Bablich, Andreas
5 results
Now showing 1 - 5 of 5
- Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , High-speed focus-induced photoresponse in amorphous silicon photodetectors for optical distance measurementsThe Focus-Induced Photoresponse (FIP) enables 3D sensing capabilities by evaluating the irradiance dependent non-linear detector response in defect-based materials. Since this advantage is intricately associated to a slow response, the electrical bandwidth of previous FIP sensors is limited to a few kHz only. We report the FIP in amorphous silicon pin photodiodes and propose a sensor read out based on a harmonics analyses. We achieve modulation frequencies of 500 kHz and a non-linear beat frequency detection up to at least 3.5 MHz, surpassing the bandwidth of state-of-the-art architectures by at least a factor of 175. The FIP sensors further achieve signal-to-noise ratios of ∼50 dB, depth resolutions of at least 5.4 mm at 126 cm and a DC FIP detection limit of 1.3 μW/mm2.Source Type:Article318 73 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , High-speed nonlinear focus-induced photoresponse in amorphous silicon photodetectors for ultrasensitive 3D imaging applicationsA large and growing number of applications benefit from simple, fast and highly sensitive 3D imaging sensors. The Focus-Induced Photoresponse (FIP) can achieve 3D sensing functionalities by simply evaluating the irradiance dependent nonlinear sensor response in defect-based materials. Since this advantage is intricately associated to a slow response, the electrical bandwidth of present FIP detectors is limited to a few kHz only. The devices presented in this work enable modulation frequencies of 700 kHz and beat frequency detection up to at least 3.8 MHz, surpassing the bandwidth of reported device architectures by more than two orders of magnitude. The sensors achieve a SNR of at least ∼53dB at 115cm and a DC FIP detection limit of 0.6 µW/mm2. The mature and scalable low-temperature a-Si:H process technology allows operating the device under ambient air conditions waiving additional back-end passivation, geometrical fill factors of 100% and tailoring the FIP towards adjustable 3D sensing applications.Source Type:Article266 242 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Intrinsic photomixing detector based on amorphous silicon for envelope mixing of optical signalsIn this work, a promising device for direct optical envelope mixing, the Intrinsic Photomixing Detector (IPD) based on hydrogenated amorphous silicon, is reported. The IPD directly generates a photocurrent proportional to the nonlinear mixing of two optical modulation envelope functions. Experiments illustrate efficient mixing in the visible range at low light levels down to ϕ1 = 4.36 mW/cm2 (444 nm) and ϕ2 = 1.03 mW/cm2 (636 nm). Modulation frequencies exceeding the MHz range are demonstrated. Electro-optical simulations identify defectinduced electrical field screening within the absorber to cause the nonlinear mixing process, opening-up the opportunity to tailor devices toward application-specific requirements. The IPD functionality paves the way toward very simple but high-performance photodetectors for 3D imaging and ranging for direct optical convolutional sensors or for efficient optical logic gates. Using amorphous silicon provides a photodetector material base, which can easily be integrated on top of silicon electronics, enabling fill factors of up to 100%.Source Type:Article294 185 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Modellierung, Herstellung und Optimierung von a-Si:H Mehrfarbdioden für eine verbesserte Farbseparation(2014)The object of this PhD thesis is the development of novel light sensitive and spectral selective photodiodes based on amorphous silicon and its alloys. Typically, color selectivity of state of the art crystalline silicon sensors is achieved by stacking additional optical filter arrays on sensors surfaces being just sensitive to light intensity. The wavelength dependent optical absorption in amorphous silicon combined with an adequate $mutau$-engineering of the absorbing multilayer stack, results in a field-adjustable drift-profile. This enables the opportunity to manipulate the spectral response. The sensor architectures developed are capable to generate almost an infinite number of space-resolved color information signals in just one single sensing device. The development process presented ranges from simple light intensity detectors to multicolor sensors with an optimized discrete bandgap structure. At the end of the process, characteristics of high complex and continuous bandgap adjusted hyperspectral sensors are discussed. Detector development requires an exact and well-founded knowledge of electro-/optical characteristics of the thin film layers; these are absorbing-, doping- and contact thin films. In this work, a variety of layers is examined by current-/voltage-, spectral sensitivity- and constant photocurrent measurements. Beneath optical simulations to analyze absorption-, reflection- and transmission spectra, scanning electron microscopy studies were performed to monitor film thicknesses, etching processes and the structural quality of the deposited thin films. An additional focus is put on the transient and capacitive behavior of the devices developed. To understand physical fundamentals like transport-, generation- and recombination processes in an amorphous hydrogenated silicon pin-photosensor, a simple analytical model and a more complex numerical model of a-Si:H devices are compared to calculate essential parameters like current density. Furthermore, those models support the interpretation of the measurement results. Especially, the course of the electrical field and the product of charge carrier mobility and life-time, the mutau-product, give an insight in understanding the functionality of the devices presented. This special transport parameter defines the drift-length, the fundamental value enabling a voltage adjustable spectral response. Those models do not allow a fully characterization of the spectral response curves, but they support the fundamental understanding of the devices functionality and help in interpreting the measurement results. In this work, a model describing the correlation between the cathode material and the interference fringes, occurring in the falling edge of the spectral response, is developed and highlighted in a separate chapter. One of the main research results being presented in this work is the realization of an innovative hyperspectral sensor being not just sensitive in the visible spectral range, but being able to scan optical signals in the near ultraviolet, too. Another highlight presented, is the development of a novel process, enabling an in-situ structuring of thin films in a high vacuum process, without etching the material with a fluid solvent. At the end of this thesis, an innovative sensor structure comprising an internal, discrete a-Si:H filter structure which successfully suppresses the green sensitivity of a multicolor sensor is characterized. All thin film detectors presented, reveal that this kind of innovative sensor technology is predestined to be used in color recognition systems. Therefore, they offer a lot of potential for improvement and redevelopment. Possible sensor applications may exist in fields of civil security technologies, for example in the detection of hazardous materials, like explosives or illegal drugs. Moreover, applications in fields of environmental engineering are imaginable to classify waste or tissue samples. These sensors also may be useful for improving photovoltaic cells, medical diagnostic tools, fluorescence and spectrophotometric measurement systems, chemical analysis tools or colorimetric and hyperspectral imagery systems.Source Type:Doctoral Thesis581 305 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Thin-Film Device Development and Technologies - Sensing Principles and Application-Specific Examples(2023)Advanced on-chip integrated photonic and electronic devices, such as hyperspectral photodetectors, depth sensors or memristors, obtain significant drawbacks with respect to performance and/or the technological integration effort. To overcome such limitations, optimized materials and innovative device concepts were developed to maximize performance and integration densities for specific applications. The selected thin and ultra-thin film material examples can obtain significant advantages and exhibit fundamentally different and adjustable material properties compared to their bulk monocrystalline counterparts. Exploiting the benefitial properties of two dimensional (2D) and amorphous semiconducting materials allows the development of high-performance optoelectronic devices, especially for sensing applications. The aim of this work is to demonstrate how novel 2D-material and conventional thin-film semiconductor processing platforms and technologies can be combined to enable a heterogenous device integration on top of chip electronics with enhanced performance. As device examples, 2D-material heterostructure photodetectors for enhanced sensing applications, nonlinear amorphous silicon and graphene photodetectors for depth sensing as well as thin-film memristors for the development of neuro-inspired “smart” cameras are presented, discussed and compared with the state-of-the-art.Source Type:Habilitation12 59