常压MOCVD生长Ga2O3薄膜及其分析

以去离子水(H₂O)和三甲基镓(TMGa)为源材料,用常压MOCVD方法在蓝宝石(0001)面上生长出β-Ga₂O₃薄膜.用原子力显微镜(AFM)、X射线衍射(XRD)以及二次离子质谱(SIMS)实验表征Ga₂O₃外延膜的质量.在X射线衍射谱中有一个强的Ga₂O₃(102)面衍射峰,其半峰全宽(FWHM)为0.25°,表明该Ga₂O₃外延膜是(102)择优取向.在二次离子质谱中除了C、H、O和Ga原子外,没有观测到其他原子.     

Suppression of persistent photoconductivity in high gain Ga2O3 Schottky photodetectors

The defect-related photoconductivity gain and persistent photoconductivity (PPC) observed in Ga₂O₃ Schottky photodetectors lead to a contradiction between high responsivity and fast recovery speed. In this work, a metal-semiconductor-metal (MSM) Schottky photodetector, a unidirectional Schottky photodetector, and a photoconductor were constructed on Ga₂O₃ films. The MSM Schottky devices have high gain (> 13) and high responsivity (> 2.5 A/W) at 230-250 nm, as well as slow recovery speed caused by PPC. Interestingly, applying a positive pulse voltage to the reverse-biased Ga₂O₃/Au Schottky junction can effectively suppress the PPC in the photodetector, while maintaining high gain. The mechanisms of gain and PPC do not strictly follow the interface trap trapping holes or the self-trapped holes models, which is attributed to the correlation with ionized oxygen vacancies in the Schottky junction. The positive pulse voltage modulates the width of the Schottky junction to help quickly neutralize electrons and ionized oxygen vacancies. The realization of suppression PPC functions and the establishment of physical models will facilitate the realization of high responsivity and fast response Schottky devices.     

氧化镓薄膜的制备及其日盲紫外探测性能研究

采用射频磁控溅射方法在蓝宝石单晶衬底上沉积氧化镓(Ga2O3)薄膜,并通过光刻剥离工艺(Lift-off)制备了金属-半导体-金属结构的Ga2O3日盲紫外探测器。对不同温度下沉积的Ga2O3薄膜分析表明,在800℃下获得的薄膜结晶质量最好,薄膜的导电性则随着沉积温度的上升先增大后减小。在800℃制备的β-Ga2O3薄膜的可见光透光率大于90%,光学吸收边在255 nm附近。在10 V偏压下,探测器的暗电流约为1n A,光电流达800 n A,对紫外光响应迅速。器件的响应度达到0.3 A/W,260 nm波长处的响应度是290 nm波长对应响应度的40倍,可实现日盲紫外波段的探测。     

Luminescence properties of β-(Ga1−xInx)2O3 solid solutions

In this work, luminescence properties of β-(Ga_1−xIn_x)₂O₃ solid solutions were investigated with the purpose of making the new thermoluminophors for ultraviolet (UV) dosimetry. The doping of aliovalent cation admixture (Mg, Mo) in the β-Ga₂O₃ ceramic sample brings about the appearance of high-temperature thermoluminescence glow peaks with a maximum at 395 and 435 K. The maximum of the thermoluminophor photosensitivity shifts when the composition of solid solution changes.     

Cu_2O/ZnO氧化物异质结太阳电池的研究进展

介绍了近年来低成本Cu_2O/ZnO氧化物异质结太阳电池方面的研究进展.应用于光伏器件的吸收层材料Cu_2O是直接带隙半导体材料,天然呈现p型;其原材料丰富,且对环境友好.Cu_2O/ZnO异质结太阳电池结构主要有平面结构和纳米线/纳米棒结构.纳米结构的Cu_2O太阳电池提高了器件的电荷收集作用;通过热氧化Cu片技术获得的具有大晶粒尺寸平面结构Cu_2O吸收层在Cu_2O/ZnO太阳电池应用中展现出了高质量特性.界面缓冲层(如i-ZnO,a-ZTO,Ga_2O_3等)和背表面电场(如p~+-Cu_2O层等)可有效地提高界面处能级匹配和增强载流子输运.10 nm厚度的Ga_2O_3提供了近理想的导带失配,减少了界面复合;Ga_2O_3非常适合作为界面层,其能够有效地提高Cu_2O基太阳电池的开路电压V_(oc)(可达到1.2 V)和光电转换效率.p~+-Cu_2O(如Cu_2O:N和Cu_2O:Na)能够减少器件中背接触电阻和形成电子反射的背表面电场(抑制电子在界面处复合).利用p型Na掺杂Cu_2O(Cu_2O:Na)作为吸收层和Zn_(1-x)Ge_x-O作为n型缓冲层,Cu_2O异质结太阳电池(器件结构:MgF_2/ZnO:Al/Zn_(0.38)Ge_(0.62)-O/Cu_2O:Na)光电转换效率达8.1%.氧化物异质结太阳电池在光伏领域展现出极大的发展潜力.     

n(Zn)：n(Ga)比值对合成ZnGa2O4结构及光致发光性能的影响

以ZnO和HGaO₂为原料,用不同配比合成出系列ZnGa₂O₄,并对其晶体结构和发光性能进行了研究。用荧光分光光度计检测了ZnGa₂O₄的激发和发射光谱,用X射线衍射仪检测了ZnGa₂O₄的衍射图谱,用热重差热仪绘制了TGA-DAT曲线。对检测结果分析认为:1.ZnGa₂O₄属于尖晶石结构,稍过量的Zn或Ga能进入ZnGa₂O₄结构中,并对ZnGa₂O₄的晶格常数产生一定影响。2.ZnGa₂O₄存在两个自激发光中心,当Ga稍过量时,自激发光中心是四面体镓氧键[T_d(Ga-O)],最大激发波长约248nm,最大发射波长约367nm;当Zn稍过量时,自激发光中心是八面体镓氧键[O_h(Ga-O)],最大激发波长约270nm,最大发射波长约441nm。当n(Zn):n(Ga)在理论值附近,激发和发射光强度最大,而且光谱峰位发生了红移。3.ZnGa₂O₄的热稳定性能非常好。上述结论对研究ZnGa₂O₄基质或掺杂的发光材料具有一定意义。     

Interfacial properties of 2D WS2 on SiO2 substrate from X-ray photoelectron spectroscopy and first-principles calculations

Two-dimensional (2D) WS₂ films were deposited on SiO₂ wafers, and the related interfacial properties were investigated by high-resolution X-ray photoelectron spectroscopy (XPS) and first-principles calculations. Using the direct (indirect) method, the valence band offset (VBO) at monolayer WS₂/SiO₂ interface was found to be 3.97 eV (3.86 eV), and the conduction band offset (CBO) was 2.70 eV (2.81 eV). Furthermore, the VBO (CBO) at bulk WS₂/SiO₂ interface is found to be about 0.48 eV (0.33 eV) larger due to the interlayer orbital coupling and splitting of valence and conduction band edges. Therefore, the WS₂/SiO₂ heterostructure has a Type I energy-band alignment. The band offsets obtained experimentally and theoretically are consistent except the narrower theoretical bandgap of SiO₂. The theoretical calculations further reveal a binding energy of 75 meV per S atom and the totally separated partial density of states, indicating a weak interaction and negligible Fermi level pinning effect between WS₂ monolayer and SiO₂ surface. Our combined experimental and theoretical results provide proof of the sufficient VBOs and CBOs and weak interaction in 2D WS₂/SiO₂ heterostructures.     

超宽禁带半导体β-Ga_2O_3及深紫外透明电极、日盲探测器的研究进展

β-Ga_2O_3是一种新型的超宽禁带氧化物半导体,禁带宽度约为4.9 eV,对应日盲区,对波长大于253 nm的深紫外一可见光具有高的透过率,是天然的日盲紫外探测及深紫外透明电极材料.本文介绍了Ga_20_3材料的晶体结构、基本物性与器件应用,并综述了β-Ga_2O_3在深紫外透明导电电极和日盲紫外探测器中的最新研究进展.Sn掺杂的Ga_2O_3薄膜电导率可达到32.3 S/cm,透过率大于88%,但离商业化的透明导电电极还存在较大差距.在日盲紫外探测器应用方面,基于异质结结构的器件展现出更高的光响应度和更快的响应速度,ZnO/Ga_2O_3核/壳微米线的探测器综合性能最佳,在-6 V偏压下其对254 nm深紫外光的光响应度达1.3×10~3A/W,响应时间为20μs.     

Energy band alignment of 2D/3D MoS2/4H-SiC heterostructure modulated by multiple interfacial interactions

The interfacial properties of MoS₂/4H-SiC heterostructures were studied by combining first-principles calculations and X-ray photoelectron spectroscopy. Experimental (theoretical) valence band offsets (VBOs) increase from 1.49 (1.46) to 2.19 (2.36) eV with increasing MoS₂ monolayer (1L) up to 4 layers (4L). A strong interlayer interaction was revealed at 1L MoS₂/SiC interface. Fermi level pinning and totally surface passivation were realized for 4H-SiC (0001) surface. About 0.96e per unit cell transferring forms an electric field from SiC to MoS₂. Then, 1L MoS₂/SiC interface exhibits type I band alignment with the asymmetric conduction band offset (CBO) and VBO. For 2L and 4L MoS₂/SiC, Fermi level was just pinning at the lower MoS₂ 1L. The interaction keeps weak vdW interaction between upper and lower MoS₂ layers. They exhibit the type II band alignments and the enlarged CBOs and VBOs, which is attributed to weak vdW interaction and strong interlayer orbital coupling in the multilayer MoS₂. High efficiency of charge separation will emerge due to the asymmetric band alignment and built-in electric field for all the MoS₂/SiC interfaces. The multiple interfacial interactions provide a new modulated perspective for the next-generation electronics and optoelectronics based on the 2D/3D semiconductors heterojunctions.     

基于Au/TiO_2/FTO结构忆阻器的开关特性与机理研究

采用简单的一步水热法在FTO导电玻璃上外延生长了锐钛矿TiO_2纳米线,制备了具有Au/TiO_2/FTO器件结构的锐钛矿TiO_2纳米线忆阻器,系统研究了器件的阻变开关特性和开关机理.结果表明,Au/TiO_2/FTO忆阻器具有非易失的双极性阻变开关特性.同时,在103s的时间内,器件在0.1 V的电阻开关比始终保持在20以上,表明器件具有良好的非易失性.此外,器件在低阻态时遵循欧姆导电特性,而在高阻态时则满足陷阱控制的空间电荷限制电流传导机制,同时提出了基于氧空位导电细丝形成与断开机制的阻变开关模型.研究结果表明Au/TiO_2/FTO忆阻器将是一种很有发展潜力的下一代非易失性存储器.     

Enhanced luminescence from transparent Ni-doped MgO–Al2O3–SiO2 glass ceramics by Ga2O3 addition

Transparent Ni²⁺-doped MgO–Al₂O₃–SiO₂ glass ceramics without and with Ga₂O₃ were synthetized. The precipitation of spinel nanocrystals, which was identified as solid solutions in the glass ceramics, could be favored by Ga₂O₃ addition and their sizes were about 7.6 nm in diameter. The luminescent intensity of the Ni²⁺-doped glass ceramics was largely enhanced by Ga₂O₃ addition which could mainly be caused by increasing of Ni²⁺ in the octahedral sites and the reduction of the mean frequency of phonon density of states in the spinel nanocrystals of solid solutions. The full width at half maximum (FWHM) of emissions for the glass ceramics with different Ga₂O₃ content was all more than 200 nm. The emission lifetime increased with the Ga₂O₃ content and the longest lifetime is about 250 μs. The Ni²⁺-doped transparent glass ceramics with Ga₂O₃ addition have potential application as broadband optical amplifier and laser materials.     

Degradation of β-Ga_2O_3 Schottky barrier diode under swift heavy ion irradiation

The electrical characteristics and microstructures of β-Ga_2 O_3 Schottky barrier diode(SBD) devices irradiated with swift heavy ions(2096 Me V Ta ions) have been studied. It was found that β-Ga_2 O_3 SBD devices showed the reliability degradation after irradiation, including turn-on voltage Von, on-resistance Ron, ideality factor n, and the reverse leakage current density Jr. In addition, the carrier concentration of the drift layer was decreased significantly and the calculated carrier removal rates were 5 × 10~6–1.3 × 10~7 cm~(-1). Latent tracks induced by swift heavy ions were observed visually in the whole β-Ga_2 O_3 matrix. Furthermore, crystal structure of tracks was amorphized completely. The latent tracks induced by Ta ions bombardments were found to be the reason for the decrease in carrier mobility and carrier concentration. Eventually,these defects caused the degradation of electrical characteristics of the devices. In terms of the carrier removal rates, theβ-Ga_2 O_3 SBD devices were more sensitive to swift heavy ions irradiation than Si C and Ga N devices.     

Study on a novel vertical enhancement-mode Ga2O3 MOSFET with FINFET structure

A novel enhanced mode(E-mode)Ga₂O₃ metal-oxide-semiconductor field-effect transistor(MOSFET)with vertical FINFET structure is proposed and the characteristics of that device are numerically investigated.It is found that the concentration of the source region and the width coupled with the height of the channel mainly effect the on-state characteristics.The metal material of the gate,the oxide material,the oxide thickness,and the epitaxial layer concentration strongly affect the threshold voltage and the output currents.Enabling an E-mode MOSFET device requires a large work function gate metal and an oxide with large dielectric constant.When the output current density of the device increases,the source concentration,the thickness of the epitaxial layer,and the total width of the device need to be expanded.The threshold voltage decreases with the increase of the width of the channel area under the same gate voltage.It is indicated that a set of optimal parameters of a practical vertical enhancement-mode Ga₂O₃ MOSFET requires the epitaxial layer concentration,the channel height of the device,the thickness of the source region,and the oxide thickness of the device should be less than 5×10¹⁶ cm^-3,less than 1.5μm,between 0.1μm-0.3μm and less than 0.08μm,respectively.     

Ce3+掺杂SiO2-Al2O3-Gd2O3玻璃的闪烁性能

通常, Ce离子掺杂的低密度玻璃有较高的发光效率, 而高密度的Ce离子掺杂玻璃其发光效率很低. 为了解释这一现象, 采用高温熔融法获得了SiO₂-Al₂O₃-Gd₂O₃三元系统的玻璃形成区, 并在还原气氛下制备了Ce³⁺掺杂SiO₂-Al₂O₃-Gd₂O₃以及SiO₂-Al₂O₃-Gd₂O₃-Ln₂O₃ (Ln=Y, La, Lu)闪烁玻璃, 研究了其光谱和闪烁性能. 测试结果显示: 随着Gd₂O₃含量增加, 玻璃紫外截止波长发生红移, 荧光强度降低, 衰减时间缩短; 加入Lu₂O₃, La₂O₃, Y₂O₃后, 紫外截止波长发生红移, 荧光强度降低, 衰减时间变短; 当Gd₂O₃超过10% mol时, X射线荧光积分光产额从相当于锗酸铋 晶体的61%降低到13%. 荧光强度降低、衰减时间缩短的原因是随着玻璃的紫外截止波长红移玻璃的能带宽度变窄, 使得Ce³⁺离子的d电子轨道开始接近玻璃的导带, Ce³⁺离子受辐射后跃迁到d电子轨道的电子会通过导带与玻璃中的空穴复合, 产生电荷迁移猝灭效应.     

外电场辅助化学气相沉积方法制备网格状β-Ga2O3纳米线及其特性研究

利用外电场辅助化学气相沉积（CVD）方法,在蓝宝石衬底上制备出了由三组生长方向构成的网格状β-Ga₂O₃纳米线.研究了不同外加电压大小对β-Ga₂O₃纳米线表面形貌、晶体结构以及光学特性的影响.结果表明：外加电压的大小对样品的表面形貌有着非常大的影响,有外加电场作用时生长的β-Ga₂O₃纳米线取向性开始变好,只出现了由三组不同生长方向构成的网格状β-Ga₂O₃纳米线;并且随着外加电压的增加,纳米线分布变得更加密集、长度明显增长.此外,采用这种外电场辅助的CVD方法可以明显改善样品的结晶和光学质量.     

Performance and reliability improvement of La_2O_3/Al_2O_3 nanolaminates using ultraviolet ozone post treatment

La-based binary or ternary compounds have recently attracted a great deal of attention as a potential candidate to replace the currently used Hf-based dielectrics in future transistor and capacitor devices for sub-22 generation. However, the hygroscopic nature of La₂O₃ hampers its application as dielectrics in electron devices. To cope with this challenge, ultraviolet (UV) ozone post treatment is proposed to suppress the moisture absorption in the H₂O-based atomic layer deposition (ALD) La₂O₃/Al₂O₃ nanolaminates which is related to the residual hydroxyl/hydrogen groups after annealing. The x-ray photoelectron spectroscopy (XPS) and conductive atomic force microscopy (AFM) results indicate that the moisture absorption of the H₂O-based ALD La₂O₃/Al₂O₃ nanolaminates is efficiently suppressed after 600 ℃ annealing, and the electrical characteristics are greatly improved.     

Infrared optical response of YBa2Cu3O7 and PrBa2Cu3O7 An ellipsometric study

Ellipsometry was used to study (110) and (001) oriented films of YBa₂Cu₃O₇ and PrBa₂Cu₃O₇ in the mid-and near-infrared spectral regions. Below a photon energy of 0.1 eV, the in-plane component of the dielectric tensor of YBa₂Cu₃O₇ is dominated by a Drude term with a squared plasma energy of (3.0 ± 0.3) eV². This “oscillator strength”, and the Lorentzian broadening energy of (0.104 ± 0.005) eV at room temperature, are confirmed by the changes induced in Pr-substituted material, and by low-temperature measurements in the near-infrared. The deviation from the Drude behavior observed above 0.1 eV is accounted for by a broad absorption band with an oscillator strength of (3.6 ± 0.1) eV² in YBa₂Cu₃O₇ which shifts to higher energies and takes over almost all of the oscillator strength of the Drude term when Y is substituted by Pr. The response to electric fields perpendicular to the planes is much weaker, with an upper bound of 0.63 eV² for the squared plasma energy. The in-plane loss function computed from the measured dielectric function follows the Drude-like lineshape, modified by the bound-state absorption band, down to the lowest energy reached in our measurements (0.058 eV).     

Energy band alignment at Cu_2O/ZnO heterojunctions characterized by in situ x-ray photoelectron spectroscopy

With the increasing interest in Cu_2O-based devices for photovoltaic applications, the energy band alignment at the Cu_2O/ZnO heterojunction has received more and more attention. In this work, a high-quality Cu_2O/ZnO heterojunction is fabricated on a c-Al_2 O_3 substrate by laser-molecular beam epitaxy, and the energy band alignment is determined by x-ray photoelectron spectroscopy. The valence band of ZnO is found to be 1.97 eV below that of Cu_2O. A type-II band alignment exists at the Cu_2O/ZnO heterojunction with a resulting conduction band offset of 0.77 eV, which is especially favorable for enhancing the efficiency of Cu_2O/ZnO solar cells.     

基于FTO/VO2/FTO结构的VO2薄膜电压诱导相变光调制特性

采用直流磁控溅射和后退火工艺在掺氟的SnO₂(FTO)导电玻璃衬底上制备VO₂薄膜, 研究了不同退火时间和不同比例的氮氧气氛对VO₂薄膜性能的影响, 对VO₂薄膜的结晶取向、表面形貌、表面元素的相对含量和透过率随波长变化进行了测试分析, 结果表明在最佳工艺条件下制备得到了组分相对单一的VO₂薄膜. 基于FTO/VO₂/FTO结构在VO₂薄膜两侧的透明导电膜上施加电压并达到阈值电压时, 观察到了明显的电流突变. 当接触面积为3 mm×3 mm时, 阈值电压为1.7 V, 阈值电压随接触面积的增大而增大. 与不加电压的情况相比, FTO/VO₂/FTO结构在电压作用下高低温的红外透过率差值可达28%, 经反复施加电压, 该结构仍保持性能稳定, 具有较强的电致调控能力.     

Fixed charge and interface traps at heterovalent interfaces between Si(1 0 0) and non-crystalline Al2O3–Ta2O5 alloys

Characterization by Auger electron spectroscopy (AES) and Fourier transformation infrared spectroscopy (FTIR) confirms (Ta₂O₅)_x(Al₂O₃)_1−x alloys are homogeneous pseudo-binary alloys with increased thermal stability with respect to end member oxides, Ta₂O₅ and Al₂O₃. Capacitance–voltage (C–V) and current density–voltage (J–V) data as a function of temperate show that the Ta d-states of the alloys act as localized electron traps, and are at an energy approximately equal to the conduction band offset of Ta₂O₅ with respect to Si.