Papers by Keyword: Photodiode

Abstract: We are investigating 4H-SiC avalanche photodiodes for use as solar-blind, single-photon UV detectors, which could enable low cost, size, weight, and power devices that are reliable and robust, suitable for many sensing applications. One concern for these devices is the spatially-nonuniform gain which limits the useful device area and impedes the scaling necessary to compete with leading UV sensor architectures. We examined various potential sources of the nonuniformity, and conclude that the typically observed phenomenon is likely caused by impact ionization anisotropy and the 4° wafer offcut angle needed to maintain a consistent polytype during epitaxial growth. Additionally, we present both linear and Geiger-mode spatial maps on the same devices to explain the observed differences in each.

Abstract: This study presents the design, construction, and performance analysis of a cost-effective solar irradiance meter using photodiodes and operational amplifiers. The device employs a high-speed, low-noise AD8615 operational amplifier in a transimpedance circuit, integrated with a BPW34 photodiode sensor, and an averaging network to minimize noise. An ESP32 microcontroller facilitates remote monitoring by transmitting irradiance data to a Thingspeak server via Wi-Fi. Simulation results showed a correlation coefficient (R) of 0.999983 between current and irradiance, while practical tests demonstrated a correlation of 0.9961 between the device and a reference meter. The project achieved a significant reduction in cost, approximately 8% of traditional pyranometer prices. The strategy of using multiple photodiodes and averaging their outputs effectively mitigates noise and directional errors, making this device versatile for various solar irradiance measurement applications.

Abstract: A numerical model is presented for the simulation of ultraviolet ion-implanted 4H-SiC photodiodes with shallow p^- emitter doping profiles. An existing model for SiC pin photodiodes, taken from literature, is modified with a dedicated SiO₂-SiC interface layer to account for degradation of carrier mobility and lifetime at the interface. Furthermore, aluminum compensation in 4H-SiC is included and its impact on the spectral response and carrier recombination is analyzed. The simulated spectral response in the wavelength range from 200 to 400 nm is compared to experimental data. While the existing model, taken from literature, fails to predict the performance of VUV photodiodes with a shallow p^- emitter, the newly designed model successfully achieves high accuracy, even with a basic modeling approach featuring an abrupt material parameter transition.

Abstract: Visible light communication has advantages over acoustic and radio wave transmissions in free-space and underwater. The optical transmitters are usually light emitting diodes or laser diodes, and the optical receivers are usually photodiodes or its variants. Solar panels are used for solar energy harvesting to electricity, but the panels are also available in small sizes, and hence, are finding increasing use in optical communications due to larger aperture compared to photodiodes. This work investigated by experiments the characteristics of solar panels as receivers in visible light communication (VLC). In the work, four solar panels of different physical sizes were selected for experiments and measurement. Two characteristics important to communication were investigated. First is the internal resistance at different low illumination levels of white light. Second is response to sinusoidally varying intensity of white light at varying frequencies. For the first study, two of the four panels were investigated; and for the second study, the four solar panels were investigated. An array of seven white LEDs was used as the light source. Also, underwater data communication in saline water was performed for one of the solar panels, and a photodiode in comparison. Results showed that under steady illumination, the internal resistance is both illumination level-dependent and surface area-dependent. It decreases with increase in illumination level, and surface area. Also, the rate of decrease of the internal resistance with illumination increases with surface area. For the frequency response, the cut-off frequency of the solar panel is surface area-dependent, and load-dependent. It decreases with increase in surface area, and increases with decrease in load resistance values (increased loading). For data communication, the maximum data rate obtainable with the solar panel is less to that of the photodiode. The frequency response is important in considering the bandwidth of the solar panels, which also varies with the load, while the internal resistance is important in maximum power point tracking and impedance matching with front end circuits in optical communication receivers.

Abstract: 4H silicon carbide (SiC) based pin photodiodes with a sensitivity in the vacuum ultraviolet spectrum (VUV) demand newly developed emitter doping profiles. This work features the first ever reported 4H-SiC pin photodiodes with an implanted p-emitter and a noticeable sensitivity at a wavelength of 200 nm. As a first step, Aluminum doping profiles produced by low energy ion implantation in 4H-SiC were characterized by secondary-ion mass spectrometry (SIMS). Photodiodes using these shallow emitters are compared to one with a deep p-emitter doping profile employing IV characteristics and the spectral response. SIMS results demonstrate the possibility of shallow Alimplantation profiles using low implantation energies with all emitter profiles featuring characteristic I-V results. For some shallow doping profiles, a meassurable signal at the upper limit of the VUV spectrum could be demonstrated, paving the way towards 4H-SiC pin photodiodes with sensitivities for wavelengths below 200 nm.

Abstract: The study of amorphous semiconductors is of great interest because they find important applications in many electronic devices, like large area solar cells and photosensors. We have developed a methodology for the analysis of transient response of amorphous photodiodes when switched off from steady-state and when they are exposed to a δ pulse of light. For this purpose continuity equations and the transit time effect have been calculated. For the p-i-n photodiodes, characteristics of photo current decay have been analyzed for an ideal case in which the diode is assumed to have a unit current gain. It is found that characteristics either due to decay from steady-state or due to light pulse excitation is transit time dominated. The short-circuit performance of solar cells resembles to a p-i-n diode because a solar cell is essentially a p-i-n diode which is used as an energy converter. Thus short circuit current decay of solar cells behaves similar to the photocurrent decay of the diode and the same method of analysis can be applied.

Abstract: Multilayer low temperature co-fired ceramic (LTCC) is well known in usage as interconnect substrate, especially in high frequency application due to high electrical conductivity of the conductors and low loss of the LTCC dielectric. As substrate and packaging materials, there are many chips or devices placed on the multilayer LTCC board. In this paper, multilayer LTCC is implemented as the packaging at PIN photodiode (PD) module of the Radio over Fiber (RoF) system with the reason to increase thermal dissipation capacity of the PD module.

Abstract: For Visible Light Communication (VLC) systems, photo receiver is very important for obtaining low noisy modulated signal at receiver side since the pure modulated signal is easy demodulated. Therefore, we give a comparison of performance of three type photo receivers in this paper. In first application, we use a photoresistor to detect the modulated signal. It is referred as CDS (cadmium-sulfide) resistor. Another detector is solar cell unit. The other receiver is selected photodiode detector. It is shown from experimental results that the most appropriate modulated signal is obtained at output of photodiode. The output of solar cell consists of very complex signal compared with output of photoresistor. Additionally, we use PPM (Pulse Position Modulation) technique for transmission of data signal.

Abstract: 4H-SiC UV-photodetectors based on full-epitaxial p ⁺p^-n⁺ multilayer structures werefabricated. The diodes were irradiated with fast neutrons up to the fluence of 1·10¹⁴ cm^-2 . Current-voltage characteristics, life time of non-equilibrium charge carriers as well as photosensitivityspectra of the diodes before and after irradiation were investigated. The studies showed that PiNUV-photodiodes with base doping below 1·10¹⁵ cm^-3 retain their performance up to the fluence of5·10¹² neutrons per cm² . The further increase in fast neutron fluence stimulates the creation ofexcessive deep recombination centers. This leads to degradation of I-V-characteristics, reduction ofcarrier life time and, consequently, to degradation of the photosensitivity of devices.

Abstract: The spectral responsivity of 4H-SiC photodiodes was studied and optimized in this paper with the aim to realize UV photo-sensors, selectively sensitive either to harder or to softer UV radiation. The spectral selectivity of the SiC-photodiodes was achieved by optimizing doping profiles in the active regions of the photodiodes and of the anti-reflective coating. A shallow doping profile of the p⁺-emitter allowed an enhancement of sensitivity for hard UV radiation. Deeper doping profiles were chosen for detection of softer UV radiation. The impact of the variations of the thickness of protective and anti-reflective layers was studied as well.