Xingjun Wang

Chinese Academy of Sciences | CAS · Shanghai Institute of Technical Physics

A photodetector based on a hybrid dimensional heterostructure of laterally aligned multiwall carbon nanotubes (MWCNTs) and multilayered MoS2 was prepared using the micro-nano fixed-point transfer technique. Thanks to the high mobility of carbon nanotubes and the efficient interband absorption of MoS2, broadband detection from visible to near-infrar...

Strain engineering is a powerful tool that can modulate semiconductor device performance. Here, we demonstrate that the bandgap of thin film (∼40 nm) black phosphorus (bP) can be continuously tuned from 2.9 to 3.9 μm by applying an in-plane uniaxial strain, as evidenced by mid-infrared photoluminescence (PL) spectroscopy. The deduced bandgap strain...

With the further miniaturization and integration of multi-dimensional optical information detection devices, polarization-sensitive photodetectors based on anisotropic low-dimension materials have attractive potential applications. However, the performance of these devices is restricted by intrinsic property of materials leading to a small polariza...

Manganese-cobalt-nickel oxides (Mn-Co-Ni-O) materials have been widely applied as infrared detectors due to its superior thermistor properties and one-dimensional Mn-Co-Ni-O nanowires are expected to significantly enhance the detecting performance. We herein present a novel approach for successfully growing Mn0.79Co1.71Ni0.50O4 nanowires with Au as...

It is challenging to obtain wafer-scaled aligned films for completely exploiting the promising properties of semiconducting single-walled carbon nanotubes (s-SWCNTs). Aligned s-SWCNTs with a large area can be obtained by combining water evaporation and slow withdrawal-induced self-assembly in a dip-coating process. Moreover, the tunability of depos...

GaAs‐based semiconductors are highly attractive for diverse nonlinear photonic applications, owing to their non‐centrosymmetric crystal structure and huge nonlinear optical coefficients. Nanostructured semiconductors, for example, nanowires (NWs), offer rich possibilities to tailor nonlinear optical properties and further enhance photonic device pe...

High-quality lattice-matched and mismatched strained GaAs1−xSbx (0.37 < x < 0.57) sub-micrometer epilayers are grown on InP by molecular beam epitaxy. Based on a heat conduction model regarding the heat transfer process between the thin GaAsSb films and thick InP substrates, the corresponding thermal conductivity of GaAsSb epilayers was accurately...

NiMn2O4 (NMO) thin films with different thicknesses (0.47–1.90 μm) were grown on Yttria-stabilized zirconia (YSZ)(100) substrates by chemical solution deposition (CSD). The effects of different growth conditions on the structural and thermal properties of NMO films were investigated. X-ray diffraction (XRD) and atomic force microscopy (AFM) measure...

High-index semiconductor nanoantennae represent a powerful platform for nonlinear photon generation. Devices with reduced footprints are pivotal for higher integration capacity and energy efficiency in photonic integrated circuitry (PIC). Here, we report on a deep subwavelength nonlinear antenna based on dilute nitride GaNP nanowires (NWs), whose s...

All-inorganic cesium lead halide perovskite quantum dots have recently received much attention as promising optoelectronic materials with great luminescent properties and bright application prospect in lighting, lasing, and photodetection. Although notable progress has been achieved in lighting applications based on such media, the performance coul...

In this work, we show electrical polarization of ferroelectric P (VDF-TrFE) polymer can be used to engineer the photoluminescence (PL) at bilayer WSe2. The total PL intensity substantially is suppressed under negative polarization and enhanced in positive polarization with increasing the polarization intensity of P (VDF-TrFE) polymer. And the elect...

High‐quality lattice‐matched and mismatched GaAs1‐xSbx (0.37< × <0.57) epilayers are grown on InP by molecular beam epitaxy. The localized states are confirmed by the S‐shape behavior of the temperature‐dependent photoluminescence (PL). With the help of a model based on a redistribution process of localized excitons, the degree of carrier localizat...

Effects of Bi incorporation on recombination process in wurtzite (WZ) GaBiAs nanowire are studied by employing micro-photoluminescence (µ-PL) and time-resolved PL spectroscopies. It is shown that at low temperatures (T < 75 K) Bi-induced localization effects cause trapping of excitons within band-tail states, which prolongs their lifetime and suppr...

Nanoscale laser sources with downscaled device footprint, high energy efficiency and operation speed are pivotal for a wide array of opto-electronic and nanophotonic applications ranging from on-chip interconnects, nano-spectroscopy, sensing to optical communication. The capability of on-demand lasing output with reversible and continuous wavelengt...

We report on the first successful growth of wurtzite (WZ) GaBiAs nanowires (NWs) and reveal effects of Bi incorporation on electronic band structure by using polarization-resolved optical spectroscopies performed on individual NWs. Experimental evidence for a decrease of the bandgap energy and an upward shift of the topmost three valence subbands u...

InAs nanowires (NWs) have been considered to be highly suitable for future nanoscale photonic applications in mid-wave infrared region. However, progress in this area has been seriously hampered because of the poor radiative efficiency of InAs NWs attributed to their non-radiative surface. Herein, we demonstrated that a significant improvement of o...

Low-temperature photoluminescence (PL), photoreflectance (PR), and temperature dependent time-resolved PL spectroscopies are employed to investigate optical emission processes and exciton dynamics in graded GaAsSb epilayers. The nonuniformity in the Sb composition along the growth direction is disclosed by low-temperature PL and PR measurements. Fu...

Raman spectra of undoped GaAs1-xBix (0 < x < 0.037) grown on GaAs by molecular beam epitaxy were investigated. With an increase of Bi component, we find that the longitudinal optical phonon-hole-plasmon-coupled (LOPC) mode first appears in the vicinity of the unscreened longitudinal optical (ULO) phonon frequency, and then shifts towards the transv...

Highly ordered As/Si faceted lateral nanoprisms array with a uniform width of about 10~18 nm are fabricated on Si {103} miscut surface via thermal deposition of sub-monolayer arsenic followed by a subsequent annealing process. In situ scanning tunneling microscopy (STM) studies prove the compactly arranged As/Si nanoprisms orienting along <301> dir...

We present a temperature-dependent and time-resolved photo-luminescence (PL) study for few-layer tungsten diselenide (WSe2) that is exfoliated from the bulk crystals. The PL intensities of direct and indirect exciton emissions in monolayer and bilayer WSe2 decrease while temperature increases. However, abnormal enhancement of PL emission from direc...

The effect of the thermal annealing on the optical and spin properties in GaAs0.44Sb0.56 epilayers grown on InP was investigated via photoreflectance, power-dependent and time-resolved photoluminescence spectroscopy as well as optical orientation measurement. The carrier’s localization and the optical spin detection efficiency increase with an incr...

Photoreflectance (PR) and photoreflectance excitation (PRE) techniques are employed to investigate the optical properties of the GaAs1-xBix(x = 0%–3.7%)/GaAs heterostructure grown by molecular beam epitaxy. The relations between broadenings and intensities of E0 and E0 + ΔSO transitions in PR as a function of Bi content are disclosed. Both PR and P...

In recent years, the electrical characteristics of WSe2 field effect transistors (FETs) have been widely investigated with various dielectrics. Among them, being able to perfectly tune the polarity of WSe2 is a meaningful and promising work. In this work, we systematically study the electrical properties of bilayer WSe2 FETs modulated by ferroelect...

A modified optics based technique was developed to effectively suppress spurious background signals encountered in the photoreflectance (PR) spectra obtained from bulk semiconductors and semiconductor microstructures. Based on a traditional PR setup, the novel PR approach utilized an achromatic beam reduction system to narrow the profile of a probe...

We report the exploration of photo-induced carrier dynamics in the GaAs0.985N0.015 Alloy. The time-resolved and high magnetic field-dependent photoluminescence experiments were carried out to identify the radiative transitions, and the localized and delocalized states at various excitation power and temperature. A nonmonotonic dependence of the PL...

We demonstrate the type-II staggered band alignment in MoTe2/MoS2 van der Waals (vdW) heterostructures and an interlayer optical transition at ~1.55 μm. The photoinduced charge separation between the MoTe2/MoS2 vdW heterostructure is verified by KPFM under illumination, density function theory (DFT) simulations and PL spectroscopy. Photoelectrical...

A substantial improvement in the efficiency of spin detection based on GaAs0.94Sb0.06 is realized by applying either a longitudinal magnetic field or a postgrowth annealing process. The degree of optical spin polarization can be increased from ∼19 to ∼40% at ∼105K under a longitudinal magnetic field of 10 T. On the other hand, through the shortenin...

We report the investigation of exciton dynamics in type-II self-assembled GaSb/GaAs quantum dots. The GaSb/GaAs quantum dots (QDs) were grown using a modified liquid phase epitaxy technique. Statistical size distributions of the uncapped QDs were investigated experimentally by field-emission scanning electron microscopy (SEM) and atomic force micro...

We investigated the intensity ratio between GaBi and GaAs-LO mode in Raman scattering. Good linear dependence on the Bismuth content for x<0.03 provides a new way to determine the Bismuth composition in GaAsBi.

Continuous-wave optical orientation spectroscopy and the Hanle effect are used to investigate the optical spin polarization and spin dephasing time (gTs) in GaAsSb with a Sb concentration of ∼6% as a function of temperature. Optical and spin polarizations up to ∼21% were achieved at ∼120 K, and the scaled spin lifetime gTs decreased monotonously fr...

The origin of the two emission peaks located at ~242 nm and ~282 nm from Al0.65Ga0.35N/AlN multiple quantum wells (MQWs) structure with Al0.75Ga0.25N caplayer excited by an electron beam are investigated by using depth cathodoluminescence techniques. We observed an enhancement of deep-ultraviolet emission peak (~282 nm) intensities from MQWs by Mg...

Structural properties of ZnO/Ni core/shell nanowires (NWs) are studied in detail by means of Raman spectroscopy. It is shown that formation of the Ni shell leads to passivation of surface states responsible for the observed enhanced intensity of the A1(LO) Raman mode of the bare ZnO NWs. It also causes appearance of 490 cm−1 and 710 cm−1 modes that...

Nuclear spin hyperpolarization is essential to future solid-state quantum computation using nuclear spin qubits and in highly sensitive magnetic resonance imaging. Though efficient dynamic nuclear polarization in semiconductors has been demonstrated at low temperatures for decades, its realization at room temperature is largely lacking. Here we dem...

Comprehensive characterization of defects formed in bulk ZnO single crystals co-implanted with N and Zn as well as N and O atoms is performed by means of optically detected magnetic resonance (ODMR) complemented by Raman and photoluminescence (PL) spectroscopies. It is shown that in addition to intrinsic defects such as Zn vacancies and Zn intersti...

The effect of hyperfine interaction (HFI) on the recently discovered room-temperature defect-enabled spin-filtering effect in GaNAs alloys is investigated both experimentally and theoretically based on a spin Hamiltonian analysis. We provide direct experimental evidence that the HFI between the electron and nuclear spin of the central Ga atom of th...

The redshift (∼54 meV) of the photoluminescence (PL) peak energy of blue InGaN/GaN light-emitting diodes exposed to 60Co γ-rays was observed. Time-resolved PL indicates that the PL radiative time increases along with irradiation does. The temperature-dependent PL and photoreflectance techniques show that γ-ray irradiance leads to higher carrier loc...

Optically detected magnetic resonance is employed to identify key factors governing dynamic nuclear polarization (DNP) in a semiconductor. We demonstrate that the extent of DNP can be efficiently controlled by varying lifetime of the localized electrons that transfer spin angular momentum to nuclei. The ultimate speed of a DNP process, on the other...

Photoluminescence (PL) and optically detected magnetic resonance (ODMR) techniques are utilized to examine the effects of P implantation and post-implantation annealing on defect formation in ZnO single crystals. From ODMR, the main defects created by ion implantation include oxygen and zinc vacancies as a well as a deep donor labeled as PD. The fo...

Photoluminescence and optically detected magnetic resonance techniques are utilized to study defect properties of GaNP and GaNAs alloys subjected to post-growth hydrogenation by low-energy sub-threshold ion beam irradiation. It is found that in GaNP H incorporation leads to activation of new defects, which has a Ga interstitial (Ga{sub i}) atom at...

Effect of postgrowth hydrogen treatment on defects and their role in carrier recombination in GaNP alloys is examined by photoluminescence (PL) and optically detected magnetic resonance. We present direct experimental evidence for effective activation of several defects by low-energy subthreshold hydrogen treatment ( ≤ 100 eV H ions). Among them, t...

Recently discovered effect of spin-filtering and spin amplification in GaNAs enables us to reliably obtain detailed information on the degree of spin loss during optical spin injection across a semiconductor heterointerface at room temperature. Spin polarization of electrons injected from GaAs into GaNAs is found to be less than half of what is gen...

Optically detected magnetic resonance (ODMR) studies of molecular beam epitaxial GaNP/GaP structures reveal presence of a P-related complex defect, evident from its resolved hyperfine interaction between an unpaired electronic spin (S=1/2) and a nuclear spin (I=(1)/(2)) of a P31 atom. The principal axis of the defect is concluded to be along a crys...

Effectiveness of the recently discovered defect-engineered spin-filtering effect is closely examined in GaNAs/GaAs multiquantum wells (QWs) as a function of QW width. In spite of narrow well widths of 3–9 nm, rather efficient spin filtering is achieved at room temperature. It leads to electron spin polarization larger than 18% and an increase in ph...

Optically detected magnetic resonance measurements are carried out to study formation of Ga interstitial-related defects in Ga(In)NAs alloys. The defects, which are among dominant nonradiative recombination centers that control carrier lifetime in Ga(In)NAs, are unambiguously proven to be common grown-in defects in these alloys independent of the e...

Oxygen and zinc vacancies are unambiguously shown to be formed in as-grown ZnO bulk crystals grown from melt without being subjected to irradiation, from electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR) studies. Concentrations of the defects in their paramagnetic charge states and are estimated to be ~2 × 1014 ...

We provide experimental demonstration of a novel defect-engineered, efficient and switchable spin filter from GaNAs to generate, amplify and detect electron spin polarization at room temperature without a magnetic material or external magnetic fields.

We report on a study of spin-dependent recombination processes (SDR) for conduction band electrons on deep paramagnetic centers in a series of GaAs1?yNy epilayers by time-resolved optical orientation experiments. We demonstrate that this dilute nitride compound can be used as an effective electron spin filter under a polarized optical excitation o...

Effects of Ga incorporation on electrical, structural and optical properties of ZnO epilayers are systematically studied by employing structural and optical characterization techniques combined with electrical and secondary ion mass spectrometry measurements. A non-monotonous dependence of free electron concentrations on Ga content is observed and...

Generating, manipulating and detecting electron spin polarization and coherence at room temperature is at the heart of future spintronics and spin-based quantum information technology. Spin filtering, which is a key issue for spintronic applications, has been demonstrated by using ferromagnetic metals, diluted magnetic semiconductors, quantum point...

Temperature-dependent cw- and time-resolved photoluminescence (PL), as well as optically detected magnetic resonance (ODMR) measurements are employed to evaluate effects of deuterium (2H) doping on optical properties of ZnCdO/ZnO quantum well structures grown by molecular beam epitaxy. It is shown that incorporation of 2H from a remote plasma cause...

Strong electron spin polarization in GaNAs epilayers and multiple quantum well structures is observed upon optical orientation at room temperature. The effect is explained in terms of spin dependent recombination (SDR) involving deep paramagnetic defects formed upon N incorporation in GaNAs. Concentration of the corresponding defects is shown to be...

We employ the optically detected magnetic resonance (ODMR) technique to study and identify important grown-in defects in Ga(In)NP grown by molecular-beam epitaxy (MBE). Several types of defects were revealed from ODMR studies. The dominant defects were found to be related to Ga interstitials, evident form their characteristic hyperfine interaction...

Effects of growth conditions and post-growth treatments, such as presence of N ions, N{sub 2} flow, growth temperature, In alloying, and postgrowth rapid thermal annealing (RTA), on formation of grown-in defects in Ga(In)NP prepared by molecular beam epitaxy are studied in detail by the optically detected magnetic resonance (ODMR) technique. Severa...

Photoluminescence (PL) and optically detected magnetic resonance are employed to study effects of nonstoichiometry during the growth on defect formation in ZnO epilayers grown by molecular-beam epitaxy (MBE). Several defects are revealed via monitoring the yellow PL emission (∼2.17 eV ) and their magnetic resonance signatures are obtained. The defe...

ZnO/ZnCdO/ZnO multiple quantum well samples grown on sapphire substrates by molecular beam epitaxy and annealed in situ were exposed to D2 plasmas at 150 °C. The deuterium showed migration depths of ∼ 0.8 μm for 30 min plasma exposures, with accumulation of 2H in the ZnCdO wells. The photoluminescence (PL) intensity from the samples was increased b...

Defect formation in ZnO epilayers grown by molecular beam epitaxy (MBE) is studied by employing optical characterization techniques such as photoluminescence (PL) and optically detected magnetic resonance (ODMR). Excess of oxygen during the growth was found to cause an appearance of the PL peak at around 3.338 eV, which indicates that the correspon...

We report on our results from a systematic study of layered structures containing an InGaNAs/GaAs single quantum well (SQW) enclosed between staggered type II AlAs/GaAs superlattices (SL), by the photoluminescence (PL) and optically detected cyclotron resonance (ODCR) techniques. Besides the ODCR signal known to originate from electrons in GaAs, th...

We report on our recent results from a systematic study of layered structures containing an InGaNAs/GaAs quantum well (QW), by the optically detected cyclotron resonance (ODCR) technique. By monitoring photoluminescence (PL) emissions from various layers the predominant ODCR peak is shown to be related to carriers with a 2D character and an effect...

Ge-doped SiO2 glasses are prepared by a sol–gel method using ethyl silicate (Si(OC2H5)4) and 3-trichologermanium propanoic acid (Cl3GeCH2CH2COOH) as starting materials. The Ge-doped SiO2 glasses show a strong room-temperature photoluminescence with peaks at 585 and 654nm under the excitation of the 514.5nm line of an Ar+ laser. The peak position of...

Optical absorption and reflectance measurements are performed to evaluate compositional and temperature dependences of band gap energies of Zn _1-x Cd _x O alloys grown by molecular-beam epitaxy. The compositional dependence of the band gap energy, determined by taking into account excitonic contributions, is shown to follow the...

We have carried out comprehensive optical studies to evaluate structural and bandgap properties of Zn1-xCdxO alloys with x {less than or equal to} 0.17 grown by molecular beam epitaxy. High crystalline quality of the alloys was concluded from cathodoluminescence measurements. Based on absorption and reflectance measurements, the compositional depen...

III-V semiconductor nanocrystals rarely exist as spherical inclusions inside glasses, due to difficulties during their preparation, such as high toxic reagents or fast oxidation under usual glass technology temperatures. In this letter a sol-gel method for synthesis of InP nanocrystals embedded in silica glasses was described. Gels were synthesized...

III–V semiconductor Indium Arsenide (InAs) nanocrystals embedded in silica glasses was synthesized by combining the sol–gel process and heat treatment in H2 gas. The size of InAs nanocrystals can be easily controlled via changing the In and As content in the starting materials and the heating temperature in a H2 gas atmosphere. Absorption measureme...

III-V semiconductor nanocrystals rarely exist as spherical inclusions inside glasses, due to the difficulties during their preparation, such as high toxic reagents or fast oxidation under usual glass technology temperatures. In this paper a sol-gel method for synthesis of InAs nanocrystals embedded in silica glasses was described. Gels were synthes...

Utilizing the substrate of Ga bilayer grown on Si(111)-√3×√3-Ga, we have investigated the structural transition of pentacene monolayer induced by moderate annealing. Short-range ordering has been observed in the monolayer pentacene deposited at room temperature. Annealing the sample at ∼350K produced ordered pentacene monolayer with the “brick-wall...

Ge nanocrystals embedded in bulk SiO2 glasses were prepared by combining the sol–gel process and the heat treatment in a H2 gas atmosphere. The size of Ge nanoparticles decreases with a decrease in the heat treatment temperature in a H2 gas atmosphere, and thus the crystalline Ge–Ge phonon vibration mode shifts to lower frequencies. The SiO2 gel gl...

We present a scheme for tuning the photonic band gap (PBG) by an external electric field in a ferroelectric inverse opal structure. The inverse opals, consisting of ferroelectric (Pb,La)(Zr,Ti)O3 (PLZT) ceramics, were synthesized by a sol–gel process. Optical reflection spectra show that the PBG of the PLZT inverse opals shifts continuously with th...

Germanium nanoparticles of different sizes in silica glasses were prepared via a sol−gel method, using Cl3−Ge−C2H4−COOH and Si(OC2H5)4 as the starting materials. The size of the germanium nanoparticles decreases as the heat-treatment time in a H2 gas atmosphere increases, and, thus, the optical absorption edge shifts to higher energies. Silica gel...

We report the mechanism of color production in peacock feathers. We find that the cortex in differently colored barbules, which contains a 2D photonic-crystal structure, is responsible for coloration. Simulations reveal that the photonic-crystal structure possesses a partial photonic bandgap along the direction normal to the cortex surface, for fre...

Ge nanoparticles with different sizes in silica glasses were prepared by a sol–gel method using Cl3–Ge–C2H4–COOH as a Ge source. The size of the Ge nanoparticles decreases with a reduction in the content of Ge in the starting materials, and thus the optical absorption edge shifts to a higher energy. Silica gel glasses doped with Ge nanoparticles sh...

Si1−xGex nanocrystals were obtained by means of laser-induced crystallization of a-SiGe films deposited by plasma-enhanced chemical vapour deposition. The crystallization was confirmed by x-ray diffraction spectroscopy, Fourier transmission infrared spectroscopy and atomic force microscopy; the average diameter of the nanocrystals was about 4.1 nm....

Non-resonant micro-Raman spectra from heterostructures of ZnSe on semi-insulating (SI-), n+-, and p+-GaAs using various excitation densities are reported. The effects of the carriers generated by both doping and photo-excitation have been investigated and the results are compared with those from bare GaAs substrates. The scattering from unscreened...

Ge nanocrystals embedded in SiO2 glasses were prepared by an easy sol–gel method. The gels synthesized through hydrolysis of Si(OC2H5)4 and 3-trichloro-germaniumpropanoic acid (Cl3–Ge–C2H4–COOH) were heated at 600°C for 10h in air atmosphere to form GeO2–SiO2 glasses. The gel-glasses were further heated at 500–700°C in H2 gas atmosphere, in which G...