使用三氯硅烷（TCS）作为含氯生长源,在多片外延设备生长了高质量的4H-SiC外延材料。研究了原位预刻蚀气体HCl流量和刻蚀时间对SiC外延材料表面三角形缺陷的影响,使用光学显微镜和表面缺陷分析仪对SiC外延材料表面缺陷进行表征测试和统...使用三氯硅烷（TCS）作为含氯生长源,在多片外延设备生长了高质量的4H-SiC外延材料。研究了原位预刻蚀气体HCl流量和刻蚀时间对SiC外延材料表面三角形缺陷的影响,使用光学显微镜和表面缺陷分析仪对SiC外延材料表面缺陷进行表征测试和统计,使用傅里叶红外测试仪（FTIR）和原子力显微镜（AFM）对外延材料表面形貌进行表征。结果表明,预刻蚀气体体积流量和时间对4英寸SiC外延材料表面三角形缺陷影响明显,随着HCl体积流量和时间的增加,材料表面的三角形缺陷密度先减小后增加,在HCl流量为100 m L/min、刻蚀时间为20 min时,三角形缺陷密度最低达到0.47cm-2。此外,通过调整C/Si比和载气体积流量等参数,使4英寸SiC外延材料掺杂浓度不均匀性和厚度不均匀性均得到有效改善,结果表明该外延片质量满足SiC电力电子器件的应用。展开更多
We report dc and the first-ever measured small signal rf performance of epitaxial graphene field-effect transistors （GFETs）, where the epitaxial graphene is grown by chemical vapor deposition （CVD） on a 2-inch c-p...We report dc and the first-ever measured small signal rf performance of epitaxial graphene field-effect transistors （GFETs）, where the epitaxial graphene is grown by chemical vapor deposition （CVD） on a 2-inch c-plane sapphire substrate. Our epitaxial graphene material has a good flatness and uniformity due to the low carbon concentration during the graphene growth. With a gate length Lg = 100 nm, the maximum drain source current Ids and peak transconductance gm reach 0.92 A/mm and 0.143 S/mm, respectively, which are the highest results reported for GFETs directly grown on sapphire. The extrinsic cutoff frequency （fT） and maximum oscillation frequency （fmax） of the device are 12 GHz and 9.5 GHz, and up to 32 GHz and 21.5 GHz after de-embedding, respectively. Our work proves that epitaxial graphene on sapphire substrates is a promising candidate for rf electronics.展开更多
In this paper,high temperature direct current（DC） performance of bilayer epitaxial graphene device on SiC substrate is studied in a temperature range from 25℃ to 200℃.At a gate voltage of-8 V（far from Dirac point...In this paper,high temperature direct current（DC） performance of bilayer epitaxial graphene device on SiC substrate is studied in a temperature range from 25℃ to 200℃.At a gate voltage of-8 V（far from Dirac point）,the drainsource current decreases obviously with increasing temperature,but it has little change at a gate bias of ＋8 V（near Dirac point）.The competing interactions between scattering and thermal activation are responsible for the different reduction tendencies.Four different kinds of scatterings are taken into account to qualitatively analyze the carrier mobility under different temperatures.The devices exhibit almost unchanged DC performances after high temperature measurements at 200℃ for 5 hours in air ambience,demonstrating the high thermal stabilities of the bilayer epitaxial graphene devices.展开更多
We report on an improved metal-graphene ohmic contact in bilayer epitaxial graphene on a SiC substrate with contact resistance below 0.1 Ω.mm. Monolayer and bilayer epitaxial graphenes are prepared on a 4HoSiC substr...We report on an improved metal-graphene ohmic contact in bilayer epitaxial graphene on a SiC substrate with contact resistance below 0.1 Ω.mm. Monolayer and bilayer epitaxial graphenes are prepared on a 4HoSiC substrate in this work. Their contact resistances are measured by a transfer length method. An improved photoresist-free device fabrication method is used and is compared with the conventional device fabrication method. Compared with the monolayer graphene, the contact resistance Rc of bilayer graphene improves from an average of 0.24Ω·mm to 0. 1 Ωmm. Ohmic contact formation mechanism analysis by Landauer＇s approach reveals that the obtained low ohmic contact resistance in bilayer epitaxial graphene is due to their high carrier density high carrier transmission probability, and p-type doping introduced by contact metal Au.展开更多
In this Letter, we report large-area（600 μm diameter） 4H-SiC avalanche photodiodes（APDs） with high gain and low dark current for visible-blind ultraviolet detection. Based on the separate absorption and multiplic...In this Letter, we report large-area（600 μm diameter） 4H-SiC avalanche photodiodes（APDs） with high gain and low dark current for visible-blind ultraviolet detection. Based on the separate absorption and multiplication structure, 4H-SiC APDs passivated with SiNxinstead of SiO2 are demonstrated for the first time, to the best of our knowledge. Benefitting from the SiNx passivation, the surface leakage current is effectively suppressed. At room temperature, high multiplication gain of 6.5 × 10^5 and low dark current density of 0.88 μA∕cm^2 at the gain of 1000 are achieved for our devices, which are comparable to the previously reported small-area Si C APDs.展开更多
Ultraviolet(UV) detectors with large photosensitive areas are more advantageous in low-level UV detection applications. In this Letter, high-performance 4 H-SiC p-i-n avalanche photodiodes(APDs) with large active area...Ultraviolet(UV) detectors with large photosensitive areas are more advantageous in low-level UV detection applications. In this Letter, high-performance 4 H-SiC p-i-n avalanche photodiodes(APDs) with large active area(800 μm diameter) are reported. With the optimized epitaxial structure and device fabrication process,a high multiplication gain of 1.4 × 10^6 is obtained for the devices at room temperature, and the dark current is as low as ~10 p A at low reverse voltages. In addition, record external quantum efficiency of 85.5% at 274 nm is achieved, which is the highest value for the reported Si C APDs. Furthermore, the rejection ratio of UV to visible light reaches about 10^4. The excellent performance of our devices indicates a tremendous improvement for largearea SiC APD-based UV detectors. Finally, the UV imaging performance of our fabricated 4 H-SiC p-i-n APDs is also demonstrated for system-level applications.展开更多
文摘使用三氯硅烷（TCS）作为含氯生长源,在多片外延设备生长了高质量的4H-SiC外延材料。研究了原位预刻蚀气体HCl流量和刻蚀时间对SiC外延材料表面三角形缺陷的影响,使用光学显微镜和表面缺陷分析仪对SiC外延材料表面缺陷进行表征测试和统计,使用傅里叶红外测试仪（FTIR）和原子力显微镜（AFM）对外延材料表面形貌进行表征。结果表明,预刻蚀气体体积流量和时间对4英寸SiC外延材料表面三角形缺陷影响明显,随着HCl体积流量和时间的增加,材料表面的三角形缺陷密度先减小后增加,在HCl流量为100 m L/min、刻蚀时间为20 min时,三角形缺陷密度最低达到0.47cm-2。此外,通过调整C/Si比和载气体积流量等参数,使4英寸SiC外延材料掺杂浓度不均匀性和厚度不均匀性均得到有效改善,结果表明该外延片质量满足SiC电力电子器件的应用。
文摘本文对金属有机物化学气相淀积法在4英寸GaN衬底上生长出的高质量AlGaN/GaN HEMT外延材料进行了研究分析。生长过程采用NH_(3)/H_(2)混合气体及H_(2)交替通入的方法对衬底表面进行了预处理,阻隔了界面杂质的扩散。得益于衬底与外延的高度晶格匹配,GaN材料的螺位错密度降低到1.4×10^(7)cm^(-2),刃位错密度降低到3.0×10^(6)cm^(-2);非接触霍尔测试仪结果显示二维电子气迁移率为2159 cm^(2)/V·s,说明制备的材料晶体质量高且电学性能优异。此外,由于衬底与外延之间不存在热失配,使用拉曼光谱仪发现同质外延的Ga N E2(TO)峰位与衬底的E2(TO)峰位完全重合,表明同质外延过程中无应力应变产生。
基金Supported by the National Natural Science Foundation of China under Grant No 61306006.
文摘We report dc and the first-ever measured small signal rf performance of epitaxial graphene field-effect transistors （GFETs）, where the epitaxial graphene is grown by chemical vapor deposition （CVD） on a 2-inch c-plane sapphire substrate. Our epitaxial graphene material has a good flatness and uniformity due to the low carbon concentration during the graphene growth. With a gate length Lg = 100 nm, the maximum drain source current Ids and peak transconductance gm reach 0.92 A/mm and 0.143 S/mm, respectively, which are the highest results reported for GFETs directly grown on sapphire. The extrinsic cutoff frequency （fT） and maximum oscillation frequency （fmax） of the device are 12 GHz and 9.5 GHz, and up to 32 GHz and 21.5 GHz after de-embedding, respectively. Our work proves that epitaxial graphene on sapphire substrates is a promising candidate for rf electronics.
基金Project supported by the National Natural Science Foundation of China(Grant No.61306006)
文摘In this paper,high temperature direct current（DC） performance of bilayer epitaxial graphene device on SiC substrate is studied in a temperature range from 25℃ to 200℃.At a gate voltage of-8 V（far from Dirac point）,the drainsource current decreases obviously with increasing temperature,but it has little change at a gate bias of ＋8 V（near Dirac point）.The competing interactions between scattering and thermal activation are responsible for the different reduction tendencies.Four different kinds of scatterings are taken into account to qualitatively analyze the carrier mobility under different temperatures.The devices exhibit almost unchanged DC performances after high temperature measurements at 200℃ for 5 hours in air ambience,demonstrating the high thermal stabilities of the bilayer epitaxial graphene devices.
基金Supported by the National Natural Science Foundation of China under Grant No 61306006
文摘We report on an improved metal-graphene ohmic contact in bilayer epitaxial graphene on a SiC substrate with contact resistance below 0.1 Ω.mm. Monolayer and bilayer epitaxial graphenes are prepared on a 4HoSiC substrate in this work. Their contact resistances are measured by a transfer length method. An improved photoresist-free device fabrication method is used and is compared with the conventional device fabrication method. Compared with the monolayer graphene, the contact resistance Rc of bilayer graphene improves from an average of 0.24Ω·mm to 0. 1 Ωmm. Ohmic contact formation mechanism analysis by Landauer＇s approach reveals that the obtained low ohmic contact resistance in bilayer epitaxial graphene is due to their high carrier density high carrier transmission probability, and p-type doping introduced by contact metal Au.
基金supported by the National Natural Science Foundation of China(Nos.61604137 and 61674130)
文摘In this Letter, we report large-area（600 μm diameter） 4H-SiC avalanche photodiodes（APDs） with high gain and low dark current for visible-blind ultraviolet detection. Based on the separate absorption and multiplication structure, 4H-SiC APDs passivated with SiNxinstead of SiO2 are demonstrated for the first time, to the best of our knowledge. Benefitting from the SiNx passivation, the surface leakage current is effectively suppressed. At room temperature, high multiplication gain of 6.5 × 10^5 and low dark current density of 0.88 μA∕cm^2 at the gain of 1000 are achieved for our devices, which are comparable to the previously reported small-area Si C APDs.
基金supported by the National Natural Science Foundation of China(Nos.61604137 and 61674130)
文摘Ultraviolet(UV) detectors with large photosensitive areas are more advantageous in low-level UV detection applications. In this Letter, high-performance 4 H-SiC p-i-n avalanche photodiodes(APDs) with large active area(800 μm diameter) are reported. With the optimized epitaxial structure and device fabrication process,a high multiplication gain of 1.4 × 10^6 is obtained for the devices at room temperature, and the dark current is as low as ~10 p A at low reverse voltages. In addition, record external quantum efficiency of 85.5% at 274 nm is achieved, which is the highest value for the reported Si C APDs. Furthermore, the rejection ratio of UV to visible light reaches about 10^4. The excellent performance of our devices indicates a tremendous improvement for largearea SiC APD-based UV detectors. Finally, the UV imaging performance of our fabricated 4 H-SiC p-i-n APDs is also demonstrated for system-level applications.
