Electrical Carrier Injection Research Articles

Effect of firing process on electrical properties and efficiency of n-TOPCon solar cells

In the large-scale production of solar cells, metallization is a very important process, which directly affects the opening-circuit voltage, short-cut current, shunt resistance, and fill factor, thus affecting the efficiency of the solar cell. In this paper, the n-TOPCon process is matched by changing the firing temperature and belt speed of each zone to change the peak temperature and the width of the firing curve. After low-temperature slow firing (A1), the front contact resistance of the solar cell is the largest, and the Uoc and the Eff are the highest. However, after the electric injection, the Uoc and the FF increase are small, and the Eff is low, with an average value of 24.23 % and an increase of 0.04 %. After higher temperature and faster firing (AB2), the front-specific contact resistance of the solar cell is the smallest. Affected by the specific contact resistance, the solar cell has the highest FF, the lowest Uoc, and the lowest Eff. However, the electrical injection significantly increases the Uoc. The Eff after electric injection is the highest, with an average of 24.42 %, an increase of 0.36 %. The H ions in SiNx have different effects of passivation on the wafer under different firing conditions, but the difference is narrowed by the electrical carrier injection of H ions on the surface into the wafer. Therefore, solar cells with excellent electrical performance can be obtained by firing at appropriate peak temperature and firing width, obtaining low contact resistance first, and then increasing the Uoc and Jsc by electric injection.

Non‐Equilibrium Bose–Einstein Condensation of Exciton‐Polaritons in Silicon Metasurfaces

AbstractExciton‐polaritons (EPs) are hybrid light–matter quasi‐particles with bosonic character formed by the strong coupling between excitons in matter and photons in optical cavities. Their hybrid character offers promising prospects for the realization of non‐equilibrium Bose–Einstein condensates (BECs), and room‐temperature BECs are possible with organic materials. However, the thresholds required to create BECs of organic EPs remain still high to allow condensation with electrical injection of carriers. One of the factors behind these high thresholds is the very short cavity lifetimes, leading to a fast EP decay and the need to inject higher exciton densities in the reservoir to form the condensate. Here a BEC of EPs in organic dyes and all‐dielectric metasurfaces at room temperature is demonstrated. By using dielectric metasurfaces that exhibit very low losses it is possible to achieve cavity lifetimes long enough to allow an efficient population of EP states via vibrational relaxation and radiative pumping. It is shown how polariton lasing or non‐equilibrium Bose–Einstein condensation is achieved in several cavities, and one of the lowest reported thresholds for BECs in organic materials is observed.

Enhanced Photoluminescence and Electrical Properties of n-Al-Doped ZnO Nanorods/p-B-Doped Diamond Heterojunction.

The hydrothermal approach has been used to fabricate a heterojunction of n-aluminum-doped ZnO nanorods/p-B-doped diamond (n-Al:ZnO NRs/p-BDD). It exhibits a significant increase in photoluminescence (PL) intensity and a blue shift of the UV emission peak when compared to the n-ZnO NRs/p-BDD heterojunction. The current voltage (I-V) characteristics exhibit excellent rectifying behavior with a high rectification ratio of 838 at 5 V. The n-Al:ZnO NRs/p-BDD heterojunction shows a minimum turn-on voltage (0.27 V) and reverse leakage current (0.077 μA). The forward current of the n-Al:ZnO NRs/p-BDD heterojunction is more than 1300 times than that of the n-ZnO NRs/p-BDD heterojunction at 5 V. The ideality factor and the barrier height of the Al-doped device were found to decrease. The electrical transport behavior and carrier injection process of the n-Al:ZnO NRs/p-BDD heterojunction were analyzed through the equilibrium energy band diagrams and semiconductor theoretical models.

Design study for an efficient semiconductor quantum light source operating in the telecom C-band based on an electrically-driven circular Bragg grating.

The development of efficient sources of single photons and entangled photon pairs emitting in the low-loss wavelength region around 1550 nm is crucial for long-distance quantum communication. Moreover, direct fiber coupling and electrical carrier injection are highly desirable for deployment in compact and user-friendly systems integrated with the existing fiber infrastructure. Here we present a detailed design study of circular Bragg gratings fabricated in InP slabs and operating in the telecom C-band. These devices enable the simultaneous enhancement of the X and XX spectral lines, with collection efficiency in numerical aperture 0.65 close to 90% for the wavelength range 1520 - 1580 nm and Purcell factor up to 15. We also investigate the coupling into a single mode fiber, which exceeds 70% in UHNA4. Finally, we propose a modified device design directly compatible with electrical carrier injection, reporting Purcell factors up to 20 and collection efficiency in numerical aperture 0.65 close to 70% for the whole telecom C-band.

Enhanced Spin Accumulation in Semiconductor at Room Temperature Using Ni0.65Zn0.35Fe2O4(NZFO) as Spin Injector in NZFO/MgO/p-Si Device

In this article, the fabrication of a Ni0.65Zn0.35Fe2O4/MgO/p-Si heterostructure device has been optimized using the pulsed laser deposition (PLD) technique, and a detailed investigation of its structural, electrical, and magnetic features has been performed experimentally. The electronic and magneto-transport characteristics have been explored in the temperature range of 100–300 K. The current-voltage (I-V) characteristics of the heterojunction have been recorded, which displayed an excellent rectifying magnetic tunnel diode-like behavior throughout that temperature regime. The application of an external magnetic field parallel to the plane of the NZFO film causes the current (I) across the junction to decrease, clearly indicating positive junction magnetoresistance (JMR) of the heterostructure. The root of displaying positive magnetoresistance in our heterojunction has been well justified using the standard spin injection model. The electrical injection of spin-polarized carriers and its accumulation and detection in a p-Si channel have been demonstrated using the NZFO/MgO tunnel contact using a three-terminal (3-T) Hanle device. The parameters such as spin lifetime (99 ps), spin diffusion length (276 nm), and spin polarization (0.44) have been estimated from the Hanle curve detected in our heterostructure at room temperature, making the Ni0.65Zn0.35Fe2O4/MgO/p-Si device a very favorable promising junction structure in the field of spintronics for several device appliances in the future.

Robust and Efficient Electrical Injection of Spin-Polarized Carriers from a Zero-Spin-Gap Half-Metal V2NiAl into n-Si at Room Temperature

In recent times, an engrossing and newly discovered class of materials with unique electronic band properties, namely, zero-spin-gap half-metal, has gained acute attraction worldwide because of its...

Electrical modulation of the LWIR absorption and refractive index in InAsSb-based strained layer superlattice heterostructures

InAsSb-based strained layer superlattices (SLS) have strong fundamental absorption, which can be easily modified in a controlled manner by injecting excess carriers. This makes them attractive for intensity modulation of infrared lasers as well as beam steering and spatial beam shaping with a nanosecond-scale time response. This paper reports the modulation of the fundamental absorption and the refractive index by carrier injection in a 3.45-nm-period InAsSb0.65/InAsSb0.35 SLS with a low temperature energy gap of 85 meV grown by molecular beam epitaxy on a GaSb substrate with a GaInSb metamorphic buffer. The SLS absorber was sandwiched by n- and p-type wider energy gap layers for electrical injection and confinement of excess carriers. The population of conduction band states was obtained by measuring the intensity modulation of a 10.6 μm CO2 laser for temperatures ranging from T = 77 to 200 K. An increase of the electron quasi-Fermi level with electrical injection up to 20 meV was observed. The experimental data imply a decrease in the Auger coefficient with temperature, from 3 × 1024 cm6/s at 77 K to 1 × 1024 cm6/s at T = 200 K attributed to recombination involving two electrons and a heavy hole. The refractive index changes obtained by electrical injection of excess carriers can reach 0.05 at T = 77 K and 0.035 at T = 200 K, which are at least three orders of magnitude greater than those obtained with electro-optical materials.

Room temperature upconversion electroluminescence from a mid-infrared In(AsN) tunneling diode

Light emitting diodes (LEDs) in the mid-infrared (MIR) spectral range require material systems with tailored optical absorption and emission at wavelengths λ > 2 μm. Here, we report on MIR LEDs based on In(AsN)/(InAl)As resonant tunneling diodes (RTDs). The N-atoms lead to the formation of localized deep levels in the In(AsN) quantum well (QW) layer of the RTD. This has two main effects on the electroluminescence (EL) emission. By electrical injection of carriers into the N-related levels, EL emission is achieved at wavelengths significantly larger than for the QW emission (λ ∼ 3 μm), extending the output of the diode to λ ∼ 5 μm. Furthermore, for applied voltages well below the flatband condition of the diode, EL emission is observed at energies much larger than those supplied by the applied voltage and/or thermal energy, with an energy gain ΔE > 0.2 eV at room temperature. We attribute this upconversion luminescence to an Auger-like recombination process.

Electrical modulation of degenerate semiconductor plasmonic interfaces

We demonstrate electrical modulation of plasmonic interfaces in semiconductor p-n++ junctions fabricated from both III–V and Si materials. Junction diodes are grown/fabricated, consisting of degenerately doped n-type material and heavily doped p-type material, where the n++ semiconductor acts as a plasmonic material capable of supporting infrared propagating surface plasmon polaritons. Devices were characterized electrically and optically, and we achieved tuning of the reflectivity under applied bias with amplitude reaching 1.5% in mid-IR wavelengths. We developed a model of electrical carrier injection at the degenerately doped interface, which we used to model the bias-dependent optical properties of the system. A strong agreement between our model and experimental results is demonstrated. The presented devices offer the opportunity for electrical modulation of propagating plasmonic modes in an all-semiconductor system.

Unexpected Outstanding Room Temperature Spin Transport Verified in Organic-Inorganic Hybrid Perovskite Film.

Fundamental understanding on the spin transport properties of semiconducting organic-inorganic hybrid perovskites (OIHP) is of great importance for advancing their applications for spin-optoelectronic devices. Herein, the study of spin-pumping induced inverse spin Hall effect in Ni80Fe20(Py)/CH3NH3PbCl3-xIx/Pt trilayers with different OIHP spacer thicknesses concludes the spin diffusion length in CH3NH3PbCl3-xIx as large as 61 ± 7 nm at room temperature. In addition, spin-valves with a structure of Ni80Fe20(Py)/CH3NH3PbCl3-xIx/AlOx/Co was fabricated as well. Using a ∼160 nm-thick CH3NH3PbCl3-xIx spacer, the present spin valve exhibits a positive magnetoresistance (MR) of 0.57% at 10 K. Thus, the present spin related results demonstrate that electrical spin-polarized carrier injection, transport, and detection, which are essential in spintronic devices, can be successfully established in OIHP films. The outstanding spin transport in the present CH3NH3PbCl3-xIx should be owing to its highly out-of-plane oriented crystalline texture and Rashba spin splitting at domain boundaries between crystallographic orientations. These results demonstrate OIHP as very attractive materials for spintronics.

Single-photon light-emitting diodes based on preselected quantum dots using a deterministic lithography technique

In the present study, we developed a deterministic fabrication process for an electrically driven single-photon light-emitting diode based on InP quantum dots (QDs) emitting in the red spectral range, where the wavelength of interest coincides with the high efficiency window of most commonly available standard Si avalanche photodiodes (APDs). A deterministic lithography technique allowed for the preselection of a suitable QD, here exclusively operated under electrical carrier injection. The final device was characterized under micro-electroluminescence in the direct current as well as in pulsed excitation mode. In particular, under pulsed excitation of one device, single-photon emission has been observed with graw(2)(0)=0.42 ± 0.02, where the nonzero g(2)-value is mainly caused by background contribution in the spectrum and re-excitation processes due to the electrical pulse length. The obtained results constitute an important step forward in the fabrication of electrically driven single-photon sources, where deterministic lithography techniques can be used to sensibly improve the device performances. In principle, the developed process can be extended to any desired emitter wavelength above 600 nm up to the telecom bands.

Spin-dependent giant junction magnetoresistance in simple Fe/p-Si(001) Schottky heretrojunction at low temperature

We report on the giant junction magnetoresistance observed at low temperature in Fe/p-Si Schottky heterojunction. The device shows good rectifying characteristics at room temperature and a dual—Schottky as well as magnetic diode—characteristics at low temperature, below 50 K. Formation of a magnetic field-dependent potential barrier due to electrical injection of spin-polarized carriers from the ferromagnetic electrode into the semiconductor is speculated to result in such large junction resistance. The magnetoresistance value is of the order of $$10^{4}\%$$ at 10 K and saturates at $$\sim 0.5\,\hbox {kOe}$$ , showing dual functionality—working as a magnetic diode as well as a magnetoresistive element.

(Invited) Epitaxy of Direct Bandgap Group IV Si-Ge-Sn Alloys towards Heterostructure Light Emitters

The recent development of optically pumped lasers made from Si-congruent GeSn alloys have strengthened the efforts to fabricate a monolithically integratable light source. Such fully Si-compatible solution may allow merging of state-of-the-art electronics with photonic components on the same chip for on-chip optical interconnects. To advance this prospering field, we investigated the epitaxy of different GeSn/SiGeSn heterostructures, based on GeSn active layers. Double heterostructures allow confinement of carriers in GeSn, though with the deleterious presence of misfit dislocations in the rather thick active regions. This can be overcome, however, in multi quantum well (MQW) structures. Microdisk resonators made from different heterostructures were fabricated, indicating enhanced properties of MQW layers. Epitaxy of in-situ doped p-i-n heterostructure diodes shows paths towards electrical carrier injection into GeSn optoelectronic devices.

Distinguishing between Deep Trapping Transients of Electrons and Holes in TiO2 Nanotube Arrays Using Planar Microwave Resonator Sensor.

A large signal direct current (DC) bias and a small signal microwave bias were simultaneously applied to TiO2 nanotube membranes mounted on a planar microwave resonator. The DC bias modulated the electron concentration in the TiO2 nanotubes and was varied between 0 and 120 V in this study. Transients immediately following the application and removal of DC bias were measured by monitoring the S-parameters of the resonator as a function of time. The DC bias stimulated Poole-Frenkel-type trap-mediated electrical injection of excess carriers into TiO2 nanotubes, which resulted in a near-constant resonant frequency but a pronounced decrease in the microwave amplitude due to free electron absorption. When ultraviolet illumination and DC bias were both present and then stepwise removed, the resonant frequency shifted due to trapping-mediated change in the dielectric constant of the nanotube membranes. Characteristic lifetimes of 60-80, 300-800, and ∼3000 s were present regardless of whether light or bias was applied and were also observed in the presence of a hole scavenger, which we attributed to oxygen adsorption and deep electron traps, whereas another characteristic lifetime >8000 s was only present when illumination was applied, and is attributed to the presence of hole traps.

Optical characterization of magnesium incorporation in p-GaN layers for core–shell nanorod light-emitting diodes

III-nitride nanostructures are of interest for a new generation of light-emitting diodes (LEDs). However, the characterization of doping incorporation in nanorod (NR) structures, which is essential for creating the p-n junction diodes, is extremely challenging. This is because the established electrical measurement techniques (such as capacitance–voltage or Hall-effect methods) require a simple sample geometry and reliable ohmic contacts, both of which are difficult to achieve in nanoscale devices. The need for homogenous, conformal n-type or p-type layers in core–shell nanostructures magnifies these challenges. Consequently, we demonstrate how a combination of non-contact methods (micro-photoluminescence, micro-Raman and cathodoluminescence), as well as electron-beam-induced-current, can be used to analyze the uniformity of magnesium incorporation in core–shell NRs and make a first estimate of doping levels by the evolution of band transitions, strain and current mapping. These techniques have been used to optimize the growth of core–shell nanostructures for electrical carrier injection, a significant milestone for their use in LEDs.

Hybrid organic-inorganic polariton laser

Organic materials exhibit exceptional room temperature light emitting characteristics and enormous exciton oscillator strength, however, their low charge carrier mobility prevent their use in high-performance applications such as electrically pumped lasers. In this context, ultralow threshold polariton lasers, whose operation relies on Bose-Einstein condensation of polaritons – part-light part-matter quasiparticles, are highly advantageous since the requirement for high carrier injection no longer holds. Polariton lasers have been successfully implemented using inorganic materials owing to their excellent electrical properties, however, in most cases their relatively small exciton binding energies limit their operation temperature. It has been suggested that combining organic and inorganic semiconductors in a hybrid microcavity, exploiting resonant interactions between these materials would permit to dramatically enhance optical nonlinearities and operation temperature. Here, we obtain cavity mediated hybridization of GaAs and J-aggregate excitons in the strong coupling regime under electrical injection of carriers as well as polariton lasing up to 200 K under non-resonant optical pumping. Our demonstration paves the way towards realization of hybrid organic-inorganic microcavities which utilise the organic component for sustaining high temperature polariton condensation and efficient electrical injection through inorganic structure.

Hybrid indium phosphide-on-silicon nanolaser diode

By exploiting one-dimensional photonic crystal nanocavities, an ultra-compact indium phosphide-on-silicon laser diode with low current threshold, high wall-plug efficiency and high integrability is demonstrated. The most-awaited convergence of microelectronics and photonics promises to bring about a revolution for on-chip data communications and processing1. Among all the optoelectronic devices to be developed, power-efficient nanolaser diodes able to be integrated densely with silicon photonics and electronics are essential to convert electrical data into the optical domain. Here, we report a demonstration of ultracompact laser diodes based on one-dimensional (1D) photonic crystal (PhC) nanocavities2,3,4 made in InP nanoribs heterogeneously integrated on a silicon-waveguide circuitry. The specific nanorib design enables an efficient electrical injection of carriers in the nanocavity without spoiling its optical properties. Room-temperature continuous-wave (CW) single-mode operation is obtained with a low current threshold of 100 µA. Laser emission at 1.56 µm in the silicon waveguides is obtained with wall-plug efficiencies greater than 10%. This result opens up exciting avenues for constructing optical networks at the submillimetre scale for on-chip interconnects and signal processing.

Isomerization structure of photochromic diarylethene film based on electrical carrier injection

Photochromic films have attracted interest as an organic semiconductive memory material. Isomerization structures of a photochromic diarylethene (DAE) film induced by electrical carrier injection were investigated and were made clear for the coloring-reaction mode (CRM) and decoloring-reaction mode (DRM). Filaments consisting of the colored molecules in the colorless matrix were generated in the CRM, while random distribution of isomerized molecules occurred in the DRM. The ON-OFF ratio in current in the CRM was larger than that in the DRM. These results would be important for constructing organic semiconductor memory device using DAE.

Low-energy electro- and photo-emission spectroscopy of GaN materials and devices

In hot-electron semiconductor devices, carrier transport extends over a wide range of conduction states, which often includes multiple satellite valleys. Electrical measurements can hardly give access to the transport processes over such a wide range without resorting to models and simulations. An alternative experimental approach however exists which is based on low-energy electron spectroscopy and provides, in a number of cases, very direct and selective information on hot-electron transport mechanisms. Recent results obtained in GaN crystals and devices by electron emission spectroscopy are discussed. Using near-band-gap photoemission, the energy position of the first satellite valley in wurtzite GaN is directly determined. By electro-emission spectroscopy, we show that the measurement of the electron spectrum emitted from a GaN p-n junction and InGaN/GaN light-emitting diodes (LEDs) under electrical injection of carriers provides a direct observation of transport processes in these devices. In particular, at high injected current density, high-energy features appear in the electro-emission spectrum of the LEDs showing that Auger electrons are being generated in the active region. These measurements allow us identifying the microscopic mechanism responsible for droop which represents a major hurdle for widespread adoption of solid-state lighting.

Observation of excitonic fine structure in a 2D transition-metal dichalcogenide semiconductor.

Two-dimensional (2D) semiconductors, such as transition-metal dichalcogenide monolayers (TMD 1Ls), have attracted increasing attention owing to the underlying fundamental physics (e.g., many body effects) and the promising optoelectronic applications such as light-emitting diodes. Though much progress has been made, intrinsic excitonic states of TMD 1Ls are still highly debated in theory, which thirsts for direct experimental determination. Here, we report unconventional emission and excitonic fine structure in 1L WS2 revealed by electrical doping and photoexcitation, which reflects the interplay of exciton, trion, and other excitonic states. Tunable excitonic emission has been realized in a controllable manner via electrical and/or optical injection of charge carriers. Remarkably enough, the superlinear (i.e., quadratic) emission is unambiguously observed which is attributed to biexciton states, indicating the strong Coulomb interactions in such a 2D material. In a nearly neutral 1L WS2, trions and biexcitons possess large binding energies of ∼ 10-15 and 45 meV, respectively. Moreover, our finding of electrically induced robust emission opens up a possibility to boost the luminous efficiency of emerging 1L TMD light emitting diodes.