Transparent Conductive Oxide Contact Research Articles

Hot Hole Utilization in Au-TiO2 and Au-C3N4-TiO2 Core-Shell Heterojunctions for High Performance Photoelectrochemical Water Splitting

Gold nanoparticles (Au NPs) coated with TiO2 shells exhibit strong localized surface plasmon resonance (LSPR) peaks at ~550-600 nm. The Au plasmons decay in femtoseconds through both interband and intraband damping processes to produce hot electron-hole pairs. These hot carriers have excess energy at room temperature which can be utilized to generate electricity or drive a chemical reaction. However, the hot carriers experience ultrafast recombination and thermal relaxation in hundreds of femtoseconds to a few picoseconds due to electron-electron scattering and collisions with phonons. A Schottky barrier heterojunction between Au and a n-type semiconductor such as TiO2 is an ideal method to separate the hot carrier pairs. In Au-TiO2 Schottky junctions, hot electrons are injected into TiO2 through thermionic emission and/or field emission before recombination and thermal equilibration, at timescales of roughly 250 fs. However the harvesting of residual hot holes in Au remains problematic partly because of the difficulty in forming Schottky junctions between Au and p-type semiconductors. The harvesting of hot holes is particularly important considering that hot holes in Au are on average, more energetic than hot electrons.In this work, we use an innovative photoanode architecture to harvest hot holes. Our photoanode architecture consists of Au NPs coated with a thin layer of amorphous TiO2 and deposited on transparent conductive oxide (TCO)-coated glass substrates. Hot electrons are extracted from the Au into the TCO contact through the TiO2 shell. Hot holes tunnel through the TiO2 to reach the alkaline electrolyte whether they oxidize hydroxyl ions and dissolved oxygen species to generate oxygen. Another novelty is the use of a layer of graphitic carbon nitride (g-C3N4) quantum dots to pump the plasmon through exciton-to-plasmon energy transfer and increase the production of hot carriers. g-C3N4 works to enhance the plasmonic light harvesting due to the excellent overlap between the emission of g-C3N4 and the LSPR absorption band of Au. Photocurrent densities as high as 3.7 mA/cm2 were achieved under AM1.5G one sun illumination with concomitant high Faradaic efficiencies. Photoelectrochemical action spectra collected using filtered AM1.5G illumination and monochromatic LEDs revealed the prominent role of visible photons in water-splitting performed using Au-C3N4-TiO2 core-shell ternary heterojunctions. A key goal moving forward is to replace the noble metal (Au) with transition metal nitride plasmonic absorbers while sustaining the high level of photoelectrochemical performance.

Dramatic Reduction of Contact Resistance via Ultrathin LiF in Two-Dimensional MoS2 Field Effect Transistors.

Molybdenum disulfide (MoS2) has been regarded as one of the most important n-type two-dimensional (2D) transition metal dichalcogenide semiconductors for nanoscale electron devices. Relatively high contact resistance (RC) remains as an issue in the 2D-devices yet to be resolved. Reliable technique is very compelling to practically produce low RC values in device electronics, although scientific approaches have been made to obtain a record-low RC. To resolve this practical issue, we here use thermal-evaporated ultrathin LiF between channel and source/drain metal to fabricate 2D-like MoS2 field effect transistors (FETs) with minimum RC. Under 4-bar FET method, RC less than ∼600 Ω·μm is achieved from the LiF/Au contact MoS2 FET. Our normal 2-bar FET with LiF thus shows the same mobility as that of 4-bar FET that should have no RC in principle. On the basis of these results, ultrathin LiF is also applied for transparent conducting oxide contact, successfully enabling transparent MoS2 FETs.

Heavily Si-doped pulsed sputtering deposited GaN for tunneling junction contacts in UV-A light emitting diodes

We report the characteristics of heavily Si-doped GaN prepared by pulsed sputtering deposition (PSD) and its application as tunneling junction (TJ) contacts for nitride-based light-emitting diodes (LEDs). We determined that the use of PSD allows us to grow extremely heavily Si-doped wurtzite GaN epitaxial layers with [Si] = 1.0 × 1021 cm−3 on commercially available UV-A LED wafers. Then, we processed these samples into LED structures to investigate their device characteristics as TJ-contact LEDs. Compared to commercially available UV-A LEDs with transparent conductive oxide contacts, TJ-contact LEDs with [Si] = 1.0 × 1021 cm−3 at the tunnel-junction interface showed lower differential resistance and, consequently, worked well under a high injection current density of ∼1 kA/cm2 without any degradation. These results indicate that PSD-grown heavily doped n-type GaN is promising for application as a TJ-contact in group III nitride-based optoelectronic devices.

Bifacial photovoltaic performance of semitransparent ultrathin Cu(In,Ga)Se2 solar cells with front and rear transparent conducting oxide contacts

We report the bifacial photovoltaic performance of semitransparent ultrathin Cu(In,Ga)Se2 (CIGS) solar cells with Sn-doped In2O3 front and F-doped SnO2 rear contacts prepared using a single-stage co-evaporation process under front- and rear-illumination conditions. The power conversion efficiencies (PCEs) of the solar cells measured at 100 mW/cm2 increased with increasing ultrathin CIGS absorber thickness (200–400 nm), from 6.89 to 9.75% when front illuminated, and from 4.91 to 6.46% when rear illuminated, while the corresponding average visible transmission values (420–720 nm) gradually decreased from 18.53% to 5.06%. The bifacial photovoltaic performance of semitransparent solar cells with 200-nm- and 300-nm-thick CIGS absorber layers was also investigated under low-light conditions (100–10 mW/cm2). The PCE of the solar cell with a 300-nm-thick CIGS absorber layer remained almost constant with decreasing light intensity (100–10 mW/cm2), at ~8% (front illumination) and ~6% (rear illumination), while that of the solar cell with 200-nm-thick layer decreased from 6.84% to 3.43% (front illumination) and from 4.91% to 2.41% (rear illumination). The enhanced bifacial performance of the solar cell with the 300-nm-thick CIGS absorber layer is attributed to high shunt resistance in the solar cell owing to the improved microstructural qualities.

Influence of Interfacial Oxides at TCO/Doped Si Thin Film Contacts on the Charge Carrier Transport of Passivating Contacts

Minimizing transport losses in novel solar cell concepts is often linked to improvements at the transparent conductive oxide (TCO)/doped silicon contact. A detailed understanding of the determining factors for an efficient transport at this heterojunction is essential, such as work function matching and efficient tunneling transport. In this article, we analyze the different TCO contact parameters experimentally and by numerical device simulations. We show that work function matching by using a proper interlayer [e.g., tungsten oxide (WO x )] can be an effective means to improve the fill factor of silicon heterojunction solar cells. However, we showcase that an improved work function matching achieved by changing the doping of a TCO interlayer can be superimposed by a less efficient tunneling transport, for e.g., due to an interfacial oxide. Furthermore, we show that for n-tunnel oxide passivating contacts, an unintentionally grown oxide at the TCO/poly-Si contact could be a possible explanation for recently observed transport losses.

Energy harvesting performance of bifacial and semitransparent amorphous silicon thin-film solar cells with front and rear transparent conducting oxide contacts

Bifacial and semitransparent hydrogenated amorphous silicon (a-Si:H) thin-film solar cells were prepared with front and rear transparent conducting oxide (TCO) contacts using a plasma-enhanced chemical vapor deposition process. Increased power conversion efficiencies (PCEs) and average visible transmissions (AVTs) in the visible wavelength range were realized in the cases of the bifacial and semitransparent solar cells based on the optimization of the device designs, such as front TCO contacts, intrinsic a-Si:H absorbers (i-a-Si:H), p-type hydrogenated nanocrystalline silicon carbide, and n-type hydrogenated nanocrystalline silicon layers. The dependencies of the performance parameters of the solar cells on the illumination direction and intensity were also investigated systematically. As the film thickness of the i-a-Si:H absorber layers increased from 150 nm to 450 nm, the PCEs of the solar cells respectively increased in the ranges of 6.01–7.50% and 5.25–6.25% when front and rear illuminations were used for a standard light intensity of 100 mW/cm2, while the AVTs decreased from 22.76% to 15.67% irrespective of illumination direction. The best PCEs of the bifacial and semitransparent solar cells that were fabricated with the use of optimal conditions were respectively equal to 7.94% and 6.20% when front and rear illumination conditions were used. The corresponding AVT was equal to 14.34%. The performance parameters of bifacial and semitransparent a-Si:H solar cells at varying illumination intensities in the range of 10–100 mW/cm2 were also investigated, and yielded consistent PCE values in the range of 6.39–6.62% with front illumination, and 4.95–5.15% with rear illumination.

Carrier Dynamics Engineering for High-Performance Electron-Transport-Layer-free Perovskite Photovoltaics

Summary Electron-transport-layer-free (ETL-free) device architectures are promising designs for perovskite photovoltaics because they offer simpler configurations, low cost, and convenience for versatile optoelectronics. However, the development of ETL-free photovoltaics is hindered by their low performance. Herein, we reveal that a low electron-injection rate at the ETL-free interface is responsible for the performance loss. Moreover, we demonstrate that improving carrier lifetimes in the perovskite films can remedy the poor carrier extraction at interfaces, enabling carrier collection efficiency in ETL-free photovoltaics to approach that in ETL-containing devices. Using perovskite films with microsecond carrier lifetimes, we obtained ETL-free devices with a power conversion efficiency (PCE) of 19.5%, nearly eliminated hysteresis, and good stability. Such a PCE value is comparable to that (20.7%) of the analogous ETL-containing photovoltaics. These results offer opportunities for ETL-free architecture designs in the perovskite photovoltaics family. More importantly, this research provides a general approach to improving the performance of photovoltaics with low-injection-rate interfaces.

Large‐Area Chemical Vapor Deposited MoS2 with Transparent Conducting Oxide Contacts toward Fully Transparent 2D Electronics

Abstract2D semiconductors are poised to revolutionize the future of electronics and photonics, much like transparent oxide conductors and semiconductors have revolutionized the display industry. Herein, these two types of materials are combined to realize fully transparent 2D electronic devices and circuits. Specifically, a large‐area chemical vapor deposition process is developed to grow monolayer MoS2 continuous films, which are, for the first time, combined with transparent conducting oxide (TCO) contacts. Transparent conducting aluminum doped zinc oxide contacts are deposited by atomic layer deposition, with composition tuning to achieve optimal conductivity and band‐offsets with MoS2. The optimized process gives fully transparent TCO/MoS2 2D electronics with average visible‐range transmittance of 85%. The transistors show high mobility (4.2 cm2 V−1 s−1), fast switching speed (0.114 V dec−1), very low threshold voltage (0.69 V), and large switching ratio (4 × 108). To our knowledge, these are the lowest threshold voltage and subthreshold swing values reported for monolayer chemical vapor deposition MoS2 transistors. The transparent inverters show fast switching properties with a gain of 155 at a supply voltage of 10 V. The results demonstrate that transparent conducting oxides can be used as contact materials for 2D semiconductors, which opens new possibilities in 2D electronic and photonic applications.

TCO contacts for high efficiency c-Si solar cells: Influence of different annealing steps on the Si substrates and TCO layers properties

Different Transparent Conductive Oxide (TCO) layers properties are evaluated after annealing steps at temperatures above 200°C, in order to study their potential use in crystalline silicon (c-Si) solar cells fabrication processes. While the conductivity of Indium Tin Oxide (ITO) layers obtained by magnetron sputtering (MS) is almost stable after annealing in air, Aluminum doped Zinc Oxide (AZO) layers deposited by Atomic Layer Deposition (ALD) need a controlled atmosphere to maintain high carrier densities and mobilities. During the annealing processes, contaminating atoms (such as Zn) diffuse into the c-Si bulk and may potentially decrease its quality. Thus, both the contamination of the c-Si bulk and the properties of the AZO layer have been analyzed.

(Invited) Zinc Oxide As a Potential Material for Future Electronic Device Applications

Zinc oxide is a II-VI compound semiconductor that is in possession of a unique constellation of interesting material properties. While at the present moment zinc oxide is primarily being used as an electronic material for low-field thin-film transistors, transparent conducting oxide contacts, sensing, and field emitter device applications, recent electron transport work has pointed to the potential of this material for high-field and high-frequency electronic device applications. In this paper, we present some recent results on the steady-state and transient electron transport within zinc oxide, suggesting that this material, having higher peak and saturation electron drift velocities than silicon carbide and gallium nitride, may also be considered as an alternative material to silicon carbide and gallium nitride for high-power and high-frequency field effect transistors. Limits on expectations for zinc oxide based device performance will be projected and contrasted with those expected for silicon carbide and gallium nitride based devices. Upon the basis provided by these results, possible future applications for zinc oxide based devices will be suggested.

Influence of Molecular Aggregation on Electron Transfer at the Perylene Diimide/Indium-Tin Oxide Interface.

Chemisorption of an organic monolayer to tune the surface properties of a transparent conductive oxide (TCO) electrode can improve the performance of organic electronic devices that rely on efficient charge transfer between an organic active layer and a TCO contact. Here, a series of perylene diimides (PDIs) was synthesized and used to study relationships between monolayer structure/properties and electron transfer kinetics at PDI-modified indium-tin oxide (ITO) electrodes. In these PDI molecules, one of the imide substituents is a benzene ring bearing a phosphonic acid (PA) and the other is a bulky aryl group that is twisted out of the plane of the PDI core. The size of the bulky aryl group and the substitution of the benzene ring bearing the PA were both varied, which altered the extent of aggregation when these molecules were absorbed as monolayer films (MLs) on ITO, as revealed by both attenuated total reflectance (ATR) and total internal reflection fluorescence spectra. Polarized ATR measurements indicate that, in these MLs, the long axis of the PDI core is tilted at an angle of 33-42° relative to the surface normal; the tilt angle increased as the degree of bulky substitution increased. Rate constants for electron transfer (ks,opt) between these redox-active modifiers and ITO were determined by potential-modulated ATR spectroscopy. As the degree of PDI aggregation was reduced, ks,opt declined, which is attributed to a reduction in the lateral electron self-exchange rate between adsorbed PDI molecules, as well as the heterogeneous conductivity of the ITO electrode surface. Photoelectrochemical measurements using a dissolved aluminum phthalocyanine as an electron donor showed that ITO modified with any of these PDIs is a more effective electron-collecting electrode than bare ITO.

Optical confinement in chalcopyrite based solar cells

Potential gains in short-circuit current density related to improvements in optical confinement in chalcopyrite based solar cells are studied and quantified by means of optical simulations. In the first part idealised optical conditions – anti-reflection at front interfaces, high reflection at back contact and light scattering - are introduced by simulating realistic scenarios of Cu(In, Ga)Se2 (CIGS) solar cells with 2000nm thick and 300nm ultra-thin CIGS absorber, including the encapsulation at the front. For anti-reflection effect at front interfaces simulations revealed that in the photovoltaic module structure the most critical reflectance is the reflectance of the front surface of the protecting glass (possible 4.4% gain in short-circuit current density) and not the one at the front transparent conductive oxide contact, as in the case of non-encapsulated solar cell. Introduction of a highly reflective, highly diffusive back reflector is the most crucial point to improve the short-circuit current density of the ultra-thin devices. Potential for 15.8% gain in short-circuit current density related to ideal reflectance and additional 17.4% related to ideal scattering introduced at the back contact was revealed. A concrete example of light management structure was investigated in the second part by employing fully three-dimensional rigorous optical simulations. A semi-ellipsoidal texture was introduced to the substrate of the ultra-thin device. By using ZrN back reflector in simulations the gains in short-circuit current density related to the optimised size of the texture reach 10%, whereas in the case of an ideal highly reflective contact the gain is >22% according to simulations.

Epitaxial Sb-doped SnO2 and Sn-doped In2O3 transparent conducting oxide contacts on GaN-based light emitting diodes

We demonstrate the growth of epitaxial (100)-oriented, rutile Sb-doped SnO2 (ATO) and (111)-oriented, cubic Sn-doped In2O3 (ITO) transparent conducting oxide (TCO) contacts on top of an InGaN/GaN(0001) light emitting diode (LED) by plasma-assisted molecular beam epitaxy (PAMBE). Both oxides form rotational domains. The in-plane epitaxial alignment of the two ITO(111) rotational domains to the GaN(0001) was: GaN [21-10]||ITODomain1[‐211]|| ITODomain2[‐1‐12]. A growth temperature as low as 600°C was necessary to realize a low contact resistance between ATO and the top p-GaN layer of the LED but resulted in non-optimal resistivity (3.4×10−3Ωcm) of the ATO. The current–voltage characteristics of a processed LED, however, were comparable to that of a reference LED with a standard electron-beam evaporated ITO top contact. At short wavelengths, the optical absorption of ATO was lower than that of ITO, which is beneficial even for blue LEDs. Higher PAMBE growth temperatures resulted in lower resistive ATO but higher contact resistance to the GaN, likely by the formation of an insulating Ga2O3 interface layer. The ITO contact grown by PAMBE at 600°C showed extremely low resistivity (10−4Ωcm) and high crystalline and morphological quality. These proof-of-principle results may lead to the development of epitaxial TCO contacts with low resistivity, well-defined interfaces to the p-GaN to help minimize contact losses, and enable further epitaxy on top of the TCO.

Improved open-circuit voltage in Cu(In,Ga)Se2 solar cells with high work function transparent electrodes

Hydrogenated indium oxide (IOH) is implemented as transparent front contact in Cu(In,Ga)Se2 (CIGS) solar cells, leading to an open circuit voltage VOC enhanced by ∼20 mV as compared to reference devices with ZnO:Al (AZO) electrodes. This effect is reproducible in a wide range of contact sheet resistances corresponding to various IOH thicknesses. We present the detailed electrical characterization of glass/Mo/CIGS/CdS/intrinsic ZnO (i-ZnO)/transparent conductive oxide (TCO) with different IOH/AZO ratios in the front TCO contact in order to identify possible reasons for the enhanced VOC. Temperature and illumination intensity-dependent current-voltage measurements indicate that the dominant recombination path does not change when AZO is replaced by IOH, and it is mainly limited to recombination in the space charge region and at the junction interface of the solar cell. The main finding is that the introduction of even a 5 nm-thin IOH layer at the i-ZnO/TCO interface already results in a step-like increase in VOC. Two possible explanations are proposed and verified by one-dimensional simulations using the SCAPS software. First, a higher work function of IOH as compared to AZO is simulated to yield an VOC increase by 21 mV. Second, a lower defect density in the i-ZnO layer as a result of the reduced sputter damage during milder sputter-deposition of IOH can also add to a maximum enhanced VOC of 25 mV. Our results demonstrate that the proper choice of the front TCO contact can reduce the parasitic recombination and boost the efficiency of CIGS cells with improved corrosion stability.

Development of plasma-enhanced chemical vapor deposition microcrystalline silicon oxide as a replacement for N-type or back transparent conducting oxide layers in amorphous silicon single-junction solar cells

The n-type hydrogenated microcrystalline silicon oxide (μc-SiOx:H(n)) thin films with varied electrical and optical properties were prepared. We employed μc-SiOx:H(n) as a replacement for n-type hydrogenated amorphous silicon (a-Si:H(n)) or back transparent conducting oxide (TCO) layers in hydrogenated amorphous silicon (a-Si:H) single-junction solar cells. Compared to the standard cell with a-Si:H(n)/ITO/Ag back reflecting structure, the cell using a-Si:H(n)/μc-SiOx:H(n)/Ag or μc-SiOx:H(n)/Ag showed a similar or even better performance. This improvement of cell performance mainly arose from the increased short-circuit current density (JSC) that originated from the increased long wavelength (580–660 nm) absorption in the absorber confirmed by the quantum efficiency measurement. The “all plasma-enhanced chemical vapor deposition ” (if the front TCO and metal contact are disregarded) process without TCO (indium tin oxide, ITO) sputtering can simplify the fabrication and result in better interface quality. Compared to the standard cell, the conversion efficiency of a-Si:H cells using an 80 nm thick μc-SiOx:H(n)/Ag back reflecting structure was enhanced from 9.32% to 9.84%, with VOC = 0.90 V, JSC = 14.84 mA/cm2, and FF = 73.7%.

Impact of transparent electrode on photoresponse of ZnO-based phototransistor

ZnO-based photo-thin film transistors with enhanced photoresponse were developed using transparent conductive oxide contacts. Changing the electrode from opaque Mo to transparent In-Zn-O increases the photocurrent by five orders of magnitude. By changing the opacity of each source and drain electrode, we could observe how the photoresponse is affected. We deduce that the photocurrent generation mechanism is based on an energy band change due to the photon irradiation. More importantly, we reveal that the photocurrent is determined by the energy barrier of injected electrons at the interface between the source electrode and the active layer.

Optimisation of surface treatments of TiO2:Nb transparent conductive coatings by a post-hot-wire annealing in a reducing H2 atmosphere

Transparent and electrically conductive niobium-doped TiO2 thin films have been deposited on glass surfaces by d.c.-pulsed reactive magnetron sputtering from a composite Ti:Nb target, using oxygen as reactive gas. A rapid 1min annealing at 500°C in an atomic hydrogen rich atmosphere, obtained by flowing H2 on a Ta filament resistively heated to 1750°C in vacuum (hot-wire), proved to be very efficient in enhancing the electrical properties of these ~100nm thick TiO2:Nb thin films. Dark conductivity (σd) and its activation energy were measured as a function of (inverse) temperature and the value of σd at room temperature was used to assess the effect of the H2 annealing on the transport properties. A 5-order of magnitude increase in electrical conductivity was observed for optimised treatment conditions at a hydrogen pressure of 10Pa. A maximum value of σd in the range of ~1.4×103S/cm was attained for optimised conditions, where a level of ~6at.% of H doping was measured close to the film surface. X-ray photoelectron spectroscopy, elastic recoil detection analysis, Rutherford backscattering and Raman spectroscopies were used to access information of composition and film structure for the explanation of the strong enhancement of the film's electrical conductivity and band-gap widening to 3.45eV following hot-wire treatments. These thin films can be used as transparent conductive oxide contact layers for photovoltaic applications.

Analysis of a-Si:H/TCO contact resistance for the Si heterojunction back-contact solar cell

Abstract The contact resistance of amorphous Si ( a- Si:H)/transparent-conducting oxide (TCO) is evaluated and analyzed in terms of the contribution to the series resistance ( R s ) and fill factor ( FF ) in the Si heterojunction back-contact (HBC) solar cell. It is shown that p-a- Si:H (emitter) and n-a- Si:H (back surface field: BSF)/TCO contact resistance are of similar values (0.37–38 Ω cm 2 ) which are much higher than those of doped crystalline Si/metal contacts used in conventional Si solar cells. Of some factors affecting R s loss in the HBC solar cell, BSF/TCO contact is the most significant one when considering the contact area. By interleaving the n -type microcrystalline Si ( n-μc- Si) between n-a- Si:H and TCO, 6-inch HBC solar cell with 20.5% efficiency is obtained, which was attributed to the reduced R s and improved FF . It is noteworthy that the variations of R s and FF are well estimated by measuring BSF-contact resistance, and are close to the empirical data: reduction in R s to 1.77 Ω cm 2 and the increase in FF by 6.0% compared to the cell without n-μc- Si interface layer. The results indicate that there is much room for higher efficiency by reducing the emitter- and BSF-contact resistance. Nonetheless, the method developed here can be a powerful tool to analyze the resistance component in HBC cell.

Low-loss amorphous silicon waveguides grown by PECVD on indium tin oxide

Low-loss hydrogenated amorphous silicon (α-Si:H) waveguides were realized by plasma enhanced chemical vapour deposition (PECVD) on a transparent conductive oxide (TCO) layer which is intended to provide the buried contact for the application of an external bias in active devices, e.g. switches and modulators. In particular we propose a technological solution to overcome both the strong reduction in optical transmittance due to the very high extinction coefficient of metal contacts and, at the same time, the optical scattering induced by the texturization effect induced in α-Si:H films grown on TCO. The very high optical propagation losses were minimized by depositing a spin-on-glass (SOG) layer between the α-Si:H core-layer and the TCO bottom contact. In this case, propagation losses of 2.5 dB/cm at 1550 nm were measured. All the fabricated samples were optically characterized and the surface roughness was accurately measured using a mechanical profilometer. We observed that, for an α-Si:H core-layer directly deposited on the TCO contact, the surface roughness is of the order of 100 nm leading to totally opaque waveguides. The experimental performances have been compared to those obtained through calculations using an optical simulation package. The results are found to be in agreement with the experimental data.

On the Light Emission in GaN Based Heterostructures at High Injection

AbstractFor light emitting diodes (LEDs) to be used for general lighting, high efficiencies would need to be retained at high injection levels to meet the intensity and efficiency requirements. In this regard, it is imperative to overcome the observed drop in LED efficiency at high injection levels beyond that would be expected from junction temperature. The suggested genesis of efficiency degradation includes electron overflow or spillover, also suggested to be aided by polarization induced electric field, Auger recombination, current crowding, and elevated junction temperature. Setting the junction temperature aside, the degree to which or even whether each of these mechanisms plays a role is still under debate. We have undertaken a series of experiments to isolate, whenever possible, the aforementioned processes in an effort to determine the causes of efficiency loss at high injection levels. By using 1μs pulsed electrical injection with 0.1% duty cycle, we were able to minimize the effect of the junction temperature. By changing the design of the multiple quantum well region as well as by employing or not employing electron blocking layers, we demonstrated the important role that electron overflow plays on efficiency. Furthermore, by also exploring the same on non polar surfaces and observing any lack of dispersion in terms of the effect of the electron blocking layer we can conclude that the polarization induced field does not seem to play a major role. LEDs on non polar surface with no notable efficiency degradation, up to current densities of about 2250 Acm-2 used for measurements, have been obtained which seems to imply that Auger recombination up to these injection levels is not of major importance, at least in the structures investigated. The effect of current crowding on efficiency droop was investigated by comparing semitransparent Ni/Au p-contacts and transparent conducting oxide contacts (Ga-doped ZnO). Because the latter showed notably reduced efficiency degradation at high injection levels, we can conclude that current crowding plays a role as well.