Decrease In Dark Current Research Articles

Neutron Radiation Effects on the Performance of the CdSe Thin Film for Photodetector Applications

Cadmium Selenide CdSe thin films were deposited on (7.5×1.3×0.1 cm3) glass substrates and (1×1 cm2) p-type silicon substrates using pulsed laser deposition technique (Nd: YAG laser beam with 80 mJ energy, λ = 1064 nm). Then, they were annealed at 300 °C for 1 h to get diodes as visible light detectors. Some of these samples (diodes) were exposed to different intervals (5, 7, 9, 12) days of neutron radiation using (241Am -10Be) source with a flux of 3×105 n/cm2.s and energy of 5.71 MeV. For comparison purposes, the other diodes were kept without any irradiation The morphological and electrical properties of these samples were studied by XRD, FE-SEM and I-V measurements. Results have shown all these thin films exhibit a hexagonal structure. However, there is a slight shift in the preferred orientation (100) for the irradiated films. Also, there was a new (102 - SiO2) peak that appeared in the irradiated thin film pattern. The crystallite size of pristine and (5, 7, 9, 12) days irradiated CdSe thin films were (26.9, 18.3, 24.9, 20.3 and 24.5) nm respectively, whereas, the mean particle size of the pristine film was 37 nm whereas for the irradiated films 53, 64, 73 and 92 nm. Results also show that the band gap of these samples increased from 2.17 eV for pristine thin films to 2.3, 2.48, 2.25, and 2.3 eV for the irradiated thin films. On the other hand, the results of I-V characteristics show the dark/light current. The current under illumination increases when exposed to small values of neutron radiation then it decreases with higher values of exposure. In contrast, the dark current decreases significantly with the irradiation. The effect of the irradiation was clear on the response/recovery period for all devices. Nevertheless, it was more profound in the response/recovery time of pristine devices. Also, the photo-responsivity of the pristine device was larger than the other devices and it was decreased with increasing absorbed doses. HIGHLIGHTS Hexagonal Structure: All CdSe thin films (both pristine and irradiated) exhibit a hexagonal structure, with a slight shift in orientation due to neutron irradiation. Neutron Radiation Impact: Neutron radiation causes a significant shift in crystallite size, decreasing the size for irradiated films. Additionally, a new (102 SiO2) peak emerges in irradiated samples, indicating radiation-induced changes. Band Gap Increase: The optical band gap of the CdSe films increased with neutron irradiation, starting from 2.17 eV in pristine films to values as high as 2.48 eV after irradiation. Morphological Changes: Irradiated films showed increased grain sizes, with neutron exposure leading to the enlargement of mean particle sizes from 37 nm in pristine samples to 92 nm in the most heavily irradiated samples. Electrical Behavior: Neutron irradiation impacted the photodetectors' electrical properties. The light current initially increased with small neutron doses but decreased with higher doses, while dark current consistently decreased after irradiation. GRAPHICAL ABSTRACT

Fabrication of PSCs with light absorption chips utilizing double-metal-cladding waveguide technology

Metal nanoparticles or periodic metal nanostructures exhibit localized surface plasmon resonance (LSPR) effects, widely employed in photovoltaic devices to enhance the light absorption. In this study, we used a double-metal-cladding waveguide (DMCW) structure to fabricate hexagonal metal nanostructures on the front side of the indium tin oxide (ITO) glass, positioned away from the incident light direction. We then prepared perovskite solar cells under various reaction conditions. The analysis results indicate that the metal nanostructure chip excites near-field coupling, generating strong localized fields, and enhances the light absorption through the LSPR effect. The perovskite solar cells (PSCs) with the chip structures exhibited a significant increase in short-circuit current density (JSC) and fill factor (FF), accompanied by a decrease in dark current, indicating improved photovoltaic characteristics of the cells. Altering the evaporative deposition time of the silver film and the concentration of the reaction solution led to a 12.79% increase in the power conversion efficiency (PCE) of the PSCs.

Which Parameters Determine the Low-Light Behaviour of CIGSSe-Based Thin-Film Solar Cells?

The performance of solar cells in realistic operating conditions usually differs from the specified efficiency at standard test conditions (STC). Among other factors, the illumination intensity (irradiance) is often lower than at STC, which leads to a lower device efficiency. Therefore, it becomes important to optimize the output power at low-light conditions in order to achieve a high energy yield at a specific location. For this purpose, it is essential to have a detailed knowledge of the relevant parameters that govern the low-light behaviour. This study investigates the impact of the diode parameters on the low-light performance of thin-film solar cells based on chalcopyrite Cu(In,Ga)(S,Se)2 absorbers. Experimental irradiance-dependent current-voltage results are analysed with the help of an analytical model. For each parameter the contributions of its absolute value and its irradiance dependence are assessed. Additionally, relations between the diode parameters and material parameters are examined by analysing different cell variations. The results show that cell performance at low-light conditions is primarily governed by the irradiance dependence of the fill factor, which in turn is mainly determined by the parallel resistance of the device. Moreover, a reduction of the dark saturation current and the ideality factor towards lower irradiances is observed which indicates an irradiance-dependent change of recombination dynamics. The consequence is an increase of the open-circuit voltage at low-light conditions which indirectly also boosts the fill factor. The results suggest that cell optimization for low-light conditions should focus on improving the parallel resistance and tuning recombination in a way that the dark saturation current decreases with decreasing irradiance.

Noise behaviors of SWIR InxGa1-xAs/InP focal plane arrays as a function of lattice-mismatch degree

A quantitatively investigation on the dark noise behaviors of In0.53Ga0.47As/InP, In0.75Ga0.25As/In0.75Al0.25As/InP and In0.83Ga0.17As/In0.83Al0.17As/InP short-wavelength infrared (SWIR) focal plane arrays (FPAs) with cutoff wavelengths (λc) of 1.7, 2.2 and 2.5 μm, respectively, is presented. Theoretical FPA noise model consisting of the diode thermal noise, the dark current shot noise, the operational transimpedance amplifier (OTA) thermal noise, the 1/f noise, the sample and hold noise of the circuit, and etc. were fully taken into consideration. The results show that the dark noises are mainly composed of the OTA thermal noise of the readout circuit under short integration times (Tint) for all three FPAs. Under long Tint, the thermal noises from the photodiode arrays at 300 K is acting as the primary source for the dark noise of the lattice-matched In0.53Ga0.17As FPA, whereas noises of the lattice-mismatched 2.2 and 2.5 μm FPAs are identified to be mainly comes from the diode thermal noise, the dark current shot noise, and the 1/f noise at 150 and 180 K. In addition, an overall trend that the contribution of the 1/f noise increases significantly even if the junction impedance increases and the dark current decreases by cooling down for the extended wavelength detector, which is related to the existence of high density misfit dislocation defect-related trap states in the materials. These results suggest that lowering the junction capacitance and increasing the junction resistance are effective routes to suppress the total readout noise of the InGaAs FPAs, which essentially relies on the improvements on the material epitaxial growth and photodiode array processing recipes.Index Terms: readout noise, lattice-mismatch, focal plane array, InGaAs, noise model.

High-performance photodetector based on an interface engineering-assisted graphene/silicon Schottky junction

Graphene/silicon Schottky junctions have been proven efficient for photodetection, but the existing high dark current seriously restricts applications such as weak signal detection. In this paper, a thin layer of gadolinium iron garnet (Gd3Fe5O12, GdIG) film is introduced to engineer the interface of a graphene/silicon Schottky photodetector. The novel structure shows a significant decrease in dark current by 54 times at a −2 V bias. It also exhibits high performance in a self-powered mode in terms of an Ilight/Idark ratio up to 8.2 × 106 and a specific detectivity of 1.35 × 1013 Jones at 633 nm, showing appealing potential for weak-light detection. Practical suitability characterizations reveal a broadband absorption covering ultraviolet to near-infrared light and a large linear response with a wide range of light intensities. The device holds an operation speed of 0.15 ms, a stable response for 500 continuous working cycles, and long-term environmental stability after several months. Theoretical analysis shows that the interlayer increases the barrier height and passivates the contact surface so that the dark current is suppressed. This work demonstrates the good capacity of GdIG thin films as interlayer materials and provides a new solution for high-performance photodetectors.

Solution-processed Li-doped ZnSnO metal-semiconductor-metal UV photodetectors

The electrical performance of thin-film transistors that use an amorphous oxide semiconductor (AOS) is significantly improved by incorporating metal cations as carrier suppressors. However, the effect of these elements on the performance of AOS-based photodetectors (PDs) is still unknown. This study uses a precursor containing lithium (Li) element and a sol-gel process to produce a Li-doped amorphous ZnSnO (a-ZTO) thin-film for UV PD applications. The results of x-ray photoelectron spectroscopy analysis show that the number of oxygen vacancies (V o) in a-ZTO thin-films decreases significantly from ∼32.1% to ∼14.4% after Li-doping (3 at%). The dark current decreases and the photocurrent increases in the ZTO-based PD so an ultra-high photo-to-dark current ratio (PDCR) of 1185 is achieved. The significant increase in PDCR means that solution-processed a-ZTO are eminently suited to use in UV PDs that use In-free AOSs.

Enhanced performance of UV photodetector of MoS2 quantum dots-decorated ZnO nanorods

Two-dimensional transition metal dichalcogenides such as molybdenum disulfide (MoS2) have attracted great attention due to their unique optical, electrical and chemical properties. MoS2 quantum dots (QDs) exhibit strong quantum confinement, high surface area and notable active edge sites compared to their bulk. In this work, MoS2 QDs were attached on the surface of ZnO nanorods (NRs) grown on interdigitated ITO substrates and then used as photodetector. MoS2 QDs were synthesized by a new ultrafast way pulsed laser ablation (PLA) in liquid method and then spincoated on the surface of ZnO NRs. The pristine ZnO and ZnO/MoS2 QDs photodetector were investigated under UV and visible light (325 nm, 505 nm and 635 nm) with the bias voltage -5 V to 5 V. The results show that the decoration of ZnO NRs by MoS2 QDs could enhance the sensitivity, responsivity and detectivity under UV irradiation. This may due to the decrease of dark current as the result of passivation of surface defects of ZnO NRs by MoS2 QDs.

Comparative study of In/CdTe/Au Schottky- and p–n junction-diode detectors formed by backside laser irradiation doping

Two types of In/CdTe/Au diode structures were fabricated using detector-grade p-CdTe single crystals: (i) by vacuum evaporation of In and Au contacts on the chemically treated (111) surfaces; (ii) by backside laser doping when the In/CdTe structures were irradiated from the crystal side with a wavelength for which the semiconductor was transparent. Thus, diodes with a Schottky contact (In/CdTe) and a p–n junction were obtained, respectively. To prove the doping of the thin region near the In/CdTe interface by In (donor) and study thermal tolerance of both types of In/CdTe/Au diode detectors, room temperature I–V characteristics and 57Co isotope emission spectra were measured before and after annealing of the diodes at temperatures below and above the In melting point. Thermal annealing at lower temperatures led to a slight increase and decrease in reverse dark current of the unirradiated and laser-irradiated samples, respectively. Heating up to 200 °C resulted in a significant increase in reverse current and complete spectra degradation in the samples fabricated without laser processing. After such annealing, the electrical characteristics of the p–n junction diodes, formed by the backside laser doping technique, became optimized and 57Co spectra were almost unchanged. It was supposed that a Schottky barrier at the In/CdTe interface was degraded, while a p–n junction, created in a deeper region of the CdTe crystal, remained functional even after melting and solidifying the In contact.

Особенности цАМФ-зависимой регулировки каскада фототрансдукции в колбочках

Retinal photoreceptor cells, rods and cones, are capable of light adaptation in a wide range of illuminations due to a set of regulatory mechanisms. Among them, the most studied are calcium feedbacks, and they may account approximately 50% of actual regulation of photosensitivity. There are other regulating mechanisms that contribute to adjusting photoreceptor reaction to light depending on the level of illumination, for example, regulation of phototransduction cascade under circadian cycle. During the phase of the circadian cycle, the level of cAMP increases and the sensitivity of rods also increases, which can be considered as an adaptive effect. In cone photoreceptors, operating under high light intensities and losing their contribution in the twilight, rise of photosensitivity may not have adaptive significance. In present study we investigated how the change in [cAMP]in affect the function of phototransduction cascade in carp cones. [cAMP]in in cones was elevated using adenylate cyclase activator forskolin. It has been shown that in cones, forskolin slows down both rising and declining phases of photoresponse. As a result, in cones, unlike rods, forskolin does not increase photosensitivity but causes nearly two-fold decrease of current. Thus, reaction of the cone phototransduction cascade to an increase in cAMP level is distinctly different from reaction of rod photoreceptors. For cones, this effect of [cAMP]in may also have an adaptive significance, not in the sense of increasing sensitivity, but for the purpose of reduction of metabolic load on cells that do not function in the dark phase.

Interface engineering on ZnO/Au based Schottky junction for enhanced photoresponse of UV detector with TiO2 inserting layer

Metal-oxide semiconductor ZnO shows enormous potential in the field of photoelectric detection. However, the adsorption of H2O/O2 on its surface unavoidably results in degradation in the photoresponse. Herein, Au–TiO2–ZnO (ATZ) ultraviolet (UV) photodetectors were designed to benefit the photosensing performance by weaken the surface state effect through tuning the Schottky junction interface with TiO2 insertion layer. As expect, 97% enhancement of IPh response together with three orders of magnitude decrease of dark current was triggered. This enhancement is owing to the efficiently separation and extraction of photoexcites under the effect of the stronger and expanding built-in field, which is a result of reduction of space charge density in barrier region induced by inhibiting H2O/O2 adsorption at the ZnO/Au interface. These findings here provide a promising method to boost performances of optoelectronic devices by interface engineering and could be extended to other semiconductor devices.

Nano-scale planar photodetector based on ring form MQWs for FIR regime

In this paper, we proposed a new design of infrared photodetector structure based on ring-shaped multiple quantum wells for long-infrared and far-infrared (FIR) regimes. The absorption coefficient of the proposed photodetector that consists of GaAs/Al0.25Ga0.75As quantum wells with a thickness of 4 nm and a barrier of 40 nm has been calculated, from which a dominant peak of 50 um locates in the FIR regime. The proposed device has a planar structure with small thickness compared with ordinary rectangular multiple quantum well photodetectors. Also, there is 100% enhancement in typical IR absorption versus these ordinary photodetectors. Electronic states and wave functions calculated through solving the Schrodinger equation and then the effect of quantum well number on important parameters of photodetectors, such as gain mode and dark current, are investigated. According to the results, dark current decreases 1 order of magnitude when the number of quantum wells increases from 3 to 4. Also, absorption has redshift and simultaneously increases.

OSQAR chameleon afterglow search experiment

Abstract OSQAR experiment has been extended to the quest of chameleon particles with environment-dependent mass from the search of a magnetic afterglow effect. OSQAR-CHASE (chameleon afterglow search) has been run in 2017 using one spare LHC dipole providing a 9 T transverse magnetic field with an 18.5 W laser and state-of-the art CCD detector. Experimental results with and without magnetic field were preliminary analyzed and no clear evidence for a photon-coupled chameleons was confirmed. The very weak false signals was observed with decay time 4300 s. It can be explained by decrease of dark current from initial higher values during CCD cooling in detection phase. Increasing of the sensitivity of the OSQAR-CHASE experiment over the previous GammeV reference experiment assumes that the present coupling constant limit can be reduced around factor of 4.

Improvement in crystallinity of ZnO and Zn2SiO4 phases by rf sputter deposition; effect of substrate bias

We report on enhancement in crystallinity of wurtzite ZnO and rhombohedral Zn2SiO4 phase using rf sputtering deposition with substrate bias. Substrates were kept at floating potential and subjected to a bias upto −60 V for shallow implantation of Zn and O ions in SiO on Si and local energy deposition. Crystalline Zn2SiO4 phase improved upto −20 V applied bias above which it deteriorated. Wurtzite ZnO phase formed on rhombohedral Zn2SiO4 phase and showed opposite trend and a decrease in strain. The improvement in crystallinity of ZnO phase resulted in decrease in defects identified from a decrease of visible light absorption and dark current. The mechanisms identified to be responsible for the improvement in ZnO phase and formation of zinc silicate phase is transfer of energy through elastic collisions from the plasma species to the deposited atoms on the growing film and shallow implantation of Zn and O ions into SiO/Si.

Photo Sensitivity Enhanced By the Modulation of Oxide Thickness in MIS(p) Structure

It was found that the ratio of light to dark current can be enhanced by coupling effect with simple MIS(p) on concentric MIS structure [1]. Gate with bias can largely decrease dark current, and thereby improve the ratio. In this work, to research deeper about it, the enhancement of ratio with gate voltage is concentrated on the modulation of oxide thickness. The topside and cross section of the studied MIS(p) structure with the concentric pattern is shown in Fig. 1(a). The radius of inner circle r1 is 85um. The space between inner and outer gate, i.e., s, is 20um. The outer radius of the ring is 300um. Here, the inner circle is defined as diode and the outer ring is defined as gate. Also, according to the previous work [1], a specific gate voltage of VX is defined as when it causes the lowest diode dark current in ID-VG curve (the inset in Fig. 1(b)) and therefore exhibits the largest enhanced ratio. Fig. 1(b) a shows I-V curve of light current and dark current with VG=VX in two oxide thickness of 2.5nm and 3nm. The ratio is defined by the light current to dark current at 2.5V which is located at the diode current saturation region. Comparing the ratio of light to dark current in two thickness, it is obvious to show that the ratio is dependent on oxide thickness and MIS structure with a thicker oxide might have a higher ratio. To further study the relation of ratio and thickness, samples with different thickness were explored to examine their light to dark current ratios as shown in Fig. 2(a). From Fig. 2(a), it obviously shows that the ratio is highly increased for thicker oxide. Also, in order to see the effect of illumination, three strength of illumination with 131lux, 306lux, and 410lux were studied. Fig. 2(b) shows that thicker oxide indeed has a higher ratio than thinner counterpart no matter what the strength of illumination is. To analyze the dependency of the saturation current on oxide thickness, the dark current, light current and the ratio of light to dark current are separately presented for various thicknesses as shown in Fig. 3(a). It’s clear to indicate that the dark current reduces with the oxide thickness and light current has no obvious relation with thickness. Hence, the discussion is divided into two parts. To discuss about dark current, Fig. 3(b) demonstrates of the carrier and two currents part of dark diode current from the gate region under VG=VX in dark environment. Because gate voltage is biased in the minimum diode current which is near VFB, minority carrier gathered under gate region is very few. Then, the diffusion current from gate to diode is very small due to the subtle divergence of carrier concentration. Therefore, the diffusion current by coupling effect is largely reduced and contributed less to the barrier height modulation of diode. As a result, diode current is mainly dominated by the injection current part from the gate region. In Fig. 3(c), because the gate current which induces the injection current is strongly dependent on oxide thickness, it implies that thicker sample which has lower injection current has lower saturation current. It confirms that dark current is clearly decreased with increasing thickness under VG=VX in Fig. 3(a). For the light current part, because the light current is also contributed from light-induced electron-hole pairs, the light current is not solely dependent on oxide thickness. Hence, light current does not show similar dependence of thickness. The ratio of light to dark current is largely enhanced by the largely decrease of dark current due to the increase of oxide thickness. Furthermore, the ratio of light to dark current increases with the stronger strength of illumination in the thicker MIS sensor as shown in Fig. 2(b). The result indicates that there is a larger light current in the stronger illumination because of more electron-hole pairs. Therefore, the ratio of light to dark current is increased with the strength of illumination. In conclusion, the modulation of oxide thickness is of importance to the photo sensitivity of MIS(p) tunnel diode. This work was supported by the Ministry of Science and Technology of Taiwan, ROC, under Contract No. MOST 105-2221-E-002-180-MY3 and MOST 106-2221-E-002-196-MY3. [1] W.T. Hou and J.G.Hwu*, 2017, “Photo Response Enhancement in MIS(p) Tunnel Diode via Coupling Effect by Controlling Neighboring Device Inversion Level”. Electronic and Photonic Devices and Systems, ECS Journal of Solid State Science and Technology, 6(10), pp. Q143-147, 2017 Figure 1

Influence of post-deposition annealing on structural, optical and transport properties of nanocomposite ZnO-Ag thin films

Thin films of ZnO and ZnO-Ag were grown by rf sputter deposition and post-annealed in air in the 300–600 °C temperature range. Annealing caused variation in strain in ZnO films and significant improvement of ZnO in ZnO-Ag films. The partial oxidation of Ag into AgxO upon annealing of ZnO-Ag films in air resulted in increase of transmittance, absorption due to AgxO phase, weakening of surface plasmon resonance absorption due to Ag nanocrystals and an increase in fluorescence. Surface studies indicate temperature induced particle transport cause agglomeration of nanocrystals in ZnO-Ag films during post-annealing. Annealed ZnO films showed a decrease in dark current and a sixteenfold increase in photocurrent at 3 V applied bias under white light illumination due to the formation of charged acceptors / oxygen vacancy centres, which was comparable to the white light photosensitivity of as-deposited ZnO-Ag film. For low applied bias voltages, Metal-Semiconductor-Metal photoconductive detectors made with annealed ZnO-Ag films showed potential for application as efficient deep ultraviolet (DUV) photodetectors with negligible sensitivity to white light and high sensitivity to DUV light.

Improved characteristics of conventional and inverted polymer photodetectors using phosphonic acid-based self-assembled monolayer treatment for interfacial engineering of Ga-doped ZnO electrodes

The characteristics of conventional and inverted polymer photodetectors based on a blend of a donor, poly(3-hexylthiophene) (P3HT), and an acceptor, fullerene derivative [6,6]phenyl-C61-butyric acid methyl ester (PCBM) using Ga-doped ZnO (GZO) electrodes modified by phosphonic acid-based self-assembled monolayer (SAM) treatment in a short time are investigated. Fluoroalkyl SAM, 1H,1H,2H,2H-perfluorooctane phosphonic acid (FOPA) treatment leads to efficient hole extraction from the active layer. The characteristics of the conventional device with GZO modified by FOPA treatment are almost the same as those with indium tin oxide modified by FOPA. Cs2CO3 and aminoalkyl SAM, 11-aminoundecylphosphonic acid (11-AUPA) treatments suppress the hole injection from GZO to the organic layer. For the inverted devices with GZO cathodes using Cs2CO3 and 11-AUPA, the dark current decreases, which results in the improved photodetector detectivity. An inverted device with both Cs2CO3 and 11-AUPA exhibits incident-photon-to-current conversion efficiency (IPCE) of approximately 65% (80%) at 0 V (−6 V) under light irradiation (λ = 500 nm), high on/off ratio, and improved durability. Improved open-circuit voltage and IPCE at low voltages are achieved by these treatments, which are related with the improved internal built-in field, the reduction of recombination probability in the vicinity of GZO, and the modified charge collection efficiency.

Study of various n-type organic semiconductors on ultraviolet detective and electroluminescent properties of optoelectronic integrated device

Organic optoelectronic integrated device (OID) with both ultraviolet (UV) detective and electroluminescent (EL) properties was fabricated by using a thermally activated delayed fluorescence (TADF) semiconductor of (4s, 6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) as an emitter. The effect of five kinds of n-type organic semiconductors (OSCs) on the enhancement of UV detective and EL properties of OID was systematically studied. The result shows that two orders of magnitude in UV detectivity from 109 to 1011 Jones and 3.3 folds of luminance from 2499 to 8233 cd m−2 could be achieved. The result shows that not only the difference of lowest unoccupied molecular orbital (LUMO) between active layer and OSC but also the variety of electron mobility have a significant effect on the UV detective and EL performance through adjusting electron injection/transport. Additionally, the optimized OSC thickness is beneficial to confine the leaking of holes from the active layer to cathode, leading to the decrease of dark current for high detective performance. This work provides a useful method on broadening OSC material selection and device architecture construction for the realization of high performance OID.

Reduction of dark current and gain increase in InAs avalanche photodiode with AlGaAs blocking layer

This article presents a new method to reduce the dark current and increase the avalanche gain in InAs avalanche photodiode (APD) by adding Al0.84Ga0.16As blocking layer. This photodiode has displayed a high avalanche gain around 400 in 8V bias voltage. Furthermore, a very low dark current and low excess noise factor between 0.1 and 1.9 in a temperature of 180K to 300K is observed. Finally, in comparison with other devices, a considerable increase of the gain along with decrease in dark current is observed.

Device performance enhancement via a Si-rich silicon oxynitride buffer layer for the organic photodetecting device

An advanced organic photodetector (OPD) with a butter layer of Si-rich silicon oxynitride (SiOxNy) was fabricated. The detector structure is as follows: Indium tin oxide (ITO) coated glass substrate/SiOxNy(10 nm)/naphthalene-based donor:C60(1:1)/ITO. Values of x and y in SiOxNy were carefully controlled and the detector performances such as dark current and thermal stability were investigated. When the values of x and y are 0.16 and 0.66, the detector illustrates low dark current as well as excellent thermal stability. In the OPD, silicon oxynitride layer works as electron barrier under reverse bias, leading to the decrease of dark current and increase of detectivity. Since the band gap of silicon oxynitride unlike conventional buffer layers can also be controlled by adjusting x and y values, it can be adapted into various photodiode applications.

Effects of electron doping level on minority carrier lifetimes in n-type mid-wave infrared InAs/InAs1−xSbx type-II superlattices

The minority carrier lifetime (τMC) and equilibrium electron concentration (i.e., the doping level, n0) are both important values that directly determine diffusion current in infrared photodetectors utilizing n-type absorbing regions. Here, time-resolved microwave reflectance measurements are used to non-destructively measure both of these values in mid-wave infrared InAs/InAs1−xSbx type-II superlattices with varying n-type doping levels between 2×1014 cm−3 and 2×1016 cm−3. The measured data are analyzed using carrier recombination theory to determine the doping level ranges where Shockley-Read-Hall (SRH), radiative, and Auger recombination limit τMC. The optimal doping level, which minimizes dark current, is experimentally determined and corresponds to the electron density at which τMC switches from SRH limited to Auger limited behavior. A comparison of two InAs/InAs1−xSbx photodetectors of different equilibrium electron densities demonstrates a decrease in dark current for a doping level near the optimal n0τMC product.