ICMCTF 2026 Session PP3-ThA: CVD, ALD, and Laser-based Deposition & Microfabrication Technologies

Interfacial defects remain a significant impediment to the development of high-performance, stable perovskite light-emitting diodes (PeLEDs). This work presents a comprehensive approach to surface and interface control via complementary chemical vapor deposition methodologies. We employ Atomic Layer Deposition (ALD) to fabricate nanoscale, conformal metal oxide layers such as Al₂O₃, ZnO, SnO₂, and NiO that serve as both efficient charge-transport layers and moisture barriers. The self-limiting nature of ALD ensures perfect coverage on complex nanostructures, mitigating current leakage and shunt paths. On the other hand, we use Aerosol-Assisted Chemical Vapor Deposition (AACVD) to deposit the perovskite emissive layer, where the precursor solution mixture ratio controls the composition and crystalline phase. AACVD overcomes the limitations of spin-coating by enabling the deposition of uniform, pinhole-free films over large areas with precise control of cation stoichiometry, thereby enhancing photoluminescence quantum yield (PLQY) and spectral purity. The talk will detail the optoelectronic and morphological characterization of these interfaces and correlate them with the device performance. Our results, demonstrating PeLEDs with improved external quantum efficiency (EQE) and a lifetime extended by an order of magnitude, underscore the transformative potential of combining ALD and AACVD for large-area and low-cost optoelectronic devices.

Modern ambient pressure X-ray photoelectron spectroscopy (AP-XPS), in addition to its real-time sub-monolayer sensitivity, now covers the pressure range typical of standard plasma processing applications, naturally expanding the capabilities of AP-XPS for operando plasma-assisted control. We recently demonstrated that XPS spectra can be successfully collected under plasma conditions, extending the application of XPS to plasma-surface-liquid-vapor interactions [1]. In previous work [2], we highlighted the importance of plasma chamber wall reactions on sample surface chemistry and showed that plasma-XPS can capture plasma chemistry both at the surface and in the gas phase. We recently applied plasma-XPS to industry-relevant and realistic poorly conducting surfaces, where we observed anomalous XPS binding energy shifts due to sample charging during an AC plasma exposure. We propose mechanisms that explain these plasma-induced shifts. Additionally, we noted plasma-induced binding energy shifts and peak splitting when measuring XPS from the plasma gas phase. The latter can be used for local diagnostics of the local plasma environment.

Overall, plasma-XPS metrology is a new emerging tool that offers significant potential for advancing real-time diagnostics of plasma-assisted deposition processes, and immediate mitigation strategies to reduce the damage of wafers, which is a well-known challenge in semiconductor fabrication [3].

References

[1] J.T. Diulus, A.E. Naclerio, J.A. Boscoboinik, A.R. Head, E. Strelcov, P.R. Kidambi, A. Kolmakov, The Journal of Physical Chemistry C, 128 (2024) 7591-7600.

[2] ] J. T. Diulus, A. R. Head, J. A. Boscoboinik, and A. Kolmakov, J. Vac. Sci. Technol. A 43, 040401, (2025)

[3] K.P. Cheung, Plasma charging damage, Springer-Verlag, London, 2000.

However, recent advances in femtosecond laser burst-mode operation (coupling MHz and/or GHz bursts), where multiple ultrashort pulses are delivered in rapid succession, enable precise control over the temporal energy deposition compared to single-pulse irradiation. In this study, we investigate burst-mode ablation of metallic targets, including vanadium and tungsten, under varying burst parameters, using ICCD imaging resolved on the nanosecond timescale. These measurements reveal that intra-burst pulse spacing strongly modulates plasma density, particle emission, and expansion dynamics.

Our results show that GHz burst-mode irradiation produces larger plasmas with controlled vapor plume characteristics, substantially reducing nanoparticle formation and facilitating smoother thin-film deposition. These results are confirmed by thin-film characterizations using electron microscopy and atomic force microscopy, demonstrating the ability to obtain smooth surfaces. This work provides fundamental insights into energy coupling and material removal in fs burst-mode ablation and highlights its potential for tailored plasma-assisted fabrication and optimized vapor deposition processes, particularly for including metals in multilayers or even for optimizing Atomic Layer Deposition.

Gallium Nitride (GaN) vertical power devices are pivotal for next-generation high-voltage applications. A critical challenge in their fabrication, particularly for devices utilizing deep mesa etch termination (DEMT) for field management, is the severe surface damage and trench-like defects induced by aggressive etching processes. These defects become dominant leakage paths, severely degrading breakdown voltage and preventing the realization of ideal avalanche breakdown. Conventional dielectric deposition methods like plasma-enhanced chemical vapor deposition (PECVD) struggle to conformally cover these high-aspect-ratio features, leading to interfacial voids and inadequate passivation.

This work presents a microfabrication strategy to overcome this limitation by employing plasma-enhanced atomic layer deposition (PEALD) for conformal silicon nitride (SiN_x) passivation. We demonstrate the growth of high-quality SiN_x films via an optimized PEALD process using a Si₂Cl₆ precursor under ultra-high vacuum. The process, stabilized at 450℃ and 150 W plasma power, yields films with exceptional uniformity (<±1% thickness variation on a 6-inch wafer), low surface roughness (RMS ~0.3 nm), and near-zero oxygen contamination.

The efficacy of this PEALD-SiN_x film was investigated in GaN vertical Schottky barrier diodes (SBDs) with a 6 µm deep mesa. Cross-sectional HRTEM and EDS analysis confirmed that the PEALD-SiN_x provides a conformal, void-free interface, effectively filling etching-induced trenches and mitigating the underlying damaged GaN layer. In stark contrast, PECVD-SiN_x passivation resulted in a defective interface with significant Si diffusion and incomplete coverage. Electrical characterization revealed a transformative improvement in device performance. SBDs passivated with PECVD-SiN_x alone suffered from severe voltage-dependent leakage, reaching 1 mA at just 80 V without breakdown. Conversely, PEALD-passivated devices exhibited a stable, ultra-low leakage current (~10^-11 A) until a sharp avalanche breakdown at approximately 400 V, a five-fold increase in breakdown voltage and a 10⁴-10⁵ reduction in leakage. Inter-anode leakage measurements further confirmed that PEALD passivation completely suppressed the sidewall conduction path, restoring bulk-limited conduction.

In conclusion, this study establishes PEALD-SiN_x as an essential micro-fabrication technology for enabling high-voltage GaN vertical devices. Its superior conformality and interface quality directly address the core challenge of etching-induced damage, unlocking the full voltage-blocking potential of DEMT structures and paving the way for robust, high-performance GaN power electronics.