Study of depth-dependent tetragonal distortion of quaternary AIInGaN epilayer by Rutherford backscattering/channeling

<正>A 240-nm thick Al_0.4In_0.02Ga_0.58N layer is grown by metal organic chemical vapour deposition,with an over 1-μm thick GaN layer used as a buffer layer on a substrate of sapphire（0001）.Rutherford backscattering and channeling are used to characterize the microstructure of AlInGaN.The results show a good crystalline quality of AlInGaN(x_min= 1.5%) with GaN buffer layer.The channeling angular scan around an off-normal（1213） axis in the {1010} plane of the AlInGaN layer is used to determine tetragonal distortion e_T,which is caused by the elastic strain in the AlInGaN.The resulting AlInGaN is subjected to an elastic strain at interfacial layer,and the strain decreases gradually towards the near-surface layer.It is expected that an epitaxial AlInGaN thin film with a thickness of 850 nm will be fully relaxed （e_T=0）.     

氧气氛中p-GaN/Ni/Au电极在相同温度不同合金时间下的欧姆接触形成机制和扩散行为

用卢瑟福背散射/沟道技术研究了p-GaN上的Ni/Au电极在氧气氛下相同合金温度(500℃)不同合金时间后的微结构演化,以揭示欧姆接触的形成机制.利用背散射随机谱和RUMP模拟程序研究了电极金属之间的互扩散,用沟道谱探测了电极金属中的氧分布.结合不同合金时间下比接触电阻ρ_c的变化,发现随着合金时间的延长比接触电阻持续降低,在合金时间60 s后降低的速度减慢, Au扩散到GaN的表面,在p-GaN上形成外延结构,O向电极内部扩散反应生成NiO对降低ρ_{关键词： GaN 卢瑟福背散射/沟道 欧姆接触}     

Structure Characterization of Modified Polyimide Films Irradiated by 2MeV Si Ions

Structures of polyimide （6051） films modified by irradiation of 2.0 MeV Si ions with different fluences are studied in detail. Variations of the functional groups in polyimide are investigated by attenuated total reflection Fourier transform infrared spectroscopy （ATR-FTIR） and Raman spectroscopy. The results indicate that the functional groups can be destroyed gradually with the increasing ion fluenee. The variations of structure and element contents are characterized by x-ray diffraction （XRD）, Rutherford backscattering spectrometry （RBS） and x- ray photoelectron spectroscopy （XPS）. The results indicate that the contents of N and O decrease significantly compared with the original samples, some graphite-like and carbon-rich phases are formed in the process of irradiation.     

Charge Transport and Magnetotransport Properties of Polyimide Irradiated by 80keV Co Ions

Charge transport properties of polyimide films implanted with 80 keV Co ions at two different fluences （series I： 1.25 × 10^17 ions/cm^2, series Ⅱ： 1.75 × 10^17 ions/cm^2） are studied in detail. For series I, the temperature dependence of surface resistivity fits Mott＇s equation very well. It is on the insulating side of the insulator-metal transition （IMT）. However, for series Ⅱ, the temperature dependence of surface resistivity is not in agreement with Mott＇s equation. It is on the metallic side of lMT. The magnetotransport properties of these two series are also studied. No significant magnetoresistive effect is observed for series I at both 5 K and 300 K. For series Ⅱ, an obvious magnetoresistive effect is observed at 5 K, while there is no magnetoresistive effect at 300 K. Rutherford backscattering spectrometry （RBS） is applied to confirm the actual fluence for these two series.     

Low temperature testing and neutron irradiation of a swept charge device on board the HXMT satellite

We present the low temperature testing of an SCD detector, investigating its performance such as readout noise, energy resolution at 5.9 keV and dark current. The SCD's performance is closely related to temperature, and the temperature range of -80 ℃ to -50 ℃ is the best choice, where the FWHM at 5.9 keV is about 130 eV. The influence of the neutron irradiation from an electrostatic accelerator with fluence up to 1×10⁹ cm^-2 has been examined. We find the SCD is not vulnerable to neutron irradiation. The detailed operations of the SCD and the test results of low temperature are reported, and the results of neutron irradiation are discussed.     

Measurements of charge transfer ef f iciency in a proton-irradiated swept charge device

Charged Coupled Devices(CCDs) have been successfully used in several low energy X-ray astronomical satellites over the past two decades. Their high energy resolution and high spatial resolution make them a perfect tool for low energy astronomy, such as observing the formation of galaxy clusters and the environment around black holes. The Low Energy X-ray Telescope(LE) group is developing a Swept Charge Device(SCD) for the Hard Xray Modulation Telescope(HXMT) satellite. A SCD is a special low energy X-ray CCD, which can be read out a thousand times faster than traditional CCDs, simultaneously keeping excellent energy resolution. A test method for measuring the charge transfer efficiency(CTE) of a prototype SCD has been set up. Studies of the charge transfer inefficiency(CTI) with a proton-irradiated SCD have been performed at a range of operating temperatures. The SCD is irradiated by 3×108cm-210 MeV protons.     

Design and optimization of the readout system for X-ray CCDs

A readout system for X-ray CCDs based on an improved architecture is presented; by optimizing several critical circuit blocks along the analog signal chain, the conflict between the readout speed and readout noise is greatly alleviated. Using CCD47-10 as its target CCD, the readout system has achieved 8.6e^- readout noise and 142 eV FWHM at 5.9 keV Mn m K_α under a pixel rate of 80 kHz. Also its performance of imaging has been investigated.     

Tetragonal Distortion of GaN Epilayer with Multiple Buffer Layers on Si （111） Studied by RBS/Channelling and HRXRD

Rutherford backscattering （RBS）/channelling and high resolution x-ray diffraction （HRXRD） have been used to characterize the tetragonal distortion of a GaN epilayer with four Alx Ga1-xN and single AIN buffer layers grown on a Si （111） substrate by metal-organic vapour phase epitaxy （MOVPE）. The results show that a 1000nm GaN epilayer with a perfect crystal quality （Xmin = 1.54%） can be grown on the Si （111） substrate in virtue of multiple buffer layers. Using the RBS/channelling angular scan around an off-normal （1213） axis in the （1010） plane and the conventional HRXRD θ - 20 scans normal to GaN （0002） and （1122） planes at the 0° and 180° azimuth angles, the tetragonal distortion eT, which is caused by the elastic strain in the epilayer and different buffer layers, can be obtained respectively. The two experiments are testified at one result, the tetragonal distortion of GaN epilayer is nearly to a fully relaxed （eT = 0）.     

He,Au离子辐照AuCu_3致元素表面偏析

采用磁控溅射方法在单晶硅(111)衬底上制备了AuCu_3薄膜,用2 MeV He离子和1 MeV Au离子对薄膜进行辐照,用卢瑟福背散射对He,Au离子辐照前后AuCu_3薄膜近表面的成分变化进行了分析,对不同离子辐照导致的表面元素偏析行为进行了研究.结果表明:当2 MeV He离子辐照时,随着辐照剂量增大,观察到样品近表面Au元素偏析的趋势;当1 MeV Au离子辐照时,随着辐照剂量增大,观察到样品近表面Cu元素偏析的趋势,与He离子辐照相反.通过对He,Au离子在样品中产生的靶原子空位及其分布分析,发现靶原子空位浓度分布的梯度是导致两种不同表面元素偏析趋势的原因,空位扩散是其中的主要机理.     

硬X射线调制望远镜低能探测器量子效率标定

低能X射线望远镜是硬X射线调制望远镜卫星的主要载荷之一,探测器采用CCD236.探测器的量子效率会影响能谱拟合和绝对流量,有必要对其进行标定.利用~(55)Fe放射源,以硅漂移探测器为标准探测器,标定了CCD236在Mn-K_α(5.899 keV)和Mn-K_β(6.497 keV)能量点处的量子效率,此能段在Fe线附近,对X射线天文观测有重要价值.考虑探测器的分裂事例后,Mn-K_α和Mn-K_β处的量子效率分别为71%和62%.在-95—-30?C工作温度范围内,CCD量子效率与温度无关.利用CCD236的结构及实测的量子效率,不考虑沟阻影响,得到耗尽层厚度为38μm.对CCD236施加不同的电压,其量子效率基本不变,表明其在两相驱动下高低电平的耗尽层厚度相等,进而说明CCD236一直工作在深耗尽状态,其耗尽层到了外延层和衬底层边界,已达最大值.