Electronic structure and optical properties of F-doped β-Ga2O3 from first principles calculations

The effects of F-doping concentration on geometric structure, electronic structure and optical property of β-Ga₂O₃ were investigated. All F-doped β-Ga₂O₃ with different concentrations are easy to be formed under Ga-rich conditions, the stability and lattice parameters increase with the F-doping concentration. F-doped β-Ga₂O₃ materials display characteristics of the n-type semiconductor, occupied states contributed from Ga 4s, Ga 4p and O 2p states in the conduction band increase with an increase in F-doping concentration. The increase of F concentration leads to the narrowing of the band gap and the broadening of the occupied states. F-doped β-Ga₂O₃ exhibits the sharp band edge absorption and a broad absorption band. Absorption edges are blue-shifted, and the intensity of broad band absorption has been enhanced with respect to the fluorine content. The broad band absorption is ascribed to the intra-band transitions from occupied states to empty states in the conduction band.     

Growth and fundamentals of bulk β-Ga_2O_3 single crystals

The rapid development of bulk β-Ga_2O_3 crystals has attracted much attention to their use as ultra-wide bandgap materials for next-generation power devices owing to its large bandgap(～ 4.9 eV) and large breakdown electric field of about8 MV/cm. Low cost and high quality of large β-Ga_2O_3 single-crystal substrates can be attained by melting growth techniques widely used in the industry. In this paper, we first present an overview of the properties of β-Ga_2O_3 crystals in bulk form. We then describe the various methods for producing bulk β-Ga_2O_3 crystals and their applications. Finally, we will present a future perspective of the research in the area in the area of single crystal growth.     

Research on the hydrogen terminated single crystal diamond MOSFET with MoO3 dielectric and gold gate metal

The single crystal diamond with maximum width about 10 mm has been grown by using microwave plasma chemical vapor deposition equipment.The quality of the grown diamond was characterized using an X-ray diffractometer.The FWHM of the (004) rocking curve is 37.91 arcsec,which is comparable to the result of the electronic grade single crystal diamond commercially obtained from Element Six Ltd.The hydrogen terminated diamond field effect transistors with Au/MoO3 gates were fabricated based on our CVD diamond and the characteristics of the device were compared with the prototype Al/MoO3 gate.The device with the Au/MoO3 gate shows lower on-resistance and higher gate leakage current.The detailed analysis indicates the presence of aluminum oxide at the Al/MoO3 interface,which has been directly demonstrated by characterizing the interface between Al and MoO3 by X-ray photoelectron spectroscopy.In addition,there should be a surface transfer doping effect of the MoO3 layer on H-diamond even with the atmospheric-adsorbate induced 2DHG preserved after MoO3 deposition.     

High Purity and Large-scale Preparation of β-Ga2O3 Nanowires and Nanosheets by CVD and Their Raman and Photoluminescence Characteristics

Ga2O3 nano-structures, nanowires and nanosheets are produced on Au pre coated（111） silicon substrates with chemical vapor deposition（CVD） technique. By evaporating pure Ga powder in the H2O atmosphere under ambient pressure the large-scale preparation of β-Ga2O3 with monoclinic crystalline structure is achieved. The crystalline structures and morphologies of produced Ga2O3 nano-structures are characterized by means of scanning electron microscope（SEM）, X-ray diffraction（XRD）, selected area electron diffraction （SAED） and transmission electron microscope（TEM）. Raman spectrum reveals the typical vibration modes of Ga2O3 The vibration mode shifts corresponding to Ga2O3 nano-structures are not found. Two distinguish photoluminescence（PL） emissions are found at about 399 nm and 469 nm owing to the VO-VGa excitation and VO-VGaO excitation, respectively. The growth mechanisms of Ga2O3 nanowires and nanosheets are discussed with vapor liquid-solid（VLS） and vapor-solid（VS） mechanisms.     

Elaboration and characterization of a KCl single crystal doped with nanocrystalsof a Sb2O3 semiconductor

Undoped and doped KCl single crystals have been successfully elaborated via the Czochralski（Cz） method.The effects of dopant Sb₂O₃ nanocrystals on structural and optical properties were investigated by a number of techniques,including X-ray diffraction（XRD）,scanning electron microscopy（SEM）,energy dispersive X-ray（EDAX） analysis,UV-visible and photoluminescence（PL） spectrophotometers.An XRD pattern of KCl:Sb₂O₃ reveals that the Sb₂O₃ nanocrystals are in the well-crystalline orthorhombic phase.The broadening of diffraction peaks indicated the presence of a Sb₂O₃ semiconductor in the nanometer size regime.The shift of absorption and PL peaks is observed near 334 nm and 360 nm respectively due to the quantum confinement effect in Sb₂O₃ nanocrystals.Particle sizes calculated from XRD studies agree fairly well with those estimated from optical studies.An SEM image of the surface KCl:Sb₂O₃ single crystal shows large quasi-spherical of Sb₂O₃ crystallites scattered on the surface.The elemental analysis from EDAX demonstrates that the KCl:Sb₂O₃ single crystal is slightly rich in oxygen and a source of excessive quantities of oxygen is discussed.     

Optical and electrical properties of electrochemically deposited polyaniline-CeO2 hybrid nanocomposite film

This paper reports the optical and electrical properties of electrochemically deposited polyaniline (PANI)-cerium oxide (CeO2) hybrid nano-composite film onto indium-tin-oxide (ITO) glass substrate. UV–visible spectroscopy and I-V characteristic were performed to study the optical and electrical parameters of the electrochemically deposited film. The film exhibited a strong absorption below 400 nm (3.10 eV) with a well defined absorbance peak at around 285nm (4.35 eV). The estimated band gap of the CeO2 sample was 3.44 eV and this value is higher than bulk CeO2 powder (Eg = 3.19 eV) due to quantum confinement effect.     

Physical properties of sprayed antimony doped tin oxide thin films:The role of thickness

Transparent conducting antimony doped tin oxide（Sb:SnO₂） thin films have been deposited onto preheated glass substrates using a spray pyrolysis technique by varying the quantity of spraying solution.The structural, morphological,X-ray photoelectron spectroscopy,optical,photoluminescence and electrical properties of these films have been studied.It is found that the films are polycrystalline in nature with a tetragonal crystal structure having orientation along the（211） and（112） planes.Polyhedrons like grains appear in the FE-SEM images. The average grain size increases with increasing spraying quantity.The compositional analysis and electronic behaviour of Sb:SnO₂ thin films were studied using X-ray photoelectron spectroscopy.The binding energy of Sn3d_5/2 for all samples shows the Sn⁴⁺ bonding state from SnO₂.An intensive violet luminescence peak near 395 nm is observed at room temperature due to oxygen vacancies or donor levels formed by Sb⁵⁺ ions.The film deposited with 20 cc solution shows 70%transmittance at 550 nm leading to the highest figure of merit(2.11×10^-3Ω^-1). The resistivity and carrier concentration vary over 1.22×10^-3 to 0.89×10^-3Ω·cm and 5.19×10²⁰ to 8.52×10²⁰ cm^-3,respectively.     

The effect of solution concentration on the physical and electrochemical properties of vanadium oxide films deposited by spray pyrolysis

Vanadium oxide thin films were prepared on glass substrates by using the spray pyrolysis technique.The effect of solution concentration(0.1 M,0.2 M and 0.3 M) on the nanostructural,electrical,optical,and electrochromic properties of deposited films were investigated using X-ray diffraction,scanning electron microscopy,UV–vis spectroscopy,and cyclic volta-metrics.The X-ray diffraction shows that only the sample at 0.1 M has a single β-V2O5phase and the others have mixed phases of vanadium oxide.The lowest sheet resistance was obtained for the samples prepared at 0.3 M solution.It was also found that the optical transparency of the samples changes from 70% to 35% and the optical band gap of the samples was in the range of 2.20 to 2.41 eV,depending on the morality of solution.The cycle voltammogram shows that the sample prepared at 0.3 M has one-step electerochoromic but the other samples have two-step electerochoromic.The results show a correlation between the cycle voltammogram and the physical properties of the films.     

Optical and electrical properties of electrochemically deposited polyaniline/CeO2 hybrid nanocomposite film

This paper reports the optical and electrical properties of electrochemically deposited polyaniline （PANI）/cerium oxide（CeO₂） hybrid nano-composite film onto indium-tin-oxide（ITO） glass substrate.UV-visible spectroscopy andⅠ-Ⅴcharacteristic were performed to study the optical and electrical parameters of the electrochemically deposited film.The film exhibited a strong absorption below 400 nm（3.10 eV） with a well defined absorbance peak at around 285 nm（4.35 eV）.The estimated band gap of the CeO₂ sample was 3.44 eV,higher than bulk CeO₂ powder（E_g = 3.19 eV） due to the quantum confinement effect.Optical and electrochemical characteristics indicated that the electrical properties of PANI/CeO₂ hybrid nanocomposite film arc dominated by PANI doping.     

Carbon agent chemical vapor transport growth of Ga2O3 crystal

Beta-type gallium oxide (β-Ga₂O₃) is a new attractive material for optoelectronic devices. Different methods had been tried to grow high quality β-Ga₂O₃ crystals. In this work, crystal growth of Ga₂O₃ has been carried out by chemical vapor transport (CVT) method in a closed quartz tube using C as transport agent and sapphire wafer as seed. The CVT mass flux has been analyzed by theoretical calculations based on equilibrium thermodynamics and 1D diffusional mass transport. The crystal growth experimental results are in agreement with the theoretical predictions. Influence factors of Ga₂O₃ crystal growth, such as temperature distribution, amount of C as transport agent used, have also been discussed. Structural (XRD) and optical (Raman spectroscopy, photoluminescence spectrum) properties of the CVT-Ga₂O₃ crystal are presented.     

Studies on morphology,electrical and optical characteristics of Al-doped ZnO thin films grown by atomic layer deposition

Al doped ZnO (AZO) films deposited on glass substrates through the atomic layer deposition (ALD)technique are investigated with various temperatures from 100 to 250 ℃ and different Zn ∶ Al cycle ratios from 20 ∶ 0 to 20 ∶ 3.Surface morphology,structure,optical and electrical properties of obtained AZO films are studied in detail.The Al composition of the AZO films is varied by controlling the ratio of Zn ∶ Al.We achieve an excellent AZO thin film with a resistivity of 2.14 × 10-3 Ω·cm and high optical transmittance deposited at 150 ℃ with 20 ∶ 2 Zn ∶ Al cycle ratio.This kind of AZO thin films exhibit great potential for optoelectronics device application.     

β-Ga_2O_3 thin film grown on sapphire substrate by plasmaassisted molecular beam epitaxy

Monoclinic gallium oxide(Ga_2O_3) has been grown on(0001) sapphire(Al_2O_3) substrate by plasma-assisted molecular beam epitaxy(PA-MBE). The epitaxial relationship has been confirmed to be [010]( 2ˉ01) β-Ga_2O_3||[ 011ˉ0](0001)Al_2O_3 via in-situ reflection high energy electron diffraction(RHEED) monitoring and ex-situ X-ray diffraction(XRD) measurement. Crystalline quality is improved and surface becomes flatter with increasing growth temperature, with a best full width at half maximum(FWHM) of XRD ω-rocking curve of( 2ˉ01) plane and root mean square(RMS) roughness of 0.68° and 2.04 nm for the sample grown at 730 °C,respectively. Room temperature cathodoluminescence measurement shows an emission at ～417 nm, which is most likely originated from recombination of donor–acceptor pair(DAP).     

Effect of Co doping on structural, optical, electrical and thermal properties of nanostructured ZnO thin films

Nanocrystalline Zn1-x CoxO(where x varies from 0 to 0.04 in steps of 0.01) thin films were deposited onto glass substrate by the spray pyrolysis technique at a substrate temperature of 350 ℃. The X-ray diffraction patterns confirm the formation of hexagonal wurtzite structure. The crystal grain size of these films was found to be in the range of 11–36 nm. The scanning electron micrographs show a highly crystalline nanostructure with different morphologies including rope-like morphology for undoped ZnO and nanowalls and semispherical morphology for Co-doped Zn O. The transmittance increases with increasing Co doping. The optical absorption edge is observed in the transmittance spectra from 530 to 692 nm, which is due to the Co2C absorption bands corresponding to intraionic d–d shifts. The direct and indirect optical band gap energies decrease from 3.05 to 2.75 eV and 3.18 to 3.00 eV, respectively for 4 mol% Co doping. The electrical conductivity increases with increasing both the Co doping and temperature, indicating the semiconducting nature of these films. The temperature dependence thermal electromotive force measurement indicates that both undoped and Co-doped ZnO thin films show p-type semiconducting behavior near room temperature. This behavior dies out beyond 313 K and they become n-type semiconductors.     

Current-voltage characteristics of light-emitting diodes under optical and electrical excitation

The factors influencing the current-voltage(I-V) characteristics of light-emitting diodes(LEDs) are investigated to reveal the connection of I-V characteristics under optical excitation and those under electrical excitation.By inspecting the I-V curves under optical and electrical excitation at identical injection current,it has been found that the I-V curves exhibit apparent differences in voltage values.Furthermore,the differences are found to originate from the junction temperatures in diverse excitation ways.Experimental results indicate that if the thermal effect of illuminating spot is depressed to an ignorable extent by using pulsed light,the junction temperature will hardly deflect from that under optical excitation,and then the I-V characteristics under two diverse excitation ways will be the same.     

用第一性原理研究n型Sn/F共掺杂β-Ga2O3

用第一性原理计算了Sn掺杂 β-Ga2O3、F掺杂β-Ga2O3和Sn/F共掺杂 β-Ga2O3的形成能、电子结构和光学性能。用LDA方法计算的本征β-Ga2O3和Sn掺杂 β-Ga2O3的晶格常数和电子结构与实验值吻合。形成能计算表明Sn掺杂 β-Ga2O3、F掺杂β-Ga2O3和Sn/F共掺杂 β-Ga2O3在富氧条件下比在富镓条件下容易形成。Sn掺杂 β-Ga2O3、F掺杂β-Ga2O3和Sn/F共掺杂 β-Ga2O3显示n型半导体特性。Sn/F共掺杂 β-Ga2O3具有最小的电子有效质量和最大的相对电子数,具有潜在的良好导电性。Sn/F共掺杂 β-Ga2O3在可见光区域显示强的光吸收。     

First-principles study of the electronic structures and optical properties of C-F-Be doped wurtzite ZnO

正The electronic structure and optical properties of pure,C-doped,C-F codoped and C-F-Be clusterdoped ZnO with a wurtzite structure were calculated by using the density functional theory with the plane-wave ultrasoft pseudopotentials method.The results indicate that p-type ZnO can be obtained by C incorporation,and the energy level of C_O above the valence band maximum is 0.36 eV.The ionization energy of the complex Zn_(16)O_(14)CF and Zn_(15)BeO_(14)CF can be reduced to 0.23 and 0.21 eV,individually.These results suggest that the defect complex of Zn_(15)BeO_(14)CF is a better candidate for p-type ZnO.To make the optical properties clear,we investigated the imaginary part of the complex dielectric function of undoped and C-F-Be doped ZnO.We found that there is strong absorption in the energy region lower than 2.7 eV for the C-F-Be doped system compared to pure ZnO.     

Growth-temperature-dependent optical and acetone detection properties of ZnO thin films

Zinc oxide (ZnO) thin films were prepared onto glass substrates at moderately low growth temperature by two-stage spray pyrolysis technique. The effects of growth temperature on structural, optical and acetone detection properties were investigated with X-ray diffractometry, a UV-visible spectrophotometer, photoluminescence (PL) spectroscopy and a homemade gas sensor testing unit, respectively. All the films are polycrystalline with a hexagonal wurtzite phase and exhibit a preferential orientation along [002] direction. The film crystallinity is gradually enhanced with an increase in growth temperature. The optical measurements show that all the films are physically highly transparent with a transmittance greater than 82% in the visible range. The band gap of the film is observed to exhibit a slight red shift with an increasing growth temperature. The PL studies on the films show UV/violet PL band at ～ 395 nm. Among all the films investigated, the film deposited at 250 ℃ demonstrates a maximum sensitivity of 13% towards 20 ppm of acetone vapors at 300 ℃ operating temperature.     

Correlation between the structural, morphological, optical, and electrical properties of In2O3 thin films obtained by an ultrasonic spray CVD process

Indium oxide (In₂O₃) thin films are successfully deposited on glass substrate at different deposition times by an ultrasonic spray technique using Indium chloride as the precursor solution; the physical properties of these films are characterized by XRD, SEM, and UV-visible. XRD analysis showed that the films are polycrystalline in nature having a cubic crystal structure and symmetry space group Ia3 with a preferred grain orientation along the (222) plane when the deposition time changes from 4 to 10 min, but when the deposition time equals 13 min we found that the majority of grains preferred the (400) plane. The surface morphology of the In₂O₃ thin films revealed that the shape of grains changes with the change of the preferential growth orientation. The transmittance improvement of In₂O₃ films was closely related to the good crystalline quality of the films. The optical gap energy is found to increase from 3.46 to 3.79 eV with the increasing of deposition time from 4 to 13 min. The film thickness was varied between 395 and 725 nm. The film grown at 13 min is found to exhibit low resistivity (10^-2 Ω·cm), and relatively high transmittance (~ 93%).     

Photoelectric properties of ITO thin films deposited by DC magnetron sputtering

As anti-reflecting thin films and transparent electrodes of solar cells,indium tin oxide（ITO） thin films were prepared on glass substrates by DC magnetron sputtering process.The main sputtering conditions were sputtering power,substrate temperature and work pressure.The influence of the above sputtering conditions on the transmittance and conductivity of the deposited ITO films was investigated.The experimental results show that, the transmittance and the resistivity decrease as the sputtering power increases from 30 to 90 W.When the substrate temperature increases from 25 to 150℃,the transmittance increases slightly whereas the resistivity decreases.As the work pressure increases from 0.4 to 2.0 Pa,the transmittance decreases and the resistivity increases.When the sputtering power,substrate temperature and work pressure are 30 W,150℃,0.4 Pa respectively,the ITO thin films exhibit good electrical and optical properties,with resistivity below 10^-4Ω·cm and the transmittance in the visible wave band beyond 80%.Therefore,the ITO thin films are suitable as transparent electrodes of solar cells.     

Synthesis of monoclinic structure gallium oxide film on sapphire substrate by magnetron sputtering

Gallium oxide (Ga2O3) films were deposited on singlecrystalline sapphire (0001) substrate by radio frequency (RF) magnetron sputtering technique in the temperature range of 300—500 °C. The microstructure of the β-Ga2O3 films were investigated in detail using X-ray diffractometer (XRD) and scanning electron microscope (SEM). The results show that the film prepared at 500 °C exhibits the best crystallinity with a monoclinic structure (β-Ga2O3). Structure analysis reveals a clear out-of-plane orientation of β-Ga2O3 || Al2O3 (0001). The average transmittance of these films in the visible wavelength range exceeds 90%, and the optical band gap of the films varies from 4.68 eV to 4.94 eV which were measured by an ultraviolet-visible-near infrared (UV-vis-NIR) spectrophotometer. Therefore, it is hopeful that the β-Ga2O3 film can be used in the UV optoelectronic devices. #$TABThis work has been supported by the National Natural Science Foundation of China (Nos.61274113, 61404091, 61505144, 51502203 and 51502204), the Opening Fund of Key Laboratory of Silicon Device Technology in Chinese Academy of Sciences, and the Tianjin Natural Science Foundation (Nos.14JCZDJC31500 and 14JCQNJC00800).#$TABE-mail:miwei1986@yeah.net