Reverse Bias Voltage Research Articles

High-speed lateral PIN germanium photodetector with 4-directional light input.

We experimentally demonstrate a high-speed lateral PIN junction configuration germanium photodetector (Ge-PD) with 4-directional light input. The typical internal responsivity is about 1.23 A/W at 1550 nm with 98% quantum efficiency and dark current 4 nA at 1V reverse-bias voltage. The equivalent circuit model and theoretical 3-dB opto-electrical (OE) bandwidth of Ge-PD are extracted and calculated, respectively. Compared to the conventional lateral PIN Ge-PD with 1-directional light input, our proposed device features uniform optical field distribution in the absorption region, which will be benefit to realize high-power and high-speed operation. In particular, in the condition of 0.8 mA photocurrent, the measured 3-dB OE bandwidth is about 17 GHz at bias voltage of -8 V which is well matched to the theoretical estimated bandwidth. With additional digital pre-compensations provided by the Keysight arbitrary waveform generator (AWG), the root raised cosine (RRC) filter and roll-off factor of 0.65 are employed at transmitter (TX) side without utilizing any offline digital signal processing (DSP) at receiver (RX) side. The 50 Gbit/s, 60 Gbit/s, 70 Gbit/s, and 80 Gbit/s non-return-to-zero (NRZ), and 60 Gbit/s, 70 Gbit/s, 80 Gbit/s, and 90 Gbit/s four-level pulse amplitude modulation (PAM-4) clear opening of eye diagrams are realized. In order to verify the high-power handling performance in high-speed data transmission, we also investigate the 20 Gbit/s NRZ eye diagram variations with the increasing of photocurrent.

Fano Effect and Spin-Polarized Transport in a Triple-Quantum-Dot Interferometer Attached to Two Ferromagnetic LeadsSupported by the National Natural Science Foundation of China (Grant No. 11447132), the “Chunhui Plan” Cooperative Scientific Research Project of China (Grant No. 6101020101), and the Science and Technology Research Program of Chongqing Education Commission of China (Grant No. KJQN201801402).

We report the conductance and average current through a triple-quantum-dot interferometer coupled with two ferromagnetic leads using the nonequilibrium Green’s function. The results show that the interference between the resonant process and the non-resonant process leads to the formation of Fano resonance. More Fano resonances can be observed by applying a time-dependent external field. As a Zeeman magnetic field is applied, the spin-up electron transport is depressed in a certain range of electron energy levels. A spin-polarized pulse device can be realized by adjusting the spin polarization parameters of ferromagnetic leads. Moreover, the I–V characteristic curves show that under the influence of Fano resonance, the spin polarization is significantly enhanced by applying a relatively large reverse bias voltage. These results strongly suggest that the spin-polarized pulse device can be potentially applied as a spin-dependent quantum device.

Enhanced image sensing with avalanche multiplication in hybrid structure of crystalline selenium photoconversion layer and CMOSFETs

The recent improvements of complementary metal–oxide–semiconductor (CMOS) image sensors are playing an essential role in emerging high-definition video cameras, which provide viewers with a stronger sensation of reality. However, the devices suffer from decreasing sensitivity due to the shrinkage of pixels. We herein address this problem by introducing a hybrid structure comprising crystalline-selenium (c-Se)-based photoconversion layers and 8 K resolution (7472 × 4320 pixels) CMOS field-effect transistors (FETs) to amplify signals using the avalanche multiplication of photogenerated carriers. Using low-defect-level NiO as an electric field buffer and an electron blocking layer, we confirmed signal amplification by a factor of approximately 1.4 while the dark current remained low at 2.6 nA/cm2 at a reverse bias voltage of 22.6 V. Furthermore, we successfully obtained a brighter image based on the amplified signals without any notable noise degradation.

Passive mode-locking of p-doped quantum dot semiconductor lasers

Quantum dot based monolithic edge-emitting semiconductor lasers at 1.25 µm are ideal sources for the generation of broad optical frequency combs for optical communication applications. In this work, InAs/InGaAs quantum dot lasers with different total laser length to absorber length ratio and with different p-doping concentrations in the GaAs barrier sections are investigated experimentally in dependence on the gain injection current and absorber reverse bias voltage. A smaller mode-locking area is found for the p-doped device in dependence on the laser biasing conditions. For the undoped active region 1.3 ps short pulse widths at a pulse repetition rate of 20 GHz with a pulse-to-pulse timing jitter of 111 fs are reported for an absorber section length of 12% to the total cavity length. For an undoped and p-doped device short pulse emission between 2.5 ps and 5.5 ps is attained and a shorter absorber section length of 8% or 5%.

Fabrication of high quantum efficiency p-i-n AlGaN detector and optimization of p-layer and i-layer thickness

In this paper, the fabrication process and structure of AlGaN based p-i-n photodetectors with different layer thicknesses are described. The maximum external quantum efficiency (EQE) of back illumination is 87.87% at zero bias. According to the Poisson equation, the electric field distribution of the devices is analysed, and a detailed method to estimate the reverse bias voltage required for the p-layer and i-layer to be completely depleted is proposed. The reliability of the method is also well proven by the responsivity measurement results under zero bias and reverse bias. Finally, based on the experimental data and theoretical calculation, the optimization method of p-layer and i-layer thickness in p-i-n photodetector is analysed.

Separate absorption and multiplication solar-blind photodiodes based on p-NiO/MgO/n-ZnO heterostructure

High-performance solar-blind separate absorption and multiplication avalanche photodiodes (SAM-APDs) were fabricated based on a p-NiO/MgO/n-ZnO dual heterojunction structure. The prepared SAM-APDs exhibited a separated absorption and multiplication structure that used NiO and ZnO as absorption layers, and ultrawide-bandgap MgO as a multiplication layer. When the reverse-bias voltage exceeded 6 V, carrier avalanche multiplication occurred, and the avalanche gain reached a high value of 2.7 × 103, corresponding to a 1120% quantum efficiency, at a reverse-bias voltage of 10 V. These solar-blind SAM-APDs had an ultraviolet (UV) (310 nm)/visible (500 nm) rejection ratio as high as 563.6 at a 2 V reverse-bias voltage. These features render the SAM-APDs highly suitable for practical applications as UV solar-blind photodetectors.

Study of a neutron-resistant p+-Si/n-ZnO photodetector with avalanching gain

The photo detection properties under large reverse bias voltage and neutron irradiation effects of the p+-Si/n-ZnO photodetector were investigated. Intrinsic defects, VO, VZn, and Oi, were observed in the non-irradiated ZnO film from the photoluminescence spectroscopy. The neutron induced defects in the neutron irradiated ZnO film reacted with the VZn, Oi and grain boundary defects resulting in the degradation of mid band emissions. The p+-Si/n-ZnO heterojunction shows a rectifying factor of >1000 at 300 K under ±1.5 V and an avalanche breakdown voltage of ∼13 V. The impact ionization process is taken place in the p+-Si region revealed from the numerical calculation of the breakdown voltage of the p+-Si/n-ZnO heterojunction. The device can well perform as a linear and fast response photodetector with good repeatability. When operating under large reverse bias voltage, the p+-Si/n-ZnO can also act as an avalanching photodiode with the avalanche gain of ∼ 30. The p+-Si/n-ZnO detector continues to be operative as an avalanche photodiode as well after neutron irradiation with the fluence of 1015 n/cm2 unless the gain degenerating to ∼10, indicating the good neutron tolerance of the p+-Si/n-ZnO photodetector.

Lateral monolayer MoS2 homojunction devices prepared by nitrogen plasma doping

Monolayer MoS2 possesses good electron mobility, structural flexibility and a direct band gap, enabling it to be a promising candidate for flexible and wearable optoelectronic devices. In this article, the lateral monolayer MoS2 homojunctions were prepared by a nitrogen plasma selective doping technique. The monolayer MoS2 thin films were synthesized by chemical vapor deposition and characterized by photoluminescence, atom force microscope and Raman spectroscopy. The electronic and photoelectric properties of the lateral pn and npn homojunctions were discussed. The results showed that the rectifying ratio of the pn homojunction diode is ∼103. As a photodetector of pn homojunction, the optical responsivity is up to 48.5 A W−1, the external quantum efficiency is 11 301%, the detectivity is ∼109 Jones and the response time is 20 ms with the laser of 532 nm and the reverse bias voltage of 10 V. As a bipolar junction transistor of npn homojunction, the amplification coefficient reached ∼102. A controllable plasma doping technique, compatible with traditional CMOS process, is utilized to realize the monolayer MoS2 based pn and npn homojunctions, and it propels the potential applications of 2D materials in the electronic, optoelectronic devices and circuits.

Graphene/InP Schottky junction near-infrared photodetectors

Graphene and P-type indium phosphide (P-InP) could be combined by van der Waals forces to form a Schottky junction, which can be applied in photodetection. This study reported a graphene/P-InP Schottky junction near-infrared photodetector with a 3-nm-thick $${\text{Al}}_{2} {\text{O}}_{3}$$ passivation layer and investigated the photoelectric characteristics of such device. As a result, the near-infrared photodetector had a Schottky barrier of 0.89 eV. Besides, this device had a significant response to the wavelength of 808 nm near-infrared light with responsivity and detectivity up to 5.2 mA/W and $$1.3 \times 10^{10} \;{\text{cm Hz}}^{1/2} \;{\text{W}}^{ - 1}$$ , respectively, under a reverse bias voltage of 0.4 V. It is expected that the Graphene/P-InP Schottky junction near-infrared photodetector with an $${\text{Al}}_{2} {\text{O}}_{3}$$ passivation layer may play a vital role in the field of optoelectronic devices in future.

Suppressing Ion Migration across Perovskite Grain Boundaries by Polymer Additives

AbstractPassivation of organometal halide perovskites with polar molecules has been recently demonstrated to improve the photovoltaic device efficiency and stability. However, the mechanism is still elusive. Here, it is found that both polymers with large and small dipole moment of 3.7 D and 0.6 D have negligible defect passivation effect on the MAPbI3 perovskite films as evidenced by photothermal deflection spectroscopy. The photovoltaic devices with and without the polymer additives also have comparable power conversion efficiencies around 19%. However, devices with the additives have noticeable improvement in stability under continuous light irradiation. It is found that although the initial mobile ion concentrations are comparable in both devices with and without the additives, the additives can strongly suppress the ion migration during the device operation. This contributes to the significantly enhanced electrical‐field stress tolerance of the perovskite solar cells (PVSCs). The PVSCs with polymer additives can operate up to −2 V reverse voltage bias which is much larger than the breakdown voltage of −0.5 V that has been commonly observed. This study provides insight into the role of additives in perovskites and the corresponding device degradation mechanism.

A Fast Simulation Tool for Silicon-Pad Detectors

Several types of detectors are used to detect charged particles in particle and nuclear physics experiments. Since the semiconductor detector has superior spatial and kinematic resolutions as well as good response time than other types of detectors, it has become one of the most important detectors recently. When charged particles pass through the semiconductor detector, electron-hole pairs are formed inside the detector and move toward the electrode by the electric field inside the detector. At this time, the trajectory and momentum can be determined through the generated current signal. In this study, we introduce an open-source application named Fast Silicon Device Simulation that is developed for fast simulation of a typical silicon semiconductor detector, such as a p-type pad on an n-type wafer with a reverse-bias voltage. Iterative and multi-grid methods are used to calculate the potential and electric field in the simulation fast. Current signals produced by the simulation are compared with results by Silvaco TCAD and Garfield++ simulations. The simulation program is based on the ROOT that has been developed by CERN.

The dark current suppression of black silicon photodetector by a lateral heterojunction

Femtosecond laser hyperdoped silicon, known commonly as black silicon (b-Si), has attracted substantial interest from various fields due to its high absorptance and responsivity ranging from visible to near-infrared wavelengths. However, due to the non-uniformity of b-Si layer and the lattice defects present in it, the processing technique used presently introduces high noise in devices manufactured using b-Si. In this study, a lateral heterojunction is designed and manufactured at the b-Si and silicon interface to restrain the leakage current. Precisely, the lateral structure could support the b-Si photodetector in suppressing the dark current to 783 nA at a bias of -5 V, quite low in terms of orders of magnitude compared to that for the vertical ones. Simultaneously, the photo-to-dark current ratio of 155 is obtained at the same bias voltage with a pertinent external quantum efficiency (EQE) of 371%. Riding on the advantages of low noise, high signal-to-noise ratio, and high sensitivity, this work shows promising prospects for the application of b-Si-based photodetectors toward large-scale integration in optical-electronics or flip-chip interconnection systems. • The dark current of b-Si photodetector is suppressed by a lateral heterojunction. • The detector exhibits a high photo-to-dark current ratio at reverse bias voltage. • The photoconductive gain is achieved for a wide coverage of wavelength.

3D-graphene-laser patterned p-type silicon Schottky diode

The influence of the laser patterning (LP) process on the quality of graphene (Gr) film and Schottky diode characteristics was researched in this study. First of all, p-type silicon (Si) was patterned by homemade femtosecond laser source. To compare the resulting effect, non-patterned n-Si and p-Si were used as substrates. To achieve vertically oriented three-dimensional (3D) Gr nanosheets (VGNs) onto the laser patterned p-type Si, non-patterned n-Si, and p-Si substrates, we used Radio-Frequency Plasma Enhanced Chemical Vapor Deposition (RF-PECVD) technique. Then, Raman analyses for VGNs obtained on patterned and non-patterned p-Si and n-Si substrates were conducted. All results indicate that the Gr obtained on all substrates is vertically oriented. Scanning electron microscopy (SEM) analyses were also performed to obtain information about the morphological properties of the 3D Gr structure. In addition, the influence of the laser patterning at the Gr-Si interface was evaluated by comparing two sets of devices which are junctions of Gr-Laser Patterned Si (Gr-LPSi) and Gr-Insulator-Silicon (Gr-I-Si) at 300 K in the dark medium. D1 device consists of a Gr-LPSi junction that involves RF-PECVD grown Gr on the silicon, whose surface exposed the laser beam for patterning. D2 device consists of a Gr-I-Si junction that involves RF-PECVD grown Gr onto the silicon, whose surface involves a thin native oxide layer (~2 nm). The results show that the laser treatment causes an increment in Schottky barrier height (SBH) and decreases leakage currents under a reverse bias voltage of the diode. Notably, we have seen the influence of the laser patterning process on 3D Gr nano-sheets which is that the entire surface of the substrate has now reformed new structures in the nano-sphere and nano-rose morphology, so we believe that this is the first work that shows these structures in this form.

Frequency comb investigation of monolithic mode‐locked GaSb‐based laser at 1.7 µm by heterodyne detection

In this work, monolithic mode-locked GaSb-based lasers at 1.7 µm emission wavelength with heterodyne measurement of the frequency comb are presented. Mode-locking operation was confirmed by measuring the optical beatnote at the round-trip frequency of 9.56 GHz and analysing the frequency comb. Mode-locking operation occurred from 0.1 to 3.3 V reverse bias voltages at the absorber section and driving currents from 160 to 400 mA at the laser section with a minimum beatnote width of 6.6 kHz. The frequency comb spans over 13 nm with a mode spacing of 0.10 nm, measured by heterodyne-detection with a distributed feedback laser.

Effect of the Electric Field Strength on the Energy Resolution of Cr/CdTe/Pt Detectors

The electrical and spectrometric characteristics of the Cr/cadmium telluride (CdTe)/Pt structure with a metal–semiconductor type rectifying contact, used in X/ $\gamma $ -ray detectors, are investigated. For the detectors fabrication, chlorine-doped CdTe crystals with a resistivity of (3–6) $\times 10^{{9}}\,\,\Omega $ cm at 293 K were used. 137Cs spectra and their modification by applied voltage change were obtained. The reverse bias voltage corresponding to the best energy resolution of the Cr/CdTe/Pt structure is experimentally determined. The concentration of impurities N in the crystal, which determines the thickness of the space-charge region, is estimated. An energy resolution deterioration of the Cr/CdTe/Pt structure with increasing voltage is explained due to the Gunn effect.

Silicon Waveguide Integrated with Germanium Photodetector for a Photonic-Integrated FBG Interrogator.

We report a vertically coupled germanium (Ge) waveguide detector integrated on silicon-on-insulator waveguides and an optimized device structure through the analysis of the optical field distribution and absorption efficiency of the device. The photodetector we designed is manufactured by IMEC, and the tests show that the device has good performance. This study theoretically and experimentally explains the structure of Ge PIN and the effect of the photodetector (PD) waveguide parameters on the performance of the device. Simulation and optimization of waveguide detectors with different structures are carried out. The device’s structure, quantum efficiency, spectral response, response current, changes with incident light strength, and dark current of PIN-type Ge waveguide detector are calculated. The test results show that approximately 90% of the light is absorbed by a Ge waveguide with 20 μm Ge length and 500 nm Ge thickness. The quantum efficiency of the PD can reach 90.63%. Under the reverse bias of 1 V, 2 V and 3 V, the detector’s average responsiveness in C-band reached 1.02 A/W, 1.09 A/W and 1.16 A/W and the response time is 200 ns. The dark current is only 3.7 nA at the reverse bias voltage of −1 V. The proposed silicon-based Ge PIN PD is beneficial to the integration of the detector array for photonic integrated arrayed waveguide grating (AWG)-based fiber Bragg grating (FBG) interrogators.

Experimental investigation and modeling of electrical properties for phenol red thin film deposited on silicon using back propagation artificial neural network

A heterojunction of a thin film of phenol red and silicon was constructed by applying the thermal evaporation technique. The current-voltage (I-V) characteristics of phenol red/Si heterojunction were studied experimentally and theoretically in the temperature range from 303 to 353 K. The thermionic emission mechanism for the conduction was established from the forward bias current density-voltage characteristics. The behavior of both the ideality factor and series resistance was deduced. The barrier height (φ) was determined as 0.26 eV. The reverse bias voltage exposed a thermally motivated behavior. Modeling of electric current in terms of voltage and temperature was carried out using an artificial neural network (ANN model) that depends on the experimental data. The learning ANN method was applied based on trial and error technique. The optimum network architect which represents the most satisfactory performance was obtained. The simulation and prediction results of the ANN model offered a high-reaching accuracy in comparison with experimental data. The ANN model utilized as an active tool to estimate the electrical properties of heterojunction for organic compounds.

1.3-µm passively mode-locked quantum dot lasers epitaxially grown on silicon: gain properties and optical feedback stabilization

This work reports on an investigation of the optical feedback in an InAs/InGaAs passively mode-locked quantum dot (QD) laser epitaxially grown on silicon. Under the stably-resonant optical feedback condition, experiments demonstrate that the radio-frequency linewidth is narrowed whatever the bias voltage applied on the saturable absorber (SA) is; on the other hand, the effective linewidth enhancement factor of the device increases with the reverse bias voltage on the SA, hence it is observed that such an increase influences the mode-locking dynamic and the stability of device under optical feedback. This work gives insights for stabilizing epitaxial QD mode-locked lasers on silicon which is meaningful for their applications in future large-scale silicon electronic and photonic applications requiring low power consumption as well as for high-speed photonic analog-to-digital conversion, intrachip/interchip optical clock distribution and recovery.

Formation and control of the center in implanted β-GaO by reverse-bias and zero-bias annealing

Deep-level transient spectroscopy measurements are conducted on β-GaO thin-films implanted with helium and hydrogen (H) to study the formation of the defect level ( = 0.71 eV) during heat treatments under an applied reverse-bias voltage (reverse-bias annealing). The formation of during reverse-bias annealing is a thermally-activated process exhibiting an activation energy of around 1.0 eV to 1.3 eV, and applying larger reverse-bias voltages during the heat treatment results in a larger concentration of . In contrast, heat treatments without an applied reverse-bias voltage (zero-bias annealing) can be used to decrease the concentration. The removal of is more pronounced if zero-bias anneals are performed in the presence of H. A scenario for the formation of is proposed, where the main effect of reverse-bias annealing is an effective change in the Fermi-level position within the space-charge region, and where is related to a defect complex involving intrinsic defects that exhibits several different configurations whose relative formation energies depend on the Fermi-level position. One of these configurations gives rise to , and is more likely to form if the Fermi-level position is further away from the conduction band edge. The defect complex related to can become hydrogenated, and the corresponding hydrogenated complex is likely to form when the Fermi level is close to the conduction band edge. Di-vacancy defects formed by oxygen and gallium vacancies (V−V) fulfill several of these requirements, and are proposed as potential candidates for .

Quantum Yield of a Silicon Avalanche Photodiode in the Wavelength Range of 120–170 nm

We have designed a silicon avalanche photodiode for detecting vacuum ultraviolet radiation. The external quantum yield of a silicon avalanche photodiode has been investigated in the wavelength range of 120–170 nm. It is shown that the avalanche photodiode has an external quantum yield of 24–150 electrons/photons at a reverse bias voltage of 230–345 V. Testing of this avalanche photodiode with pulsed illumination at wavelengths of 280 and 340 nm has shown performance corresponding to a transmission band no narrower than 25 MHz.