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In this work we have characterized screen-printed passivating contacts formed by different commercially available fire-through pastes on phosphorus doped (n+) polysilicon (poly-Si) layers at the rear side of monoPoly™ solar cells. Extremely low recombination current density under metal contacts (J01,metal) of 35–45 fA/cm2 and excellent specific contact resistivity (ρc) values of ~ 1.3 mΩ-cm2 are obtained for two different thicknesses of poly-Si (150 nm and 250 nm) used in this work. We demonstrate that, although the metal induced recombination increases with reducing thickness of the poly-Si layer, thinner poly-Si layers can lead to higher efficiencies on account of reduced parasitic absorption leading to higher cell current. A champion efficiency of 22.6% is reported for busbarless monoPoly™ cells with the best performing fire-through (FT) paste on large area (244.3 cm2) commercially available Czochralski grown Si wafers.

Analytical methods for investigating deep levels in GaN are reviewed. Quantitative accuracy of deep-level transient spectroscopy (DLTS) technology is discussed. The isothermal method allows a quick measurement and is useful to characterize trap states for the case that a temperature scan causes reaction of defects or the occupancy condition for each filling pulse needs to be kept constant. The DLTS measurement for hole traps in p-type GaN needs special considerations due to the relatively large ionization energy of magnesium acceptors, where the low-frequency DLTS system is utilized. For investigation of minority carrier traps, DLTS using injection bias pulses for p-n junctions is the most reliable method for the quantitative evaluation. DLTS methods using light filling pulses such as minority carrier transient spectroscopy and optical DLTS are applied for samples without p-n junctions, which needs considerations of light absorption, the minority carrier diffusion length, and the optical capture cross sections of deep levels. Investigation of deep levels far from both band edges requires the approaches without the use of thermal emission process. For this aim, this chapter overviews deep-level optical spectroscopy, photoluminescence involving a time-resolved method, positron annihilation spectroscopy, and an analysis of recombination current in a p-n junction.

One of the main causes of low performance of Cu2ZnSnS4 (CZTS) based thin film solar cells is its high recombination current. In this paper, the effects of the carrier concentration and recombination current in the CZTS thin film solar cells have been carefully scrutinized. In continue, for comparison and validation, two simulated structures based on the CZTS absorber layer have been reproduced and the influence of the absorber layer defects and carrier concentration has been analyzed. In this work, two different structures using p+-CZTS intermediate layer (between the CZTS absorber layer and Mo back-contact) and dual CZTS layer have been proposed and optimized to decrease recombination and extract the desired photovoltaic parameters. By using and optimizing these structures as p+pn junction, 15.62% and 19.08% efficiencies have been achieved in p+-CZTS intermediate layer and p+pn CZTS dual layer structures, respectively. The highest efficiency of dual absorber based solar cell is achieved when the carrier concentration of the p+-CZTS and p-CZTS absorber layers is 1 × 1018 cm−3 and 5 × 1015 cm−3, respectively. Moreover, the optimum thickness of the p+-CZTS and p-CZTS absorber layers in p+pn CZTS dual layer structure is 1 and 1.5 µm, respectively. Finally, the total recombination current density is reduced to 2.05 mA/cm2.

A study of how electron irradiation affects the current-voltage (I-V) and electroluminescence (EL) characteristics of two types of 4H-SiC n+p structures with p-base and base doping to ~5∙1015 cm-3 is presented. The characteristics were measured prior to irradiation and after each of five stages of irradiation with 0.9 MeV electrons at doses in the range from 1∙1015 to 1.1∙1016 cm-2. The irradiation leads to an increase in the recombination current, decrease in the intensity of the edge EL (hνmax≈3.18 eV), and increase in the intensity of the infra-red (IR) EL (hνmax≈1.35 eV), which starts to predominate. Presumably, this indicates that the nonequilibrium carrier lifetime decreases and the concentration of acceptor type defects grows as a result of the irradiation. The IR EL, attributed to a complex defect containing a silicon vacancy, is of interest for development of single-photon sources of light.

Neutron irradiation (~1 MeV, dose 1014-5.6∙1015 neutron/cm2) of packaged diodes based on 6H-SiC pn structures (with the base n-layer doped to ~5∙1016 cm-3) has been studied. In addition to the well-known rise in the series resistance of the diodes, the effect of a partial suppression of the excess current in both forward-and reverse-biased diodes and that of an increase in the recombination current, probably associated with the decrease in the nonequilibrium carrier lifetime, were discovered and discussed. These effects are common to 6H-and 4H-SiC pn structures.

In this paper, the degradation characteristics of the series diodes under DC high voltage operation are investigated. Five series connected diodes are operated at a reverse bias voltage of 1500V. The influence of the DC high voltage on the diode parameters is analyzed after the I-V characteristic test. Finally, an annealing experiment is performed on a diode that stressed under DC high voltage. The results show that the high voltage will introduce defects into the diodes, which leads to the increases of the recombination current and the ideality factor. The degradation degree of five diodes is basically the same. For the annealing experiment, the recoverability of defects can be observed.

It is well known that the quality of contact passivation can greatly influence the efficiency of Si solar cells. In this work, the impact of annealing a wet-chemically formed silicon oxide (SiOx) tunnel layer (prior to poly-Si capping) to form SiOx/n+ poly-Si passivated contacts for high efficiency solar cells is investigated. The effect of different annealing temperatures (ranging from 425 to 900 °C) and ambients (air and forming gas), on the overall performance of the resulting SiOx/n+ poly-Si passivated contacts are studied. The efficiency potential of these SiOx/n+ poly-Si contacts is calculated from the measured values of the recombination current density (J0,contact), and the effective contact resistivity (ρcontact), according to the generalized Brendel's model. The results are compared to the reference case, i.e. non-annealed SiOx tunnel layer with poly-Si deposition. The lifetime, the fixed charge and also the SiOx tunnel layer thickness increase upon annealing at higher temperatures. The sample annealed in forming gas at 900 °C shows an increase in field effect passivation (Qtot = 1 × 1012 cm−2) as well as in chemical passivation (Dit = 3 × 1011 eV−1 cm−2), along with reduced ρcontact, indicating pinhole formation upon annealing at 900 °C. The best SiOx/n+ poly-Si passivated contact achieved J0,contact = 4.2 fA cm−2, ρcontact = 0.27 Ω cm−2 and a corresponding maximum ideal efficiency potential of 27.9%. This is 1.2% absolute higher as compared to the reference case, when no annealing of the tunnel layer is performed.

In this paper, the impact of deep level traps on the I-V and C-V characteristics of InP/InGaAs heterojunction have been studied by introducing deep level traps in pre and post-irradiation samples. In this case, forward recombination current and junction capacitance in dependence of the deep level density and energy have been analyzed by TCAD simulation and experiments. The simulation results are in good agreement with the experimental results. The junction capacitance and recombination current both increase with the increasing of deep level density. Apart from this, the radiation induces deeper level traps, which contributes more to these increased trends.

We discuss the effect of out-of-plane excess carrier density variations on contact recombination currents extracted from quasi steady state photoconductance (QSSPC) measurements on a dedicated test structure. The test structure features lattices of point contacts. The contacts are thick and non-transparent. Therefore, asymmetric test structures are generally used to ensure a homogeneous in-plane generation rate. As a result, the QSSPC measurements are relatively prone to out-of-plane excess carrier density variations. Their effect on the extracted contact recombination characteristic is discussed theoretically and the theory is confirmed by experiment. The resulting framework contributes to the set of design rules and best practices for contact recombination current characterization using QSSPC measurements on point contact lattice based test structures.

We recently proposed a novel test structure for the extraction of recombination characteristics of metal-contacted areas on silicon wafers using quasi-steady state photoconductance measurements. In this test structure, photoconductance measurements are performed on several wafer areas with different contact fractions. Each area consists of a lattice of point contacts on an otherwise passivated wafer. The requirement of constant excess carrier densities throughout the quasi-neutral wafer bulk is absolutely essential for the simple extraction of figures of merit for contact recombination. In this study, we first discuss the requirements for constant injection levels during photoconductance measurements, without reference to a particular geometry. Then, we use a simple 1-D model to elucidate how injection levels vary in the test structure plane. We use the model to investigate limiting cases for which the requirement of constant injection levels is satisfied. In addition, we investigate the breakdown of the assumption of constant injection levels. We discuss the influence of nonconstant excess carrier concentrations on photoconductance measurements in the context of our test structure. Finally, we validate our model by comparison with experiments. Our analysis is particularly useful in the context of understanding the design rules for contact size and pitch in our test structure.

In this work, we evaluate the impact of implementing a selective back surface field (BSF) on the performance of bifacial n-type Passivated Emitter and Rear Totally diffused (PERT) cells with Ni/Ag co-plated contacts. For this, we compare bifacial nPERT cells featuring a homogeneous BSF etched-back to ~100 Ω/sq and patterned by laser ablation to cells featuring an identical front side design and a selective BSF obtained by means of laser doping. In the first part of this paper, we demonstrate using test structures that selective BSF cells benefit from drastically lower area weighted recombination current density (J0) contributions at the BSF side resulting in estimated Voc improvement from ~657 mV to ~ 681 mV. In the second part of this paper, we confirm at cell level that implementing a selective BSF results in gains in Voc ~ 30 mV, jsc~ 0.2 mA/cm2, and Fill Factors FF ~ 0.9%abs. resulting in average cell efficiencies improving from 20.7±0.4 % to 22.0±0.2 %. This clearly confirms that a selective BSF is required in nPERT cells with Ni/Ag co-plated contacts to maximize cell efficiencies. Finally, we fabricated a 9-cells bifacial glass-glass laminate for proof-of-concept and discuss several possible improvements to bring 60-cells module front maximum power values under standard test conditions (STC) above 340 Wp.

DC, RF and noise characteristics of advanced InP/InGaAs and Si/SiGe heterojunction bipolar transistors (HBTs) were measured and modeled in a broad frequency range. Equations for systematically modeled correlated noise in bipolar transistors and their implementation in the compact models HICUM/L0 and L2 are proposed. The models are verified for advanced SiGe HBTs up to 300 GHz by hydrodynamic device simulation and by results from the Boltzmann transport equation. The verified model was used for analyzing the noise of advanced InP/InGaAs and Si/SiGe HBTs. Compared to Si/SiGe HBTs a higher noise at lower frequencies was observed in InP/InGaAs HBTs due to a higher base recombination current. InP HBTs shows a good noise performance beyond 100 GHz and due to their better $$f_{\mathrm{T}}\,\times ~BV_{\mathrm{CE0}}$$fT×BVCE0 product can compete with advanced Si/SiGe HBTs for LNA design at mm-wave frequencies.

The electric parameters of Cu doped ZnTe/Si junction grown by thermal evaporation before and after irradiation have been investigated and presented in this article. Current–voltage (I–V) studies under forward and reverse bias at room temperature were carried out for this purpose. The higher values of ideality factor and series resistance were due to the generation-recombination of carriers in the space-charge region. This recombination current was caused by defects states. The current conduction mechanism was slightly altered by irradiation. Capacitance–voltage (C–V) characteristics measured at room temperature also identified the presence of defect levels in the device.

It is shown that the increase in the current of an asymmetric p-n-junction, caused by perturbation of potential barrier height and increasing recombination current in a strong microwave field, is suppressed by light generated photo carriers, leading to the displacement of current-voltage characteristics of p-n-junction into the direction of smaller current values.

Recent results show the potential of silicon heterojunction solar cells working as a bottom cell in tandem with wide band gap materials. The surface quality of the bottom cell is critical to reduce the recombination current and promote a good interface between the top and bottom cell. In this paper, we investigate the impact on performance of surface defects that are present after the i-p/i-n junction formation in silicon heterojunction cells. We induce controlled distribution of defects after the junction formation using a laser, which amounts to 1% of the total area of the cell. We measured an 8% relative power loss between samples with and without the induced damages. The most affected parameter is the voltage at the maximum power point that shows a drop of 13 mV after the induced damages.

We investigate the dark low-frequency noise characteristics of P3HT:PCBM bulk heterojunction organic solar cells in both forward and reverse bias conditions. The current noise power spectral density (SI) is “1/f”-like and is compared among cells annealed at different temperatures (60 °C to 140 °C). The asymmetric relationship of SI versus DC dark current (IDC) can be explained by the competition between the recombination current noise and tunneling current noise. Among the different annealing temperatures, we find that higher annealing temperature yields smaller ratio of the Hooge parameter to the carrier recombination lifetime, which is reflected in the forward bias SI versus IDC relationship. We demonstrate that the low-frequency noise can serve as a non-destructive diagnostic indicator of the performance of organic solar cells.

Electronics components such as bipolar junction transistors, diodes, etc. which are used in deep space mission are required to be tolerant to extensive exposure to energetic neutrons and ionizing radiation. This paper examines neutron radiation with pneumatic transfer system of TRIGA Mark-II reactor at the Malaysian Nuclear Agency. The effects of the gamma radiation from Co-60 on silicon NPN bipolar junction transistors is also be examined. Analyses on irradiated transistors were performed in terms of the electrical characteristics such as current gain, collector current and base current. Experimental results showed that the current gain on the devices degraded significantly after neutron and gamma radiations. Neutron radiation can cause displacement damage in the bulk layer of the transistor structure and gamma radiation can induce ionizing damage in the oxide layer of emitter-base depletion layer. The current gain degradation is believed to be governed by the increasing recombination current in the base-emitter depletion region.

We investigate contacting of n- and p-type polysilicon (polySi) passivating contact layers with industrial screen-printed metal pastes, examining both fire through (FT) and non-fire through (NFT) pastes. The n- and p-type polySi layers, deposited by low pressure chemical vapour deposition and doped by POCl3 diffusion, phosphorus implant, or BBr3 diffusion, result in excellent Jo, even for 50 nm thickness (

We analyzed the degradation mechanism of GaInP/GaInAs/Ge triple junction solar cells without coating any protective film. Gradual degradation in the dark and light I-V characteristics of the solar cells were observed after the step stress accelerated degradation tests (SSADT) were conducted on these devices sequentially at 90, 110, 130 and 150°Cfor 25, 55, 85 and 135 hours, respectively. The recombination current in the depletion region at the chip perimeter of solar cells, resulting in the decrease of open-circuit voltage (VOC), fill factor (FF) and efficiency, is suggested to be the important degradation mechanism for GaInP/GaInAs/Ge triple junction solar cells.

We study the structure of SiC/SiO2 interface defects and the effects of negative bias temperature stress (NBTS) in lateral 4H silicon carbide (SiC) PMOSFETs. Our devices have 90 nm thick SiO2 gate oxides thermally grown in N2O ambient at 1280°C on n-type SiC. We investigate virgin (unstressed) and stressed devices using two different techniques: (i) for electrical characterization, we use the direct-current current-voltage (DCIV) technique [1] which measures a recombination current via interface defects and charge pumping (CP) which measures the number of interface defects within a certain range of the SiC band gap; (ii) to study the structure of the defects, we use electrically detected magnetic resonance (EDMR) via spin dependent recombination (SDR) [2]. The elevated temperature during NBTS is provided by in-situ heated test structures. This is the first EDMR study of p-doped SiC MOSFETs and the first negative bias temperature instability (NBTI) study of SiC MOSFETs using in-situ (on-chip) heating during stress.

N-type silicon with aluminum emitters for rear junctions was studied; aluminum back surface fields were replaced with n-type silicon wafers. Aluminum rear emitters for n-type silicon solar cells were studied with various rapid thermal processing conditions. With fast ramping-up and fast cooling, an aluminum rear junction was formed uniformly with low emitter recombination current. The effects of junction quality on solar cell efficiency were investigated.

Atomic layer deposition (ALD) of thin Al2O3 (≤10 nm) films is used to improve the rear surface passivation of large-area screen-printed p-type Si passivated emitter and rear cells (PERC). A blister-free stack of Al2O3/SiOx/SiNx is developed, leading to an improved back reflection and a rear recombination current (J0,rear) of 92 ± 6 fA/cm2. The Al2O3/SiOx/SiNx stack is blister-free if a 700°C anneal in N2 is performed after the Al2O3 deposition and prior to the SiOx/SiNx capping. A clear relationship between blistering density and lower open-circuit voltage (VOC) due to increased rear contacting area is shown. In case of the blister-free Al2O3/SiOx/SiNx rear surface passivation stack, an average cell efficiency of 19.0% is reached and independently confirmed by FhG-ISE CalLab. Compared with SiOx/SiNx-passivated PERC, there is an obvious gain in VOC and short-circuit current (JSC) of 5 mV and 0.2 mA/cm2, respectively, thanks to improved rear surface passivation and rear internal reflection. Copyright © 2012 John Wiley & Sons, Ltd.

This paper is proposed to extract the local carrier generation lifetime from forward current-voltage (I-V) characteristics of p-n junctions in case of non-uniform defects. The different geometry p-n junctions have been fabricated by a standard CMOS technology. The forward I-V and high frequency capacitance-voltage (C-V) characteristics of p-n junctions have been measured. The recombination current density can be extracted from the area forward current density by subtracting with the area diffusion current density. Form the recombination current density, the local generation and recombination lifetime can be obtained.

In this paper, the gettering potential of phosphorus dopant pastes used in single-sided screen-printing processes is investigated including the consequences for essential solar cell parameters. These results are supported by minority carrier lifetime measurements with the quasi-steady-state photoconductance method and certified by the analysis of the recombination current density in solar cells on mc-Si wafers. Copyright © 2011 John Wiley & Sons, Ltd.

A new interpretation of high injection effect of minority carriers,np, which is happened in solar cell under sunlight concentration and imposed a limitation on its expected efficiency- has been introduced. This interpretation declare that: increasing of minority carrier, np, recombination current Irecom in deplation region when sunlight concentration C increase,s due to the depletion layer widen because the increasing of drift electric field at the junction boundary correspond to population inversion phenomena which happens at the interfaces between the base region and the depletion region. Experiments was performed with operating solar cells under high injection conditions (sunlight concentration simulator) to get I-V characteristics, then we characterize the relation between the depletion region width w and Irecom, by suggesting a new model which enable us to optimize a solar sell under sunlight concentration. In consequence we cocnlude that: Irecom is responsible of depleting a significant part of minority carrier, consequently, Irecom causes the solar cell efficiency degradation.

Active layers of i-In 0.13 Ga 0.87 N p-i-n photovoltaics (PVs) with a single antireflection layer (SARL) and a multi-antireflection layer (MARL), respectively, were fabricated. Reflectance simulation results show that the PVs with a SARL or a MARL have performance superior to those without an antireflection layer (ARL). In particular, the surface reflectance of PVs with a MARL was reduced to 6% at wavelengths between 330 and 500 nm. The ARL reduced the reflectance and recombination current, as well as boosting shunt resistance without increasing series resistance. Compared with PVs without an ARL, the open-circuit voltage and fill factor of PVs with a MARL increased by 100% and 54.5%, respectively. The ideal factor was improved by 19.4% and 31.9% in devices with a SARL (SiO 2 ) and a MARL (Ta 2 O 5 /SiO 2 ), respectively.

(Ga,In)P/GaAsSb DHBTs with different emitter sizes were fabricated with the standard triple-mesa process on wafers with GaInP [Ga] emitter contents of 0, 0.15, 0.24 in the emitter. The effect of the gallium content on the DC and RF characteristics of the DHBTs was studied. It was found that gain increases as the Ga mole fraction increases. This is due to a reduced surface recombination current and intrinsic recombination current with increasing [Ga]. 0.45 × 9.5 μm2 devices with a Ga content of 0.24 show the highest cut-off frequency of 387 GHz. This is attributed to the reducing barrier at the E/B interface, which eases the injection of electrons from the emitter into the GaAsSb base. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The current-voltage (I-V) characteristics of most industrial silicon solar cells deviate rather strongly from the exponential behavior expected from textbook knowledge. Thus, the recombination current may be orders of magnitude larger than expected for the given material quality and often shows an ideality factor larger than 2 in a wide bias-range, which cannot be explained by classical theory either. Sometimes, the cells contain ohmic shunts although the cell’s edges have been perfectly insolated. Even in the absence of such shunts, the characteristics are linear or super-linear under reverse bias, while a saturation would be classically expected. Especially in multicrystalline cells the breakdown does not tend to occur at -50 V reverse bias, as expected, but already at about -15 V or even below. These deviations are typically caused by extended defects in the cells. This paper reviews the present knowledge of the origin of such non-ideal I-V characteristics of silicon solar cells and introduces new results on recombination involving coupled defect levels.

a b s t r a c t The non-ideal behavior of the dark current–voltage (I–V) characteristics of typical silicon solar cells is characterized by (1) an unexpectedly large recombination current, often characterized by an ideality factor larger than 2, (2) an ohmic characteristic at low reverse bias, and (3) pre-breakdown at a reverse bias far below the expected breakdown voltage. Experimental evidence, especially from lock-in thermography results, shows that all these features are due to currents flowing locally in the edge region, or at certain extended crystal defects like grain boundaries. Detailed investigations on local breakdown sites in industrial solar cells are introduced. Though a realistic theory of these processes is still missing, a unified explanation of non-ideal darkI–V characteristics ispresentedandseveraltheoreticalapproachestoexplaindifferent aspects of this non-ideal behavior are discussed.

We analyze the voltage and temperature dependent recombination current of organic light-emitting diodes (OLED) by the exponential current-voltage characteristic. Its correct description is of great importance for understanding the prospects of OLEDs.

The effect of the different types of passivation layers on the current gain of SiC BJTs has been investigated. Measurements have been compared for BJTs passivated with thermal SiO2, plasma deposited (PECVD) SiO2 and BJTs without passivation. The maximum DC current gain of BJTs with thermal SiO2 was about 62 at IC=20 mA and Vce=40 V. On the other hand, the BJTs with a passivation by PECVD SiO2 had a DC current gain of only 25. The surface recombination current was extracted from measurements with BJTs of different emitter widths. The surface recombination current of BJTs with a thermally grown oxide was about 25 % lower than unpassivated BJTs and 65 % lower than that of PECVD passivated BJTs.

This paper presents the effect of surface treatment on the electrical properties of an AlGaAs/GaAs heterojunction bipolar transistor (HBT). The extrinsic base surface of the HBT was treated in sequence with a (NH 4 ) 2 S x :H 2 O = 1:1 solution, H 2 plasma, and NH 3 plasma. The treated HBT had a lower surface recombination current, base resistance, and low-frequency base current noise than the untreated HBT. These values decreased by 32%, 42%, and ∼3 dB, respectively. Because of the reduced base resistance, the maximum frequency of oscillation f max , which was 40.3 GHz without surface treatment, improved to 57.8 GHz.

There has been some substantial interest in studying current transport in organic light-emitting devices (OLEDs) because of their potential as solid-state light sources. While some of the physics remain to be resolved, there is in place a fair amount of understanding on the device operation to develop a working model for properties such as the J – V characteristics. This paper is an extension of an earlier publication [Solid-State Electron. 46 (2002) 645] to model mathematically the rate of exciton formation in OLEDs based on bimolecular recombination. The earlier work relied on knowing the spatial distribution of the carrier densities and this allowed one to study position dependent properties such as selective doping in OLEDs. Our current work extends the previous model to include space charge effect at low bias and suggests a possible mechanism bridging the transition between space charge limited current at low bias and recombination current at large bias. To validate our model, we compared our simulation results to data reported in the literature in the case of a ITO/TPA-PPV/Al device [Phys. Rev. 60 (1999) R8489]. In particular, effort was spent to explain the existence of a current peak at low bias in the J – V characteristics. Our overall result appeared to suggest that the operation of the OLEDs may well be accounted for by a simple model involving the capture of space charge injected holes at some unknown sites (possibly “trap” centers). This would be followed by “recombination”, which appeared to be strictly limited by the availability of the electrons within the active region. The transition from space charge limited current to recombination current was used to explain the existence of the current peak at low bias.

Compact physical models for SSOI MOSFETs are presented. The models consider specific features for strained-Si devices including SSOI such as mobility enhancement, band offsets, junction capacitance, and self-heating effects. All of the floating-body current components in conventional SOI structure, which are generation/recombination current, reverse-bias (band-to-band and trap-assisted) junction tunneling currents, gate-induced drain leakage current, gatebody oxide tunneling current, and impact ionization current are applied to the SSOI device, and their effects are discussed. The model validity is confirmed by fabricated 70 nm bulk-Si (control) and strained-Si devices.

In this paper, the forward-biased gated-diode technique is proposed as a simple and reliable method for the determination of the recombination parameters in thin-film, fully depleted SOI MOS devices. Using modeling of gated-controlled volume and surface recombination components the behavior of the recombination current in a thin-film SOI gated-diode is analyzed. Measurement conditions simplifying the extraction of the recombination parameters and enabling discrimination between volume and surface contributions are described. The method has been applied to study recombination processes in the devices made on different SOI materials (UNIBOND, SIMOX, ZMR). (C) 2003 Elsevier Ltd. All rights reserved.

In this paper, a new InP/InGaAs superlattice-emitter resonant tunneling bipolar transistor (SE-RTBT) has been successfully fabricated and demonstrated. The employing of a thin n-InGaAs emitter between InP/InGaAs superlattice and p+-InGaAs base helps to lower potential spike and reduce neutral-emitter recombination current, simultaneously. Furthermore, InP/InGaAs superlattice resulted from tunneling injection can reduce the spread of thermal distribution and non-radiative recombination cross-section. Experimentally, the studied device exhibits a common-emitter current gain as high as 670 and low collector–emitter offset voltage of 60 mV at room temperature. To our knowledge, the device exhibits the largest current gain when compared to the previously reported SE-RTBTs.

It is widely known that under normal bias conditions, GaAs heterojunction bipolar transistor (HBT) device degradation proceeds by a gradual buildup of defects in the base and base–emitter junction depletion regions. The buildup of these defects is associated with a solid-state phenomenon known as recombination enhanced defect reaction, which is the formation and migration of defects associated with nonradiative electron–hole recombination events. These defects are often associated with midgap traps, which serve as additional recombination centers for electron–hole pairs. The resulting increased recombination current is an additional base leakage current, which reduces current gain. By extension, a high electron–hole recombination density in a region with an initially high defect density––such as an unpassivated or poorly passivated base surface––will lead to quick device degradation. This paper reports the modeling of the effects of various different extrinsic base passivation ledge parameters––material composition, thickness, width, and spacing from ledge to base contact––to determine the microscopic effects these parameters have on electron–hole recombination density. Through this we can qualitatively predict the effects these parameters will have on HBT reliability.

In the development of new structures for solar cells, it has become important to extract the true ideality factor of a diode, disentangling it from other loss mechanisms in the device. We use the open circuit voltage decay (OCVD) transient to obtain ideality factors and isolate the internal loss mechanisms in P3HT:PCBM bulk heterojunction solar cells. We compare two different structures using OCVD transients over more than six orders in timescale. The equivalent circuit parameters of diodes can be reliably extracted from such decays. Specifically, the numerical solution of the transient allows the determination of the diode ideality factor, and the saturation leakage current. In addition, this technique makes it possible to determine the diode current in the presence of excess carriers under photo irradiance, and hence, the light induced recombination current and shunt resistance can be separately extracted. We compare the decay transients of an efficient device with a leaky device and demonstrate that th...

We investigate the challenges and potential for high-efficiency n-type Cz Si solar cells having a hybrid structure - a diffused B emitter on the front side, and an amorphous Si heterojunction (SHJ) passivated full-area contact on the rear. This cell design has benefits over comparable high-efficiency geometries such as PERL (passivated emitter rear locally diffused) and SHJ cells with heterojunctions both front and rear. We show that an advantage of the HJ rear contact is excellent passivation of the backside, with measured contact recombination current density J 0,b,c oc > 700 mV. As an initial demonstration of the concept, we fabricate a hybrid-structure cell having V oc = 671 mV, J sc = 36.7 mA/cm2, FF = 0.75 and efficiency of 18.5%.

Electrically active defects in the device region are routinely monitored by CV measurements of reverse-biased field-induced (FI) pn junctions in MOS structures. While useful, this approach is sensitive only to near mid gap defects. Here, we demonstrate a method for interrogation of forward-biased FI pn junctions, which can reveal defect levels over a significantly wider region of the band gap. The method proposed is based on a simultaneous measurement of the gate current and the high frequency gate capacitance in non-equilibrium non-steady state in response to a linear gate voltage ramp which drives the MOS capacitor from inversion equilibrium towards accumulation. This recombination-sensitive technique enables a self-consistent determination of the forward current–voltage characteristic of the FI pn junction. It makes a wider range of important impurities, especially metallic contaminants, accessible to detection by MOS CV approaches. Since the approach satisfies the low-injection condition, the results can be directly related to the properties of the defect centres, thus facilitating defect identification and control.

A method for device characterization is experimented to qualify the relaxable damage in hot-carrier stressing ofn-MOS transistors. The degradation of physical parameters of the body-drain junction of power HEXFETs is presented for applied stress conditionVg=Vd/2. Large decrease of the resistance series, of the ideality factor, and of the reverse recombination current are shown to be related to relaxation time, and are significant atVg=–Vd. These effects are discussed and explained by the evolution of the interface states.

Effects of surface defects on performance of kV-class 4H– and 6H–SiC epitaxial mesa pn junction diodes were investigated. Mapping studies of surface morphological defects have revealed that triangular-shaped defects severely degrade high-blocking capability of the diodes whereas shallow round pits and scratch give no direct impact. The perimeter recombination and generation, instead of the bulk process, are responsible for forward recombination current and reverse leakage current of the diodes, respectively. Effective minority carrier lifetimes are mainly limited not by bulk recombination but by perimeter recombination.

We report the brightness characteristics of KPT-1608PBC (SMD) blue light emitting diodes and the key features of emission propagation through the SMD case. The luminosity pattern of the diode is presented. The external quantum yield is determined as a function of the current through the diode, and the quantum yield is shown to correlate with the mechanism responsible for the recombination current.

Recombination current at the oxide-semiconductor interface of metal-oxide-semiconductor devices has been analyzed and compared with the experimental result. The activity of interface traps is dependent on the energy level and on the operating conditions. A model is shown to be powerful to describe the effect of energy level of bulk recombination centers on the values of reverse recombination current.

A laser operating at low threshold current is indispensable for the construction of superparallel optical interconnections. Initially we examine the current threshold characteristics of surface emitting InGaAs/GaAs lasers, and demonstrate the possibility for working with a threshold current below 100 μA. Next, vertical-cavity AlAs oxide layers are used, since they are helpful in achieving a low threshold surface-emitting laser, and the optimum conditions for forming the AlAs oxide layer are determined. New InGaAs/GaAs surface-emitting lasers with AlAs oxide layer are fabricated and a low threshold current operation of 70 μA is achieved by current injection through micro-domains and reduction of the dark recombination current. Further low threshold current operation should be achievable by fine control and micronization of oxide layers. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(1): 13–20, 1998

Device degradation due to hot-carrier in n-channel HEXFETs is shown to be related to the device geometrical structure. The form of I-V characteristics of the body-drain junction is found dependent of the hot-carrier stressing and of the layer dimensions. A large increases of the ideality factor, of the reverse recombination current, and of the series resistance are shown to be more significant for small values of L and W. It is demonstrated that the degradation of parameters is mainly caused by the generation of interface traps.

This paper reports InP/InGaAs double heterojunction bipolar transistors (DHBTs) made with composite-collector designs. The current gains of the DHBTs without and with emitter edge-thinning designs are 125 and 180, respectively. The composition of the collector and the base currents is analysed from the Gummel plots. Experimental data demonstrate that emitter edge thinning can further reduce the surface recombination current of the InP/InGaAs DHBTs and thus dramatically improve current gain, even though the surface recombination in InP/InGaAs DHBTs is much less than in GaAs-based DHBTs.

Purpose – The purpose of this paper is to investigate the dark properties as a function of reverse current induced defects. Dark characteristics of solar modules are very essential in the understanding the functioning of these devices. Design/methodology/approach – Reverse currents were applied on the photovoltaic (PV) modules to create defects. At several time intervals, dark characteristics along with surface temperature were measured. Findings – Current-voltage (I-V) and capacitance-voltage (C-V) characteristics furnished valuable data and threshold values for reverse currents. Maximum module surface temperatures were directly related to each of the induced reverse currents and to the amount of leakage current. Microstructural damages, in the form of hot spots and overheating, are linked to reverse current effects. Experimental evidence showed that different levels of reverse currents are a major degrading factor of the performance of solar cells and modules. Originality/value – These results give a reliable method to predict most of the essential characteristics of a silicon solar cell or a module. Similar test could help predict the amount of degradation or even the failure of PV modules.