AVS 71 Session EM-ThP: Electronic Materials and Photonics Poster Session

Titanium nitride (TiN) and its isostructural oxide derivative, Titanium oxynitride (TiNO) has gained interest in industry as a cost-effective alternative material to noble metals and refractory metals with wide range of applications especially in the optoelectronics and plasmonic. However, there still remain some gaps and disagreement in the literature on specific optical and photoelectrochemical properties of TiN and TiNO, due to difficulty and the varying approach in quantifying defects, vacancies, oxidation state and direct impact of impurities in experimental results.

In this study, thin films of TiN and TiNO were synthesized via pulse laser deposition on sapphire. Structural properties of these thin films were investigated using X-ray Diffraction and Reflection (XRD, XRR), X-ray Photoelectron Spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), Raman Spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR). To corroborate our experimental observations, the phonon dispersions and Raman active modes are calculated using the virtual crystal approximation for rutile TiO₂ and rocksalt TiNO and molecular dynamics simulations were used to calculate the phonon density of states. The results shows that the incorporation of nitrogen atoms does not significantly alter the phonon dispersions of rutile TiO₂. However, it results in the emergence of new phonon modes at approximately 7.128 THz (237.65 cm^-1) at the Gamma point, which corresponds to the experimentally observed Multi-Photon Phase-MPP (240 cm-¹-R). From the experimental and theoretical studies, a multilayer optical model has been proposed for the TiN/TiNO epitaxial thin films for obtaining individual complex dielectric functions from which many other optical parameters can be calculated.

This work was supported by a DOE EFRC on the Center for Electrochemical Dynamics and Reactions on Surfaces (CEDARS) via grant # DE-SC0023415. Part of the work has used resources established by the Center for Collaborative Research and Education in Advanced Materials (CREAM) via NSF PREM grant # DMR-425119 PREM.ML and GG are jointly supported by the CEDARS and CREAM projects.

The objective of this study has been to develop high power 850 nm vertical-cavity surface-emitting laser (VCSEL) using oxidation confinement technique. The active layer consisted of three pairs of Al_0.3Ga_0.7As/GaAs semiconductor nanostructures and it exhibited a photoluminance emission wavelength of 835 nm. Distributed Bragg reflector mirror nanostructures of 40 pairs in n-type and 21 pairs in p-type were designed to confine the resonance. The multi-layered epitaxial wafers were further processed by photolithography techniques. Inductively coupled plasma etching was employed to create the platform during the mesa process. Various non-oxidized aperture sizes have been achieved by a wet-oxidation method. The experimental results showed that the VCSEL device exhibited low threshold current of 0.6-0.8 mA. The optical output power was about 6.0-6.8 mW at the injection current of 6 mA. The slope of efficiency was found to be about 3.2~3.7 mW/mA. The corresponding voltage was in the range of 1.7~2.1 V. On the other hand, an eye diagram could be clearly observed under the high data rate of 25 Gbit/sec. The response frequency was measured at 17.1 GHz at -3 dB, also at the injection current of 6 mA. In addition, a high thermal conducting AlN (~230 W/m-K) dielectric bonding substrate was employed to improve device reliability. The related electro-optical characteristics would be presented and further discussed.

Metal halide perovskites (HaPs) have garnered widespread interest for light-harvesting and light-emitting applications due to their exceptional optoelectronic properties and relatively simple fabrication methods. However, like with other semiconductors, HaP-based solar cells lose excess energy through thermalization when absorbing photons with energy that exceeds the absorber bandgap.¹ A promising strategy to reduce these losses and improve photon utilization is to exploit singlet fission, whereby a high-energy singlet exciton formed in an adjacent layer splits into two triplet excitons.^2,3 By transferring these triplet excitons into a HaP film engineered with a composition that aligns the absorber’s bandgap closely with the exciton energy, one can effectively harvest this otherwise wasted energy. In our work, we demonstrate that singlet fission in the molecular semiconductor tetracene (Tc) efficiently generates triplet excitons⁴ that are energetically matched to the bandgap of a Sn–Pb based HaP, offering a viable pathway toward improved device performance.

In this study, we investigate the electronic structure of Sn–Pb-based HaP films and their interfaces with Tc using ultraviolet photoelectron spectroscopy (UPS) and inverse photoemission spectroscopy (IPES). Based on the work by Nagaya et al.,⁵ we introduce a second molecular donor, zinc phthalocyanine (ZnPc), at the interface to engineer a more staggered energy alignment between Tc and the perovskite film, thereby promoting an energetically more favorable sequential electron transfer plus formation of a charge transfer (CT) state (ZnPc⁺ - HaP^-). UPS/IPES measurements suggests that the CT state lies approximately between the Tc triplet energy and the HaPenergy gap, which is favorable for triplet transfer. Complementary photoluminescence (PL) and time-resolved PL (tr-PL) measurements provide guidance for selecting alternative donors with deeper or shallower HOMO levels to replace ZnPc and further refine the interfacial energetics. Moreover, optoelectronic characterization reveals insights into undesirable charge carrier recombination pathways at the organic/HaP interface. Collectively, our results underscore the potential of singlet fission to enhance the efficiency of perovskite solar cells and reduce the cost of the energy that they generate.

1. Shockley, W. & Queisser, H. J. J. Appl. Phys. 32, 510–519 (1961).

2. Smith, M. B. & Michl, J. Chem. Rev. 110, 6891–6936 (2010).

3. Yost, S. R. et al. Nat. Chem. 6, 492–497 (2014)

4. Geacintov, N., Pope, M. & Vogel, F. Phys. Rev. Lett. 22, 593–596 (1969).

5. N Nagaya et al., arXiv preprint arXiv:2407.21093 (2024)

In semiconductor manufacturing, lithography is a critical process in which the mask (reticle) plays an essential role in accurately transferring patterns. Although Inverse Lithography Technology (ILT) offers a powerful way to optimize masks, it typically incurs high computational costs. To address this challenge, deep learning (DL)–based ILT models have been actively explored, with one notable example, Litho-GAN, reporting a 190× speedup in mask generation compared to traditional methods.

However, many recently proposed GAN-based DL-ILT approaches still encounter limitations due to convolution’s restricted receptive field, which can fail to capture sufficient global context and instead focus on local patterns, thereby increasing mask complexity. In response, we introduce an ILT model leveraging the Double Attention mechanism in StyleSwin. By effectively handling both global and local information, our approach maintains the required accuracy while significantly reducing mask complexity.

This study employs LithoBench, a benchmark dataset for evaluating DL-based ILT models. LithoBench contains about 140,000 pattern samples, used to train and assess multiple DL-ILT methods. Its results indicate that the GAN-based DAMO ILT model attains the highest performance. Building on that, we replaced the Deconvolution block in DAMO ILT with the Transformer-based GAN model, StyleSwin, and developed a modified architecture.

In this work, we replaced the Deconvolution layers in DAMO ILT with StyleSwin Transformer blocks. Specifically, the target pattern context extracted via five convolution layers and four residual connections is fed into three stages of StyleSwin blocks to generate an optimized mask. Each stage contains two double-attention blocks that incorporate a style-latent vector. For evaluation, we used the same MetalSet (metal line patterns) dataset employed in previous studies.

Compared to DAMO ILT, which achieved state-of-the-art (SOTA) results in the LithoBench framework, our proposed model maintains the same edge placement error (EPE=5.2) while reducing the shot count by about 15. By incorporating learnable style-latent injections and double attention at each stage, the model introduces controlled noise at the global pattern level, thereby lowering local mask complexity without sacrificing accuracy. These findings suggest that our method can offer valuable insights for future DL-based ILT applications, potentially enhancing not only accuracy but also mask fabrication processes.

We introduce a PE-ALD route for depositing aluminum-zinc oxynitride (AZON) films using alternating pulses of triethylaluminum (TEAl), diethylzinc (DEZ), oxygen plasma, and N₂/H₂ remote plasma. By precisely controlling the oxygen-to-nitrogen incorporation ratio during deposition at, we achieve continuous tuning of the AZON bandgap enable tailored alignment with both valence and conduction bands of the novel material.

In-depth structural and compositional analyses using spectroscopic ellipsometry, Rutherford backscattering (RBS), and grazing incidence X-ray diffraction (GIXRD) confirm that ALD-grown AZON films exhibit uniform density, amorphous character, and atomically sharp interfaces. Ultraviolet photoelectron spectroscopy (UPS) and in situ Kelvin probe measurements reveal controlled shifts in the work function of over 0.8 eV, enabling their application as either electron or hole transport layers depending on the ALD cycle ratio and post-deposition annealing. When incorporated as an electron transport interlayer, between the perovskite and the hole transport layer, AZON-enhanced devices exhibit a stabilized power conversion efficiency (PCE) of 23.8% with negligible hysteresis and retain over 91% of initial performance after 1500 h under continuous 1 Sun illumination. Furthermore, thermally accelerated aging tests reveal suppressed ion migration at the interface, attributed to the passivating nature of the nitrogen-rich surface.

Hybrid halide perovskites such as methylammonium lead iodide (MAPbI₃) offer exceptional promise for ionizing radiation detection due to their high atomic number, strong photon absorption, low trap densities (~10¹⁰ cm⁻³)and excellent defect tolerance. In particular, single-crystal MAPbI₃ stands out for its excellent charge transport properties, including high mobility–lifetime (μτ) products ~1.2 × 10⁻² cm²/V and X-ray sensitivities exceeding 250 μC Gy⁻¹ cm⁻², which are critical for achieving high-sensitivity, low-noise performance in X-ray and gamma-ray detectors.

This study focuses on the growth of MAPbI₃ single crystals dissolving methylammonium iodide (MAI) and lead iodide (PbI₂) in gamma-butyrolactone (GBL), followed by controlled heating to induce crystal formation. Experimental efforts will explore the effects of precursor concentration, temperature ramp rates, and growth dynamics on crystal size, morphology, and electronic characteristics. Theharvested crystals are intended for use in radiation detection and broader sensor applications, and they will also serve as a baseline for future comparisons with triple-cation and doped perovskite systems.

By establishing a reliable and reproducible synthesis and growth protocol, this work aims to produce high-purity, low-defect MAPbI₃ crystals suitable for device integration. Future steps include evaluating charge transport characteristics, assessing detector performance under radiation exposure, and exploring strategies for enhancing long-term material and device stability. The insights gained from this study are expected to contribute to the development of scalable, low-cost perovskite-based radiation detectors with improved resolution and sensitivity.

Tandem CdSeTe thin-film photovoltaic devices represent a promising frontier in solar energy technology, utilizing innovative bandgap engineering to enhance efficiency (>30 %) by broadening absorbing spectrum of impinging light. Although CdSeTe cells have been heralded for their high conversion efficiency (23.1 %), but limitations arise when single-junction designs fail to capture the full spectrum of solar radiation. Tandem devices (dual-junction or muti-junction) address this challenge by integrating multiple subcell absorber layers, each with optimized bandgap energy to selectively absorb different portions of the solar spectrum.

The introduction of alternative subcell absorber layers in the tandem structure is pivotal for expanding device performance by overcoming the fundamental limitation of a single-layer photovoltaic device by capturing larger ranges of wavelength of sunlight. Absorber layers are carefully selected and engineered to achieve bandgap tuning that maximizes spectral overlap while maintaining material compatibility. A top cell has larger bandgap, which can absorb shorter wavelength light. A bottom cell has smaller bandgap, capturing longer wavelength light.

For dual-junction tandem device configurations, we investigated the band alignment of top and bottom subcell materials to achieve the optimized bandgap between two subcells through bandgap engineering. From the theoretical study, bandgaps of dual-junction tandem devices are 1.5 - 1.8 eV and 1.4 - 1.5 eV for top and bottom (CdSeTe) subcells, respectively. The theoretical maximum power conversion efficiency (PCE) is 33.16 %. Multiple top and bottom absorber candidates were explored, including CdZnTe (Eg = 1.75-1.8 eV) and CdMnTe (1.7-1.75 eV) for a top subcell and CdSeTe (1.4 - 1.5 eV) for a bottom subcell. To optimize tandem devices, the current matching technique is used to determine the optimal thickness of each subcell. For the top layers, the thickness of CdMnTe is 450 nm, and for CdZnTe, it is 398 nm. The thickness of the bottom layer is approximately 2.4 um to achieve the best performance in a two-terminal tandem device. With spectral filtering and current matching, CdMnTe/CdSeTe tandem devices demonstrate an open-circuit voltage (Voc) of 1.52 V, a short-circuit current density (Jsc) of 15.7 mA/cm², and a fill factor (FF) of 82.1%, resulting in power conversion efficiency of 19.61 %. In contrast, CdZnTe/CdSeTe tandem devices demonstrate an Voc 1.51 V, Jsc 16.2 mA/cm², and FF 75.52 % with PCE 18.54 %. In summary, the best PCE is MgZnTe 19.61%, indicating that these devices are promising candidates for high-performance tandem solar cells.