SiO2/4H-SiC界面氮化退火

通过1 300℃高温干氧热氧化法在n型4H-SiC外延片上生长了厚度为60 nm的SiO2栅氧化层.为了开发适合于生长低界面态密度和高沟道载流子迁移率的SiC MOSFET器件产品的栅极氧化层退火条件,研究了不同退火条件下的SiO2/SiC界面电学特性参数.制作了MOS电容和横向MOSFET器件,通过表征SiO2栅氧化层C-V特性和MOSFET器件I-V特性,提取平带电压、C-V磁滞电压、SiO2/SiC界面态密度和载流子沟道迁移率等电学参数.实验结果表明,干氧氧化形成SiO2栅氧化层后,在1 300℃通入N2退火30 min,随后在相同温度下进行NO退火120 min,为最佳栅极氧化层退火条件,此时,SiO2/SiC界面态密度能够降低至2.07×1012 cm-2·eV-1@0.2 eV,SiC MOSFET沟道载流子迁移率达到17 cm2·V-1·s-1.     

SiC MOS界面氮等离子体改性及电学特性评价

降低SiO2/SiC界面态密度是SiCMOS器件研究中的关键技术问题。采用氮等离子体处理SiO2/SiC界面,制作MOS电容后通过I-V、C-V测试进行氧化膜可靠性及界面特性评价,获得的氧化膜击穿场强约为9.96MV/cm,SiO2/SiC势垒高度2.70eV,同时在费米能级附近SiO2/SiC的界面态密度低减至2.27×1012cm-2eV。实验结果表明,氮等离子体处理SiO2/SiC界面后能有效降低界面态密度,改善MOS界面特性。     

氮钝化SiC MOS界面特性的Gray-Brown法研究

降低SiO2/SiC界面态密度,尤其是SiC导带附近的界面态密度,是SiC MOS器件研究中的关键技术问题。采用氮等离子体钝化处理SiO2/SiC界面,制作成MOS电容后通过I-V和低温C-V测试进行氧化膜击穿特性及界面特性评价。氧化膜击穿电场为9.92MV/cm,SiO2与SiC之间的势垒高度为2.69eV。使用Gray-Brown法结合Hi-Lo法分析C-V曲线,获得了距导带底EC0.05～0.6eV范围内的界面态分布,其中距EC0.2eV处的界面态密度降低至1.33×1012cm-2eV-1。实验结果表明,氮等离子体处理能有效降低4H-SiC导带附近的界面态密度,改善界面特性。     

HfTiO氮化退火对MOS器件电特性的影响

采用磁控溅射方法,在Si衬底上淀积HfTiO高k介质,研究了NO、N2O、NH3和N2不同气体退火对MOS电特性的影响。结果表明,由于NO氮化退火能形成类SiO2/Si界面特性的HfTiSiON层,所制备的MOS器件表现出优良的电特性,即低的界面态密度、低的栅极漏电和高的可靠性。根据MOS器件栅介质(HfTiON/HfTiSiON)物理厚度变化(ΔTox)和电容等效厚度变化(ΔCET)与介质(HfTiON)介电常数的关系,求出在NO气氛中进行淀积后退火处理的HfTiON的介电常数达到28。     

6H-SiC氧化层中Na离子的C-V测试研究

半导体热氧化过程中,不可避免会沾污Na离子,造成MOS电容的C-V曲线平带电压漂移.在1200℃下热氧化,生成SiC/SiO2界面,进而制作MOS电容.采用高电压偏置,在高温度条件下作用于MOS电容;利用Keithley590 C-V分析仪,测量其C-V曲线.计算出氧化层Na离子密度为2.26×1012/cm2,高温负高压偏置不能完全恢复MOS电容的C-V特性,且高压偏置处理后的MOS电容在积累区的电容值减小,与Si材料MOS的情况不同.主要原因是SiC氧化层和界面质量较差,在高温和高压下弱键断裂、固定电荷重新分布.     

氧化后退火技术对SiO2/4H-SiC界面态密度的影响

采用等离子体增强化学气相沉积(PECVD)低温处理和高温快速退火的技术,研究了退火条件对SiO2/4H-SiC界面态密度的影响.在n型4H-SiC外延片上高温干氧氧化50 nm厚的SiO2层并经N2原位退火,随后在PECVD炉中对样品进行350℃退火气氛为PH3,N2O,H2和N2的后退火处理,之后进行高温快速退火,最后制备Al电极4H-SiC MOS电容.I-V和C-V测试结果表明,各样品的氧化层击穿场强均大于9 MV/cm,PH3处理可以降低界面有效负电荷和近界面氧化层陷阱电荷,但PH3处理样品的界面态密度比N2O处理的结果要高.经N2O氛围PECVD后退火样品在距离导带0.2和0.4 eV处的界面态密度分别约为1.7× 1012和4×1011eV-1·cm-2,有望用于SiC MOSFET器件的栅氧处理.     

SiC MOS器件界面钝化研究进展

从氧化后退火处理、氮化处理、碳帽、钡夹层、淀积氧化物后退火处理五个方面介绍了碳化硅钝化工艺。通过改进钝化工艺可以有效降低界面态密度。针对这几种钝化工艺对SiC/SiO₂界面态密度的影响进行讨论,分析几种钝化工艺的优劣,并重点介绍了氧化后退火处理和氮化处理两种钝化方法。研究发现,NO氮化工艺能有效降低界面态密度,提高界面可靠性。该工艺适用于SiC MOS器件的制造。     

氮氢混合等离子体处理对SiC MOS电容可靠性的影响

研究了ECR(Electron cyclotron resonance)氮氢混合等离子体表面处理及氧化后退火处理工艺对SiC MOS电容可靠性的影响。通过I-V特性及经时击穿特性测试对处理后样品可靠性进行评价,结果表明经过ECR氮氢混合等离子体氧化后退火处理后,样品绝缘性、击穿电荷量及寿命等可靠性能均明显提高,再经过ECR氮氢混合等离子体表面处理后样品可靠性进一步提升,预计在3 MV/cm场强下平均寿命可达到10年左右。通过C-V特性测试及界面组成分析对改善样品可靠性的物理机理进行研究,发现ECR氮氢混合等离子体处理可以有效的降低界面态密度,其中氧化后退火处理很好地钝化了SiOxCy和碳团簇等界面缺陷,而表面处理使SiC表面平整化,有效降低表面态密度,抑制了界面态的产生,进而共同增强了SiC MOS电容的可靠性。     

SiC掺氯热氧化技术与SiC MOS电容偏压温度不稳定性

偏压温度不稳定性(BTI)是影响SiC MOS器件性能的关键因素。提出了一种制备SiC MOS电容的新工艺，即在SiC干氧氧化气氛中掺入氯化氢(HCl),并对比了不同HCl与O₂体积流量比对SiC MOS电容电学性能的影响。结果表明，该工艺有效地改善了SiC MOS电容的栅氧击穿特性，降低了界面态密度，提升了平带电压稳定性。二次离子质谱(SIMS)和X射线光电子能谱(XPS)测试分析表明，掺氯热氧化技术能够有效消除界面缺陷。进一步分析表明，SiC掺氯热氧化技术能够降低可动离子面密度和氧化层陷阱电荷密度，能够有效改善器件的BTI特性。     

退火气氛对Ge MOS电容电特性的影响

采用反应磁控溅射法在Ge衬底上制备了HfTiO高介电常数k栅介质薄膜,研究了不同气体(N2、NO、N2O)淀积后退火对Ge金属-氧化物-半导体(MOS)电容性能的影响.透射电子显微镜和电特性测量表明,湿N2退火能有效抑制界面层的生长,提高界面质量,改善栅极漏电流特性,从而得到最优的器件性能,即Al/HfTiO/n-Ge MOS电容的栅介质等效氧化物厚0.81 nm,k=34.5,带隙中央界面态密度为2.4×1011cm-2·eV-1,1 V栅偏压下的栅极漏电流为2.71×10-4A·cm-2.     

Electrical characterization of high-k gate dielectrics fabricated using plasma oxidation and post-deposition annealing of a Hf/SiO2/Si structure

High permittivity (high-k) gate dielectrics were fabricated using the plasma oxidation of Hf metal/SiO₂/Si followed by the post-deposition annealing (PDA), which induced a solid-phase reaction between HfO_x and SiO₂. The oxidation time and PDA temperature affected the equivalent oxide thickness (EOT) and the leakage current density of the high-k dielectric films. The interfacial structure of the high-k dielectric film/Si was transformed from HfO_x/SiO₂/Si to HfSi_xO_y/Si after the PDA, which led to a reduction in EOT to 1.15 nm due to a decrease in the thickness of SiO₂. These high-k dielectric film structures were investigated by X-ray photoelectron spectroscopy. The leakage current density of high-k dielectric film was approximately four orders of magnitude lower than that of SiO₂.     

Performance analysis of 20 nm gate-length In0.2Al0.8N/GaN HEMT with Cu-gate having a remarkable high ION/IOFF ratio

Abstract： We propose a new structure of InxAll-xN/GaN high electron mobility transistor （HEMT） with gate length of 20 nm. The threshold voltage of this HEMT is achieved as -0.472 V. In this device the InA1N barrier layer is intentionally n-doped to boost the ION/IOFF ratio. The InAlN layer acts as donor barrier layer for this HEMT which exhibits an ION = 10-4.3 A and a very low IOFF = 10-14.4 A resulting in an ION/IoFF ratio of 1010.1. We compared our obtained results with the conventional InAlN/GaN HEMT device having undoped barrier and found that the proposed device has almost l0s times better ION/IOFF ratio. Further, the mobility analysis in GaN channel of this proposed HEMT structure along with DC analysis, C-V and conductance characteristics by using small-signal analysis are also presented in this paper. Moreover, the shifts in threshold voltage by DIBL effect and gate leakage current in the proposed HEMT are also discussed. InAlN was chosen as the most preferred barrier layer as a replacement of AlGaN for its excellent thermal conductivity and very good scalability.     

CH3NH3PbI3/p-Si异质结的光电特性研究

利用一步溶液法在p型Si衬底上生长有机/无机杂化钙钛矿CH3NH3PbI3薄膜,构成CH3NH3PbI3/p-Si异质结。利用原子力显微镜(AFM)、扫描电子显微镜(SEM)对薄膜形貌和结构进行表征,通过无光照和有光照条件下的电流-电压(I-V)、电容-电压(C-V)测试对异质结的光电特性进行研究。I-V测试结果显示CH3NH3PbI3/p-Si异质结具有整流特性,正反偏压为±5V时,整流比大于70,并在此异质结上观察到了光电转换现象,开路电压为10mV,短路电流为0.16uA。C-V测试结果显示Ag/CH3NH3PbI3/p-Si异质结具有与MIS(金属-绝缘层-半导体)结构相似的C-V特性曲线,与理想MIS的C-V特性曲线相比,异质结的C-V曲线整体沿电压轴向正电压方向平移。C-V特性曲线的这种平移表明Ag/CH3NH3PbI3/p-Si异质结界面存在界面缺陷,CH3NH3PbI3层也可能存在固定电荷。这种界面缺陷是导致CH3NH3PbI3/p-Si异质结开路电压的大幅度降低的重要原因。此外,CH3NH3PbI3薄膜的C-V测试结果显示其具有介电非线性特性,其介电常数约为4.64。     

Performance improvement of c-Si solar cell by a combination of SiNx/SiOx passivation and double P-diffusion gettering treatment

SiN_x/SiO_x passivation and double side P-diffusion gettering treatment have been used for the fabrication of c-Si solar cells. The solar cells fabricated have high open circuit voltage and short circuit current after the double P-diffusion treatment. In addition to better surface passivation effect, SiN_x/SiO_x layer has lower reflectivity in long wavelength range than conventional SiN_x film. As a consequence, such solar cells exhibit higher conversion efficiency and better internal quantum efficiency, compared with conventional c-Si solar cells.     

微波法制备高活性H1-xSr2Nb3-xMoxO10 (x = 0, 0.05, 0.1, 0.15 and 0.2) 光催化剂

通过微波辅助法制备出高活性H1-xSr2Nb3-xMoxO10光催化材料,制备过程和时间均被大大缩短。采用X射线粉末衍射（XRD）、扫描电镜（SEM）、紫外-可见吸收吸收光谱（UV-Vis DRS）等表征其材料性能。考察了催化材料在40W汞灯辐照下催化降解甲基橙的催化性能。实验结果表明,MoO3的掺入量为15%（摩尔分数）时,材料的光催化性能最优。     

Chemical compositions and optical properties of HfOxNy thin films at different substrate temperatures

High-k HfO_xN_y thin films have been grown by radio frequency (rf) reactive sputtering of metal Hf target in N₂/Ar/O₂ ambient at different substrate temperatures. The chemical compositions of the films have been investigated as a function of substrate temperature by X-ray photoelectron spectroscopy (XPS). XPS measurements showed that nitrogen concentration increases with an increase in substrate temperature. Room-temperature spectroscopic ellipsometry (SE) with photon energy 0.75–6.5 eV was used to investigate the optical properties of the films. SE results demonstrated that refractive index n increases with an increase in substrate temperature. Based on TL parameters which were obtained from the best fit results used in a simulation of the measured spectra, meanwhile, we conclude that the energy band gap (E_g) decreases with an increase in substrate temperature.     

Optical characterization of as-prepared and rapid thermal oxidized partially strain compensated Si1−x−y GexCy films

The optical properties of as-prepared and rapid thermal oxidized (RTO) heteroepitaxial Si_1−x−yGe_xC_y alloys grown on Si substrate have been characterized using spectroscopic ellipsometry. The critical points E₁, E₀′, E₂ band gaps were determined by line shape fitting in the second derivative spectra of the pseudo-dielectric functions. For as-prepared films, the E₁ gap increases with C concentration and a linear dependence on C content was observed. However, the E₂ gap decreases as the C concentration increases. For the RTO samples, the amplitude of E₂ transition reduces rapidly and the E₁ transition shifts to a lower energy. The reduction in the amplitude of E₂ transitions is due to the presence of oxide layer. A high Ge content layer and the low C content in the RTO films account for the E₁ shift to lower energy and the increase of the refractive indices.     

Melt growth and stoichiometry control of (Cd1−xZnx)1+yTe single crystals

Growth of (Cd_1−xZn_x)_1+yTe(CZT) single crystals is tried by a modified Bridgman method using a reservoir chamber containing Cd and Zn metals with a fixed mole ratio. The aim of this method is to obtain the single crystals with controlled deviation y from stoichiometry and homogeneous target composition x. A suitable growth condition was examined experimentally and the effectiveness of this method for controlling the deviation y from stoichiometry and the composition x is confirmed.     

Structural and interfacial properties of high-k HfOxNy gate dielectric films

The thermal stability and interfacial characteristics for hafnium oxynitride (HfO_xN_y) gate dielectrics formed on Si (1 0 0) by plasma oxidation of sputtered HfN films have been investigated. X-ray diffraction results show that the crystallization temperature of nitrogen-incorporated HfO₂ films increases compared to HfO₂ films. Analyses by X-ray photoelectron spectroscopy confirm the nitrogen incorporation in the as-deposited sample and nitrogen substitution by oxygen in the annealed species. Results of FTIR characterization indicate that the growth of the interfacial SiO₂ layer is suppressed in HfO_xN_y films compared to HfO₂ films annealed in N₂ ambient. The growth mechanism of the interfacial layer is discussed in detail.     

利用拉曼谱鉴别锗硅合金微结构变化

随着硅浓度的增大,计算的拉曼谱结果表明,Ge-Si模式和Si-Si模式向高波数移动,而Ge-Ge模式向低波数移动,这种拉曼谱的变化强烈的依赖于合金微结构的变化。它的模式频率的线性变化依赖于Ge/Si的力学常熟的变化。这种现象可以用来鉴别合金中Si含量的浓度。可以通过拉曼散射表征这种复杂的微结构变化。