An inorganic-blended p-type semiconductor with robust electrical and mechanical properties

The development of high-performance p-type semiconductors is crucial for advancing complementary metal-oxide-semiconductor (CMOS) technology and various optoelectronic applications. Traditional inorganic semiconductors, however, often suffer from limitations in their p-type behavior due to factors such as the scarcity of holes, the localized valence band maximum (VBM), and strong self-compensation effects. These challenges are particularly pronounced in materials relying on covalent bonding, where high-temperature processing is often required, limiting tunability and flexible integration. While compound semiconductors utilizing ionic or polar covalent bonds show respectable electron mobility, their p-type counterparts lag significantly in hole mobility. This inferior performance is attributed to localized VBMs, self-compensation effects, and poor material stability, as seen in materials like CuOx, SnO, and CuI, where vacancies act as compensating defects that capture holes. This study addresses this critical gap by proposing a novel approach: an inorganic blending strategy to design a high-mobility, air-stable p-type semiconductor. This strategy focuses on utilizing the unique properties of group 16 elements (Te, Se, and O) to create a TeSeO system with tunable properties and superior performance compared to existing p-type semiconductors.

Extensive research has been dedicated to improving p-type semiconductors. Studies on group 14 elements like Si, Ge, and C highlight the challenges of covalent bonding in achieving desirable p-type characteristics and flexible integration. The inherent directional nature of atomic orbitals restricts design flexibility, while lattice mismatch issues further complicate the development of stable and tunable materials. High-temperature processing, frequently necessary for producing high-quality covalent semiconductors, further limits the potential for flexible applications. In contrast, compound semiconductors formed through ionic or polar covalent bonds, often involving transition metal cations, have exhibited promising electron mobility. However, their p-type counterparts consistently show inferior hole mobility, largely due to factors such as localized VBMs, self-compensation, and poor stability. The literature underscores the need for alternative material design strategies to overcome these limitations and unlock the potential of high-performance p-type semiconductors.

This study employed a room-temperature physical vapor deposition (PVD) method combined with post-oxygen implantation to synthesize TeSeO thin films. The Te and Se source materials were mixed and ground before deposition to ensure homogeneous distribution. The ratio of Te and Se was carefully controlled to adjust the resulting properties. Oxygen implantation was performed to introduce oxygen into the TeSe films, forming the TeSeO system. Material characterization techniques, including grazing-incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, ultraviolet photoemission spectroscopy (UPS), and absorption spectroscopy were used to analyze the crystal structure, morphology, elemental composition, chemical bonding, band structure, and optical properties of the synthesized TeSeO thin films. Bottom-gate top-contact (BGTC) thin-film transistors (TFTs) were fabricated using the TeSeO films as the channel layer and Ni as the source/drain electrodes. Electrical characterizations, including output and transfer curve measurements, were performed to determine hole mobility, on/off current ratio, and threshold voltage. The Hall effect measurement was used to determine the carrier concentration and Hall mobility. For photodetector fabrication, a nanosphere lithography process was employed to create nanopatterned honeycomb TeSeO structures on flexible polyimide (PI) substrates. Finite element analysis (FEA) simulations were used to model the mechanical behavior of the nanopatterned structures under bending conditions. Photoresponse measurements were performed using UV, visible, and short-wave infrared (SWIR) light sources to assess the photodetector performance, including responsivity and response time. The long-term stability of the devices was evaluated through extensive testing.

The study demonstrated the successful synthesis of TeSeO thin films and nanostructures with tunable bandgaps ranging from 0.7 to 2.2 eV, achieved by varying the Te/Se ratio. The TeSeO films exhibited a smooth, uniform, and crack-free morphology. XPS analysis revealed the presence of Te-Te, Te-Se, and O-Te-O bonds, with Se content affecting the oxidation state of Te. The optical bandgap was found to increase linearly with increasing Se content. UPS measurements confirmed the p-type conductivity of the TeSeO system across different compositions. TeSeO TFTs exhibited excellent p-channel transistor behavior, with Te0.5Se0.5O0.8 TFTs showing a high hole field-effect mobility (µFE) of 48.5 cm²/Vs and a high Ion/Ioff ratio of ~10⁶. The devices showed negligible hysteresis, indicating low trap density. Wafer-scale TFT arrays demonstrated high uniformity with 100% device yield. The TeSeO TFTs exhibited exceptional long-term stability, showing no significant degradation after 300 days of ambient storage. Nanopatterned honeycomb TeSeO photodetectors on flexible PI substrates demonstrated high responsivity (up to 603 A/W for TeO1.16 at 1550 nm), ultrafast response time (5 µs rise time and 7 µs decay time for Te0.7Se0.3O0.59 at 1550 nm), and excellent flexibility, exhibiting no performance degradation after 6000 bending cycles. FEA simulations confirmed the ability of the honeycomb structure to effectively disperse strain under bending.

This work successfully demonstrates a novel inorganic blending strategy to overcome the inherent limitations of traditional p-type inorganic semiconductors. The synthesized TeSeO system exhibits excellent electrical and mechanical properties, surpassing many previously reported p-type materials. The tunable bandgap, high hole mobility, and robust stability of TeSeO offer significant advantages for various applications. The high performance of the TeSeO TFTs and the exceptional flexibility and speed of the TeSeO photodetectors highlight the potential of this material for next-generation electronic and optoelectronic devices. The findings address the longstanding challenge of developing high-performance p-type semiconductors, paving the way for more balanced and efficient CMOS technology and enabling new possibilities in flexible electronics and optoelectronics.

This study introduces TeSeO, a versatile p-type inorganic semiconductor, fabricated as thin films and honeycomb nanostructures at room temperature. The inorganic blending strategy enables tunable band structures, leading to high hole mobility in TFTs and ultrafast response in flexible photodetectors. The robust stability and performance exceed those of existing p-type thin films. Future research could explore further optimization of TeSeO composition for specific applications and investigate its integration into complex circuits and systems.

While this study demonstrates significant progress, limitations exist. The oxygen implantation process might not be perfectly uniform across the entire film, potentially affecting device-to-device variability. Further investigation into the long-term stability under extreme environmental conditions is needed. The current study focuses on specific device architectures; exploring alternative device designs and integration schemes could further expand the application potential.