bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sapphire Substrate Geometrical Effects on III-N Blue LED Material Properties
Authors: Armour Eric A , Hu MingShien , Byrnes Daniel P , Sun Kenny , Papasouliotis George D , Maiocco Lisa B , Brosnan Maureen A , Gasdaska Charles J 
Published: February 2020

Solid-state lighting modules based upon III-N light-emitting diodes (LEDs) are now progressing towards widespread adoption in residential and commercial applications. LED manufacturers are driving die performance and yield upwards while reducing cost. However, color binning due to the sensitivity of the human eye response, which can resolve differences in dominant wavelength within a 2 nm range, remains one of the primary yield and cost limiters. As we continue to improve and understand growth process-related reproducibility, we have observed that some of the within-wafer and wafer-to-wafer characteristics cannot be explained through known physical phenomena from the epitaxy, and are more likely related to substrate properties.
In this presentation, we will analyze a set of experiments designed to understand the effect of (0001) sapphire c-plane substrate physical dimensions (thickness, diameter, bow/warp/TTV, edge beveling) and crystal properties (misorientation, surface roughness) on uniformity and reproducibility of constituent LED layers. Our initial studies have found that precisely controlled crystal misorientation (offcut) towards the m-plane is a significant factor influencing wafer-to-wafer peak wavelength variation, GaN surface roughness, and p-doping levels. Quantitative analysis of these results with respect to variation in typical substrate manufacturing capabilities will be presented; the trends are in agreement with the materials characteristics explored in our previous studies [1, 2]. Warp and bow are critical parameters for control over GaN material characteristics. Furthermore, tight control over the total thickness variation (TTV) is needed to obtain highly uniform, repeatable sub-micron dimensions used to create current patterned substrate (PSS) wafers.
[1] D. Lu, D.I. Florescu, D.S. Lee, V. Merai, J.C. Ramer, A. Parekh, and E.A. Armour, “Sapphire substrate misorientation effects on GaN nucleation layer properties”, J. Crystal Growth
272:353, (2004).
[2] D. Lu, D.I. Florescu, D.S. Lee, V. Merai, A. Parekh, J.C. Ramer, S.P. Guo, and E. Armour, “Advanced characterization studies of sapphire substrate misorientation effects on GaN-based LED device development”, Phys. Stat. Sol.(a)
200:71, (2003).
(Invited) Effects of Environmental Exposure on Stability and Conductance Poly-l-lysine Coated AlGaN/GaN High Electron Mobility Transistors
Authors: Rohrbaugh Nathaniel , Bryan Isaac , Bryan Zachary , Collazo Ramon , Ivanisevic Albena 
Published: February 2020

A study of AlGaN/GaN high electron mobility transistors (HEMTs) was done to assess their implementation as functionalized in situbiosensors [1]. Gallium nitride presents itself as a viable option in sensors which require a high degree of stability in aqueous and biological settings while also being a suitable wide band gap semiconductor for HEMTs [2]. The functionalization of HEMT biosensors bestows high specificity binding groups to the surface enabling characterization of singular biological functions or environmental conditions [3][4]. However, peptide adherence and stability over a given operational cycle are unknown and thus the efficacy and usable lifetime are yet to be determined.
Here, GaN based biosensors were fabricated, functionalized, and then tested with simulated solutions in which the HEMT biosensors would be expected to function. AlGaN/GaN HEMTs were grown via MOCVD (Fig. 1) and functionalized via physisorption of recognition peptides. HEMTs were tested in physiologically relevant solutions as well as controlled solution. Analysis was done upon initial peptide binding via AFM, XPS, and IV measurements. This was repeated after environmental exposure was completed over variable periods of time. The results show the stability of the surface over extended cycles along with the benefits associated with the functionalization of the device. The detailed surface and electrical characterization is essential for quality control and integrity of future sensor development based on GaN devices.

References

[1] M.S. Makowski, and A. Ivanisevic, “Molecular analysis of blood with micro/nanoscale field-effect-transistor biosensors,” Small, 7(14)1863 (2011)
[2] S. Jewett, M.S. Makowski, B. Andrews, M. Manfra, A. Ivanisevic, “Gallium nitride is biocompatible and non-toxic before and after functionalization with peptides,” Acta Biomaterialia, 8(2)728 (2012)
[3] A. Ramesh, F. Ren and P. Berger, “Towards in vivo biosensors for low-cost protein sensing,” Electronics Letters, 49(7) 450 (2013)
[4] M.S. Makowski, I. Bryan, R. Collazo, Z. Sitar, A. Ivanisevic, J. Xie, and C. Arellano, “Kinase detection with gallium nitride based high electron mobility transistors,” Applied Physics Letters, 103(8) (2013)
(Invited) Fundamental Modeling of Radiation Effects in AlGaN/GaN HEMTs
Authors: Patrick Erin , Law Mark E , Li Shun , Hwang Ya-Hsi , Ren Fan , Pearton Stephen J. 
Published: February 2020

AlGaN/GaN HEMTs have high radiation tolerance compared to Si and GaAs transistors. They are also well suited for high power and high frequency applications and thus may be advantageous for satellite-based communication systems. Radiation studies have shown the following DC performance changes: threshold voltage shift (positive), transconductance reduction, and saturation drain current reduction.
The basic phenomenon leading to degradation of DC performance is the creation of point defects such as Ga or N vacancies and subsequent ionization of the traps. We have successfully modeled DC degradation due to radiation effects with FLOODS, a TCAD finite-element simulator. The simulation of trapped negative charges in the GaN buffer layer explained experimental results. As Figure 1 shows, there is a positive shift in threshold voltage that increases with the concentration of negatively charged traps.
Another phenomenon that occurs in irradiated AlGaN/GaN HEMTs is an increase in breakdown voltage and apparent enhanced reliability. The fundamental mechanism for this phenomenon is unclear. We have shown that the negatively-trapped charges in the GaN buffer are not the primary mechanism and that charging at the AlGaN surface is a plausible reason. This work explores the fundamental mechanisms for charging of the AlGaN surface. We look at the transient effects of electron and hole creation during radiation and subsequent interfacial trapping mechanisms.
Figure 1. Positive shift in threshold voltage with respect to trap concentration in GaN buffer layer.
(Invited) AlGaN/GaN HEMT Reliability and Trap Detection Using Optical Pumping
Authors: Cheney David 
Published: February 2020

Although the AlGaN/GaN HEMT continues to draw attention because of its high-thermal stability, extended frequency response, and high break-down voltage, it has not gained the full confidence of designers due to its inconsistent reliability. One of the prominent reliability issues that plague AlGaN/GaN HEMTs is the creation of traps that not only degrade performance, but can lead to device failure. By optically pumping the device, with different wavelengths of light in the visible spectrum (red, green, blue, and violet) and measuring the drain current response, trap energies, trap densities, and time constants are determined.
The light sources used in the optical pumping technique consist of four low power lasers: red, green, blue, and violet. The response of the drain current to the illumination is measured using high-speed data acquisition equipment with sampling rates up to 100k samples/s. In the initial experiments a device was exposed to each laser independently from longest to shortest wavelength, i.e., red then green then blue then violet.
AlGaN/GaN HEMTs with gates ranging from 0.125x150 to 0.170x150 microns were pumped before and after high temperature dc stress. The dc stress was at the bias point of VG=-2 and the channel power was maintained at one watt by adjusting the drain voltage at constant temperature of 150⁰C. Devices that degraded gradually have significant increases in the blue energy range which suggests an increase oxygen on nitrogen substitutional defects [M.A. Reshchikov and H. Morkoc; JAP 97, 061301 (2005)]. Other devices showed degradation with noisy fluctuations in drain current (up to 20 mApp), but when optically pumped, showed very little change from the pre-stress response. Trap creation is not suspected in the degradation in these parts, but may be a result of contact or final metal failure.
Trap energies can be determined by analyzing the decay of the drain current after the part has been illuminated. Curve fitting techniques determine the time constants of the decaying curve and when measured at multiple temperatures, activation energies are determined with Arrhenius analysis. An example using this technique with the blue laser (450nm) at 10 temperatures showed a trap of 0.14eV which the literature suggests a carbon on gallium substitutional [Levinshtein, et al., Properties of Advanced Semiconductor Materials : Gan, Aln, InN, BN, SiC, SiGe, 1st ed. New York: Wiley-Interscience, 2001].
The author gratefully acknowleges the support of a DOD MURI monitored by the AFOSR and colleagues who contributed to this work: Rick Deist, Dr. Brent Gila, and Prof. Steve Pearton.
(Invited) Crystal Defects in Wide Bandgap Semiconductors
Authors: Shenai Krishna , Christou Aristos , Dudley Michael , Ragothamachar Balaji , Singh Rajendra 
Published: February 2020

The state-of-the-art power switching devices made from SiC and GaN semiconductors contain a high density of crystal defects [1]. Most of these defects are present in starting wafers and some are generated during device processing. There is little conclusive evidence so far on the exact role crystal defects paly on device performance, manufacturing yield, and more importantly, long-term field-reliability especially when devices are operating under extreme environments. This paper will review the current state-of-the-art of material defects in SIC and GaN power semiconductors, and the potential role these defects may have on high-density power switching electronics. A review of silicon technology development and manufacturing evolution will be made to draw a parallel between the state of silicon and wide bandgap power electronics.
[1] K. Shenai et al, “Current status and emerging trends in wide bandgap (WBG) semiconductor power devices,” ECS J. Solid State Sci. and Tech.
2(8), N3055-N3063, Jul 2013
(Invited) Hydrogen Sensing Characteristics of Gallium Nitrides with Various Crystal Planes
Authors: Kim Hyonwoong , Baik Kwang Hyeon , Ren Fan , Pearton Stephen J. , Jang Soohwan 
Published: February 2020

Hydrogen has driven great attention as one of the most promising alternative energies. It does not produce any harmful byproducts such as carbon dioxide and nitrogen oxide during the conversion. However, energy conversion using hydrogen is still at research stage due to the possibility of explosion in the air even though it is almost matured in the respect of scientific technology. It is very important to detect low concentration of hydrogen promptly without false alarm in that it can promote the use of hydrogen energy to daily life applications.
Recently, we demonstrated ultra-sensitive hydrogen sensors based on GaN using platinum nano-networks grown by facile solution method. Extremely large surface to volume ratio of nano-networks dramatically improved the sensitivities of the hydrogen sensors. Size, density and distribution of nano-networks can be controlled and optimized by the synthesis conditions and coating methods, and the selective area deposition of platinum nano-networks on the GaN surface was achieved for the fabrication of sensors.
Nonpolar and semipolar GaN is of great current interest due to its promise for eliminating internal electric fields, which exist in conventional c-plane III-nitrides. In the polar crystal orientations, both spontaneous and piezoelectric polarization cause the quantum-confined Stark Effect (QCSE), resulting in the reduction of radiative recombination rate in quantum wells used as active layers in LEDs due to the separation of wavefunctions of electron and hole. There have been recent many reports on growth and fabrication of LEDs with nonpolar and semipolar GaN on SiC, LiAlO2, Al2O3 and bulk GaN substrates.
In this study, we investigated dependence of hydrogen sensing characteristics on various crystal planes of GaN including conventional gallium polar c-plane (0001), nitrogen polar c-plane (000-1), a-plane (11-20), m-plane (1-100), and semipolar plane (11-22). Density functional theory indicates much higher affinity of nitrogen in GaN to hydrogen and stronger bonding. Each plane has its own surface configuration and shows different hydrogen responsivity. In case of (11-22) plane GaN, its current response to hydrogen is very large even though its surface is terminated with gallium atoms, since nitrogens position right beneath the gallium atoms.
Air-Hybrid Dbr Structure for the Improvement of Light Output Power in Algainp-Based LED
Authors: Oh Hwa Sub 
Published: February 2020

In this paper, we report the air gap induced hybrid DBR-based LED (AH-DBR LED) structures for the efficient light extraction efficiency. For verifying the influence of the AH-DBR structures in 630 nm emitting LED devices, we compare two LED structures with conventional and air gap induced hybrid DBRs.
The conceptual light paths reflected from conventional DBR and AH-DBR structures are depicted in Fig. 1. The conventional DBRs mainly reflect the light within the yellow region propagating vertically. However, the reflectivity becomes negligible when the incident angle is larger than the critical angle (θc) and the only small portion of light can be extracted out of chip through side facet. For supplementing this drawback of the conventional DBR structures, air gap is inserted in the side of the DBR structures. In the AH-DBR structures, the incident light larger than the θc can be effectively reflected by the air gap to enhance the light extraction through the side facet of the chip.
To verify the performance of our proposed LED structures, AlGaInP-based LEDs with the conventional DBRs and AH-DBR structures are prepared. Fig. 2 shows the cross-sectional schematics and actual scanning electron microscope (SEM) images of the conventional DBR LED structures and the AH-DBR LED structures. The AlxGa1-xAs DBRs are well etched away to 38 mm in depth and formed relatively well-defined AH-DBR structures as shown in Fig. 2(b). Also, phosphide LED structures are not etched seriously and well maintained.
(Invited) Surface Modification of Wide Band-Gaped Anode of Dye-Sensitized Solar Cells by Ionic Liquid Molecules
Authors: Wu Wei-Lin , Chen Yijia J , Lin Ivan J. B. , Lin Ken , Huang Sheng-Fu 
Published: February 2020

Dye-sensitized solar cells have attracted worldwide attention due to its unique properties such as cost effective, temperature insensitive, and with high quantum efficiency under low illuminations. Among all studies, the topic of replacement of commonly used liquid electrolyte solution to reduce solution leakage becomes one of the emerging research focuses. The replacement of solvent of electrolyte solution by ionic liquid is one of the approaches. The reduced leakage by these approaches is expected to realize yet at the expense of reduced solar cell efficiency, due to lowered charge transfer rates in the electrolyte solutions. However, we found that the partial replacement of commonly used electrolyte solution by imidazolium salt solution enhances the solar cell efficiency instead.
In this study, we report that the surface treatment of the wide band-gaped anode of titanium oxide by ionic liquid molecules accounts for at least part of the solar cell efficiency enhancement. We found that the imidazole-derived molecules act as barrier for electron-hole premature recombination between photoelectrons transported on the conduction band of anode and the holes in the electrolyte on the anode/electrolyte interface. The significant efficiency enhancement is not necessarily due to increased dye adsorption on anodes, because we can manage a reduced dye adsorption condition while the solar cell still provides enhanced efficiency.
The ligand of imidazolium salts plays a very crucial role on the effectiveness of imidazole-derived molecules on the enhancement of solar cell efficiency. The presence of sulfite ligand secures the molecule adhesion on titanium oxide through the sulfite ligand itself.
We would like to present the parameters of treatment of such sequence of imidazole and dye adsorption, the use of solvent, dip duration time, and solution concentration. From the interrogation of the experiment results, we can confirm the exact role of imidazole-derived molecules on the enhancement of the solar cell efficiency.
(Invited) Rare Earth Luminescence in Nanostructured Amorphous Silicon Alloys
Authors: Tessler Leandro R. 
Published: February 2020

Amorphous silicon and its alloys are widely used in semiconductor industry. Due to short range order, doping can be achieved by substituting phosphorus or boron for silicon. Moreover, the optical bandgap can be increased by alloying with C, N or O or decreased by alloying with Ge. Due to its amorphous nature the network can accommodate a variety of elements up to relatively high concentrations at the expense of an increased density of defects in the bandgap. Rare earth elements (RE) have been introduced in the form of trivalent ions in amorphous silicon or its wider bandgap alloys. They present characteristic intra-4f luminescence if their chemical neighborhood is non-centrosymetric and the electric dipole forbidden transitions become partially allowed. In the amorphous alloys excitation through the network can be efficiently achieved when a RE transition corresponds to roughly half the bandgap. The RE act as nucleation centers to induce formation of Si nanocrystals under high temperature annealing.
Samples were prepared by reactive RF sputtering from a Si target partially covered with metallic RE platelets using appropriate reactive atmospheres. Annealing was used either to optimize the photoluminescence or to induce the formation of Si nanocrystals.
We will present characterization by photoluminescence and EXAFS of Er, Nd, Eu and Tb in a-Si:H, a-SiOx:H and a-SiNx:H.
The RE ions tend to occupy low coordination low symmetry sites in the network in the amorphous samples. This favors relatively strong wide photoluminescence lines. The RE present two luminescence lifetimes, the fast component determined by the host and the slow associated to the local symmetry of the RE ions.
Models for the excitation of luminescence and recombination processes and their relation with the local nanostructure around the RE ions will be presented.
(Invited) Lanthanides Fluorides Doped Nanocrystals for Biomedical Applications
Authors: Podhorodecki Artur , Noculak Agnieszka , Banski Mateusz , Sojka Bartlomiej , Zelazo Anna , Misiewicz Jan , Cichos Jakub , Karbowiak Miroslaw , Zasonska Beata , Horak Daniel , Sikora Bozena , Elbaum Danek , Dumych T , Bilyy Rostyslav , Szewczyk M 
Published: February 2020

Introducing to medicine and biology concept of optical markers in tremendous way has changed the recent status of these two important disciplines. This was mainly due to strong development in imaging techniques which recently allow us to investigate both static as well dynamic properties of living cells, their components and their interactions with external factors. Recently used molecular markers including organic dyes, fluorescent proteins or chelates containing lanthanide ions have several significant limitations. One of the alternatives for molecular markers are inorganic quantum dots (ie. CdSe, CdS) which are recently commonly used in many academic works. However, even if they are much better from physico-chemical point of view, from the application point of view at this moment they use is still questionable mainly because of their high risk of toxicity and difficulties in obtaining infrared excitation/emission. One of the solutions, combining advantages of both concepts, is to make nontoxic inorganic nanocrystals doped with lanthanide ions (RENCs).
In this work, we will present optical (photoluminescence (PL), PL excitation, PL decay, FTIR, Raman) and structural (XRD, HR-TEM) results obtained for NaYF4 and NaGdF4 nanocrystals doped with Eu, Er, Tm and Yb ions. Based on obtained results, we will discuss examples of ion-ion interaction like: cross-relaxation, energy migration or up-conversion [1, 2] and influence of these interactions on resultant emission properties of RENCs. Additionally, we will discuss the effect of the nanocrystals surface and their core-shell geometry on the excitation and emission properties of lanthanides in RENCs [1, 3]. Finally, we will discuss a few examples of potential application of RENCs in bio-medicine.

Acknowledgements

The authors would like to thank the Polish National Centre for Research and Development for their financial support under the LIDER project No. 014/L-2/10.

References

[1] A. Podhorodecki, M.Banski, A. Noculak, B. Sojka, G. Pawlik, J. Misiewicz, On the nature of carriers relaxation and ion-ion interactions in ultrasmall
b
-NaYF4 nanocrystals-effect of the surface, Nanoscale 5 (2013) 429.
[2] A. Podhorodecki, M.Banski, J.Misiewicz, M. Afzaal, P. O Brien, D. Cha, X. Wang, The Multicolor light emitters based on energy exchange between Tb and Eu ions co-doped into ultrasmall
b
-NaYF4 nanocrystals, J.Materials Chemistry 22 (2012) 5356.
[3] M. Banski, M. Afzaal, A. Podhorodecki, Jan Misiewicz, Paul O'Brien, Passivation of lanthanide surface sites in ultrasmall NaYF4:Eu3+ nanocrystals, J. Nanoparticles Research 14 (2012) 1228.