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

The study addresses the longstanding challenge that many inorganic semiconductors exhibit poor p-type performance due to localized valence band maxima, self-compensation by intrinsic defects, and stability issues, which hamper complementary devices and circuits. Conventional covalent semiconductors (e.g., Si, Ge) are constrained by directional bonding, lattice mismatch sensitivity, and high-temperature processing, limiting bandgap tunability and flexible integration. In contrast, ionic/polar-covalent compound semiconductors often show respectable electron mobility but inferior hole mobility. The authors propose a new inorganic blending strategy combining group-16 elements Te, Se, and O—chosen for similar s2p4 configurations and compatible radii—to engineer a p-type system (TeSeO) with tunable properties. Te provides intrinsic high hole mobility pathways (Te–Te/Te–Se covalent chains), Se tunes bandgap and crystallinity, and O introduces O–Te–O polar covalent bonding to enhance durability. The purpose is to realize room-temperature, wafer-scale, band-tunable, and robust p-type thin films and nanostructures for electronics and optoelectronics.

Background work indicates that in transition-metal oxides and halides (e.g., CuOx, SnO, CuI), high concentrations of anion vacancies act as compensating defects that trap holes, leading to poor p-type transport. Conventional strategies to tune bandgaps and band edges in p-type semiconductors are limited: dopant incorporation can introduce donor-like defects and disturb thermodynamic equilibria, often counteracting p-doping and degrading mobility. Prior reports show high electron mobility in amorphous/crystalline ionic or polar-covalent compounds, but achieving comparable p-type mobility has remained difficult. Tellurium, with high intrinsic hole mobility and small effective mass, and selenium alloys have been explored for tunable optoelectronics (including SWIR photodetectors), while TeO2 provides a wide bandgap and stability. The present work integrates these components to overcome limitations noted in earlier literature by blending p-type semimetal (Te), p-type semiconductor (SexTe1−x), and p-type wide-bandgap semiconductor (TeO2) within one system.

Synthesis: TeSeO thin films were fabricated at room temperature via thermal evaporation of mixed Te/Se precursors followed by post oxygen implantation. Te (99.997%) and Se (99.99%) powders were premixed and ground; due to higher Se vapor pressure, the precursor contained less Se than the target Te/Se film ratio (examples: to target Te/Se = 7/3, 5/5, 3/7, the Se powder percentages in the source were 17%, 38%, and 55%). TeSe deposition rate: 2 Å/s; chamber pressure: <4×10−6 Torr; thickness controlled by quartz crystal monitor. Oxygen implantation: plasma system (PC-150), 30 W RF power, O2 flow 50 sccm, pressure 0.26 Torr, duration 60 s. Characterization: Crystallinity by grazing-incidence XRD (Cu Kα, 1° incidence). Microstructure by HRTEM (JEOL 2100F) and SAED; elemental mapping by EDS in STEM (JEOL JEM-ARM300F2). Surface morphology by SEM and AFM (10×10 µm scans). Chemical states by XPS (Te 3d, O 1s, Se 3d) and band alignment by UPS; samples Ar+ etched prior to measurements; XPS calibrated to C 1s at 284.8 eV. Optical bandgaps from absorption spectra via Tauc plots. Device fabrication: Bottom-gate top-contact TFTs on p+-Si/50 nm SiO2; patterned channels (~10 nm TeSeO) and 70 nm Ni source/drain (W/L = 100 µm/40 µm). Electrical characterization with Agilent 4155C; linear-regime field-effect mobility µFE = L gm / (W Ci VDS), with Ci from parallel plate model (ε=3.9, d=50 nm). Hall measurements via Ecopia HMS 5300 (0.54 T, van der Pauw). Nanosphere lithography: Close-packed PS nanosphere monolayers (600 nm diameter, 10 wt%) assembled at water-air interface and transferred to PI substrates as masks. Oxygen plasma etch (O2 50 sccm, 0.26 Torr, 30 W, 45 s) shrank spheres to ~500 nm. After TeSeO deposition, lift-off in toluene (ultrasonic 60 s) produced honeycomb nanomesh with ~100 nm inter-aperture wire width. FEA: ABAQUS simulations modeled honeycomb TeSeO on PI under bending to 1.5 mm radius. Linear elastic model: TeSeO E=31.1 GPa, ν=0.33; PI E=2.5 GPa, ν=0.39. Slip neglected; maximum principal strain distribution extracted. Photodetector measurements: UV (261 nm), visible (532 nm), and SWIR (1550 nm) lasers used; power measured by Thorlabs PM400. Responsivity R = Iph / (Popt A); rise/decay times defined as 10–90% and 90–10% transitions of peak photocurrent. Mechanical bending tests up to 6000 cycles for nanomesh devices; stability tests included on/off switching cycling and long-term ambient storage (~300 days) without encapsulation.

• Composition–structure: GIXRD shows Te-rich films (Te:Se ≥ 7:3) are polycrystalline; Se-rich (Te:Se ≤ 6:4) become amorphous. Peak shifts to higher angles with more Se indicate lattice contraction; increased FWHM evidences reduced crystallinity. HRTEM/SAED corroborate polycrystalline-to-amorphous transition with added Se; no O-related crystalline phase detected, suggesting amorphous oxides.
• Chemical bonding: XPS reveals Te4+ and Te0 coexistence; Te4+/(Te4++Te0) decreases from ~58% (TeO1.16) to ~25% (Te0.3Se0.7O0.15) with increasing Se, indicating Se suppresses Te oxidation. No Se4+ peak observed; O 1s at ~530.2 eV indicates lattice O–Te–O. Bonds summarized: Te–Te and Te–Se (covalent) enabling hole transport and bandgap modulation; O–Te–O (polar covalent) providing stability.
• Band structure: Optical bandgap tunable from 0.7 to 2.2 eV across compositions, covering UV–visible–SWIR. UPS shows Fermi levels below mid-gap and close to VBM across all samples, confirming p-type nature. VBM shifts nearly linearly with composition; CBM exhibits strong bowing (~1 eV) with composition.
• TFT performance: p-channel operation across compositions. Te0.9Se0.1O0.98 shows high conductance/“always-on” due to high hole density. Optimized Te0.8Se0.2O0.8 device exhibits µFE = 48.5 cm2/(Vs), Ion/Ioff ~10^6, low hysteresis. Other compositions: Te0.9Se0.1O0.98 (µFE 65.5 cm2/(Vs), Ion/Ioff ~10^2, VTH ~25 V); Te0.7Se0.3O0.59 (µFE 23.1 cm2/(Vs), Ion/Ioff ~10^4, VTH ~5.3 V). Wafer-scale 10×10 arrays show 100% yield with µh = 48.2 ± 8.4 cm2/(Vs), Ion/Ioff 10^4–10^5, VTH = 4.2 ± 1.3 V.
• Robustness and stability: Negligible hysteresis indicates few traps. On/off switching exhibits stable performance over extensive cycling. Long-term ambient storage (300 days, no encapsulation) shows no discernible degradation in current, mobility, or hysteresis.
• Photodetectors: Honeycomb TeSeO nanomesh on PI delivers broadband response. Under 1550 nm SWIR, responsivity reaches 603 A/W (TeO1.16) and 225 A/W (Te0.7Se0.3O0.59), outperforming intrinsic Te PDs and comparable to state-of-the-art wideband PDs. Ultrafast response with rise/decay times of 5/7 µs at 1550 nm (10 kHz chopping) without signal distortion.
• Mechanical flexibility: FEA indicates strain dispersion in honeycomb channels at 1.5 mm bending radius. Experimental bending up to 6000 cycles shows no photocurrent deterioration for nanomesh devices, whereas flat films crack and fail under bending.

The inorganic blending of Te, Se, and O creates a p-type semiconductor system where Te–Te/Te–Se networks provide high hole mobility pathways, Se tunes the bandgap and crystallinity, and O–Te–O bonding enhances environmental and operational stability. This design yields p-type thin films with room-temperature, wafer-scale processability, bandgaps spanning 0.7–2.2 eV, and Fermi levels close to VBM across compositions. Device-level results validate the approach: TFTs achieve high µFE and large Ion/Ioff with excellent uniformity and long-term stability, addressing the typical limitations of p-type thin-film semiconductors (low mobility, instability, self-compensation). Nanopatterned honeycomb structures further enhance mechanical resilience and speed due to increased surface-to-volume ratio and strain accommodation, enabling high-responsivity, µs-scale SWIR photodetection on flexible substrates. Collectively, these findings directly address the research aim of realizing robust, scalable, and tunable p-type semiconductors for complementary electronics and high-speed flexible optoelectronics.

This work introduces TeSeO as a room-temperature, wafer-scalable, p-type inorganic semiconductor platform with continuously tunable bandgaps (0.7–2.2 eV), high hole mobility (up to ~48.5 cm2/(Vs) in optimized TFTs with Ion/Ioff ~10^6), excellent uniformity and long-term ambient stability, and strong optoelectronic performance (responsivity up to 603 A/W and 5/7 µs response at 1550 nm) in mechanically robust honeycomb nanostructures. The inorganic blending strategy (Te semimetal + Te–Se semiconductor + TeO2 wide-bandgap component) offers a generalizable route to engineer p-type transport and durability beyond existing thin-film systems. Future research directions include: integrating TeSeO with n-type counterparts for complementary circuits; optimizing composition and oxygen content for threshold control and reduced always-on behavior; contact engineering and interface passivation to further boost mobility and reduce traps; extending nanopattern designs for enhanced light management; reliability studies under extreme environments and accelerated aging; and exploring heterostructures/hybrids for multifunctional (opto-)electronic systems.

• Composition-dependent trade-offs: Te-rich films (e.g., Te0.9Se0.1Ox) exhibit high hole density leading to always-on TFT behavior, which may limit low-power switching without further threshold engineering.
• Structural transition: Increasing Se content drives a polycrystalline-to-amorphous transition that can reduce mobility relative to Te-rich compositions.
• Spectral response: Se-rich devices show weak SWIR response compared to TeO1.16, indicating composition-specific performance windows that may constrain broadband applications without device stacking or grading.
• While long-term ambient stability (300 days) is demonstrated, extended reliability under high temperature, high humidity, and bias stress beyond the reported conditions remains to be assessed.