field strength that varies over several orders of magnitude and simultaneously observe variations in broadband photocarrier extraction. Schottky barrier height and surface potential are both modulated. Work function tunable indium tin oxide (ITO) is developed to precisely regulate the barrier height and collect photocarriers at 0 V bias, thus avoiding the photocurrent gain effect. All experiments demonstrate >98% broadband internal quantum efficiency. The experiments are further extended to wave interference photonic crystals and random pyramids, paving a way to estimate the photogeneration rate of diverse surface light-trapping topologies by collecting nearly all photocarriers. The insights reported here provide a systematic experimental basis to investigate interfacial effects on photocarrier spatial generation and collection.