Query: "black silicon" photodetector

title: Black silicon structured back illuminated Ge on Si photodiode arrays
abstract: Backside illumination enables an increase in photoactive area and numerical aperture of Ge on Si photodetectors for SWIR applications. The transparency of silicon in the infrared range (l 1.1 mm) allows a nearly lossless propagation of incoming light through the Si substrate and an application of various optical microstructures on the rear side of the Si substrate. Moreover, an aluminum front contact covering the whole top area serves as a mirror which extends the optical propagation of the detectable SWIR light through the absorbing layers and hence increases the quantum efficiency. We developed back illuminated Ge on Si photodiodes to apply such microstructures. Especially the usage of light trapping structures to increase the quantum efficiency of the photodiodes shows great potential. Among the different microstructures we chose black silicon (b Si) as a promising light trapping candidate. After the fabrication, photodiodes with different configurations were evaluated. The obtained results show a strong increase of the quantum efficiency due to both, the existence of an Al mirror and the application of b Si.

title: Black silicon UV photodiodes achieve>130% external quantum efficiency
abstract: At present ultraviolet sensors are utilized in numerous fields ranging from various spectroscopy applications via biotechnical innovations to industrial process control. Despite of this, the performance of current UV sensors is surprisingly poor. Here, we break the theoretical Shockley Queisser limit and demonstrate a device with a certified external quantum efficiency (EQE) 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.

title: Black silicon Schottky photodetector in sub bandgap near infrared regime.
abstract: Sub bandgap near infrared silicon (Si) photodetectors are key elements in integrated Si photonics. We demonstrate such a Si photodetector based on a black Si (b Si)/Ag nanoparticles (Ag NPs) Schottky junction. This photodetector synergistically employs the mechanisms of inner photoemission, light trapping, and surface plasmon enhanced absorption to efficiently absorb the sub bandgap light and generate a photocurrent. The b Si/Ag NPs sample was prepared by means of wet chemical etching. Compared to those of a planar Si/Ag thin film Schottky photodetector, the responsivities of the b Si/Ag NPs photodetector were greatly enhanced, being 0.277 and 0.226 mA/W at a reversely biased voltage of 3 V for 1319 and 1550 nm light, respectively.

title: Review Article: Atomic layer deposition of optoelectronic materials
abstract: Optoelectronic devices are usually systems that transduce electricity to optical signal or vice versa. Optoelectronic devices include many modern necessities such as lamps, displays, lasers, solar cells, and various photodetectors. Some important research topics in the field of optoelectronics materials are development of new materials, new technologies for fabricating materials, and design of device structures. Atomic layer deposition (ALD) is a technology that was developed in the early 1970s for manufacturing high quality luminescent and dielectric films to be used in AC driven thin film electroluminescent (TFEL) displays. Monochromic yellow black displays based on a ZnS:Mn luminescent layer have been manufactured industrially using ALD since the mid 1980s. Multicolor displays (green yellow red) were successfully realized by filtering the broad emission band of ZnS:Mn or adding another luminescent material, e.g. green emitting ZnS:Tb or SrS:Ce. However, applicable full color AC TFEL devices could not be developed because of the lack of an efficient deep blue emitting phosphor. Currently, the most promising application area in TFEL displays is transparent displays, which are commonly used in various vehicles. In the mid 1980s, epitaxial III V semiconductors were studied using ALD. It was shown that manufacturing real epitaxial [atomic layer epitaxy (ALE) films is possible for different III (Al, Ga, In) and V (N, P, As) materials. The advantages of ALE processing compared to more traditional metalorganic chemical vapor deposition or molecular beam epitaxy methods have remained low, however, and ALE is not used on a large scale. Research continues to be carried out using ALE, especially with nitride films. Thin film solar cells have continuously received attention in ALD research. ALD films may be used as both an absorber (CdTe, SnS) and a passivation [In2S3, Zn(O,S) material. However, in the solar cell field, the real industrial level use is in passivation of silicon cells. Thin ALD Al2O3 film effectively passivates all types of silicon cells and improves their efficiency. Transition metal dichalcogenides are emerging 2D materials that have potential uses as channel materials in field effect transistors, as well as phototransistors and other optoelectronic devices. The problem with achieving large scale use of these 2D materials is the lack of a scalable, low temperature process for fabricating high quality, large area films. ALD is proposed as a solution for these limitations. This review covers all of these ALD applications in detail. Optoelectronic devices are usually systems that transduce electricity to optical signal or vice versa. Optoelectronic devices include many modern necessities such as lamps, displays, lasers, solar cells, and various photodetectors. Some important research topics in the field of optoelectronics materials are development of new materials, new technologies for fabricating materials, and design of device structures. Atomic layer deposition (ALD) is a technology that was developed in the early 1970s for manufacturing high quality luminescent and dielectric films to be used in AC driven thin film electroluminescent (TFEL) displays. Monochromic yellow black displays based on a ZnS:Mn luminescent layer have been manufactured industrially using ALD since the mid 1980s. Multicolor displays (green yellow red) were successfully realized by filtering the broad emission.

title: Recent improvement of silicon absorption in opto electric devices
abstract: Silicon dominates the contemporary electronic industry. However, being an indirect band gap material, it is a poor absorber of light, which decreases the efficiency of Si based photodetectors and photovoltaic devices. This review highlights recent studies performed towards improving the optical absorption of Si. A summary of recent theoretical approaches based on the first principle calculation has been provided. It is followed by an overview of recent experimental approaches including scattering, plasmon, hot electron, and near field effects. The article concludes with a perspective on the future research direction of Si based photodetectors and photovoltaic devices.

title: Effect of MACE Parameters on Electrical and Optical Properties of ALD Passivated Black Silicon
abstract: Metal assisted chemical etching (MACE) enables efficient texturing of diamond wire sawn multicrystalline silicon wafers. However, the excellent optics are often sacrificed by polishing the surface to achieve better surface passivation with chemical vapor deposited (CVD) silicon nitride (SiN<italic><sub>x</sub>/italic> In this paper, we show that a polishing step is not required when CVD SiN<italic><sub>x</sub>/italic> is replaced with atomic layer deposited (ALD) aluminum oxide (Al<sub>2</sub>O<sub>3</sub> Indeed, while polishing increases reflectance, it has in general only very modest effect on surface recombination velocity of ALD passivated b Si. Furthermore, since ALD Al<sub>2</sub>O<sub>3</sub> is compatible with various surface morphologies due to its excellent conformality, the MACE parameters can be more freely adjusted. First, the concentration of silver nitrate (AgNO<sub>3</sub> in AgNO<sub>3</sub>/H<sub>2</sub>O solution that is used to deposit Ag nanoparticles is shown to affect the final b Si morphology. Instead of needle shaped b Si produced by 5 mmol/L AgNO<sub>3</sub> concentration, two orders of magnitude lower AgNO<sub>3</sub> concentration produces porous structures, which are more challenging to passivate. Additionally, we demonstrate that a separate Ag nanoparticle removal step in nitric acid (HNO<sub>3</sub> is not a prerequisite for high carrier lifetime. Instead, Ag nanoparticles present during polishing in a HF/HNO<sub>3</sub>/H<sub>2</sub>O solution affect the final b Si morphology by accelerating the etching of Si. The results demonstrate that no tradeoffs are necessary between optical and electrical properties of MACE b Si when using ALD.

title: Surface enhanced Raman Spectroscopy of Graphene Integrated in Three dimensional Nanostructured Plasmonic Silicon Platforms
abstract: We integrate graphene with 3D plasmonic laser nanostructured silicon substrates for SERS and we observe broadband 103 Raman enhancement. FDTD numerical simulations elucidate the advantages of the substrate topography and the flexibility of 2D materials.

title: Surface Enhanced Raman Spectroscopy of Graphene Integrated in Plasmonic Silicon Platforms with Three Dimensional Nanotopography
abstract: Integrating graphene with plasmonic nanostructures results in multifunctional hybrid systems with enhanced performance for numerous applications. In this work, we take advantage of the remarkable mechanical properties of graphene to combine it with scalable three dimensional (3D) plasmonic nanostructured silicon substrates, which enhance the interaction of graphene with electromagnetic radiation. Large areas of femtosecond laser structured arrays of silicon nanopillars, decorated with gold nanoparticles, are integrated with graphene, which conforms to the substrate nanotopography. We obtain Raman spectra at 488, 514, 633, and 785 nm excitation wavelengths, spanning the entire visible range. For all excitation wavelengths, the Raman signal of graphene is enhanced by 2 3 orders of magnitude, similarly to the highest enhancements measured to date, concerning surface enhanced Raman spectroscopy of graphene on plasmonic substrates. Moreover, in contrast to traditional deposition and lithographic methods, the f.

title: Multifunctional graphene and carbon nanotube films for planar heterojunction solar cells
abstract: Graphene and carbon nanotubes, featured with outstanding electronic, photonic and mechanical properties as well as Earth abundancy, are perfect for use as carrier selective transport and collecting layers in photovoltaics. In recent years, graphene and carbon nanotube films have underpinned significant advancement in the planar heterojunction (PHJ) solar cells, with reduced fabrication cost, improved power conversion efficiencies approaching 20% and the great potential for scalable deployment. Here we discuss the state of art progress in graphene based and carbon nanotube based PHJ solar cells leveraging advanced nanocarbon technologies as well as industrial compatible solar cell design and processing. Fabrication and functionalization strategies of graphene and carbon nanotube films for electronic and photonic optimization of PHJ solar cells are systematically reviewed. We also envision technological pathways and future prospects to exploit multifunctionality of graphene and carbon nanotubes to realize ubiquitous application of high performance, flexible PHJ solar cells.

title: Application and validity of the effective medium approximation to the optical properties of nano textured silicon coated with a dielectric layer
abstract: The emergence of nanotextures in photovoltaics has resulted in challenges associated with optical modelling. Whilst rigorous methods exist to accurately solve these textures, the computational effort required limits the scope of modeling applications. The effective medium approximation (EMA) is a potential alternative to provide rapid modeling results which can be easily integrated with ray tracing of large complex structures. However, the validity of this technique is strongly dependent on the size of features relative to the wavelength of interest, making the application of EMA ambiguous for many situations. This paper aims to address this issue by comparing the simulated results between EMA and finite element methods for three randomly distributed silicon textures with and without a dielectric layer. Criteria for which the EMA approach is valid are proposed and generalized using ratios between root mean square roughness, correlation length and incident wavelength, making these limits broadly applicable, beyond that of just the nanotexture under specific solar spectrum regimes. The results in this work apply to random, isotropic textures under normally incident light. Based on the proposed criteria, the validity of different optical simulation techniques for a set of industrial photovoltaic textures is discussed. This analysis reveals a region within which neither geometric optics nor EMA are adequate for calculating the reflectivity of a textured surface, and hence FDTD or other new approaches are required.