Conventional Photodiodes Research Articles

Assessment of quantum dot infrared photodetectors for high temperature operation

Investigation of the performance of quantum dot infrared photodetectors (QDIPs) in comparison to other types of infrared photodetectors operated near room temperature is presented. The model is based on fundamental performance limitations enabling a direct comparison between different infrared material technologies. It is assumed that the performance is due to thermal generation in the active region. Theoretical estimations provide evidence that the QDIP is suitable for noncryogenic operation especially in long-wavelength infrared region, where conventional HgCdTe photodiodes are not viable. Hence it is expected that improvement in technology and design of QDIP detectors will make it useful for practical application. The higher operating speed of QDIP and multispectral capability are considerable advantages in comparison with thermal detectors. Comparison of theoretically predicted and experimental data indicates that, as so far, the QDIP devices have not demonstrated their potential advantages and are expected to posses the fundamental ability to achieve higher detector performance. Poor QDIP performance is generally linked to nonoptimal band structure and control over the QDs size and density.

NBn detectors based on InAs∕GaSb type-II strain layer superlattice

We report on a type-II InAs∕GaSb strain layer superlattice photodetector using a nBn design with cutoff wavelength of ∼4.8μm at 250K. The surface component of dark current was eliminated. Using a shallow isolation etch, low temperature dark current was reduced by two orders of magnitude compared with conventional photodiode processing. Dark current densities were equal to 2.3×10−6 and 3.1×10−4A∕cm2 (Vb=0.1V, T=77K) for detectors with shallow isolation etch and conventional defined mesa, respectively. Quantum efficiency, responsivity, and spectral detectivity D* of the device are presented.

Via-in-pixel design of truly 2D extendable photodiode detector for medical CT imaging

This paper presents a new design of the silicon-based photodiode detector for medical imaging, especially for the X-ray computed tomography applications. The new structure of the photodiode includes a conventional front-illuminated photodiode and a through wafer interconnection. Moreover, the through wafer interconnection is integrated into the photodiode by being placed inside the active area of the photodiode. This new structure is called via-in-pixel design. Truly 2D photodiode detector can be designed with maximum free space or minimum gap between each two photodiode elements by using the via-in-pixel design. In addition, 2D photodiode detector arrays can be constructed by tiling more edgeless detectors. In the paper, the via-in-pixel photodiodes were demonstrated and the performances were measured. Together with the measurement data, a quasi-3D device simulation was performed to disclose the electrical characteristics of the via-in-pixel photodiode by using Synopsis Advanced TCAD software. The results show that the via-in-pixel design of the photodiode detector can either meet or exceed the medical imaging requirements.

Dynamic-speckle profilometer for online measurements of coating thickness

Online control of thickness of as-deposited coatings is of great importance because it directly affects the quality of protective coatings. We present a novel approach that enables online, real-time and non-contact measurements thickness of thermally sprayed coatings. The proposed technique uses dynamic speckles generated by rapidly deflecting laser beam. Within 10 ms the system can scan 500 times a small area of the deposited layer thus resulting in measurement accuracy of 5 microns irrespectively of the layer roughness. In comparison with traditional optical triangulation technique of distance measurements, our system has following advantages: (i) much simpler optical scheme that includes conventional photodiode to measure the scattered light, (ii) much simpler electronics for real-time data processing, (iii) much higher speed of measurements.

Tunable lead-chalcogenide on Si resonant cavity enhanced midinfrared detector

Midinfrared tunable resonant cavity enhanced detectors have been realized. The linewidths of 0.07μm are determined by the finesse of the cavities, while the length of the cavity can be changed with a movable mirror. This allows tuning across the 4–5.5μm midinfrared wavelength range. The thin (0.3μm) photodiodes inside the cavity are based on lead-chalcogenide narrow gap semiconductor layers grown epitaxially onto a Si substrate. Due to the thin active layer, a higher sensitivity at the higher operation temperatures is achieved as compared to conventional thick photodiodes.

Low-Noise and High-Detectivity GaN UV Photodiodes With a Low-Temperature AlN Cap Layer

Here, we present the characteristics of a novel GaN- based ultraviolet (UV) photodiode (PD) with a low-temperature (LT) AIN cap layer. The dark leakage current for the PD with the LT-AIN cap layer was shown to be about four orders of magnitude smaller than that for the conventional PDs. It was found that we could achieve larger UV to visible rejection ratio by inserting an LT-AIN cap layer. It was also found that we could improve minimum noise equivalent power and maximum normalized detectivity of the PD by inserting an LT-AIN cap layer.

Cross-differentiator image processor based on self-electro-optic effect device

An analogue optical image filter has been characterised as a cross-differentiator operating in real time/space based on spatial arrangement of conventional photodiodes integrated with multiple quantum-well modulators. Results demonstrate its linearity and the optimum bias voltage as 9 V for a readout power of 175 nW.

InGaN–GaN MQW Metal–Semiconductor–Metal Photodiodes With Semi-Insulating Mg-Doped GaN Cap Layers

InGaN-GaN multiple-quantum-well metal-semiconductor-metal photodiodes (PDs) with in situ grown 40-nm-thick unactivated semi-insulating Mg-doped GaN cap layer were successfully fabricated. The dark leakage current of this PD was comparably much smaller than that of conventional PD without the semi-insulating layer, because of a thicker and higher potential barrier of semi-insulating cap layer, and also a smaller number of surface states involved. For the PDs with the semi-insulating Mg-doped GaN cap layers, the responsivity at 380nm was 0.372A/W when biasing at 5 V. In short, incorporating a semi-insulating Mg-doped GaN cap layer into the PDs beneficially leads to the suppression of dark current and a corresponding improvement in the ultraviolet-to-visible rejection ratio

Detecting quantum light

The quantization of light is the basis for quantum optics and has led to the observation of a multitude of genuine quantum effects which cannot be explained by classical physics. Yet, there exist different views when we refer to the distinct quantum character of light as opposed to classical fields. A major impact on how we describe photonic states is caused by the detection method we use for the quantum state characterization. In the theoretical modelling measuring light always means the recording of photon statistics of some kind, though the way we interpret the results is quite different and depends mainly on the intensity of actual detected light. If we use conventional photodiodes and monitor bright light, we attribute the detected statistics to quadrature measurements in a phase space representation, or—in other words—we identify the quantum state by studying its uncertainties of its field amplitude and phase properties which correspond to conjugate quantum observables. For multi-photon states with very low intensity we have to employ avalanche photodiodes (APDs) to be able to see any signal, but photon number resolution seems difficult in this regime. Recent developments allow one to ascertain information about the photon statistics from APD measurements opening up new routes for characterizing photonic states. In this article we review the different methods for modern quantum state metrology where we include theoretical aspects as well as the description of the state-of-the-art technology for measuring photon statistics.

Silicon Photo-Diode Using Surface-Plasmon Resonance

The concept of nano-photodiode, employing surface-plasmon antenna to create sub-wavelength size nearfield, is described in relation to silicon photonics. Response time of the prototype silicon nano-photodiode was much shorter (-20 ps) than that of conventional silicon photodiodes (>1 ns). There are two reasons for the high-speed response: short distance between electrodes (-100 nm) and small electrode area (< 1 μm2). The former is realized by lapping near-field region over depletion region (Schottky barrier) in silicon thereby eliminating time-consuming carrier diffusion process. The latter results in small electrode capacitance and thus reducing response time of the photodiode circuit. This nano-photodiode technology can be applied to other semiconductor materials such as germanium and ternary compound semiconductors.

Nitride-Based MIS-Like Photodiodes With Semiinsulating Mg-Doped GaN Cap Layers

Nitride-based metal-insulator-semiconductor (MIS)-like photodiodes (PDs) with in situ grown 30-nm-thick unactivated semiinsulating Mg-doped GaN cap layers were fabricated. The authors found that the reverse leakage current of the aforementioned PD was comparably much smaller than that of conventional PD without the semiinsulating layer due to the facts that inserting a semiinsulating layer would result in a thicker and higher potential barrier, and also less amounts of interface states introduced. To sum up, it was determined that the benefits of incorporating a semiinsulating Mg-doped cap layer into the PD would encompass a larger photocurrent-to-dark-current contrast ratio and larger ultraviolet-to-visible rejection ratio

In-line channel power monitor based on helium ion implantation in silicon-on-insulator waveguides

We propose and demonstrate an in-line channel power monitor (ICPM) based on helium ion implanted silicon waveguides. The implanted waveguide can detect light at below-bandgap wavelengths (1440-1590 nm) which are normally not detectable by silicon. We study the enhanced photoresponse of helium ion implanted samples which were annealed at 200 degC, 300 degC, or 350 degC for different durations. Optical absorption and photodetector current measurements were performed for each sample. The ICPM can provide the same function as a waveguide tap coupler and a hybrid-integrated conventional photodiode

Characteristics of III-nitride photodiodes with self-assembled quantum dots

In this work, it has been demonstrated that metal–semiconductor–metal (MSM) photodiodes (PDs) with InGaN self-assembled quantum dots (QDs) were fabricated and compared with conventional InGaN MSM photodiodes. The scanning near-field optical microscope (SNOM) results revealed that such InGaN nanostructures could have better absorption for the near-field light with the wavelength of 457–514 nm. It was found that the InGaN QD photodiode with lower dark current can operate in the normal incidence mode; we could achieve a much larger photocurrent to dark current contrast ratio from MSM photodiodes with nanoscale InGaN quantum dots. It was also found that the measured responsivity of MSM photodiodes with QDs and without QDs approximated to the same in the range of 390–460 nm. Furthermore, the photodiodes with QDs showed higher spectral response than that of the photodiodes without QDs at wavelengths < 350 nm and > 480 nm.

A large-area monolithic array of silicon drift detectors for medical imaging

Monolithic arrays of silicon drift detectors (SDDs) have been recently proposed to be used with scintillators for high-position-resolution γ-ray imaging applications. Thanks to the low electronics noise due to the small value of the output capacitance, the SDD offers better noise performances with respect to conventional photodiodes of the same geometry. Small monolithic arrays of SDDs have been used as photodetector of the scintillation light in a first prototype of Anger Camera for γ-ray imaging characterized by an intrinsic resolution better than 0.3 mm. In this work, we present a new large-area monolithic array of SDDs. It consists of a single chip composed of 77 single hexagonal units, each one with an active area of 8.7 mm 2, for a total active area of the device of 6.7 cm 2. It represents the largest monolithic array of SDDs with on-chip JFETs produced up to now for X-ray and γ-ray detection. The results achieved in the experimental characterization of a first prototype of the detector array are presented, both with X and visible photons. The energy resolution measured at 6 keV with the single unit of the array is of 142 eV at −10 °C, while a QE>90% was measured at λ=550 nm.

Visible Light Communication with LED Traffic Lights Using 2-Dimensional Image Sensor

We propose a new receiving method for an information-providing system that uses LED-based traffic lights as the transmitter. We analyzed the improvements obtained when 2-dimentional image sensor replaced the conventional single-element photodiode. First, we discuss the maximum receiver's field of view (FOV) when using the 2-dimentional image sensor at a particular focal length. We analyzed the best vertical inclination for both lanes and quantified the improvements in terms of the enhancement of received signal-noise ratio (SNR) when different numbers of pixels were applied. Our results indicate that using more pixels increases the received SNR and the service area becomes wider compared to the conventional single-element system. Consequently, receivable information within the service area also increased. We also found that the optimum number of pixels to accomplish a reliable communication system is 50 × 50 because performance degradation occured with a larger number of pixels.

Luminescent ratiometric method in the frequency domain with dual phase-shift measurements: Application to oxygen sensing

A novel ratiometric method for luminescence measurements in the frequency domain is presented. The method is based on the large difference between the lifetimes of the phosphorescence and fluorescence emissions of a dual luminescent indicator. The intensity ratios long-lived/short-lived emission is calculated by measuring the phase shift between the excitation and emission signals at two different but close frequencies. Ratiometric measurements are preferred to alternative luminescent measurements due to their proved insensitivity to ambient or scattered light, instrumental fluctuations, etc. Thus, they can be applied to the development of robust luminescence optical sensors. Theoretical aspects of the new methodology proposed here, the design and construction of a fiber-optic measuring prototype system using low-cost optoelectronics, including a light emitting diode (LED) to excite the chemical sensor and a conventional photodiode to measure the luminescent emission, is presented. The drive of the LED to obtain a good ratiometric measurement is also discussed. The performance of the proposed measurement method and simple instrument has been assessed using an oxygen sensing phase prepared by immobilizing Al-Ferron in an inorganic sol–gel support. This oxygen sensitive indicator shows a strong oxygen-insensitive fluorescence emission overlapping significantly with a long-lifetime oxygen-dependent phosphorescence emission. As compared to other ratiometric approaches, the method here proposed requires only one optical path to measure the luminescent response and luminophors showing only emission intensity changes in response to a certain analyte can be used, since changes in lifetime are not required. Interestingly, the ratiometric method can even be used without losing accuracy even if a spectral overlap between the two measured emissions occurs.

Monolithic arrays of silicon drift detectors for medical imaging applications and related CMOS readout electronics

Monolithic arrays of Silicon Drift Detectors (SDDs) have been recently proposed to be used with scintillators for high-position-resolution γ-ray imaging applications. Thanks to the low electronics noise due to the small value of the output capacitance, the SDD offers better performances with respect to conventional photodiodes of the same geometry. We show the results achieved with a small monolithic array of SDDs, each one with a front-end JFET integrated at its center, used as photodetector in a first prototype of Anger Camera. An intrinsic resolution better than 200 μm has been achieved with this prototype. Moreover, we describe a new monolithic array of SDDs composed of 77 single hexagonal units, each one with an active area of 8.7 mm 2, for a total active area of the device of 6.7 cm 2. Finally, the basic principles and the first results of the CMOS readout chip specifically designed for the readout of the signals from SDDs arrays are presented.

A new surface-flattening method using single-point diamond turning (SPDT) and its effects on LPE HgCdTe photodiodes

Excellent surface flatness of HgCdTe wafers is essential for fabricating large infrared focal plane arrays (IRFPAs) within the framework of a flip-chip bonding yield. However, liquid-phase epitaxy (LPE) HgCdTe wafers, which are widely used for IRFPAs, have inherent problems pertaining to surface flatness. In this study, we introduced a single-point diamond turning (SPDT) method for use in fabricating LPE HgCdTe photodiodes. The cutoff wavelength of the wafers is ∼5 µm. The surface roughness of the LPE HgCdTe wafer has been substantially reduced but a type-converted defective layer was formed on the surface of the HgCdTe wafer after SPDT, which was confirmed using Hall and capacitance–voltage (C–V) measurements. The defective layer, however, was easily removed by bromine in methanol (Br–MeOH) etching. The fabricated photodiode showed a dynamic resistance–area product at the zero bias (R0A) value of ∼1 × 104 Ω cm2 for a junction area of 30 × 30 µm2 at 80 K, which is equivalent to that of a conventional photodiode. The flip-chip bonding efficiency has been remarkably improved from 89.43% to 99.99% for 320 × 256 IRFPA at room temperature after SPDT.

Microcavity plasma photodetectors: Photosensitivity, dynamic range, and the plasma-semiconductor interface

Detailed measurements of the photosensitivity of Si microcavity plasma photodetectors in the visible and near-infrared (420–1100 nm) are reported for input optical intensities to a 100×100μm2 inverted pyramid device varied over three orders of magnitude (10−5–10−2Wcm−2). By resolving the contribution to the overall device response from the plasma/semiconductor interaction, as opposed to bulk Si photoconductivity, the photosensitivity of the plasma photodetector operating in 500 Torr of Ne was determined to range from (2.2±0.4)A∕W for 2 nW of input power (at λ=780nm) to (1.3±0.2)A∕W at ∼0.65μW. The spectral response profile of the hybrid plasma/semiconductor detector is similar to that of a conventional pn junction photodiode, but is blueshifted by ∼60nm. Also, the peak photosensitivity (3.5A∕W at λ≃900nm) of a Si microplasma device having a 50×50μm2 aperture is approximately twice that for its larger (100×100μm2) counterpart under identical conditions. Analysis of the data suggest that bandbending at the p-Si surface is sufficiently strong for a thin n-type region to form, thereby resembling a metal-oxide-semiconductor capacitor in the inversion mode. Electrons in this thin layer tunnel through the vacuum (Si-plasma) barrier, followed by electron avalanche in the nonequilibrium plasma. These results illustrate the potential for novel optoelectronic devices when interfacing a plasma with a semiconductor and coupling the two media with a strong electric field imposed across the interface.

Polarization-insensitive optical clock recovery at 80 Gb/s using a silicon photodiode

We report an optical clock recovery system that uses two-photon absorption in a conventional silicon photodiode to synchronize a 10-GHz optical clock to an 80-Gb/s data stream. Compared to many other clock recovery techniques, the system is economical, polarization-insensitive, and can operate over a broad range of optical wavelengths. The system was tested back-to-back and in a 110-km transmission experiment, achieved error-free performance in all cases, and exhibits a root-mean-square timing jitter of 120 fs. Low timing jitter is maintained even in the presence of slow or fast polarization fluctuations.