Si-based Devices Research Articles

Electroluminescent polycrystalline Er-doped Lu3Al5O12 nanofilms fabricated by atomic layer deposition on silicon

The sub-nanometer composition and interlayer thicknesses of the silicon-based Lu2O3/Al2O3 nanolaminates are regulated by atomic layer deposition, to fabricate polycrystalline Er-doped Lu3Al5O12 (LuAG:Er) nanofilms and optimize their electroluminescence (EL) performance. The Lu:Al ratio in the nanolaminates strongly influences the crystallization temperature and the morphologies of garnet nanofilms, while the ratio sufficiently higher than stoichiometry promotes the crystallization into micrometer grains after annealing above 900 °C. EL devices based on these polycrystalline LuAG:Er nanofilms present the characteristic 1.53 µm EL from Er3+ ions, exhibit the optimal external quantum efficiency of 10.0% and the power efficiency of 0.123%, with fluorescence lifetime measured as 1.2–1.8 ms. The EL efficiencies and lifetime are closely correlated to the Lu:Al ratio and doping concentrations. The electron injection within the LuAG:Er devices is dominated by the Fowler-Nordheim tunneling, resulting in the impact-excitation of doped Er3+ ions and the characteristic emissions. This work explores the deposition of complex oxide nanofilms with designed composition and crystallinity at low temperature, and the development of Si-based optoelectronic devices from garnet films.

Millimeter-scale growth of highly ordered CsPbBr3 single-crystalline microplatelets on SiO2/Si substrate by chemical vapor deposition

Recently, all-inorganic cesium lead bromide (CsPbBr3) perovskite has attracted tremendous interest due to its promise for green light photonic and optoelectronic devices. The growth of high-quality planar micro-/nano-structures of CsPbBr3 on the technologically important silicon substrate is an important issue for these applications, which has not yet been well explored. Herein we fabricate millimeter-scale single-crystalline CsPbBr3 microplatelets (MPs) on SiO2/Si substrate by chemical vapor deposition. A preferred growth direction is demonstrated with the [110] direction parallel to the flux direction of carrier gas. Strong green emission is observed at room temperature with superior photo-stability, long lifetime, and excitonic features. Furthermore, the room temperature whispering-gallery-mode lasing is achieved from the focused ion beam fabricated microdisks with the thresholds comparable to those of pristine square MPs. These results suggest the great potentials of CsPbBr3 MPs for the Si-based photonic devices.

A review of WBG and Si devices hybrid applications

In recent years, next-generation power semiconductor devices, represented by silicon carbide (SiC) and gallium nitride (GaN), have gradually emerged. Because wide-bandgap (WBG) devices have better electrical characteristics than those of silicon (Si) based devices, they have attracted increased attention both from academic researchers and industrial engineers. Employing WBG devices will further improve the efficiency and power density of power converters. However, the current price of WBG devices remains extremely high. Thus, some researches have focused on the hybrid utilization of WBG devices and Si-based devices to achieve a tradeoff between the performance and cost. To summarize the current research on WBG/Si hybrid applications, the issues mentioned above with representative research approaches, results, and characteristics, are systematically reviewed. Finally, the current research on WBG/Si hybrid applications and their future trends are discussed.

Inversion layer electron mobility distribution in fully-depleted silicon-on-insulator MOSFETs

Magnetic-field dependent geometrical magnetoresistance measurements and high-resolution mobility spectrum analysis have been employed to characterise the inversion-layer electron mobility distribution in fully-depleted silicon-on-insulator MOS transistors. The results reveal that the room-temperature electron population in the 12 nm thick Si channel layer is characterised by a broad electron mobility distribution that significantly departs from the ideal single-value discrete carrier approximation. At temperatures below 60 K, the linewidth of the distribution is shown to become significantly narrower, approaching a delta-like function at 30 K. Self-consistent Schrödinger-Poisson numerical calculations suggest that, since the total carrier population at 295 K is comprised of electrons in the ground-state level of the two subband ladders, intervalley scattering and phonon scattering will significantly influence the linewidth of the mobility distribution in the transistor channel. To the best of our knowledge, electron mobility distributions in Si-based devices have not been previously studied nor resolved in such detail.

Investigation of the thermal tolerance of silicon-based lateral spin valves

Improvement in the thermal tolerance of Si-based spin devices is realized by employing thermally stable nonmagnetic (NM) electrodes. For Au/Ta/Al electrodes, intermixing between Al atoms and Au atoms occurs at approximately 300 °C, resulting in the formation of a Au/Si interface. The Au–Si liquid phase is formed and diffuses mainly along an in-plane direction between the Si and AlN capping layers, eventually breaking the MgO layer of the ferromagnetic (FM) metal/MgO electrodes, which is located 7 µm away from the NM electrodes. By changing the layer structure of the NM electrode from Au/Ta/Al to Au/Ta, the thermal tolerance is clearly enhanced. Clear spin transport signals are obtained even after annealing at 400 °C. To investigate the effects of Mg insertion in FM electrodes on thermal tolerance, we also compare the thermal tolerance among Fe/Co/MgO, Fe/Co/Mg/MgO and Fe/Co/MgO/Mg contacts. Although a highly efficient spin injection has been reported by insertion of a thin Mg layer below or above the MgO layer, these thermal tolerances decrease obviously.

Influence of the spatial extent of the space-charge region in c-Si on the electric-field-induced second-harmonic-generation effect

Second-harmonic-generation (SHG) spectroscopy can be used as an all-optical probe of space-charge regions (SCR) in semiconductors such as c - S i by exploiting the electric-field-induced second-harmonic-generation (EFISH) effect. To do so accurately, a thorough understanding of the EFISH effect is needed, and here a detailed model is presented, taking into account the so-far neglected spatial extent of the SCR on the spectral shape of the EFISH contribution. This shows that the spatial extent causes a significant phase shift in the EFISH contribution ranging from 0.1 π r a d to 0.4 π r a d with decreasing SCR strength. This predicted phase shift was verified by dedicated measurements of the spectral SHG phase and intensity of a series of samples covering the typical range of SCR strengths. The spectral SHG response of these samples indeed showed the predicted phase shift in the EFISH contribution and demonstrated that the extent of the SCR cannot be neglected. The obtained insights can result in improved accuracy in the determination of built-in charges near a c - S i interface, which is of interest in the context of semiconductor devices using SHG spectroscopy. Moreover, this refined understanding of the EFISH effect is beneficial in SHG experiments on 2D materials with c - S i serving as a substrate of Si-based photonic devices.

Coherent and incoherent effects of nanopores on thermal conductance in silicene

A fundamentally new approach of manipulating thermal properties is utilizing the wave nature of phonons, which can be realized by introducing secondary artificial periodicity in nanostructures. In this paper, we have studied the heat transport in silicene nanomesh (SNM, a silicene sheet with periodically arranged nanopores), using first-principles calculations and molecular dynamics simulations. The results show the thermal conductivity of SNM is obviously lower than that of silicene. Combining with the analysis of wave and particle characteristics of phonons, we reveal the main reasons responsible for the reduction in thermal conductivity of SNM. The coherent Bragg scattering from the secondary artificial periodicity leads to the reduction in phonon group velocities of LA and optical phonons. Different from the graphene nanomesh reported previously, multiple phonon bandgaps in the optical phonon spectrum of SNM are found for the first time. Moreover, it is noticed that, phonons are scattered not only at the hole boundaries, but also at the interface between the surface and interfacial regions in SNMs. In particular, the out-of-plane vibrations are easier to be scattered at the interface than the in-plane vibrations. This study uncovers the coherent and incoherent phonon transport in SNMs, which would deepen our understanding on heat conduction and shed light on the development of Si-based nanoelectronic devices.

2‐mm‐gate‐periphery GaN high electron mobility transistor s on SiC and Si substrates: A comparative analysis from a small‐signal standpoint

In this paper, a comparative analysis has been conducted on GaN high electron mobility transistor (HEMT) technology on Si and SiC substrates. Small-signal characteristics of 2-mm GaN-on-Si and GaN-on-SiC devices have been investigated. Both devices have the same gate length of 0.5 μm. Special emphasis has been put on the temperature dependence of the buffer/substrate loading effects arising from the Si substrate. As a matter of fact, the “cold” pinch-off admittance (Y-) parameter measurement showed significant loading effect for the Si-based device with respect to the SiC-based one. This has been clearly supported by the analysis of the extracted parameters of the small-signal equivalent-circuit model. The model was also validated by simulating active scattering (S-) parameters, which showed a very good agreement with the corresponding measurements. The results of this paper highlight the impact of buffer/substrate leakage currents on small-signal characteristics and the importance of taking this into account during the modeling phase of the GaN-on-Si HEMT technology. The lower thermal conductivity of this substrate increases the internal temperature, thus stimulating more leakage and reduction of the device power efficiency.

Design analysis of GOS-HEFET on lower Subthreshold Swing SOI

Due to various kind of Band-To-Band Tunneling (BTBT) operation, Heterojunction Tunnel Field Effect Transistors (HEFETs) are widely used in ultralow power applications. Anyhow, circuit complexity is a major issue in case of HEFET based memory development because of their uncomfortable size. Device scaling is a better way to eliminate such kind of issues for HEFET based memory development. Thus, development of Gate-oxide Overlapped Source-HEFET (GOS-HEFET) with lower Subthreshold Swing (SS) based Silicon on Insulator (SOI) is proposed to achieve perfect scaling in this work. Tunneling operation is done with the help of Si-based tunnel devices which are considerably lower than that of MOSFETs. Tunneling rate is enhanced by small bandgap material (Germanium (Ge)) in the source (S) while the ambipolar leakage is minimized by wide band gap material (Silicon (Si)) in the channel. Here, Ge is mainly utilized to dope the source region of P type transistor while Si is used to dope the drain (D) region of N type transistor. Moreover, the tunneling rate of BTBT is enhanced by the geometric alignment of the P and N type transistors with the gate oxide/semiconductor interface. Based on this procedure, five different kinds of SRAM (6 T, 7 T, 8 T, 9 T and 10 T) memory cells are designed. The proposed GOS-HEFET with lower SS on SOI design is implemented using SILVACO TCAD and TANNER CMOS technology. Then, power performance for different temperatures of the proposed method is compared with conventional HEFET based SRAM memory cells.

Phenyl Ethylammonium Iodide introduction into inverted triple cation perovskite solar cells for improved VOC and stability

Abstract The efficiency of more than 25% in organic-inorganic hybrid perovskite solar cells has made them very attractive in the pursuit of cheaper alternatives to Si-based devices. However, the stability of the perovskite solar cells was challenging, given their high susceptibility to moisture. Very few reports have emerged in this regard that investigated the influence of introducing large cations into a triple cation perovskite (TC-PVS), with several studies limited to single and dual cation perovskites. Further, the crystallization of TC-PVS on a polymer surface such as PEDOT is not straightforward, and their inclusion in inverted solar cell devices was limited. In this work, we investigated the impact of incorporating Phenyl ethyl ammonium cation into FAMACs triple cation composition. We demonstrated improvements in the crystallinity and more uniform coverage with little to no pinholes and smooth morphology for an optimum PEA amount of 1.67% in the precursor solution. The superior morphology, along with a passivation effect from a quasi 2D phase, led to increased photoluminescence and minority carrier lifetimes. Corresponding inverted photovoltaic devices prepared with PEA showed increased open-circuit voltage from 0.89 V for a control sample to 0.95 V for 1.67% PEA and 0.98 V for 5% PEA, doped devices in an inverted configuration. The efficiency, as a result, increased from 11.27% for a control device to 14.85% for a 1.67% PEA doped device. Further, PEA doped devices showed improved operational and thermal stability attributed to the higher moisture tolerance and light-soaking ability of the PEA doped TC-PVS compared to the undoped TC-PVS.

Theoretical Prediction of High-Performance Room-Temperature InGaAs/Si Single-Photon Avalanche Diode Fabricated by Semiconductor Interlayer Bonding

Single-photon avalanche diode (SPAD) is an ultrasensitive device for the detection of weak signals. Epitaxial InP-based devices exhibit poor avalanche characteristics and poor compatibility with Si complementary metal oxide semiconductor (CMOS) circuit, and epitaxial Si-based devices show high dark count rate (DCR) and limited detection wavelength. Here we first show a new generation of InGaAs-on-Si SPADs, achieved by semiconductor interlayer bonding, for the detection of 1550-nm infrared signals theoretically. This wafer-bonded InGaAs/Si SPAD has enabled a significant step-change in performance. The dark current of this SPAD is four orders of magnitude lower than that of the epitaxial ones (300 K). High gain-bandwidth-product of 254 and 353 GHz is achieved at the gain of ~ 24 and ~ 36, respectively, for the wafer-bonded SPAD with polycrystalline Si bonding layer at InGaAs/Si bonded interface. In comparison with epitaxial SPADs, the wafer-bonded ones exhibit low DCR ( ~ 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> Hz at 10% V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">br</sub> ), high single photon detection efficiency ( ~ 24% at 10% V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">br</sub> ), and high pulse repetition rate (1 GHz at 5% V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">br</sub> ) at 300 K. These results indicate that utilizing the wafer-bonded platform, the route toward high-performance InGaAs-on-Si SPAD arrays for use in future eye-safe laser radar (LIDAR) and quantum communication at room temperature (RT) is expected to be achieved.

LET and Range Characteristics of Proton Recoil Ions in Gallium Nitride (GaN)

A better understanding of the linear energy transfer (LET) and the range of proton recoil ions in gallium nitride (GaN) is necessary to properly evaluate GaN device radiation tolerance. By analyzing the LET and range of recoil heavy ions in GaN, we can begin to reproduce the body of knowledge that exists for Si-based devices for this upcoming technology. Although the previous data on older technology has impressive depth and breadth, we must be diligent and cautious in the application of these institutional intuitions when applied to emerging technologies such as GaN. As ever increasing materials science advances emerge, a sound methodology for evaluating new technologies must be established in order to apply what we know toward the effort of ensuring radiation tolerance.

Review on Driving Circuits for Wide-Bandgap Semiconductor Switching Devices for Mid- to High-Power Applications.

Wide-bandgap (WBG) material-based switching devices such as gallium nitride (GaN) high electron mobility transistors (HEMTs) and silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) are considered very promising candidates for replacing conventional silicon (Si) MOSFETs for various advanced power conversion applications, mainly because of their capabilities of higher switching frequencies with less switching and conduction losses. However, to make the most of their advantages, it is crucial to understand the intrinsic differences between WBG- and Si-based switching devices and investigate effective means to safely, efficiently, and reliably utilize the WBG devices. This paper aims to provide engineers in the power engineering field a comprehensive understanding of WBG switching devices’ driving requirements, especially for mid- to high-power applications. First, the characteristics and operating principles of WBG switching devices and their commercial products within specific voltage ranges are explored. Next, considerations regarding the design of driving circuits for WBG switching devices are addressed, and commercial drivers designed for WBG switching devices are explored. Lastly, a review on typical papers concerning driving technologies for WBG switching devices in mid- to high-power applications is presented.

Doping of ultra-thin Si films: Combined first-principles calculations and experimental study

This paper presents comprehensive density functional theory-based simulations to understand the characteristics of dopant atoms in the core and on the surface of ultra-thin sub-5 nm Si films. Quantum confinement-induced bandgap widening has been investigated for doped Si films considering two different doping concentrations. Thickness-dependent evolution of dopant formation energy is also extracted for the thin films. It is evident from the results that doping thinner films is more difficult and that dopant location at the surface is energetically more favorable compared to core dopants. However, the core dopant generates a higher density of states than the surface dopant. Projecting the carrier states in the doped Si film onto those of a reference intrinsic film reveals dopant-induced states above the conduction band edge, as well as perturbations of the intrinsic film states. Furthermore, to experimentally evaluate the ab initio predictions, we have produced ex situ phosphorus-doped ultra-thin-Si-on-oxide with a thickness of 4.5 nm by the beam-line ion implantation technique. High-resolution transmission electron microscopy has confirmed the thickness of the Si film on oxide. Transfer length method test structures are fabricated, and the temperature-dependent electrical characterization has revealed the effective dopant activation energy of the ion-implanted phosphorus dopant to be ≤ 13.5 meV, which is consistent with our theoretical predictions for comparable film thickness. Ultra-thin Si films are essential in the next generation of Si-based electronic devices, and this study paves the way toward achieving that technology.

Optoelectronic devices based on the integration of halide perovskites with silicon-based materials

Controlling the preparation of perovskite materials on the Si optoelectronics platform is a crucial step to realize perovskite-based optoelectronic devices. This review highlights the recent progress and remaining challenges in Si-based perovskite optoelectronic devices.

Electroluminescent Y3Al5O12 nanofilms fabricated by atomic layer deposition on silicon: using Yb as the luminescent dopant and crystallization impetus.

Silicon-based Yb-doped Y3Al5O12 garnet nanofilms are fabricated by atomic layer deposition, which are polycrystalline after annealing at 1150 °C. The sub-nanometer compositional regulation and the Yb2O3 cladding layers, which also work as the luminescent dopants, are critical for the crystallization. Characteristic Yb3+ luminescence at 1030 nm and 970 nm is identified under electrical injection, exhibiting the external quantum efficiency of 0.65% and the fluorescence lifetime of 80-200 µs. The doped Yb3+ are impact-excited by hot electrons stemming from Fowler-Nordheim tunneling mechanism within the Y3Al5O12 matrix, with the excitation cross section of 0.7×10-15 to 6.4×10-15 cm2. This work certifies the manipulation of multi-oxide nanofilms with designed composition and crystallinity, revealing the possibility of developing Si-based optoelectronic devices from crystalline garnet films.

Low-Frequency Characteristics of Silicon-Based High-Current Multijunction Thermal Current Converters Fabricated by Wet Chemical Etching

A single-unit thermal converter for precision ac current measurement is desirable because of its relatively small package and low power dissipation. In this article, high-current multijunction thermal converters (HC-MJTCs) on silicon (Si) substrates fabricated by wet chemical etching have been investigated at input rms currents of up to 2 A. The use of wet chemical etching aids the fabrication of a freestanding nitride–oxide membrane, maintaining the Si heat reservoir under the heater of the HC-MJTC intact. Below 10 mPa, the output voltage from the HC-MJTC and the thermal time-constant increase by approximately six times, implying improved efficiency of the thermal current converter. The absolute value of the ac–dc differences of the device was less than $17~\mu \text{A}$ /A over input current levels of up to 2 A at frequencies above 100 Hz. However, input current level-dependent ac–dc differences were observed at frequencies below 400 Hz even under vacuum. This behavior originated primarily from a change in the electrical resistance of the heater in this Si-based device. Therefore, these low-frequency ac–dc differences can be substantially compensated using the measured ac and dc electrical resistances of the heater.

Selectively Grown III-V Lasers for Integrated Si-Photonics

Epitaxially integrating III-V lasers with Si-photonics is the key for compact, efficient, and scalable photonic integrated circuits (PICs). Here we present an investigation of a path forward in integrating III-V functionalities on industry-standard silicon-on-insulator (SOI) platforms using selective area hetero-epitaxy. Based on our recently developed methods of selectively growing device quality InP on (001)-oriented SOI wafers, we demonstrated InP stripes and segments, with dimensions varying from a few hundred nanometers to a few micrometers. The flexible epitaxy of InP on SOI together with the unique “bufferless” trait will enable efficient light interfacing with Si-based photonic devices using either evanescent or butt coupling schemes. We simulated the possibility of employing the micrometer-scale InP on insulator to realize electrically driven lasers and found that the metal induced optical loss is negligible when the InP dimension exceeds 4.0 μm. The potential of utilizing this selective area growth method to realize fully integrated Si-photonics is illustrated.

(Invited) 200mm GaN Power: Technology and Commercialization Status on Scalable QST® Platform

In recent years, GaN has become a forefront wide bandgap semiconductor material for next-generation, energy-efficient power electronics. With its higher breakdown strength, faster switching speed and lower on-resistance, GaN power devices can convert power far more efficiently than Si-based devices. While its performance is commercially demonstrated, widespread GaN adoption requires a scalable and high-yielding manufacturable technology platform enabling economies of scale and a full spectrum of low-cost products such as lateral and vertical power switches extending from 100V to 1,200V and beyond, monolithic ICs and rectifiers.QROMIS’ disruptive commercial solution to high volume, low cost and scalable GaN device manufacturing has been steadily gaining traction, owing to unique properties of specially-designed CMOS fab-friendly and semi-spec substrate called “QST®” (QROMIS Substrate Technology) with a core having a thermal expansion that very closely matches the thermal expansion of the GaN/AlGaN epitaxial layers. QST® enables breakage-free high-volume manufacturing of standard semi-spec thickness 200mm GaN device wafers (scalable to 300mm), covering all GaN applications including 100V-to-1800V high performance power devices, RF devices, and display microLEDs.In this talk, the following status updates on 200mm QST®-based materials and device technologies will be presented: (1) commercial QST® substrate products, (2) commercial GaN-on-QST® epi-wafer products, including development studies on epi-wafers for 1,200V and beyond applications, (3) high-performance normally-off 650V p-GaN based GaN-on-QST® HEMT transistors & monolithic ICs (with integrated drivers and logic) fabricated in a CMOS fab and commercialization timelines, (4) 200mm GaN-on-QST® device foundry services for the industry players, and (5) initial high-performance GaN-on-QST® RF device results.

Crystal quality degradation in MoTe2 monolayers by a thermal annealing and its suppression by hexagonal boron nitride encapsulation

Two dimensional transition metal dichalcogenides (TMDs) have attracted great research interests owing to a crossover to a direct gap upon reduction of the layer number down to a monolayer (1L) and exciton formation at room temperature based on extraordinarily large binding energy. In particular, a semiconducting molybdenum ditelluride (MoTe2) emits photons in the near-infrared region around 1.1 eV. Furthermore, it has a strong spin-orbit coupling to result in the longer spin and valley relaxation, providing a path to practical Si-based optoelectronic device applications. However, the 1L-MoTe2 crystal has some drawbacks such as surface oxidation within several days owing to its poor structural stability and crystal defect formation by a thermal annealing at a low temperature of 200 °C. It is reported that encapsulation by hexagonal boron nitride (hBN) prevents the oxidation of 1L-MoTe2 in air. There are few reports on effects of a thermal annealing on structural stability in hBN-encapsulated 1L-MoTe2. In this study, we investigate the effects of a thermal annealing on the crystal quality of hBN-encapsulated 1L-MoTe2 by a photoluminescence (PL) measurement at low temperatures. We demonstrate that hBN encapsulation is effective for suppression of crystal defect formation in 1L-MoTe2, improving thermal stability.Bulk hBN crystals were grown using a temperature-gradient method at a high pressure (4.0-5.5GPa) and high temperature (1500-1750 °C). Monolayer MoTe2 and multilayered hBN flakes were exfoliated from bulk crystals and were prepared on a polydimethylsiloxane (PDMS) sheet. We fabricated two types of sample structures on a 100-nm-thick SiO2/Si (100) substrate by a standard dry transfer technique using these flakes. The first sample comprised 1L-MoTe2 directly deposited on the SiO2/Si substrate. The second sample comprised 1L-MoTe2 encapsulated by hBN. The fabricated sample structures were thermally annealed at temperatures ranging from 100 to 200 °C for 15min in an atmosphere.Figures 1(a) and 1(b) show the PL spectra at 25K of the SiO2-supported and hBN-encapslated 1L-MoTe2, respectively. These PL spectra are reproduced using multi-Voigt functions to evaluate PL peak intensities in each spectrum. PL emissions attributed to neutral exciton (X0), charged exciton (T), and defect-bound excitons (XB1, XB2) are observed in both samples of SiO2-supported and hBN-encapsulated 1L-MoTe2. We identify these MoTe2 crystals as monolayers from the X0 PL peak position of 1.19 eV. Figure 1(c) shows the trion spectral weight (I T /I tot) plotted as a function of the annealing temperature for the SiO2-supported and hBN-encapsulated 1L-MoTe2. For both sample structures, the I T /I tot values decreases by the thermal annealing at 200℃, implying the decrease in excess carriers in 1L-MoTe2. The excess carriers should originate from impurities and residues adsorbed on the 1L-MoTe2. Thus, the thermal annealing makes it possible to reduce the impurities and residues, realizing high-quality sample structures. Figure 1(d) shows the PL intensity ratio (I XB1 + I XB2)/I X0 plotted as a function of the annealing temperature. Here, I XB1, I XB2, and I X0 are PL intensities of XB1, XB2, and X0 peaks, respectively. For the SiO2-supported 1L-MoTe2, the (I XB1 + I XB2)/I X0 value increases by increasing the annealing temperature while it is kept to be almost constant for the hBN-encapsulated 1L-MoTe2. It is reported that the XB1 and XB2 peaks are attributed to the formation of Te vacancies by a thermal annealing and adsorption of O2 and H2O molecules at the crystal defect sites, respectively. Therefore, an increase in the (I XB1 + I XB2)/I X0 value of the SiO2-supported samples should result from the crystal defect formation in 1L-MoTe2, indicating a large density of non-radiative recombination centers at 200 °C. In contrast, for the hBN-encapsulated samples, the Te vacancy formation and adsorption of O2 and H2O molecules at the crystal defect sites should be avoided owing to the top hBN acting as the capping layer to suppress Te atom desorption.In summary, we investigated the effect of a thermal annealing on a PL spectrum for SiO2-supported and hBN-encapsulated samples. It was found that the thermal annealing at 200 °C were able to remove residues and impurities on the 1L-MoTe2. For the SiO2-supported samples, an increase in the (I XB1 +I XB2 )/I X0 value was seen by the thermal annealing, indicating crystal defect formation due to desorption of Te atoms. In contrast, for the hBN-encapsulated samples, it was kept to be almost constant even after the thermal annealing at 200 °C. It was therefore concluded that the hBN encapsulation should improve the thermal stability in 1L-MoTe2. This work was partly supported by JSPS KAKENHI Grant Numbers JP25107003, JP25107004, JP15K21722, JP26248061, JP25107002, JP16H00982, and JP20H00354 and the CREST (JPMJCR15F3), JST. Figure 1