Advanced Inorganic Semiconductor Materials, 3rd Edition

1. Introduction

Building upon our previous editions [1,2], the third edition of Advanced Inorganic Semiconductor Materials highlights the rapidly expanding frontier of inorganic and hybrid semiconductors, covering wide-bandgap oxides, functional mixed oxides, tribocatalytic materials, thin-film heterojunctions, ultra-thin chip mechanics, chiral hybrid halides, and luminescent organic–inorganic hybrids [3]. The nine featured contributions (references [4,5,6,7,8,9,10,11,12]) trace innovations at every scale—from atomic-level defect engineering and heterostructure design to macroscopic mechanical stability in ultra-thin devices—demonstrating how versatile inorganic semiconductor materials have become in modern electronics, optoelectronics, catalysis, and sensing [13]. Collectively, these works were contributed by authors from Brazil, Bulgaria, China, Germany, Portugal, Serbia, and Spain, showcasing the globally collaborative nature of semiconductor research.

These papers can be categorized into four major themes:

• Wide-bandgap and transition-metal oxide semiconductors (papers [4,5,6,7,8,9]).
• Mechanical and device engineering for flexible inorganic electronics (paper [10]).
• Hybrid and chiral metal halide semiconductors (papers [11,12]).
• Cross-cutting advances in charge transport, defect engineering, and photophysical mechanisms (spanning all nine contributions).

Below, each category is discussed in detail.

2. Wide-Bandgap and Transition-Metal Oxides: Design, Doping, and Applications

2.1. W-Doped Ga₂O₃ for Conductive Oxide Devices (Paper [4])

In the first contribution, W-doped Ga₂O₃ thin films are deposited via electron beam evaporation, achieving dramatically enhanced conductivity and n-type carrier characteristics without annealing. The increased electron mobility, reduced resistivity, and formation of high-quality heterojunction diodes on both p- and p⁺-Si substrates underscore how aliovalent doping can tune wide-bandgap oxides for power electronics and rectifiers [4].

This work exemplifies a powerful strategy: dopant-induced defect engineering to shift carrier concentration and mobility in ultra-wide-bandgap oxides, which are historically limited by deep donor levels and self-trapping behavior.

2.2. Tribocatalytic ZnO for Antibiotic Degradation (Paper [5])

Kaneva and co-workers advance the field of mechanochemistry by demonstrating a tribocatalytic pathway in which ZnO particles, synthesized by sol–gel and hydrothermal routes, interact mechanically with a PTFE-sealed magnetic stir bar to produce oxidative holes capable of degrading the antibiotic Cefuroxime Axetil even in the dark [5]. Their systematic study shows how stirring speed, magnetic rod geometry, and beaker material influence charge transfer and oxidation kinetics. Rather than treating mechanical agitation as an incidental experimental detail, this work reframes ambient mechanical energy as an intentional activation source for oxidative chemistry. The mechanistic picture—friction-induced electron transfer to the PTFE surface that leaves holes in the catalyst valence band—is supported by comparative activity measurements and highlights opportunities for designing low-energy, light-free processes for water and wastewater treatment.

2.3. Laser-Induced Resistivity Reduction in LaNiO₃ Thin Films (Paper [6])

Cichetto et al. report a versatile post-growth route to tune electrical resistivity in LaNiO₃ films by localized femtosecond laser irradiation [6]. The effect—resistivity reductions ranging from roughly 38% to 52% depending on substrate and temperature regime—appears to stem from locally modified crystallinity and defect populations induced by ultrafast laser pulses. Crucially, this approach provides a maskless, spatially selective method to program electrode resistivity, enabling patterned functionality without additional deposition steps. Such a capability is valuable for non-volatile memory electrodes and other devices where local electrical tuning is required.

2.4. Broadband Photoresponse in MoVO_x Nanobelts (Paper [7])

Ma and colleagues synthesized MoVO_x nanobelts using a one-pot approach and found pronounced broadband photoresponses from visible into the NIR (405–1064 nm) with self-powered operation [7]. V doping both narrows the bandgap and introduces defect states that, together with a strong built-in interfacial field, promote efficient separation of photogenerated carriers and suppress recombination. Notably, the photodetectors retained measurable response after two years of storage, a striking indicator of device robustness. The authors also report a subtle power-dependent inversion of the photocurrent sign, illustrating how the balance between defect populations and photogenerated carriers can produce non-intuitive device responses—an important consideration when engineering mixed-oxide photonic devices.

2.5. SnS/TiO₂ Heterostructure Thin Films for Photocatalysis (Paper [8])

Ding et al. used radio-frequency magnetron sputtering to construct SnS/TiO₂ heterostructured thin films and systematically varied the SnS layer thickness to optimize performance [8]. The optimized heterostructure (approximately 244 nm SnS over 225 nm TiO₂) shows a dramatic enhancement in photoelectrochemical activity—a photocurrent nearly 14 times greater than a pure TiO₂ film of equivalent thickness—and significantly improved dye degradation performance. The improvements are attributed to a type-II band offset [14,15,16] that increases visible light absorption while facilitating carrier separation. This study reinforces that careful control of thickness and interface quality is as important as intrinsic material choice when designing efficient photocatalytic heterojunctions.

2.6. Oxygen-Sensing Mixed Oxides TiO₂–CeO₂ (Paper [9])

Stevanović and collaborators investigate the oxygen-sensing behavior of TiO₂-modified CeO₂ created by high-energy ball milling and show that milling speed and composition strongly influence vacancy concentration, surface chemistry, and sensor performance [9]. XPS provides quantitative insight into surface oxidation states and charging behavior, while electrical testing demonstrates improved sensitivity at modest temperatures relative to pure CeO₂. The work highlights how solid-state mechanochemical processing can be used to tune defect landscapes and electron transport pathways in sensor materials.

3. Mechanics and Integration of Ultra-Thin Chips (Paper [10])

Zheng et al. address a practical but often overlooked challenge: how to integrate brittle inorganic chips as ultra-thin elements within flexible assemblies without premature debonding or fracture [10]. By formulating an energy-based mechanical model that distinguishes debonding and non-debonding regimes, they derive design rules that quantitatively relate chip thickness, interface adhesion coefficient, and bending radius to debonding risk. These theoretical predictions are corroborated with experiments: thinner chips, stronger interface adhesion, and larger bending radii markedly reduce the probability of debonding and chip failure. The study thus provides a practical engineering toolkit for designers of wearable and bendable systems who must reconcile the electrical performance of inorganic semiconductors with mechanical compliance.

4. Hybrid Metal Halides: Chiral and Luminescent Systems

4.1. Chiral OIMHs (Paper [11])

Chiral OIMHs combine structural tunability with unusual chiroptical responses. Zhu and co-authors review synthetic strategies, lattice structures, and mechanisms by which molecular chirality transfers to inorganic frameworks, producing CPL and enabling circularly polarized light detection devices [11]. They discuss the interplay between organic ligand design and inorganic lattice symmetry, emphasizing both the promise of these materials for spin-selective photonics and the practical challenges—particularly stability and integration into device architectures.

4.2. Luminescent OIMHs (Paper [12])

The complementary review by Sheng et al. surveys luminescent OIMHs, focusing on synthetic versatility, photophysical mechanisms, and diverse applications from LEDs to X-ray imaging and information security [12]. The authors synthesize recent advances in exciton management and molecular-level design strategies that deliver high radiative efficiencies. They also highlight unresolved issues such as ion migration, environmental stability, and scale-up that must be addressed for broader technological impact.

Together, papers [11,12] demonstrate how hybrid halides continue to broaden the materials palette for high-performance, solution-processable optoelectronics.

5. Thematic Integration and Comparative Summary

To situate the nine contributions within broader semiconductor research, Table 1 summarizes their key materials, techniques, and application domains, while Table 2 tabulates their performance enhancements.

Table 1. Overview of materials, methods, and applications in the third edition.

Paper/Review	Material System	Key Technique(s)	Main Phenomenon/Property	Application Domain
[4]	W-doped Ga2O3	E-beam evaporation, Hall analysis	High conductivity, n-type transport	Rectifying diodes
[5]	ZnO (sol–gel, hydrothermal)	Tribocatalysis	Dark oxidation of antibiotics	Environmental remediation
[6]	LaNiO3	Pulsed laser deposition + femtosecond laser	Resistivity reduction	Memory electrodes
[7]	MoVOx	One-pot synthesis	Broadband NIR photoresponse, self-powered	Photodetectors
[8]	SnS/TiO2	Magnetron sputtering	Type-II charge transfer	Photocatalysis
[9]	TiO2–CeO2	High-energy milling	Oxygen vacancy tuning	Gas sensors
[10]	Ultra-thin Si chips	Mechanical modelling	Debonding thresholds	Flexible electronics
[11]	Chiral OIMHs	Chiral synthesis	CPL, spin selectivity	Chiral optoelectronics
[12]	Luminescent OIMHs	Hybrid synthesis	Exciton engineering	LEDs, X-ray imaging

Table 2. Comparative performance enhancements.

Paper	Improvement Reported	Magnitude
[4]	Conductivity increase vs. undoped	Orders of magnitude decrease in resistivity
[5]	Cefuroxime degradation rate	Higher at 500 rpm with sol–gel ZnO
[6]	Resistivity reduction	38–52%
[7]	Photocurrent stability	Maintain signal after 2 years, NIR response to 1064 nm
[8]	Photocurrent vs TiO2	13.8×
[9]	Sensor resistance	Mixed oxides lower than pure CeO2

6. Cross-Cutting Insights

A coherent interpretation of the nine articles emerges when examined through shared physical mechanisms and engineering trade-offs rather than by material class alone. Below, we expand the short subheadings used previously into integrated, contextualized discussions that explain why these themes matter for both fundamental understanding and device engineering.

6.1. Defect Engineering as a Design Lever

Across oxides and hybrids, a clear message is that intentional control of defects—oxygen vacancies, aliovalent dopants, and local disorder—is not merely a method for compensating material imperfections but a primary knob for tuning electronic, optical, and catalytic behavior. For wide-bandgap oxides such as Ga₂O₃, W-doping introduces carriers and raises mobility; for MoVO_x, it creates mid-gap states that extend absorption into the NIR and enable zero-bias photodetection; for TiO₂–CeO₂ mixtures, vacancy manipulation directly enhances sensor response. The implication for materials synthesis is that reproducible, quantitative control of defect concentrations should be a central objective in any synthetic workflow, and complementary characterization (Hall, XPS, deep-level spectroscopy) must be used to connect observed device behavior to underlying defect landscapes.

6.2. Interface Engineering Drives Device Function

Interfaces dictate whether photogenerated carriers recombine or contribute to useful currents. The SnS/TiO₂ type-II junction is a prototypical example where careful band-offset alignment accelerates charge separation, converting absorbed photons into measurable photocurrent and catalysis. Similarly, the stability and built-in field at MoVO_x interfaces impart resilience and self-powered behavior. For memory and electrode engineering, the local modification of LaNiO₃ resistivity by femtosecond lasers underscores that the spatially resolved control of interface and near-surface properties can be as important as bulk composition. Taken together, these studies argue for an engineering viewpoint in which the interface is designed in parallel with the bulk material, not as an afterthought.

6.3. Ambient Energy Harvesting and Sustainable Transduction

The tribocatalytic ZnO study demonstrates that mechanical energy—stirring, friction, and surface contact—can directly drive oxidative chemistry. When combined with photovoltaically driven self-powered devices like MoVO_x, a broader paradigm emerges: materials can be engineered to transduce a variety of ubiquitous ambient energies (mechanical, optical, thermal) into chemical or electrical outputs. For environmental and off-grid applications, these low-power or zero-bias operation modes substantially expand the range of feasible deployments.

6.4. Stability, Manufacturability, and Multi-Physics Integration

Many promising demonstrations falter if stability or process compatibility are not addressed. The two-year persistence of the MoVO_x photodetectors and the sputtering-based fabrication of SnS/TiO₂ suggest paths toward manufacturability; however, hybrid halides still face stability and ion migration challenges that limit application. Moreover, the mechanical modeling of ultra-thin chips highlights that long-term performance requires simultaneous attention to electrical, chemical, and mechanical degrees of freedom: bending fatigue, interfacial adhesion, and temperature cycling can all impact device lifetime. Future work must merge in situ diagnostics, accelerated aging studies, and multi-physics modeling to close the gap between lab demonstrations and deployable technologies.

7. Outlook

The research published in this edition illustrates how inorganic semiconductors are rapidly evolving into multifunctional materials platforms. The following directions appear especially promising [17,18,19,20,21]:

• Integration of ultrafast laser processing with oxide electronics.
• Mechanochemical routes for catalytic activation under ambient conditions.
• Self-powered broadband photodetectors for internet of things and autonomous sensors.
• Chiral and hybrid halides with engineered quantum and spin interactions.
• Mechanically compliant inorganic chips for wearable and implantable technologies.

By uniting experimental innovation, theoretical modeling, and practical device demonstration, the nine papers in this edition collectively advance the science and technology of inorganic semiconductor systems.

8. Conclusions

Advanced Inorganic Semiconductor Materials—3rd Edition showcases a diverse, global, and forward-looking collection of works that expand the capabilities of inorganic and hybrid semiconductors across optics, electronics, mechanics, catalysis, and sensing [22]. The insights gained here will undoubtedly guide the design of next-generation materials and devices that are more efficient, sustainable, multifunctional, and integrable than ever before [23], which we hope will contribute to the next edition of this Special Issue—“Advanced Inorganic Semiconductor Materials: 4th Edition” [24].