At present, ultraviolet sensors are utilized in numerous fields ranging from various spectroscopy applications via biotechnical innovations to industrial process control. Despite this, the performance of current UV sensors is surprisingly poor. Here, we break the theoretical one-photon–one-electron barrier and demonstrate a device with a certified external quantum efficiency above 130% in UV range without external amplification. The record high performance is obtained using a nanostructured silicon photodiode with self-induced junction. We show that the high efficiency is based on effective utilization of multiple carrier generation by impact ionization taking place in the nanostructures. While the results can readily have a significant impact on the UV-sensor industry, the underlying technological concept can be applied to other semiconductor materials, thereby extending above unity response to longer wavelengths and offering new perspectives for improving efficiencies beyond the Shockley-Queisser limit.

In semiconductor manufacturing, black silicon (bSi) has traditionally been considered as a sign of unsuccessful etching. However, after more careful consideration, many of its properties have turned out to be so superior that its integration into devices has become increasingly attractive. In devices where bSi covers the whole wafer surface, such as solar cells, the integration is already rather mature and different bSi fabrication technologies have been studied extensively. Regarding the integration into devices where bSi should cover only small selected areas, existing research focuses on device properties with one specific bSi fabrication method. Here, we fabricate bSi patterns with varying dimensions ranging from millimeters to micrometers using three common bSi fabrication techniques, i.e., plasma etching, metal-assisted chemical etching (MACE) and femtosecond-laser etching, and study the corresponding fabrication characteristics and resulting material properties. Our results show that plasma etching is the most suitable method in the case of $\mu \text{m}$ -scale devices, while MACE reaches surprisingly almost the same performance. Femtosecond-laser has potential due to its maskless nature and capability for hyperdoping, however, in this study its moderate accuracy, large silicon consumption and spreading of the etching damage outside the bSi region leave room for improvement.

Even though efficient near-infrared (NIR) detection is critical for numerous applications, state-of-the-art NIR detectors either suffer from limited capability of detecting incoming photons, i.e., have poor spectral responsivity, or are made of expensive group III-V non-CMOS compatible materials. Here we present a nanoengineered PIN-photodiode made of CMOS-compatible germanium (Ge) that achieves a verified external quantum efficiency (EQE) above 90% over a wide wavelength range (1.2–1.6 µm) at zero bias voltage at room temperature. For instance, at 1.55 µm, this corresponds to a responsivity of 1.15 A/W. In addition to the excellent spectral responsivity at NIR, the performance at visible and ultraviolet wavelengths remains high (EQE exceeds even 100% below 300 nm) resulting in an exceptionally wide spectral response range. The high performance is achieved by minimizing optical losses using surface nanostructures and electrical losses using both conformal atomic-layer-deposited aluminum oxide surface passivation and dielectric induced electric field -based carrier collection instead of conventional pn-junction. The dark current density of 76 µA/cm² measured at a reverse bias of 5 V is lower than previously reported for Ge photodiodes. The presented results should have an immediate impact on the design and manufacturing of Ge photodiodes and NIR detection in general.

Black silicon (b-Si) is a promising surface structure for solar cells due to its low reflectance and excellent light trapping properties. While atomic layer deposited (ALD) Al2O3 has been shown to passivate efficiently lightly-doped b-Si surfaces and boron emitters, the negative fixed charge characteristic of Al2O3 thin films makes it unfavorable for the passivation of more commonly used n+ emitters. This work studies the potential of ALD SiO2/Al2O3 stacks for the passivation of b-Si phosphorus emitters fabricated by an industrially viable POCl3 gas phase diffusion process. The stacks have positive charge density (Qtot = 5.5·1011 cm-2) combined with high quality interface (Dit = 2.0·1011 cm-2eV-1) which is favorable for such heavily-doped n-type surfaces. Indeed, a clear improvement in emitter saturation current density, J0e, is achieved with the stacks compared to bare Al2O3 in both b-Si and planar emitters. However, although the positive charge density in the case of black silicon is even higher (Qtot = 2.0·1012 cm-2), the measured J0e is limited by the recombination in the emitter due to heavy doping of the nanostructures. The results thus imply that in order to obtain lower saturation current density on b-Si, careful optimization of the black silicon emitter profile is needed.Peer reviewe

Near‐infrared (NIR) sensors find numerous applications within various industry fields, including optical communications and medical diagnostics. However, the state‐of‐the‐art NIR sensors made of germanium (Ge) suffer from rather poor response, largely due to high reflection from the illuminated device surface. This work demonstrates a method to increase the sensitivity of Ge sensors by implementing nanostructures to the wafer surfaces. The absorbance of nanostructured Ge wafers is measured to be >99% in the whole UV–vis–NIR spectrum up to 1600 nm wavelength, which is a significant improvement to bare Ge wafers that reach absorption of only 63% in maximum. The process is shown to be capable of producing uniform nanostructures covering full 100 mm diameter substrates as well as wafers with etch mask openings of different sizes and shapes, which demonstrates its applicability to complementary metal oxide semiconductor (CMOS) sensor manufacturing. The results imply that nanostructured Ge has potential to revolutionize the sensitivity of Ge‐based sensors.