Purpose: To test the hypothesis that rod photoreceptor mitochondria function in vivo progressively declines over time.

Methods: 2, 12, and 24 mo dark- and light-adapted C57BL/6J (B6J) mice were examined by OCT. We measured i) an index of mitochondrial configuration within photoreceptors measured from the profile shape aspect ratio (MCP/AR) of the hyperreflective band posterior to the external limiting membrane (ELM)], ii) a proxy for energy-dependent pH-triggered water removal, the thickness of the ELM-retinal pigment epithelium (ELM-RPE), and its correlate iii) the hyporeflective band (HB) signal intensity at the photoreceptor tips. Visual performance was assessed by optokinetic tracking.

Results: In 2 mo and 24 mo mice, MCP/AR in both inferior and superior retina were smaller in light than in dark; no dark-light differences were noted in 12 mo mice. Dark-adapted inferior and superior, and light-adapted superior, ELM-RPE thickness increased with age. The dark-light difference in ELM-RPE thickness remained constant across all ages. All ages showed a decreased HB signal intensity magnitude in dark relative to light. In 12 mo mice, the dark-light difference in HB magnitude was greater than in younger and older mice. Anatomically, outer nuclear layer thickness decreased with age. Visual performance indices were reduced at 24 mo compared to 2 mo mice.

Conclusions: Whilst the working hypothesis was not supported herein, the results raise the possibility of a mid-life adaptation in rod mitochondrial function during healthy aging in B6J mice, a plasticity that occurred prior to declines in visual performance. 


Do Multiple OCT Biomarkers Indicate Age-related Decline in Rod Mitochondrial Function in C57BL/6J Mice? 

Purpose: Age-related macular degeneration (AMD) is characterized by pathologic extracellular lipid-rich deposits below and above the retinal pigment epithelium (RPE), respectively termed drusen and reticular pseudodrusen (RPD). Given apolipoprotein E (apoE) is one of the major components in drusen and RPD, the polarity of apoE secretion by the RPE likely contributes to whether RPD, drusen, or both dominate in an AMD patient. The mechanism dictating the polarity of apoE secretion in the RPE remains unknown. However, ATP-binding cassette A1 (ABCA1), a lipid transporter expressed in the RPE, is required for maintaining extracellular apoE levels in hepatocytes, where ABCA1 and apoE are both polarized to the sinusoidal side of the cell. We therefore investigated whether localization of ABCA1 in the RPE dictates the polarity of apoE secretion and if modulation of ABCA1 levels or function can alter extracellular apoE levels.

Methods: Human fetal (hf) RPE were plated on Transwells to allow for separate manipulation of the apical and basolateral sides of the RPE. To induce preferential apical apoE secretion, we applied two treatments we have shown will alter apoE secretion polarity: the addition of serum to only one chamber and aging cultures for more than a year. Immunocytochemistry (ICC) was then used to assess the localization of ABCA1 in hfRPE. ABCA1 was colocalized to phalloidin, an apical marker, and MCT3, a basolateral marker. Accumulation of secreted apoE was evaluated by Western Blots of the apical and basolateral media. ABCA1 expression was determined by Western Blot after treatment with Liver X Receptor (LXR) agonist, which upregulates ABCA1 expression, and after treatment with probucol, a ABCA1 inhibitor.

Results: ICC of hfRPE under conditions that favored apical apoE secretion did not show a corresponding shift in apical localization of ABCA1. In general, whether apoE secretion was polarized or not, ABCA1 had a fairly even distribution between the apical and basolateral RPE membranes. Treatment of hfRPE with LXR agonist upregulated ABCA1 but did not increase or switch the polarity of apoE secretion. Treatment with probucol caused a decrease in ABCA1 expression but no consistent effects on apoE secretion.

Conclusions: We demonstrated that the localization of ABCA1 in hfRPE is not related to the polarized secretion of apoE. Further experiments will probe other candidate mechanisms governing the polarity of apoE secretion in the RPE.

ABCA1 is Not Responsible for Polarized ApoE Secretion in the RPE

Ferroelectrics functioning at reduced dimensionality have long been pursued for the rich physics behind, including domain wall motion and energy transfer, charge compensation, phase stability, strain and interface coupling, as well as the devices enabled for highly scaled, energy efficient, multifunctional memory/sensing/computing devices and architectures. The emergent nitride ferroelectrics, including ScAlN and ScGaN, have been proposed as promising ferroelectrics with wide and tunable bandgap, large polarization and high tunable coercive field, with potentially high compatibility with both GaN and Si technology. For this new class of ferroelectrics, the ferroelectric wurtzite phase is energetically stable at room temperature, making it highly possible to maintain ferroelectric order in nitride ferroelectrics even at extremely reduced dimensionality. In this work, the thickness scaling down behavior of ScAlN thin films in the thickness range of 100 nm to 5 nm, has been studied to reveal the ferroelectric order in nitride ferroelectrics at reduced dimensionality. The ScAlN samples were grown by molecular beam epitaxy (MBE) on CMOS-compatible Mo/Si substrates. Reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD), and scanning transmission electron microscopy (STEM) confirmed the wurtzite structure of the as-grown films. The ferroelectric properties of the as-grown films have been confirmed and investigated by capacitance-voltage (C-V) loops and positive-up-negative-down (PUND) measurements. An increase in the coercive field and a significant reduction of remnant polarization are found when the ferroelectric layer is scaled down to below 20 nm. Significantly, a switching voltage of 2-3.8 V, and a saturated remnant polarization of ~23 µC/cm2 are measured in ~ 5 nm thick ScAlN. X-ray diffractions and transmission electron microscopy studies suggest that the increase in the coercive field and diminishment in switchable polarization can be attributed to the naturally formed surface oxide and the compressive strain in ultrathin ScAlN films due to a larger in-plane lattice constant of ScAlN compared to Mo (011). Our work sheds light on the fundamental thickness-scaling properties of epitaxial ferroelectric ScAlN thin films and paves the way for next-generation compact and power-efficient devices and applications based on nitride ferroelectrics.

Epitaxial Ferroelectric ScAlN—Thickness Scaling to the Nanometer Scale

Extreme bandgap (EBG) semiconductors such as AlxGa1-xN (x>0.6, bandgap energy EG > 4.88 eV) are ideal for high power, high voltage, and high temperature power electronics. Their critical breakdown field (Ec) in lateral devices scales as EG2.5, leads to an estimated value of the Baliga’s Figure of Merit (BFOM) significantly higher than that for GaN[1],[2],[3],[4] For achieving high BFOM, in addition to a large breakdown voltage (VBR), a simultaneous low device specific ON-resistance(RON,SP) is also required. For the EBG AlxGa1-xN channel HEMTs to have a low RON,SP , a 2-dimensional electron gas (2DEG) concentration >1x1013 cm-2 is needed, requiring a barrier AlxGa1-xN layer with x > 0.80. At such high value of “x”, it is challenging to make linear ohmic contacts due to large Schottky barrier height between metal-AlGaN interface. To solve these issues, we demonstrate EBG n-Al0.87Ga0.13N-Al0.64Ga0.36N heterostructures over bulk AlN substrate grown by Low Pressure-MOCVD. To facilitate ohmic contact formation, highly doped reverse-graded AlGaN layer(x=0.87 to 0.40) was grown in-situ. Reciprocal Space Map(105) and AFM analysis revealed pseudomorphic epilayers with step-flow morphology and RMS roughness ~0.18 nm. X-Ray Topography estimation of control sample gave us a TDD ~ 7 x 103 cm-2, indicating the high quality of our pseudomorphic epilayers. A planar Zr-based metal stack was deposited and subsequent removal of the reverse graded n-AlxGa1-xN layer in the access region gave linear ohmic contacts, RC~4.3 Ω-mm. Additionally, planar metal-oxide-semiconductor (MOS) diodes were fabricated and 2-terminal gate-source breakdown measurement was performed. A VBR of 739 V was measured at metal flashover point for 0.65 µm gate-source spacing, giving an electric field value ~ 11.37 MV/cm. From the breakdown data and the RON,SP (~2.4 × 10-4 Ω-cm2) value, we estimate the BFOM for our EBG n-Al0.87Ga0.13N-A0.64Ga0.36N heterostructures to be as high as 2.27 GW/cm2. This, to the best of our knowledge is the highest reported value to date for an extreme bandgap AlxGa1-xN (x>0.6) channel heterostructure.[5] References [1] B. J. Baliga, IEEE Electron Dev. Lett., 10, 455 (1989). [2] R. J. Kaplar, A. A. Allerman, A. M. Armstrong, M. H. Crawford, J. Ray Dickerson, A. J. Fischer, A. G. Baca, and E. A. Douglas, ECS J. Solid State Sci., 6, Q3061 (2016). [3] T. Nanjo, A. Imai, Y. Suzuki, Y. Abe, T. Oishi, M. Suita, E. Yagyu, and Y. Tokuda, IEEE Trans. Electron Devices, 60, 1046 (2013). [4] N. Yafune, S. Hashimoto, K. Akita, Y. Yamamoto, H. Tokuda, and M. Kuzuhara, Electronics Lett., 50, 211 (2014) [5] K. Hussain et al., Appl. Phys. Express (2023)

High Figure of Merit Extreme Bandgap Al0.87Ga0.13N-Al0.64Ga0.36N Heterostructures Over Bulk AlN Substrates

In this work, epitaxial wurtzite phase BAlN films were grown by nitrogen plasma molecular beam epitaxy on different wurtzite phase substrates (e. g. nitrided sapphire, β-Nb2N film, GaN template). Effect of different growth parameters on composition of BAlN films was explored. B incorporation was found to increase with decreasing substrate temperature and with increasing B flux. In-situ electron diffraction and ex-situ x-ray diffraction measurements confirm the growth of wurtzite BAlN films at 300 in plane orientation with sapphire substrate and at 00 orientation with bottom Nb2N films. With increasing boron content in BAlN films, the c-parameter decreases while the a-parameter shows a non-monotonic trend. Ferroelectricity (with remnant polarization of ~16 μC.cm–2 and coercive field of ~1.45 MV.cm-1) and high dielectric constant (of ~18 at 500 kHz) were also observed in these BAlN films. A slight reduction in bandgap is seen with increasing boron content in BAlN films (from ~6.12eV for AlN films to ~5.95eV for B0.15Al0.85N film). This work also reports the first demonstration of polarization-induced two-dimensional electron gas (2DEG) in the epitaxial BAlN/GaN heterojunctions. Observation of ferroelectricity with low coercive field, remnant polarization (lower than the sputtered BAlN [1] and comparable to MBE grown AlScN films [2]) and high-k, makes BAlN an attractive barrier in GaN high electron mobility transistors (HEMTs). Therefore, BAlN/GaN heterostructures were grown on 2” and 3” wafers; showing polarization-induced 2DEG with good sheet resistance of ~650 ohm/sq, ~400-500 cm2/V.s mobility (400-500 cm2/V.s), and 1.4-1.8 e13 cm-2 charge. The results presented in this paper demonstrates MBE growth of BAlN films and heterostructures with interesting properties that would enable new electronic devices. These films could be useful for combining memory and logic functionalities in digital electronics and to mingle epitaxial ferroelectric and high-k barrier technology into RF and mm-wave power electronics. For instance, a new class of ferroelectric HEMTs devices can be formed by integrating epitaxial ferroelectric, high-k nitride barrier with III-V nitride semiconductors [3].

MBE Growth, Characterization of BAlN Films and 2D Electron Gas in Epitaxial BAlN/GaN Heterojunction

Recent research efforts have unlocked substantial improvements in the performance and reliability of InAs quantum dot lasers on silicon by mitigating the effects of active-region-adjacent misfit dislocations through the introduction of defect trapping layers (TLs). These TLs enable lifetimes of lasers on silicon comparable with those grown on native GaAs substrates. Even so, current state-of-the-art lifetimes still fall somewhat short of requirements for more widespread adoption as both types of lasers exhibit gradual degradation in performance with aging. In this work, we demonstrate that this gradual degradation is a result of the generation of point defect populations during aging, which, over time, coalesce into dislocation microloops which we characterize using scanning transmission electron microscopy (STEM). We selected a single high-performing laser from each of three large aging sets of QD lasers (1) on silicon with TLs, (2) on silicon without TLs (no-TL)), and (3) on native GaAs. Each selected device was aged for between 8700 and 12,000 h at 80 °C at a current density between 1050 and 1900 A cm-2, depending on the initial threshold current and output power. After 2700 h, the no-TL device had doubled its initial threshold current (a common metric for device failure), and after 5700 h it failed to lase entirely. The TL device and the GaAs device, however, show threshold current increases of just 35% and 46% respectively after 8700 h with extrapolated lifetimes of 45,000 h and 75,000 h. Note, however, that these numbers are not directly comparable due to somewhat harsher aging conditions for the GaAs device. After aging, the devices were imaged using backside electroluminescence to check for signs of inhomogeneous degradation. For all lasers, degradation appeared largely homogeneous aside from dark line defects associated with misfit dislocations in the devices on silicon. There are also regions of decreased luminescence throughout the structure for the two devices on silicon, which we attribute to misfit dislocations lying parallel to the laser ridge for the no-TL device and to misfit dislocations escaped from the TL for the TL device, as confirmed by plan-view STEM of these regions. With sufficient thinning of the plan-view foils, dislocation microloops with diameters ranging from 5 to 20 nm are visible both in the [001] zone imaging condition overlaid with the QD contrast and more clearly in various g-3g STEM weak beam imaging modes where competing QD contrast is minimized. In the no-TL device in regions within 100-150 nm of the heavily climbed misfit dislocations, there is a dramatic increase in loop density on the order of 1010 cm-2. We believe this to be the result of a large density of point defects expelled by the misfit dislocations as they undergo climb. Thus, degradation caused by climbing misfit dislocations is multifold: first an increase in total misfit length and second the generation of a high density of point defects which coalesce into microloop defects surrounding the misfit dislocation, all of which substantially enhance non-radiative recombination processes. Meanwhile, the TL and GaAs device active regions, though largely or entirely free of climbed misfit dislocations, are still observed to contain microloop densities on the order of 108–109 cm-2, which likely accounts for the gradual, homogeneous degradation observed in these devices. These microloops coalesce from elevated point defect populations in the active region, and while there are many remaining questions, such as whether these point defects are pre-existing or are generated during aging, this work points the way for future routes to improve device and material quality.

Gradual Degradation via Dislocation Microloop Formation in InAs Quantum Dot Lasers on Si and GaAs

Supply and Cost of Substrates for Compound Semiconductors

There is little debate nowadays about the merit of GaN or SiC material for Power Electronics applications compared to the Silicon-based technologies. Power supplies and power inverter continue to drive most of the Wide Bandgap material adoption with Gallium Nitride used nowadays in nearly every power supply and Silicon Carbide as the material of choice for high efficiency power inverters for long range Electric Vehicle (EV). To enable such widespread adoption into new applications, MOCVD equipment needs to ensure not only to meet the tightest material performance requirements but also to provide solutions enabling cost reduction year after year. In addition, the current semiconductor ramps, and material constraints are accelerate the transition to larger substrate size and the focus on integrability into Silicon factory as well as tool productivity per unit for clean room floor area. We will present how AIXTRON is addressing those markets with new series of high throughput solutions for Wide Bandgap materials and how this contribute to bolst the output of existing factories.

New high throughout solutions for Wide Bandgap power semiconductors

The introduction of magnetism in topological insulators, semiconducting materials that are non-magnetic by nature, has long been sought after in order to realize exotic quantum effects. Most prominent is the quantum anomalous Hall effect (QAHE), where electronic surface states allow the dissipationless propagation of charges through a material [1]. Additionally, these states are 100% spin-polarized and immune to external perturbations, rendering them ideal candidates for spintronic applications as well as quantum computing.

The QAHE is not restricted to a particular temperature range but has so far only been observed at around 1 K in magnetically doped topological insulators [2]. Thus, the task at hand is to find new concepts to magnetize the topological insulator. Here, we investigate a new approach based on proximity induced magnetization in heterostructures, where the topological insulator Bi2Te3 and the topologically trivial, magnetic add-layer MnTe share an interface but are otherwise spatially separated [3]. We employ polarized neutron reflectivity, x-ray spectroscopy and magnetotransport measurements to evaluate the magnetic properties of each individual layer and the magnetic landscape at the MnTe/Bi2Te3 interface. We find the MnTe layer in a ferromagnetic instead of the anticipated antiferromagnetic state and that Mn constituents penetrate into the Bi2Te3 layer. Those effects go often unnoticed and can be misinterpreted as proximity induced magnetization, for which no indication can be found. Hence, we provide a robust, multitechnique approach to gain a complete picture of the magnetic structure and the toolbox to optimize the interface, thereby increasing the temperature range the QAHE can be observed in. Our work thus contributes to the transformation of magnetic topological insulators from fundamental research to practical applications. 
**References** [1] F. D. M. Haldane, Phys. Rev. Lett. 61, 2015 (1988) 
[2] C. Z. Chang et al., Science 340, 167 (2013) 
[3] G. Awana et al., Phys. Rev. Mater. 6, 053402 (2022) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/d5c679f3ec59791ae675f12a8a018980.png)

A toolbox for evaluation and optimization of proximity induced magnetism in MnTe/Bi2Te3 heterostructures

Rare-earth magnets may provide useful magnetic properties for quantum technologies, including quantum transduction and quantum memories. Here we calculate the band structure of magnons in ferromagnetic Er2O3. Erbium, in the +3 state in this material, has 11 electrons in a 4f shell which are shielded from the surroundings by valence electrons. The localization of these 4f electrons around the ion core results in long coherence times that make Er2O3 a viable candidate for emerging technologies and devices such as quantum memories, single photon emitters and transduction [1].

We consider fully saturated Er2O3 as a ferromagnetic insulator that hosts magnons and approximate the interaction of the spins as magnetic dipole-dipole interaction. Similar models will describe other dipole-dipole interactions spins, such as ensembles of molecular spins. The Holstein-Primakoff representation is employed to quantize the Hamiltonian. Er2O3 has 32 erbium atoms in a non-primitive cubic unit cell. The long-range nature of magnetic dipole-dipole interaction poses a challenging issue for considering magnonic structure from dipole-dipole interactions. The dipole-dipole interaction drops as a cube power of the separation between spins, thus the strength of the coupling of the 30th nearest neighbor is 4.3% of the first nearest neighbor while the number of neighbors increases. If these long-distance neighbors are ignored the magnonic dispersion will drastically change. We will describe approaches to reach convergence in the magnon dispersion for such long-range interactions.

This work was supported as part of the Center for Molecular Quantum Transduction, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award Number DE-SC0021314. 
**References** [1] Zhong, Tian and Goldner, Philippe. "Emerging rare-earth doped material platforms for quantum nanophotonics" Nanophotonics, vol. 8, no. 11, 2019, pp. 2003-2015.

Magnonic dispersion of Er2O3

Interest in superconducting computing is being driven by two concerns. On the one hand, large-scale computing facilities and data centers are using electrical power at an ever-increasing rate. Projections suggest that a fully superconducting computer would consume considerably less power than conventional semiconductor-based computers [1]. On the other hand, a quantum computer based on superconducting qubits would benefit from having a classical superconducting processor nearby in the cold space, to avoid a plethora of control and readout lines between room temperature and the cold space [2]. Building a large-scale memory for a superconducting computer is a challenge. One approach is to use Josephson junctions containing ferromagnetic materials as the basic memory element for such a memory [3]. In that approach, the information storage device is a Josephson junction containing a pseudo spin valve. Depending on the relative orientation of the two magnetizations in the spin valve, and with suitably chosen thicknesses of both magnetic layers, the ground-state phase difference across the junction can be either zero or π. We have demonstrated two different types of junctions that can be controllably switched between the 0-phase state and the π-phase state [4,5]. While such junctions are promising components for a scalable superconducting memory [6], much more work needs to be done to enable scaling of this approach to a large-scale memory array.
Work supported by the US DOE under grant DE-FG02-06ER46341, by Northrop Grumman Corporation, and by IARPA via U.S. Army Research Office contract W911NF-14-C-0115. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the ODNI, IARPA, or the U.S. Government. 
**References** [1] D.S. Holmes, A.L. Ripple, & M.A. Manheimer, IEEE Trans. Appl. Supercond. 23, 1701610 (2013). 
[2] E. Leonard et al., Phys. Rev. Applied 11, 014009 (2019). 
[3] A.Y. Herr & Q.P. Herr, US Patent 8,270,209 (2012). 
[4] E. C. Gingrich, B. M. Niedzielski, J. A. Glick, Y. Wang, D. L. Miller, R. Loloee, W. P. Pratt Jr., and N. O. Birge, Nature Phys. 12, 564 (2016). 
[5] J.A. Glick, V. Aguilar, A. Gougam, B.M. Niedzielski, E.C. Gingrich, R. Loloee, W.P. Pratt, Jr., and N.O. Birge, Science Advances 4, eaat9457 (2018). 
[6] I. M. Dayton et al., IEEE Magnetics Lett. 9, 3301905 (2018).

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Do Multiple OCT Biomarkers Indicate Age-related Decline in Rod Mitochondrial Function in C57BL/6J Mice?

ABCA1 is Not Responsible for Polarized ApoE Secretion in the RPE

Epitaxial Ferroelectric ScAlN—Thickness Scaling to the Nanometer Scale

High Figure of Merit Extreme Bandgap Al0.87Ga0.13N-Al0.64Ga0.36N Heterostructures Over Bulk AlN Substrates

MBE Growth, Characterization of BAlN Films and 2D Electron Gas in Epitaxial BAlN/GaN Heterojunction

Gradual Degradation via Dislocation Microloop Formation in InAs Quantum Dot Lasers on Si and GaAs

Supply and Cost of Substrates for Compound Semiconductors

New high throughout solutions for Wide Bandgap power semiconductors

A toolbox for evaluation and optimization of proximity induced magnetism in MnTe/Bi2Te3 heterostructures

Magnonic dispersion of Er2O3

Ferromagnetic Josephson Junctions for Cryogenic Memory

Packaging and integration of wide bandgap power semiconductors

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