增强型β-Ga2O3/4H-SiC异质结VDMOS的设计与研究

由于β-Ga₂O₃材料难以形成P型掺杂，目前β-Ga₂O₃功率器件大多为无结耗尽型。为了解决β-Ga₂O₃器件难以形成增强型的问题，提出了一种具有β-Ga₂O₃/4H-SiC异质结的纵向双扩散金属-氧化物-半导体场效应晶体管(VDMOS)。添加P型4H-SiC后，利用形成的PN结的单向导通性得到了正阈值电压，实现了增强型器件。使用Sentaurus TCAD仿真软件模拟了器件结构并研究了其电学特性，通过调节SiC厚度、SiC沟道浓度、外延层厚度和外延层浓度四个重要结构参数，对器件的功率品质因数进行优化设计。优化后的器件具有1.62 V的正阈值电压、39.29 mS/mm的跨导以及5.47 mΩ·cm²的比导通电阻。最重要的是器件的关态击穿电压达到了1838 V,功率品质因数高达617 MW/cm²。结果表明，该β-Ga₂O₃/...     

氧分压对脉冲激光沉积β-Ga2O3-δ薄膜光学性能的影响

在不同氧分压下,用脉冲激光沉积法在c-蓝宝石衬底上制备了高质量β-Ga₂O_3?δ薄膜。通过X-射线衍射、远红外反射光谱、X-射线光电子能谱和紫外-可见-近红外透射光谱系统地研究了β-Ga₂O_3?δ薄膜的晶格结构、化学计量比和光学性质。X-射线衍射分析表明,所有沉积的薄膜以(-201)晶向方向生长。透射光谱显示薄膜在255 nm以上的紫外-可见-近红外波段具有80%以上的高透明度,同时在255 nm附近有一个陡峭的吸收边。此外,利用Tauc-Lorentz(TL)色散函数模型和Tauc公式,我们提取了β-Ga₂O_3?δ薄膜的光学常数和光学直接带隙。更进一步,我们通过理论计算解释了氧气分压对β-Ga₂O_3?δ薄膜光学性质的影响。     

基于超宽β-Ga2O3微米带的日盲光电探测器研究

氧化镓的禁带宽度接近5 eV,是一种极具前景的日盲紫外探测半导体材料。基于碳热还原法生长高质量β-Ga₂O₃微米带制备出MSM(Metal-Semiconductor-Metal)结构光电导紫外探测器,研究了不同的结构对光电器件性能的影响。结果表明等间距叉指电极光电探测器相较于两端电阻型光电探测器有更优异的性能。在10 V/254 nm紫外光照下,其响应度、外部量子效率、比探测率和光响应时间等性能提高明显,其中光电流(I_photo)有接近2个数量级的提升,且-2 V附近光暗电流比值增大至2.29×10⁵。随着叉指电极间距从50μm缩减至20μm,器件I_photo变大,其物理机制归因于阳极附近的耗尽层占据电极间微米带的比例增大引发了更高的光生载流子输运效率。     

阳极刻蚀提升Ga2O3肖特基势垒二极管击穿特性

提出了一种采用阳极刻蚀提升Ga₂O₃肖特基势垒二极管(SBD)击穿特性的新方法。基于氢化物气相外延(HVPE)法生长的Ga₂O₃材料制备了Ga₂O₃纵向SBD。在完成阳极制备后，对阳极以外的Ga₂O₃漂移区进行了不同深度的刻蚀，刻蚀完成后，在器件表面生长了SiO₂介质层，随后制备了场板结构。测试结果显示，刻蚀后器件的比导通电阻小幅上升，而反向击穿电压均大幅提升。刻蚀深度为300 nm的β-Ga₂O₃ SBD具有最优特性，其比导通电阻(R_{on, sp})为2.5 mΩ·cm²,击穿电压(V_br)为1 410 V,功率品质因子(FOM)为795 MW/cm²。该研究为高性能Ga₂O₃ SBD的制备提供了一种新方法。     

GaAs衬底上β-Ga2O3纳米点阵薄膜的MOCVD制备

将热氧化与MOCVD工艺相结合,总结了一种在本征GaAs衬底上进行β-Ga₂O₃纳米点阵薄膜制备的工艺,该工艺不涉及金属催化剂与复杂刻蚀,工艺更为简单。使用扫描电子显微镜对所制备薄膜的形貌特征进行了表征与分析,发现所制备的纳米点阵薄膜呈现五方的柱状结构。对所制备样品进行了X射线衍射、拉曼振动、光致发光谱的测试,结果表明薄膜的晶体质量随着MOCVD生长温度与Ⅵ/Ⅲ比的提高而得到优化。使用有限元法（FEM）仿真验证了β-Ga₂O₃纳米点阵薄膜制备的高陷光特点。     

新型白光LED荧光粉Y2O3:Ti 3+的光谱性能

采用共沉淀法,在不同的烧结气氛下制备了Y₂O₃:Ti ³⁺粉体,测量了它们的激发、发射光谱以及XRD光谱,观测了形貌。在紫外光激发下,微晶Y₂O₃:Ti ³⁺在439nm附近有较强的发射带,而纳米Y₂O₃:Ti ³⁺在400~500nm范围内出现了强的发射带。随纳米粉体的晶粒尺寸减小,它的发光明显增强,覆盖了整个可见光区。结果表明Y₂O₃:Ti ³⁺纳米粉体有望成为新一代白光LED或汞灯的光转换荧光粉。     

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.     

原子层沉积方法制备低温多层Al2O3/TiO2复合封装薄膜的研究

原子层沉积(ALD)方法可以制备出高质量薄膜,被认为是可应用于柔性有机电致发光器件(OLED)最有发展前景的薄膜封装技术之一。本文采用原子层沉积(ALD)技术,在低温(80℃)下,研究了Al₂O₃及TiO₂薄膜的生长规律,通过钙膜水汽透过率(WVTR)、薄膜接触角测试等手段,研究了不同堆叠结构的多层Al₂O₃/TiO₂复合封装薄膜的水汽阻隔特性,其中5 nm/5 nm×8 dyads(重复堆叠次数)的Al₂O₃/TiO₂叠层结构薄膜的WVTR达到2.1×10^-5 g/m²/day。采用优化后的Al₂O₃/TiO₂叠层结构薄膜对OLED器件进行封装,实验发现封装后的OLED器件在高温高湿条件下展现了较好的寿命特性。     

K3B6O10Br紫外非线性光学晶体研究进展(特邀)

利用非线性光学晶体实现激光频率转换是拓展激光波长的有效手段之一,非线性光学晶体也成为全固态激光系统中的核心器件。硼酸盐由于其丰富的结构多样性和优异的光学性能,已成为开发可用于紫外激光输出的非线性光学晶体的重要体系。K₃B₆O₁₀Br晶体具有短的紫外截止边(182 nm)、较大的非线性光学系数(d₂₂为0.83 pm/V)、适中的双折射率(0.046@1064 nm),在激光二倍频、三倍频激光输出领域具有潜在应用。本文简要介绍了K₃B₆O₁₀Br晶体生长及基本性能,对晶体倍频与和频实现可见/紫外激光及光参量啁啾脉冲放大方面的研究进展进行了总结,并对K₃B₆O₁₀Br晶体未来发展及应用前景进行了简要分析。     

高k栅介质增强型β-Ga2O3 VDMOS器件的单粒子栅穿效应研究

以增强型β-Ga₂O₃ VDMOS器件作为研究对象,利用TCAD选择不同的栅介质材料作为研究变量,观察不同器件的单粒子栅穿效应敏感性。高k介质材料Al₂O₃和HfO₂栅介质器件在源漏电压200 V、栅源电压-10 V的偏置条件下能有效抵御线性能量转移为98 MeV·cm²/mg的重离子攻击,SiO₂栅介质器件则发生了单粒子栅穿效应(Single event gate rupture, SEGR)。采用HfO₂作为栅介质时源漏电流和栅源电流分别下降92%和94%,峰值电场从1.5×10⁷ V/cm下降至2×10⁵ V/cm,避免了SEGR的发生。SEGR发生的原因是沟道处累积了大量的空穴,栅介质中的临界电场超过临界值导致了击穿,而高k栅介质可以有效降低器件敏感区域的碰撞发生率,抑制器件内电子空穴对的进一步生成,降低空穴累积的概率。     

Demonstration of GaN MIS diodes by using AlN and Ga2O3(Gd2O3) as dielectrics

GaN MIS diodes were demonstrated utilizing AlN and Ga₂O₃(Gd₂O₃) as insulators. A 345 Å of AlN was grown on the MOCVD grown n-GaN in a MOMBE system using trimethylamine alane as Al precursor and nitrogen generated from a SVT RF N₂ plasma. For the Ga₂O₃(Gd₂O₃) growth, a multi-MBE chamber was used and a 195 Å oxide was E-beam evaporated from a single crystal source of Ga₅Gd₃O₁₂. The forward breakdown voltage of AlN and Ga₂O₃(Gd₂O₃) diodes are 5 and 6 V, respectively, which are significantly improved over 1.2 V from that of a Schottky contact. From the C–V measurements, both kinds of diodes showed good charge modulation from accumulation to depletion at different frequencies. The insulator/GaN interface roughness and the thickness of the insulator were measured with X-ray reflectivity.     

Plasma-Enhanced Atomic Layer Deposition of Amorphous Ga2O3 for Solar-Blind Photodetection

Wide-bandgap gallium oxide (Ga₂O₃) is one of the most promising semiconductor materials for solar-blind (200 nm to 280 nm) photodetection. In its amorphous form, amorphous gallium oxide (a-Ga₂O₃) maintains its intrinsic optoelectronic properties while can be prepared at a low growth temperature, thus it is compatible with Si integrated circuits (ICs) technology. Herein, the a-Ga₂O₃ film is directly deposited on pre-fabricated Au interdigital electrodes by plasma enhanced atomic layer deposition (PE-ALD) at a growth temperature of 250 °C. The stoichiometric a-Ga₂O₃ thin film with a low defect density is achieved owing to the mild PE-ALD condition. As a result, the fabricated Au/a-Ga₂O₃/Au photodetector shows a fast time response, high responsivity, and excellent wavelength selectivity for solar-blind photodetection. Furthermore, an ultra-thin MgO layer is deposited by PE-ALD to passivate the Au/a-Ga₂O₃/Au interface, resulting in the responsivity of 788 A/W (under 254 nm at 10 V), a 250-nm-to-400-nm rejection ratio of 9.2×103, and the rise time and the decay time of 32 ms and 6 ms, respectively. These results demonstrate that the a-Ga₂O₃ film grown by PE-ALD is a promising candidate for high-performance solar-blind photodetection and potentially can be integrated with Si ICs for commercial production.     

Ga2O3(Gd2O3)/InGaAsenhancement-mode n-channel MOSFETs

We have demonstrated the first Ga₂O₃(Gd₂O₃) insulated gate n-channel enhancement-mode In_0.53Ga_0.47As MOSFET's on InP semi-insulating substrate. Ga₂O₃(Gd₂ O₃) was electron beam deposited from a high purity single crystal Ga₅Gd₃O₁₂ source. The source and drain regions of the device were selectively implanted with Si to produce low resistance ohmic contacts. A 0.75-μm gate length device exhibits an extrinsic transconductance of 190 mS/mm, which is an order of magnitude improvement over previously reported enhancement-mode InGaAs MISFETs. The current gain cutoff frequency, f_t, and the maximum frequency of oscillation, f_max, of 7 and 10 GHz were obtained, respectively, for a 0.75×100 μm² gate dimension device at a gate voltage of 3 V and drain voltage of 2 V     

Submicrometer Inversion-Type Enhancement-Mode InGaAs MOSFET With Atomic-Layer-Deposited Al2O3 as Gate Dielectric

High-performance inversion-type enhancement-mode n-channel In_0.53Ga_0.47As MOSFETs with atomic-layer-deposited (ALD) Al₂O₃ as gate dielectric are demonstrated. The ALD process on III-V compound semiconductors enables the formation of high-quality gate oxides and unpinning of Fermi level on compound semiconductors in general. A 0.5-mum gate-length MOSFET with an Al₂O₃ gate oxide thickness of 8 nm shows a gate leakage current less than 10^-4 A/cm² at 3-V gate bias, a threshold voltage of 0.25 V, a maximum drain current of 367 mA/mm, and a transconductance of 130 mS/mm at drain voltage of 2 V. The midgap interface trap density of regrown Al₂O₃ on In_0.53Ga_0.47As is ~1.4 x 10¹²/cm² ldr eV which is determined by low-and high-frequency capacitance-voltage method. The peak effective mobility is ~1100 cm² / V ldr s from dc measurement, ~2200 cm²/ V ldr s after interface trap correction, and with about a factor of two to three higher than Si universal mobility in the range of 0.5-1.0-MV/cm effective electric field.     

Structural and optical properties of Zn-doped β-Ga_2O_3 films

正Intrinsicβ-Ga_2O_3 and Zn-dopedβ-Ga_2O_3 films were prepared using RF magnetron sputtering.The effects of the Zn doping and thermal annealing on the structural and optical properties are investigated.In comparison with the intrinsicβ-Ga_2O_3 films,the microstructure,optical transmittance,optical absorption,optical energy gap,and photoluminescence of Zn-dopedβ-Ga_2O_3 films change significantly.The post-annealedβ-Ga_2O_3 films are polycrystalline.After Zn doping,the crystallization deteriorates,the optical band gap shrinks,the transmittance decreases and the UV,blue,and green emission bands are enhanced.     

n+-SnO2/a-SiC:H/metal thin-film photodiodeswith voltage-controlled spectral sensitivity

n⁺-SnO₂/a-SiC/metal photodiodes with voltage-controlled photosensitivity have been realized by using both carbon-rich and silicon-rich a-SiC alloys. Carbon-rich devices show a response peak located at 530 nm independent of the applied voltage, which in turn only affects the peak height. At variance, in silicon-rich structures the response peak is located at 480, 510, and 570 nm when the applied voltage is -4, 0, and +4 V, respectively, with corresponding quantum yield values of 17, 3, and 25%. For explaining the observed behavior we present a simple model of n⁺-SnO₂/a-SiC/metal diodes, which takes into account light-induced modulation of n⁺-SnO₂/a-SiC barrier height, primary photocurrent generation and photoconductivity effects     

High-performance polycrystalline SiGe thin-film transistors usingAl2O3 gate insulators

The use of aluminum oxide as the gate insulator for low temperature (600°C) polycrystalline SiGe thin-film transistors (TFTs) has been studied. The aluminum oxide was sputtered from a pure aluminum target using a reactive N₂O plasma. The composition of the deposited aluminum oxide was found to be almost stoichiometric (i.e., Al₂O₃), with a very small fraction of nitrogen incorporation. Even without any hydrogen passivation, good TFT performance was measured an devices with 50-nm-thick Al₂O₃ gate dielectric layers. Typically, a field effect mobility of 47 cm²/Vs, a threshold voltage of 3 V, a subthreshold slope of 0.44 V/decade, and an on/off ratio above 3×10⁵ at a drain voltage of 0.1 V can be obtained. These results indicate that the direct interface between the Al₂ O₃ and the SiGe channel layer is sufficiently passivated to make Al₂O₃ a better alternative to grown or deposited SiO₂ for SiGe field effect devices     

High-breakdown characteristics of the InP-based heterostructurefield-effect transistor withIn0.34Al0.66As0.85Sb0.15Schottky layer

We report improved breakdown characteristics of InP-based heterostructure field-effect transistors (HFET's) utilizing In_0.34 Al_0.66As_0.85Sb_0.15 Schottky layer grown by low-pressure metalorganic chemical vapor deposition. Due to high energy bandgap and high Schottky barrier height (>0.73 eV) of the In_0.34Al_0.66As_0.85Sb_0.15 Schottky layer, high two-terminal gate-to-drain breakdown voltage of 40 V, three-terminal off-state breakdown voltage of 40 V three-terminal threshold-state breakdown voltage of 31 V, and three-terminal on-state breakdown voltage of 18 V at 300 K for In_0.75Ga_0.25As channel, are achieved. Moreover, the temperature dependence of two-terminal reverse leakage current is also investigated. The two-terminal gate-to-drain breakdown voltage is up to 36 V at 420 K. A maximum extrinsic transconductance of 216 mS/mm is obtained with a gate length of 1.5 μm     

One transistor ferroelectric memory with Pt/Pb5Ge3O11/Ir/poly-Si/SiO2/Si gate-stack

One transistor ferroelectric nonvolatile memory with gate stack of Pt/Pb₅Ge₃O₁₁/lr/poly-Si/SiO₂ /Si was successfully fabricated. This device features a saturated memory window of 3 V at a programming voltage of higher than 3 V from C-V and I-V measurements. The memory window decays rapidly within 10 seconds after programming, but remains stable at 1 V for up to 100 h. The "on" and "off" state currents are greater than 10 μA/μm and less 0.01 pA/μm, respectively, at a drain voltage of 0.1 V     

Semiconductor lasers with 2-D-photonic crystal mirrors based on awet-oxidized Al2O3-mask

We have fabricated and investigated AlGaAs-InGaAs-based ridge waveguide (RWG) lasers with two-dimensional (2-D) triangular photonic crystal (PC) mirrors using a wet-oxidized Al₂O₃ mask for the dry etching of the PC at one end of the ridge. The laser structure includes a 60-nm-thick AlAs layer positioned in the upper cladding, which is converted into Al₂O₃ after the definition of the PC by electron beam lithography and shallow etching. Etching of the holes is then continued using the Al₂O₃ mask, to a final depth of 600 nm. The continuous-wave characteristics of the lasers show a clear dependence on the period of the PC including a significant decrease of the threshold current and an increase of the efficiency for properly adjusted crystal parameters