Characteristics Of Photodiodes Research Articles

Current transport mechanisms in mercury cadmium telluride diode

This paper reports the results of modelling of the current-voltage characteristics (I-V) of a planar mid-wave Mercury Cadmium Telluride photodiode in a gate controlled diode experiment. It is reported that the diode exhibits nearly ideal I-V characteristics under the optimum surface potential leading to the minimal surface leakage current. Deviations from the optimum surface potential lead to non ideal I–V characteristics, indicating a strong relationship between the ideality factor of the diode with its surface leakage current. Diode's I–V characteristics have been modelled over a range of gate voltages from −9 V to −2 V. This range of gate voltages includes accumulation, flat band, and depletion and inversion conditions below the gate structure of the diode. It is shown that the I–V characteristics of the diode can be very well described by (i) thermal diffusion current, (ii) ohmic shunt current, (iii) photo-current due to background illumination, and (iv) excess current that grows by the process of avalanche multiplication in the gate voltage range from −3 V to −5 V that corresponds to the optimum surface potential. Outside the optimum gate voltage range, the origin of the excess current of the diode is associated with its high surface leakage currents. It is reported that the ohmic shunt current model applies to small surface leakage currents. The higher surface leakage currents exhibit a nonlinear shunt behaviour. It is also shown that the observed zero-bias dynamic resistance of the diode over the entire gate voltage range is the sum of ohmic shunt resistance and estimated zero-bias dynamic resistance of the diode from its thermal saturation current.

Passivation Effect of Atomic Layer Deposition of Al2O3 Film on HgCdTe Infrared Detectors

The passivation effect of atomic layer deposition of (ALD) Al2O3 film on a HgCdTe infrared detector was investigated in this work. The passivation effect of Al2O3 film was evaluated by measuring the minority carrier lifetime, capacitance versus voltage (C–V) characteristics of metal–insulator–semiconductor devices, and resistance versus voltage (R–V) characteristics of variable-area photodiodes. The minority carrier lifetime, C–V characteristics, and R–V characteristics of HgCdTe devices passivated by ALD Al2O3 film was comparable to those of HgCdTe devices passivated by e-beam evaporation of ZnS/CdTe film. However, the baking stability of devices passivated by Al2O3 film is inferior to that of devices passivated by ZnS/CdTe film. In future work, by optimizing the ALD Al2O3 film growing process and annealing conditions, it may be feasible to achieve both excellent electrical properties and good baking stability.

Electrical Characteristics of Mid-wavelength HgCdTe Photovoltaic Detectors Exposed to Gamma Irradiation

The study of electrical characteristics of mid-wavelength HgCdTe photodiodes irradiated by steady-state gamma rays has been carried out. The measurement of the current–voltage curves during irradiation revealed an abnormal variation of zero biased resistance R0, and it didn’t tend to change monotonically as observed in the case of post irradiation measurement. The irradiation effect was dominated by bulk effect inferred from the fitting calculations, and the generation-recombination current in the depletion region was drastically affected by gamma irradiation. Another irradiation effect was the linear increase of the series resistance with irradiation dosage which was related with the change of transportation parameters of carriers. The influence of hydrogenation on the gamma irradiation effects was also studied for comparison with the same batch of HgCdTe photodiodes, and it was found that R0 for the hydrogenated devices showed similar change to those without hydrogenation. The series resistance, however, gave a totally different irradiation effect from the non-hydrogenated detectors and showed little change up to nearly 1 Mrad(Si) of gamma irradiation, which may be explained by the annihilation of hydrogen radicals with the defects caused by gamma irradiation.

Mechanisms of the degradation of Schottky-barrier photodiodes based on ZnS single crystals

The effect of ultraviolet (UV) illumination on the electrical and spectral characteristics of Schottky-barrier photodiodes based on ZnS single crystals is studied. It is found that irradiation deteriorates their photosensitivity and changes the current–voltage and capacitance–voltage characteristics and the surface profile of the blocking electrode. It is shown that the main reason for a decrease in the photosensitivity of the diodes is the photoinduced drift of mobile donors in the electric field of the barrier. This drift depends on the crystallographic orientation of the surface being irradiated. Another photoinduced process observed in the diodes is photolysis of the ZnS crystal. This process mainly determines the change in the electrical characteristics of the diodes and in the surface profile of the electrode at an insignificant change in the photosensitivity.

Characterization of leakage current mechanisms in long wavelength infrared HgCdTe photodiodes from a study of current–voltage characteristics under low illumination

This paper presents an improved method to characterize the current–voltage (I-V) characteristics of a HgCdTe photodiode under low illumination. Such characteristics exhibit relatively small but finite zero-bias minority carrier current. The open circuit voltage of the diode is generally small and remains un-noticed due to inappropriate measurement conditions. These characteristics are often mistaken as the dark characteristics of the diode. It is shown here that these kinds of lowly illuminated characteristics may be characterized by using a recently proposed model to analyze the illuminated I-V characteristics that make use of experimentally observed photo-current due to illumination and the resulting open circuit voltage in modelling the current characteristics of the photodiode. An example of long-wavelength HgCdTe diode's I-V characteristics under low illumination that was previously analyzed as dark characteristics is discussed here to illustrate the improved method and to further emphasize the importance of taking into account the influence of illumination on the current characteristics while investigating the leakage currents in infrared photodiodes. Our results show that, by taking into account the effect of illumination, the agreement between the theory and experiment has significantly improved.

Switchable photovoltaic and polarization modulated rectification in Si-integrated Pt/(Bi0.9Sm0.1)(Fe0.97Hf0.03)O3/LaNiO3 heterostructures

We studied switchable photovoltaic and photo-diode characteristics of Pt/(Bi0.9Sm0.1)(Fe0.97Hf0.03)O3/ LaNiO3 (Pt/BSFHO/LNO) heterostructures integrated on Si (100). The directions of photocurrent (JSC) and rectification are found to be reversibly switchable after applying external poling voltages. In pristine state, metal-ferroelectric-metal capacitor Pt/BSFHO/LNO shows JSC ∼ 32 μA/cm2 and VOC ∼ 0.04 V, which increase to maximum value of JSC ∼ 303 (−206) μA/cm2 and VOC ∼ −0.32 (0.26) V after upward (downward) poling at ±8 V. We believe that Schottky barrier modulation by polarization flipping at Pt/BSFHO interface could be a main driving force behind switchable photovoltaic and rectifying diode characteristics of Pt/BSFHO/LNO heterostructures.

The response characteristics of avalanche photodiodes to ultrashort pulsed laser

The physical model of avalanche photodiode (APD) response to ultrashort pulsed laser is established. Numerical simulation of APD response characteristics is focused and presented. The simulated results show that the response peak voltage degrades approximately linearly with the laser pulse duration narrowing when the peak power of laser pulse keeps unchanged. Meanwhile, when the energy of input pulse laser is at the same quantity, the response peak voltage keeps invariably in different pulse duration. Moreover, the pulse duration of response voltage is determined by the sensitivity of APD itself, and the input duration of ultrashort pulsed laser could not be recognized by the APD. Experiments are carried out and the experimental results are in good agreement with simulated data.

The design of the totally active scintillator detector

In the project of Advanced European Infrastructures for Detectors at Accelerators (AIDA), the Institute of Nuclear Research designed and tested the Totally Active Scintillator Detector (TASD). This paper reports the results of design of TASD prototype and outlines requirements for a test beam at CERN to test these, tentatively planned on the H8 beamline in the North Area, which is equipped with a large aperture magnet. TASD consists of 50 modules of plastic scintillators. Each module is instrumented with one X and one Y plane, with 90 scintillator bars per plane. The bar width, height and length are 1.0 cm, 0.7 cm and 90 cm respectively. The distance between modules can be varied from 0 to 2.5 cm. Other components such as active detectors or passive sheets of material can be inserted in these 2.5 cm gaps if required. The full detector depth can therefore be varied from 75 cm to 200 cm and in its compact form, it is 1 m3 in volume. The paper presents measurement results for the TASD elements that included in the prototype elements (measurement of crosscurrents, the light yield of scintillators, and the characteristics of photodiodes).

Nonpolar p-GaN/n-Si heterojunction diode characteristics: a comparison between ensemble and single nanowire devices

The electrical and photodiode characteristics of ensemble and single p-GaN nanowire and n-Si heterojunction devices were studied. Ideality factor of the single nanowire p-GaN/n-Si device was found to be about three times lower compared to that of the ensemble nanowire device. Apart from the deep-level traps in p-GaN nanowires, defect states due to inhomogeneity in Mg dopants in the ensemble nanowire device are attributed to the origin of the high ideality factor. Photovoltaic mode of the ensemble nanowire device showed an improvement in the fill-factors up to 60% over the single nanowire device with fill-factors up to 30%. Responsivity of the single nanowire device in the photoconducting mode was found to be enhanced by five orders, at 470 nm. The enhanced photoresponse of the single nanowire device also confirms the photoconduction due to defect states in p-GaN nanowires.

Development of Wide Bandgap Multifunctional NiO Nanostructures and Thin Films for Sensing Applications

Realizations of transparent pn homo-junction have become more important for the development of transparent electronics for the next-generation optoelectronic devices. The tunability of the electrical conductivity of NiO thin films with both P-type and N-type conduction by varying growth kinetics using RF sputtering technique with good optical and properties in the visible region have been demonstrated. The pn homo-junction of NiO thin films has been fabricated. The room-temperature conductivities for n-type and p-type NiO thin films have been studied using Hall measurement. Glancing angle deposition (GLAD) configuration of rf sputtering technique is utilized to fabricate the array of vertically align nanorods of NiO and are exploited for the development of homojunction devices. The fabricated homo-junction exhibits good rectifying behaviour with efficient ultra-violet (UV) photodiode characteristics, and providing suitable solution for the development of low-cost UV photo-detectors with enhanced response characteristics. The obtained results on the developed UV photo-detector will be elaborated. Further, Nickel oxide (NiO) nanoparticles (NiO-NPs) have been synthesized by a simple chemical route and exploited successfully for the fabrication of urea biosensors. A thin layer of NiO nanoparticles deposited on indium tin oxide (ITO) coated glass serves as efficient platform for the immobilisation of Urease (Ur) biomolecules for the detection of Urea. The array of NiO nanorods prepared by GLAD was also used as a matrix for making bio-electrode for the efficient detection of Urea using electrochemical techniques. The prepared amperometric bio-electrodes based on NiO nanostructures (Ur/NiO/ITO/glass) exhibits a high sensitivity of about 21.0 mA/(mM-cm2) and good linearity over a wide range (up to 16.65 Mm) of urea concentration.

Improved Photoresponse of Hybrid ZnO/P3HT Bilayered Photodetector Obtained Through Oriented Growth of ZnO Nanorod Arrays and the Use of Hole Injection Layer

We report highly oriented one-dimensional (1-D) growth of zinc oxide (ZnO) nanorod arrays (NRA) which were later utilized to fabricate hybrid photodiodes having the typical photodiode configuration of indium tin oxide (ITO)/ZnO/poly(3-hexylthiophene) (P3HT)/Ag. These functional hybrid bilayered photodiodes were found to have high rectification ratio under dark conditions and demonstrated enhanced responsivity under light illumination. Further, we studied the effect of an intermediate electron blocking layer of poly(ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) on the photodiode characteristics and demonstrated ITO/ZnO/P3HT/PEDOT:PSS/Ag photodiodes, reporting very high rectification ratio and responsivity in this bilayered configuration. The observed results are explained on the basis of the increased surface area of contact between the ZnO nanorods and the P3HT, and also the efficient hole injection into the P3HT layer from the top Ag electrode.

AlGaAs/GaAs photodetectors for detection of luminescent light from scintillators

The AlxGa1-xAs / GaAs photosensitive heterostructures were grown by molecular beam epitaxy. On their basis the discrete photodiodes (PD) and phototransistors (PT) operating in the visible (0.4–0.7 μm) wavelength range and having photosensitive area diameters of 1.5 mm and 180 pm correspondingly were created. The current-voltage and spectral characteristics of discrete PD and PT were measured and analyzed. Distinctive features of the proposed photodetectors are a high monochromasy with the maximal sensitivity of 0.13 A/W at λ = 530-570 nm and a low dark current of 4.7 nA and 530 pA at 5 V reverse bias for PD and PT correspondingly.

VCSEL-Based Interconnects for Current and Future Data Centers

The vast majority of optical links within the data center are based on vertical cavity surface emitting lasers (VCSELs) operating at 850 nm over multimode optical fiber. Deployable links have evolved in speed from 1 Gb/s in 1996 to 28 Gb/s in 2014. Serial data links at 40 and 56 Gb/s are now under development and place even more demand on the VCSEL and photodiodes. In this paper, we present the characteristics of VCSELs and photodiodes used in current generation 28 Gb/s links and present several methods to extend link distances using more advanced data encoding schemes. Finally, we will present results on wavelength division multiplexing on multimode optical fiber that demonstrate 40 Gb/s Ethernet connections up to 300 m on duplex OM3 optical fiber, and present results on fiber optimized for modal bandwidth in the 850 to 980 nm range.

Fundamental limits of MWIR HgCdTe barrier detectors operating under non-equilibrium mode

The paper presents numerical considerations of temperature-dependent performance of different mid-wave infrared HgCdTe detectors (with p- and n-type active layer) for non-equilibrium operation. Current–voltage characteristics of double heterostructure PpN photodiode, pBppN barrier photodiode, nBnn and nBnnN barrier detectors are compared to find an optimal architecture for high-operating temperature conditions. Using our model, the calculated characteristics of the devices are fitted to the experimental results for HgCdTe photodiode grown on GaAs substrate by metal organic chemical vapour deposition.The performance of photodiodes with p-type absorber are limited by the generation current associated with the Shockley–Read–Hall process, while nBnn type devices (with the n-type absorber) indicate a diffusion limited dark currents associated with Auger processes. At high values of the reverse bias (over 1V), the trap states located at dislocations lead to strong band-to-band and trap-assisted tunnelling due to high electric field within the depletion layer.

An organic–inorganic rectifying contact based on a ZnPc derivative

An organic–inorganic rectifying contact was fabricated by forming a thin film of a Zinc Phthalocyanine (ZnPc) derivative, Zinc 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H,31H-phthalocyanine (oc-ZnPc), on a p-Si wafer and evaporating Al on the structure. The current–voltage (I–V) and capacitance–voltage (C–V) measurements of Al/oc-ZnPc/p-Si structure were taken in dark at room temperature. The I–V measurements proved that the structure showed excellent rectification. Some basic diode parameters like ideality factor and barrier height were calculated from lnI–V plot. Ideality factor and barrier height values were found as 1.44 and 0.78eV, respectively. The series resistance value of the structure was determined as 5.46kΩ by means of Norde functions. The C–V measurements were taken for various frequencies and it was seen that the capacitance value decreased with increasing frequency.In addition I–V measurements of the Al/oc-ZnPc/p-Si/Al were repeated under light which had illumination intensity of 40–100mW/cm2. It was observed that reverse bias current of the diode increased with the light intensity. Therefore, the structure showed photodiode characteristics and it can be used for electrical and optoelectronic applications.

Signatures of differential Log R–V characteristics for non-uniformity analysis of HgCdTe infrared photodiode arrays

In continuation to our research on the non-uniformity in infrared focal plane arrays of HgCdTe photodiodes, we have examined and found a few important signature parameters in the forward bias region of the electrical characteristics of the photodiodes. These signatures are the peaks of the first and second order derivatives of dynamic resistance–voltage characteristics. They show good correlation with the material and devices parameters and have been investigated to be good signatures for statistical performance variation analysis. In this note, by using theoretical model and statistical analysis of these signatures, we show that the variations in the proposed signatures represent underlying non-uniformity in important material/device parameters. Such signatures may be used along with the other conventional signatures of reverse biased photodiode characteristics to identify the root cause of response non-uniformity in the array with high confidence level.

Vacuum ultraviolet ellipsometer using inclined detector as analyzer to measure stokes parameters and optical constants — With results for AlN optical constants

Principle and analysis for ellipsometers usable in the vacuum ultraviolet (VUV) region up to about 25eV, which are consisting of a sample mirror and an inclined photodiode, are described. Our ellipsometer has two degrees of freedom in rotation; the main chamber can rotate around the axis of incidence and, the analyzer unit can also rotate around the axis of reflection. All the unknown parameters (Stokes parameters of the source, ellipsometric parameters of the sample and the polarization sensitivity of the inclined detector) are obtained by rotating the main chamber and analyzer independently and solving the simultaneous equations with the measurands. Measurement results on polarization characteristics of photodiodes, Stokes parameters of the beam emerging from a synchrotron radiation beamline, and optical constants of AlN film are given. It is concluded that the ellipsometer is advantageous in the simplicity and worked as intended.

Characterization of n-Ge/i-Ge/p-Si PIN photo-diode

A PIN photo-diode was fabricated from the phosphorus doped n-Ge/i-Ge/p-Si hetero-structure grown by rapid thermal chemical vapor deposition (RTCVD). The surface morphology of the n-Ge/i-Ge layer was found to be mirror like and the n-Ge/i-Ge layer was under a tensile strain of ~0.071%. The phosphorus doping concentration and the RMS surface roughness were 2×1019cm−3 and 2.46nm, respectively. Current–voltage characteristics of the PIN photo-diode showed a forward saturation current density of 0.63A/cm2 at 2V and reverse-biased characteristics behaved similar to forward-biased characteristics of the diode. Roll-off in spectral response was observed at wavelengths greater than 1600nm which could be attributed to decreased absorption of Ge at room temperature.

3-λ characterization of phase response for optical receivers

We propose a novel digital signal processing (DSP) algorithm for photodiode characterization probed by three wavelengths. The DSP algorithm has low computational complexity. The required number of measurements increases logarithmically with the number of spectral points. For the first time to our knowledge, the phase response of photodiode is characterized up to 20 GHz.

A Theoretical and Experimental Determination of the Internal Quantum Efficiency of Silicon Photodiodes

A new method of processing the experimental current-voltage characteristics of photodiodes using reference points is proposed. By comparing a trap detector, developed at the All-Russia Research Institute of Optophysical Measurements based on Hamamatsu S6337 photodiodes with an HH-03-1337 trap detector, certified using a cryogenic radiometer at the PTB, an experimental value of the internal quantum efficiency of the Hamamatsu S6337 photodiode is obtained.