Low Injection Levels Research Articles

A review of key technologies for epitaxy and chip process of micro light-emitting diodes in display application

The continuous miniaturization and integration of pixelated devices have become a main trend in the field of display. Micro light-emitting diode (micro-LED) display is composed of an array of LEDs that are sub-50-micrometers in length. It has huge advantages in brightness, resolution, contrast, power consumption, lifetime, response speed and reliability compared with liquid crystal display (LCD) and organic LED (OLED) display. Consequently, micro-LED display is regarded as the next-generation display technology with high potential applications, such as virtual reality (VR), augmented reality (AR), mobile phones, tablet computers, high-definition TVs and wearable devices. Currently, the combination of commercial 5G communication technology with VR/AR display, ultra high definition video technologies will further prompt the development of micro-LED display industry. However, some basic scientific and technological problems in micro-LED display remain to be resolved. As the chip size shrinks to below 50 μm, some problems that are not serious for large-sized LEDs appear for micro-LEDs. These problems include crystalline defects, wavelength uniformity, full-color emmision, massively tranferring and testing, etc. In the past two decades, various solutions to those problems have been proposed, which have greatly promoted the progress of micro-LED display. In this paper, an overview of micro-LED display since 2000 is given firstly, which includes the main research results and application achievements. Secondly the issues involved in the wafer epitaxy and chip process of micro-LEDs and possible solutions are discussed based on the display application in detail. The surface state induced by the dangling bonds and dry etching damages are concerned for the nonradiative recombination at a low injection level. The remedies are provided for those surface states, such as atomic-layer deposition and neutral beam etching. Some methods to reduce the threading dislocation and suppress the polarization field are summarized for micro-LED epitaxial growth. Moreover, the GaN-based LEDs on Si (100) substrate are also introduced for the future integration of micro-LEDs into the Si-based integrated circuits. As to the wavelength uniformity, the MOCVD equipment and growth technology including the laser treatment are discussed. In the chip processing part, the full-color display, mass transfer and effective inspection technology are discussed. Assembling RGB individual LEDs, quantum dot phosphor material and nanocoloumn LEDs are different routes for full-color display. Their trends in the future are provided. The pick and place, laser lift-off technologies, are strengthened in the massively transferring for micro-LEDs. In the massively and rapidly inspection technologies, the photoluminscence combined with Raman scattering, the electroluminescence combined with digital camera are discussed. Finally, the summary and outlook in these issues are also provided.

Low-level laser therapy vs local anesthetic injection with muscle relaxant splint as a combination therapy for myofascial pain dysfunction syndrome a clinical study

Purpose This study aims to evaluate the efficiency of low-level laser therapy vs injection of long acting anesthetic drug as an adjunctive treatment in combination with muscle relaxant splint in treating patients suffering from myofascial pain dysfunction syndrome (MPDS). Patients and methods A total of 36 MPDS female patients represented the candidates of the present study. They were all treated with muscle relaxant splint then randomly divided into three equal groups; group 1 was treated solely with occlusal splints; group 2 was treated with long acting anesthetic injection of both the masseter and temporalis muscles bilaterally in combination with the splint therapy, while group 3 was treated with low-level laser therapy in combination with the splint therapy. Results All patients completed the study period with improvement in their visual analog scale, mouth opening and electromyography. Group 3 showed statistical significant improvement in all measures compared to group 1 and group 2. Conclusion All the utilized treatment modalities aided in reliving the signs and symptoms of the MPD patients and improved their mouth opening and muscle activity. Utilizing low-level laser therapy in combination with splint therapy was found to be the best adjunctive treatment modality, compared to the injection of long acting anesthetic agent and splint therapy.

Detection of Potential Induced Degradation in mono and multi-crystalline silicon photovoltaic modules

Potential induced degradation (PID) is a performance limiting defect that profoundly impacts the power output of Photovoltaic (PV) modules. PID occurs because of leakage current between the solar cells and the aluminium frame. The leakage current develops due to high potential difference between the string voltage and the ground. In this work, PID is induced in a mono-crystalline and a multi-crystalline module and the severity is determined by current-voltage (I–V) measurements and Electroluminescence (EL) imaging. The Power dropped by 12.6% and 18.7% after 96 h of PID stress. The extracted parameters from the I–V curves show that the shunt resistance decreases and series resistance increases after the induction of PID. EL imaging was done at 10% of short circuit current (Isc) (low injection levels), manifesting as checkerboard like intensity distribution and distinct bimodal intensity histogram. The results of this study demonstrate different PID detection characterisation techniques in PV modules.

Measurement and analysis of the recombination coefficients distribution on the area of light-emitting InGaN/GaN heterostructures

A method and an installation for evaluation the profile of distribution of recombination coefficients and current density over the area of light-emitting heterostructures at low injection levels based on local values of the 3 dB frequency are described. Using the example of measuring the parameters of commercial blue InGaN/GaN-based LEDs, it is shown that the current density is higher in those areas of the chip where the 3 dB frequency is lower.

On the pull-in behavior of optical injection phase-lock loop

This paper presents a detailed study of the pull-in behavior of an optical injection phase-lock loop (OIPLL) neglecting the noise components of the loop. We provide formulas for pull-in voltage and pull-in range of OIPLL in terms of the loop propagation delay, line-width enhancement factor and other parameters of the loop. In addition, we give a compact expression for the frequency pulling time of OIPLL for low injection and high injection level in presence of loop-delay. The effects of loop-delay and optical injection on the pull-in performance of the OIPLL are studied for non-zero values of line-width enhancement factor. Analytical expression of the maximum allowable loop delay is presented to study the deterministic stability of the loop. From the stochastic stability of the loop, we provide formula for the maximum value of the laser line-width to achieve the desired tracking performance. The simulation results are given in partial support of the conclusions of the analysis.

Analysis of carrier lifetimes in N + B-doped n-type 4H-SiC epilayers

Control of carrier lifetimes in nitrogen (N)-doped n-type 4H-SiC epilayers was attempted by intentional boron (B) doping. Doping concentrations of B were controlled to be within 1015–1018 cm−3 by varying the triethyl boron flow rate during epitaxial growth. Time-resolved photoluminescence measurements for the band edge luminescence of the N + B-doped epilayer showed a fast decay time of less than 30 ns under a low injection level at 300 K, while a slow decay component was observed at elevated temperatures of 423–523 K. To understand the mechanism of carrier capture and recombination in N + B-doped 4H-SiC, excess carrier decay curves were simulated by solving rate equations with a simple model. As an effective “recombination enhancing layer,” the 1.6-μm-thick N + B-doped (N: 4 × 1018 cm−3, B: 7 × 1017 cm−3) buffer layer in the PiN diode showed increased intensity of D center-related electroluminescence with increasing injected hole concentrations and prevented the formation of stacking faults from basal plane dislocations in the substrate even at the injection level of 1 × 1016 cm−3 at the interface between the drift and buffer layers.

Effects of Transition Energy on Intra-Band Photoluminescence of Zinc Oxide (ZnO) Semiconductor under Low injection Level

This paper presents the effects of the transition energies on photoluminescence intensities in Zinc Oxide compound semiconductor due to the intra-band transition of free carriers. The excitation of free carriers from the valence band to conduction band and from different localized state to the conduction band by the illumination of sufficient energy is considered. A theoretical model for minority carrier trapping is also investigated to explain the dependence of the photoluminescence on the trap energy. Variation of photoluminescence intensities along with localized state energy and transition energy is considered at different temperatures. As temperature increases the photoluminescence due to the transition of free electrons from the conduction band to the valence band, from the conduction band to the localized states and from the localized states to the valence band are increasing.

Intermittent Parathyroid Hormone Injection Can Decrease Femoral Head Collapse in the Vascular Deprivation of Rat Femoral Head Model.

Backgrounds:Intermittent parathyroid hormone (intermittent PTH) injection has been shown to improve osteogenesis. We hypothesized that intermittent PTH injection could stimulate osteogenesis during the early phase of vascular deprivation-induced femoral neck osteonecrosis in a rat model.Materials and Methods:Eighteen Sprague-Dawley rats were divided into three groups (normal saline [CON], PTH 10 μg/kg [PTH-H], and PTH 1 μg/kg [PTH-L]) for 8 weeks by subcutaneous injection. All rats were sacrificed at postoperative 8 weeks, and all underwent a micro-computed tomography (μ-CT) examination for bone quality and quantity evaluation and histomorphometric analysis for microscopic histologic differences.Results:Under μ-CT examination, both the PTH-H and PTH-L groups revealed less bone resorption than the control group. The PTH-H group had a better bone protective effect than the PTH-L group. Bone mineral density was increased in the PTH-H and PTH-L groups compared to the control group. The uninjured left femoral head was enlarged in both PTH groups. The histologic examination showed that both PTH groups had new bone and cartilage formation. The control group had only dead bone without any osteogenesis.Conclusion:Intermittent PTH injection could decrease bone resorption and improve bone density, compared to the control group, in vascular deprivation of the femoral head in a rat model. High-level intermittent PTH injection had a better effect than low-level intermittent PTH injection.

Ultrafast bulk carrier dynamics in various GaN crystals at near-infrared wavelengths under one- and two-photon absorption

Femtosecond transient absorption (TA) as a probe of ultrafast carrier dynamics was conducted at near-infrared wavelengths in a series of GaN crystals. The TA kinetics in all the GaN crystals appeared to be single exponential under one-photon (1P) excitation but biexponential under two-photon (2P) excitation, which was inconsistent with previous experimental reports and model predictions. Surface recombination and carrier diffusion could be eliminated and the TA responses were identified as phonon-assisted indirect free-carrier absorption. Modelling the bulk carrier dynamics with a simplified model revealed that, at a 1P high carrier injection level, the carrier recombination was limited by the slow capture rate of electrons via deep defects, while at a 2P low carrier injection level, the initial carrier lifetime decreased remarkably due to fast hole capturing and could be further controlled by the inherent carrier and/or dislocation concentrations.

Effect of the Near Surface Depletion Layer on Photo-Response of Direct Band Gap Semiconductor

In this study, the effects of the photo-responses of the near surface depletion layer and the deep bulk of gallium antimonide (GaSb) are investigated under different doping levels, injection level and illumination energies. First, the absorption rate of photons is described as a function of illumination energies at different locations inside the sample and as a function of the depth below the illuminated surface for photons with different energies. Then, the doping level dependence of the low injection level radiative, Auger and effective excess carrier lifetimes just under the surface and in the deep bulk are investigated by considering the variation of energy bending at the surface. The variation of the low injection level excess carrier lifetimes with the depth below the illuminated surface for samples with different doping levels is also described. This is followed by the description of the combined effects of doping and illumination energy on the photo-response of the entire bulk at slightly low injection level. Finally, the excess carrier injection level dependence of excess carrier lifetimes under the illuminated surface and deep bulk is also described for samples with different doping levels. Since photon absorption rate is directly related to the free carriers generation rate, the description of the photon absorption rate as functions of illumination energies and the depth below the illuminated surface is found to be the important and factors in the investigation in the photo-response of semiconductors along with the doping and the injection levels. The analysis of the results also shows that, the under surface region is insensitive to the doping level and that of the deep bulk is highly affected by the doping level. The injection level dependence of the photo-response of the under surface region is similar for all samples with different doping. The energy of illumination each photon mainly suppresses the photo-responses of the points situated closer to the penetration depths of each photon below the illuminated surface of the sample. Keywords: photo-response, direct band gap semiconductor, gallium antimonide GaSb DOI : 10.7176/APTA/75-03

МЕТОДЫ ПОВЫШЕНИЯ ЭФФЕКТИВНОСТИ И НАДЕЖНОСТИ ИЗЛУЧАЮЩИХ ДИОДОВ НА ОСНОВЕ GaInAsP

The quantum production of the electroluminescence of semiconductor emitters of the optical range is determined by the parameters of several stages of the process of converting electrical energy into optical radiation energy. To improve the efficiency and stability of the emitting diodes, the losses at certain stages of this process were investigated. When obtaining information on the distribution of impurities in p–n junctions of light-emitting diodes, volt-farad characteristics were measured. In the studied radiators, a linear impurity distribution in the p – n junction was obtained. The electrical and electroluminescent characteristics of emitting diodes based on GaInAsP were studied. The elucidation of the mechanism of diode degradation during their current training for 3000 hours at different current densities and temperatures, on the radiation intensity, that measured at low and high injection levels, on the value of the photocurrent p-n-junction and on their electrical characteristics was carried. It is shown that the degradation of the studied radiators is due to the change in the ratio between the radiative and non-radiative components of the current in p-n-junctions, as well as the change in the electron lifetime in the active region of the heterostructures. The kinetics of degradation of diodes is explained by the drift of charged defects in an electric field. It was found that a decrease in the quantum efficiency of GaInAsP-based diodes with a decrease in the injection level is due to the presence of local narrowing of p-n-junctions. It is shown that in order to reduce degradation of emitting diodes and to increase their quantum efficiency at low injection levels, it is necessary to reduce the concentration of residual impurities and lattice defects in the used semiconductor heterostructures.

Influence of radiation-thermal defects on characteristics of p-n-p-n-structures

The article presents the results of study of the effect of radiation defects (RD) and thermally stable (up to 873 K) radiation-thermal defects (RTD), created by electron irradiation with an energy of 4 MeV and heat treatment on the static and dynamic characteristics of silicon thyristor p-n-p-n structures. The dependences of turn-on and turn-off current on the life-time of minority charge carriers at a high injection level (in the range of 1.0–10 mks) are obtained in a thick n -base of structures with RD and RTD defects and the same dependences of the minority charge carriers lifetime at a low injection level. DLTS -spectra of the investigated structures and temperature dependences of control current and control voltage in the temperature range of 77–320 K are presented as well.

Total Harmonic Modulation Distortion of an Injection-Locked Fabry-Perot Laser Diode Directly Modulated by a Multi-harmonic RF Signal

This paper describes effects of low-level light injection into a directly modulated Fabry-Perot laser diode on the external total harmonic modulation distortion when the external fundamental modulating signal is multi-harmonic contaminated. Necessary theory of the injected FPLD has been developed and an expression for total harmonic distortion of the modulating signal has been derived considering low-level light injection. The total harmonic modulation distortion has been experimentally measured for the RF modulation source and for the injection-locked slave FPLD output after photodetection.

Analytical and numerical simulation of electron beam induced current profiles in p-n junctions

The electron beam induced current (EBIC) mode of a scanning electron microscope (SEM) is a widely used technique for the quantitative assessment of minority carrier diffusion length and surface recombination. Point source (one-dimensional) and extended source (two-dimensional) analytical models are two widely used approaches to assess this information in geometry where the electron beam (e-beam) is parallel to the p-n junction. In this article, a two-dimensional (2D) analytical model is evaluated and compared with 2D finite element numerical simulations, where the electron beam-solid interaction is modeled using a Monte Carlo simulation coupled with a drift-diffusion solver. The simulations are computed for both low and high level injection conditions. The effect of an e-beam injection level on the shape of EBIC profiles is analyzed to evaluate limitations of the analytical models.

Multi-level timing and fault simulation on GPUs

In CMOS technology first-order parametric faults during manufacturing can exhibit severe changes in the timing as well as in the functional behavior of cells. Since these faults are hard to detect by conventional tests, the accurate simulation of these low-level faults plays an important role for test validation. However, pure low-level fault simulation approaches impose a high computational complexity that can quickly become inapplicable to larger simulation problems due to limitations in scalability.In this paper, the first parallel multi-level fault simulation approach on graphics processing units (GPUs) is presented. The approach utilizes both logic level and switch level descriptions concurrently in a mixed-abstraction timing simulation. The abstraction is lowered in user-defined so-called regions of interest that locally increase the modeling accuracy enabling low-level first-order parametric fault injection. Resulting signal waveforms are transformed between the different abstractions transparently. This way a fast, versatile and efficient multi-level fault simulation approach on GPUs is created that scales for designs with millions of cells while achieving high simulation throughput with runtime savings of up to 84% compared to full switch level simulations.

Further improvements of an extended Hakki-Paoli method

A modified Hakki-Paoli method, for measuring optical gain in laser diodes, proposed at the past ESREF 2017 conference is here further improved in terms of practical implementation. In particular, averaging both the spectral function and its reciprocal, over an oscillation cycle is shown to lead to the gain function replacing the calculation of maxima and minima, a cumbersome task for noisy spectra at low injection level. The ultimate goal is to get rid of the many constraints that complicate gain measurements for other than the manufacturers, and to provide a new powerful tool for laser diode characterization and diagnostics.

Estimation of the Maximum Nonequilibrium Charge-Carrier Concentration in GaN Under Electron-Beam Irradiation

An empirical expression describing the lateral distribution of the nonequilibrium charge-carrier generation rate in GaN by a focused electron beam is obtained. The maximum nonequilibrium charge-carrier concentration as a function of the beam energy and diffusion length is calculated using this expression. Comparison of the results with values obtained using previously proposed approximate expressions provides an opportunity to evaluate the applicability of these approximations. Within the study of GaN by the cathodoluminescence and electron-beam-induced-current methods, the possibility to achieve a low injection level is analyzed considering the fact that the diffusion lengths of nonequilibrium charge carriers can be measured correctly only at low injection levels. It is shown that, in spite of the submicron values of the diffusion lengths in GaN, rather low beam currents are required to achieve a low injection level.

SEPARATE DETERMINATION OF THE PHOTOELECTRIC PARAMETERS OF THE BASE REGION OF N+−P(N)−P+ SILICON STRUCTURE BY NONCONTACT METHOD BASED ON QUANTUM EFfi CIENCY RELATION MEASUREMENTS AT TWO WAVELENGTHS

A noncontact method for the determination of recombination parameters of p(n) layer local ranges of silicon n+−p(n)−p+ structures is considered. The method is based on local illumination of the investigated structure by two different absorbed light beams. Initially both beams illuminate simultaneously one side of the local range of this structure and then another side. The intensities оf the light beams are modulated at one frequency so the alternative photo−voltage becomes equal to zero. In this case the short current regime is established for its alternating component. As a consequence the nonilluminated parts of the structure do not shunt its illuminated part. The ratios of the light beam intensities are measured under these conditions. In this work we calculated nomograms for separate determination of the nonequilibrium charge carrier lifetime of the illuminated p(n) local space and its surface recombination velocity using the measured intensity ratios. The calculations were performed at low injection level for one dimensional case. The nomograms were calculated at wave lengths of 1064 and 808 nm for various thicknesses of the n+−p(n)−p+ structures and various modulation frequencies. It was found that the nomograms almost do not depend on the modulation frequency if the live time of the nonequilibrium charge carriers is less than the modulation period. Furthermore, we observed that the nomograms shift substantially and change their shape for thin structures if the diffusion time of nonquilibrium charge carriers from the rear side of the structure to its face side becomes less than their lifetime. In this case the nomograms may be only used for the determination of the surface recombination velocity of the nonquilibrium charge carriers at the rear side of the structure.

Extracting Nonradiative Parameters in III–V Semiconductors Using Double Heterostructures on Active p-n Junctions

A novel method of extracting the nonradiative lifetime of Ga0.51In0.49P lattice matched to GaAs by exploiting luminescence coupling is discussed. The method requires a GaInP double heterostructure monolithically grown on a GaAs photodetector for quantum efficiency measurements. The method then extracts the nonradiative lifetime by modeling the luminescence coupling between the GaInP and the GaAs active region. The bulk nonradiative lifetime of disordered GaInP doped to 1017 cm−3 under low-level injection (∼4 × 1012 cm−3) is determined to be 47 ns for GaInP layer thicknesses ranging from 200 to 1500 nm, with a surface recombination velocity of 660 cm/s. The results are in agreement with nonradiative lifetimes extracted using power-dependent relative photoluminescence measurements, whereby the lifetimes increase as a function of injection level to 0.5 μ s. Surface recombination velocities are also reported as a function of injection level using this technique, decreasing from 1800 cm/s under low injection to 50 cm/s under high injection (∼1017 cm−3). Lastly, the effective radiative lifetimes (accounting for photon recycling) are also reported for the studied GaInP samples.

Влияние низкодозного протонного облучения на характеристики инжекционных диодов на основе 4H-SiC

AbstractThe effect of low-dose proton irradiation (irradiation dose 10^10–1 . 8 × 10^11 cm^–2) on the capacitance–voltage, forward current–voltage, and reverse-recovery characteristics of 4 H -SiC p – n _ o junction diodes is studied. Irradiation is performed with 1.8-MeV protons through a 10-μm-thick Ni-film (the proton energy and Ni-film thickness were chosen so that the projected proton range in silicon carbide is approximately equal to the p – n _ o junction depth). It is shown that proton irradiation in the above doses (i) does not change the concentration of majority carriers, (ii) leads to a dramatic decrease in the lifetime of nonequilibrium carriers (at a low injection level) (by several tens of times at the highest irradiation dose), and (iii) decreases the reverse-recovery charge at a high injection level (by up to a factor of 3 at the highest irradiation dose).