LT-GaAs with high breakdown strength at low temperature for power MISFET applications

Low temperature grown GaAs has been fabricated containing a limited amount of excess arsenic. The material has a low conductivity in the order of 100KΩ cm, due to hopping in a deep donor band. This σ-LT-GaAs was grown reproducibly by using the lattice mismatch as the primary parameter for substrate temperature calibration. Breakdown fields, in the order of 100kV/cm, are observed for planar structures and increased at low measurement emperatures. Low hopping conductivity and high breakdown field are also observed in the lossy dielectric metal-insulator-semiconductor field-effect transistor device using σ-LT-GaAs as a surface layer. The record radio frequency power density of 4.0W/mm at 77K is extracted from the dc output characteristics.     

Defects in molecular beam epitaxial GaAs grown at low temperatures

We have utilized a variable energy positron beam and infrared transmission spectroscopy to study defects in GaAs epilayers grown at low temperatures (LT-GaAs) by molecular beam epitaxy. We have measured the Doppler broadening of the positron-electron annihilation gamma ray spectra as a function of positron implantation energy. From these measurements, we have obtained results for the depth profiles of Ga monovacancies in unannealed LT-GaAs and Ga monovacancies and arsenic cluster related defects in annealed LT-GaAs. We have also studied the effects of the Si impurities in annealed LT-GaAs. The infrared transmission measurements on unannealed LT-GaAs furnish a broad defect band, related to As antisites, centered at 0.370 eV below the conduction band.     

高辐射强度的带THz扼流圈的偶极天线阵列模拟分析

为了提高太赫兹辐射强度, 设计了带THz扼流圈的偶极天线阵列.模拟结果表明, 增加直线阵的阵元数对平均匹配效率影响很小, 却能线性增加相干辐射强度.加入THz扼流圈可减小进入到传输线的交流分量, 进而减小共振频率的偏移, 使平均匹配效率提升了两倍.相比于网格排列的平面阵, 交错排列的阵元在垂直方向上具有更小的耦合, THz发射谱更窄.通过使用聚酰亚胺透镜代替硅透镜, 可有效提高输入电阻, 并将总效率由25%提高到35%.     

Mobility of modulation doped AlGaAs/low-temperature MBE-grown GaAs heterostructures

A study of the mobility of a novel modulation doped heterostructure in which the channel region is made of low-temperature molecular beam epitaxially grown GaAs (LT-GaAs) and all other layers are grown at normal temperatures is presented for the first time. The resistivity of the as-grown samples(in- situ annealed) is very high, as is that of single layers of bulk LT-GaAs. However, in the presence of light, the resistivity of the LT-GaAs modulation-doped field effect transistor (MODFET) is significantly lower, facilitating reliable Hall measurements. We speculate that the observed decrease in resistivity of the LT-GaAs MODFET is due to the formation of a two-dimensional electron gas (2DEG) at the heterointerface under illumination. A number of samples grown under different growth conditions were investigated. Mobilities for these samples were found to be in the range of 250 to 750 cm²Vs at 300K and ∼3000 to 5500 cm²Vs at 77K. A first-order computer simulation was implemented to calculate the mobility of the 2DEG using the relaxation-time approximation to solve the Boltzmann equation, taking into account different scattering mechanisms. Scattering by the arsenic clusters and by ionized impurities in the LT-GaAs MODFET channel are found to be the two dominant mechanisms limiting the mobility of the LT-GaAs MODFET samples. Experimental values are in good agreement with theoretical results.     

小孔径螺旋型光电导天线的太赫兹辐射特性研究

研究了小孔径螺旋型光电导天线的太赫兹辐射特性.利用太赫兹时域光谱技术测量了螺旋型光导天线辐射的太赫兹波谱,得到了其时域发射光谱.通过快速傅里叶变换得到相应的频域光谱,同时对两种不同孔径螺旋天线的太赫兹辐射特性进行了比较.实验结果表明,太赫兹信号强度会随偏置电压的增大而增强;在偏置电压和泵浦光功率相同的情况下,较小孔径的...     

光激发LT—GaAs共面微带传输线THz色散与衰减特性

彩和半经验色散公式分析了ＬＴ－ＧａＡｓ衬底共面微带传输线的ＴＨｚ模式色散与切伦柯夫辐射损耗特性,同时计算了导体欧姆损耗和衬底介电损耗,结果表明,较小的横向尺寸有利于改善ＬＴ－ＧａＡｓ共面微带传输线模式色散和辐射损耗特性。较大的横向尺寸比可降低导体欧姆损耗。     

低温砷化镓的外延lift-off和范德华贴附研究

研究了低温砷化镓的外延lift-off和基于范德华力在石英新衬底上贴附的实验方法:腐蚀掉100 nm厚的AlAs牺牲层,将外延生长的500 nm厚的低温砷化镓(LT-GaAs)从生长衬底上揭下(lift-off),借助于范德华力将LT-GaAs外延膜贴附在新衬底上.Lift-off之前在LT-GaAs表面上滴附黑蜡,以增强在lift-off过程中对LT-GaAs的保护,和加快反应气体扩散离开反应区的过程.针对500 nm厚的LT-GaAs外延薄膜的揭起和贴附,给出了低温砷化镓的最佳lift-off尺寸和提高范德华力贴附质量的实验技术.此外还给出了利用所得到的lift-off后的LT-GaAs制备的共平面条形结构光导开关的时间特性:上升时间小于1.5ps,FWHM小于2 ps.     

片上太赫兹天线集成器件LT-GaAs外延转移工艺

提供了一种实现片上太赫兹天线集成器件光电导开关材料低温GaAs(LT-GaAs)外延层的转移工艺,使用HNO_3-NH_4OH-H_2O-C_3H_8O_7·H_2O溶液-H_2O_2-HCl腐蚀体系化学湿法腐蚀分子束外延(MBE)生长的外延材料,Hall测试表明MBE生长的此外延材料电阻率在106Ω·cm量级.剥离半绝缘GaAs(SI-GaAs)衬底层与Al_(0.9)Ga_(0.1)As牺牲层得到1.5μm LT-GaAs与环烯烃聚合物(COP)键合的结构.原子力显微镜(AFM)、扫描电子显微镜(SEM)、高倍显微镜形貌表征表明剥离后的结构表面平整光滑,表面粗糙度(RMS)为2.28 nm,EDAX能谱仪分析显示该结构中不含Al组分,满足光刻形成光电导开关的要求.     

Application of low temperature GaAs to GaAs/Si

Low Temperature grown GaAs (LT-GaAs) was incorporated as a buffer layer for GaAs on Si (GaAs/Si) and striking advantages of this structure were confirmed. The LT-GaAs layer showed high resistivity of 1.7 × 10⁷ ω-cm even on a highly defective GaAs/Si. GaAs/Si with the LT-GaAs buffer layers had smoother surfaces and showed much higher photoluminescence intensities than those without LT-GaAs. Schottky diodes fabricated on GaAs/Si with LT-GaAs showed a drastically reduced leakage current and an improved ideality factor. These results indicate that the LT-GaAs buffer layer is promising for future integrated circuits which utilize GaAs/Si substrates.     

低温生长GaAs非平衡载流子的超快动力学特性

采用飞秒激光光谱技术研究了ＬＴ－ＧａＡｓ受激载流子的超快弛豫特性,讨论了载流子散射、载流子－声子互作用和缺陷捕获对载流子弛豫特性的贡献,测定载流子的捕获时间约为５００ｆｓ,并发现其随载流子的过超能量减少而增加