Junction Photodetectors Research Articles

A blue-violet enhanced BDJ photodetector and its applications in the probe chip measurements of the LEDs for solid-state lighting

A blue-violet enhanced buried double p–n junction (BDJ) photodetector with its characteristics is reported in this manuscript. It was fabricated on high resistivity float-zone silicon substrate by using ion implantation and exhibits low leakage currents. It can measure both the light intensity as a photometric detector and the wavelength of quasi-monochrome light as a wavelength sensor simultaneously. It was optimized to operate at wavelength from 380 nm to 780 nm in which the light emitting diodes (LEDs) for solid-state lighting is most interested. The resolution for the wavelength measurement of the photodetector is better than 1 nm. The probe chip tests of violet, blue, green and red LED chips have been demonstrated using the fabricated detector. This simple, fast and reliable method provides an alternative to low cost and fast examination technique for LED chips in vast production.

Dark Current and Signal-to-Noise Ratio in BDJ Image Sensors

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, analytical expressions of dark currents and equivalent noise generators of a CMOS color image sensor are presented, and the signal-to-noise ratio (SNR) at both outputs is evaluated. Static measurements and simulations on Austria Micro Systems 0.35-&lt;formula formulatype="inline"&gt;&lt;tex&gt;$\mu\hbox{m}$&lt;/tex&gt;&lt;/formula&gt; CMOS test structures yield guidelines to increase the SNR of the buried double junction photodetector. </para>

Fabrication and Characterization of an InAs&amp;lt;tex&amp;gt;$_0.96hbox Sb_0.04$&amp;lt;/tex&amp;gt;Photodetector for MIR Applications

In this letter, we report an InAsSb p/sup +/-n junction photodetector grown on InAs substrate by liquid phase epitaxy. Electrical and optical characterizations of the device have been carried out at room temperature for operation of the device in the mid-infrared region. The study revealed that the dark current of the photodetector under reverse bias is dominated by a trap-assisted tunnelling current component, which degrades the detectivity of the device. Further, by operating the device at a suitable low reverse bias it is possible to improve the room-temperature detectivity significantly as compared to its value at zero bias.

The fabrication of p-Ge/n-Si photodetectors, compatible with back-end Si CMOS processing, by low temperature (&lt; 400 °C) molecular beam epitaxy and electron-beam evaporation

ABSTRACTWe report on the low temperature growth, by molecular beam epitaxy (375 °C) and electron-beam evaporation (300 °C), of p-Ge films on n-Si substrates for fabricating p-n junction photodetectors, aimed at the integration of opto-electronic components with back-end Si CMOS processing. Various surface hydrogen and hydrocarbon removal treatments were attempted to improve device properties. We invoke Ge diffusion and growth modes as a function of deposition temperature and rate to correlate structural analysis with the device performance.

InGaN/GaN MQW p–n junction photodetectors

InGaN/GaN multiquantum well (MQW) p–n junction photodetectors with semi-transparent Ni/Au electrodes were fabricated and characterized. It was found that the fabricated InGaN/GaN MQW p–n junction photodetectors exhibit a 20 V breakdown voltage and a 3.5 V forward 20 mA turn on voltage. It was also found that the photocurrent to dark current contrast ratio is higher than 10 5 when a 0.4 V reverse bias was applied to the InGaN/GaN MQW p–n junction photodetectors. Furthermore, it was found that the maximum responsivity was 1.28 and 1.76 A/W with a 0.1 and 3 V applied reverse bias, respectively.

AlGaN-based UV photodetectors

Al x Ga 1− x N alloys are very attractive materials for application to ultraviolet photodetection. AlGaN photoconductors, Schottky photodiodes, metal–semiconductor–metal photodiodes, p–n junction photodetectors and phototransistors have been recently developed. In this work we analyse the performance of AlGaN-based photodetectors, discussing present achievements, and comparing the characteristics of the various photodetector structures developed to date.

Modeling of the spectral response of AlxGa1−xN p-n junction photodetectors

We propose to model the spectral response of p - n junction photodetectors based on gallium nitride and related AlGaN alloys. The model is based on the resolution of the differential equations that govern the excess carrier variation in each layer of the photodiode taking into account all the physical parameters, in particular the presence of deep trap levels in the forbidden gap. We notice that the theoretical results are in good agreement with the experiments. We have also analysed the effect of the recombination velocity at the illuminated surface, as well as the impact of the thickness and the doping density of the p -type layer (illuminated zone) on the spectral response magnitude.

Antireflection coating for superconducting tunnel junction photodetectors in the visible range

Abstract Superconducting tunnel junctions can be used as either thermal detectors or photon counters in the visible range. One of the main mechanisms responsible for the detector losses is the reflection occurring at the surface of the irradiated film. For niobium the reflectance is about 50% in the visible range. To enhance the responsivity we have considered the effect of antireflection coatings made with hydrogenated amorphous silicon-nitrogen alloys. Such materials, having a tunable refractive index, allow multilayers to be realized which reduce the reflectivity to a few per cent. A stochastic optimization algorithm has been used for the design of the multilayer; it adopts the maximum value of the reflectance in the wavelength range of interest as the figure of merit. Some designs are presented and discussed. To test the effect of the antireflection coatings at 4·2 K, an experimental set-up has been developed where the light spot can be moved by a piezoelectric micropositioner from a coated to an unco...

Antireflection coating for superconducting tunnel junction photodetectors in the visible range

Antireflection coating for superconducting tunnel junction photodetectors in the visible range

Power minimization and technology comparisons for digital free-space optoelectronic interconnections

This paper investigates the design optimization of digital free-space optoelectronic interconnections with a specific goal of minimizing the power dissipation of the overall link, and maximizing the interconnect density. To this end, we discuss a method of minimizing the total power dissipation of an interconnect link at a given bit rate. We examine the impact on the link performance of two competing transmitter technologies, vertical cavity surface emitting lasers (VCSELs) and multiple quantum-well (MQW) modulators and their associated driver-receiver circuits including complementary metal-oxide-semiconductor (CMOS) and bipolar transmitter driver circuits, and p-n junction photodetectors with multistage transimpedance receiver circuits. We use the operating bit-rate and on-chip power dissipation as the main performance measures. Presently, at high bit rates (>800 Mb/s), optimized links based on VCSELs and MQW modulators are comparable in terms of power dissipation. At low bit rates, the VCSEL threshold power dominates. In systems with high bit rates and/or high fan-out, a high slope efficiency is more important for a VCSEL than a low threshold current. The transmitter driver circuit is an important component in a link design, and it dissipates about the same amount of power as that of the transmitter itself. Scaling the CMOS technology from 0.5 /spl mu/m down to 0.1 /spl mu/m brings a 50% improvement in the maximum operating bit rate, which is around 4 Gb/s with 0.1 /spl mu/m CMOS driver and receiver circuits. Transmitter driver circuits implemented with bipolar technology support a much higher operating bandwidth than CMOS technology; they dissipate, however, about twice the electrical power. An aggregate bandwidth in excess of 1 Tb/s-cm/sup 2/ can be achieved in an optimized free-space optical interconnect system using either VCSELs or MQW modulators as its transmitters.

Colorimetric characterization of a buried triple p–n junction photodetector

The operation of a buried triple p–n junction (BTJ) photodetector and its colorimetric characterization are described. Guidelines are given for the choice of the linear transformation between the device color space and the CIE 1931 standard system of color measurement. With a least squares fitting to the third order a mean color difference of 2.15 is obtained. The effect of the uniformity of the color space on the accuracy of the linear transformation is discussed.

High-performance GaN p-n junction photodetectors for solar ultraviolet applications

The fabrication and characterization of ultraviolet photodetectors based on GaN p-n junctions is reported. The devices are grown by metalorganic vapour phase epitaxy on basal-plane sapphire substrates. These detectors are visible-blind with a sharp wavelength cut-off at 360 nm. The photocurrent is linear with incident power from up to , with a responsivity of at 360 nm. The device time response is dominated by the effective resistance-capacitance time constant, and a 105 ns response is estimated for very low load resistances. A comparison with the response of GaN photoconductor detectors is also presented. The application of these high-performance photodetectors for solar ultraviolet monitoring is described.

Low-frequency noise and performance of GaN p-n junction photodetectors

We report on low-frequency noise characteristics of visible-blind GaN p-n junction photodetectors. Carrier hopping through defect states in the space charge region, believed to be associated with dislocations, is identified as the main mechanism responsible for the dark conductivity of the photodiodes. Under reverse bias, the dark current noise has the 1/f character and obeys the Hooge relation with α≈3. Under forward bias, we observe generation-recombination noise related to a trap level with the activation energy of 0.49 eV. Under illumination, detectivity is found to be shot noise limited. The noise equivalent power of a 200×200 μm2 photodetector is estimated at 6.6×10−15 W/Hz1/2 at a bias of −3 V.

High Quality InAs1–ySby/InAs Multilayers for mid‐IR Detectors

AbstractThe high quality InAsSb multi‐layers have been grown on InAs substrate by Gd‐doped liquid phase epitaxy between 530 and 460°C. Compositional dependence of energy band gap and of lattice constant for epilayers were studied. The material is characterized by surface morphology observation, FTIR transmittance, photoluminescence (PL), spectro‐ellipsometry, and electrical measurements. Surface‐illuminated room temperature p‐n junction photodetectors in 3–5 μm wavelength range have been obtained.

UV photodetectors in 6HSiC

Abstract We have fabricated two types of UV photodetector in 6HSiC: UV photodiodes using SiC Schottky-barrier structures; SiC photodiodes using shallow p-n junctions. The monochromatic sensitivity of the Schottky-barrier photodetectors (at a wavelength of 215 nm) is 0.15 A/W, and of the p-n junction photodetectors (at a wavelength of 225 nm) 0.13 A/W.

High-efficiency Al0.22Ga0.78As solar cells grown by molecular beam epitaxy

The quality of pn junction photodetectors made of Al0.2Ga0.8As has been investigated as a first step in the optimization of tandem solar cells. We have obtained 1 sun AM1.5 efficiencies of 16.1% for 0.25 cm2 Al0.22Ga0.78As solar cells fabricated from molecular beam epitaxy (MBE) material. This efficiency is 3.2 percentage points higher than the previously best reported efficiency of 12.9% for an Al0.2Ga0.8As solar cell fabricated from MBE material.

Germanium photodetectors with induced p-n junctions

An experimental investigation has been made of optoelectronic carrier transport processes in Au-Ge contacts and their dependence on temperature, which shows that these devices behave as induced p+-n junctions rather than as Schottky barriers. The dark currents are due predominantly to minority-carrier injection in forward bias, and to generation in the quasi-neutral region in reverse bias. The devices are formally equivalent to germanium p+-n junction photodetectors with diffused or ion-implanted junctions, but require neither high-temperature fabrication processes nor high dopant concentrations in the surface region.

On the dark currents in germanium Schottky-barrier photodetectors

It is shown that for experimentally observed values of Schottky-barrier height of metal-n-type germanium photodetector structures, the dominant component of dark current can be due to the injection of minority carriers, rather than to the usual majority-carrier component. For barrier heights approaching 0.6 eV, for doping concentrations N_{d} \lsim 10^{15} cm-3, for short minority-carrier lifetime \tau_{p} \lsim 1 µs, for narrow base width W_{b} \lsim 10 µm, or combinations of these conditions, the minority-carrier injection ratio approaches unity and these devices behave in the same way as p+-n junctions, with identical dark currents. The low-temperature fabrication requirements and processing simplicity of germanium Schottky barriers makes these devices more attractive under these conditions than germanium p-n junction photodetectors.

Optoelectronic nomenclature for solid-state radiation detectors and emitters

The author attempts to promote nomenclature standardization, both by describing relevant existing standards, and proposing new terminology where necessary. Nomenclature for radiation and for junction detectors and noncoherent emitters is considered. In the case of radiation, standards have been well established for most of the important radiometric and photometric parameters. The nomenclature originally established primarily for infrared detectors is readily applied to semiconductor junction photodetectors. Semiconductor radiation sources are relatively recent, so the introduction of several new quantities for device characterization is required.

Operation of p-n Junction Photodetectors in a Photon Flux Integrating Mode

A technique for operating a p-n junction photodiode in a photon flux integration mode is described. In this mode the p-n junction is charged to a reverse voltage (less than its breakdown voltage) and then open-circuited. The voltage across the junction, with zero incident illumination, will decay at a rate that is independent of junction area. Time constants in the order of seconds may be achieved with silicon planar structures at room temperature. Under illumination, the rate of decay of charge depends linearly on the intensity of the incident illumination, so that the total charge removed is proportional to the time integral of illumination. Operation of p-n junction photodiodes is analyzed for this mode and boundary conditions are established. A practical structure utilizing this mode of operation is discussed. This structure makes use of the nearly ideal switch characteristics of an insulated gate field-effect transistor to periodically sample a photodiode. Advantages offered by this device structure include 1) linear dependence of signal charge on light intensity over several orders of magnitude; 2) electronically controllable sensitivity; 3) ease of integration into arrays for image sensing.