Neutron irradiation effect in two-dimensional electron gas of AlGaN/GaN heterostructures

AlGaN/GaN heterostructures have been irradiated by neutrons with different influences and characterized by means of temperature-dependent Hall measurements and Micro-Raman scattering techniques. It is found that the carrier mobility of two-dimensional electron gas (2DEG) is very sensitive to neutrons. At a low influence of 6.13 x 10(15) cm(-2), the carrier mobility drops sharply, while the sheet carrier density remains the same as that of an unirradiated sample. Moreover, even for a fluence of up to 3.66 x 10(16) cm(-2), the sheet carrier density shows only a slight drop. We attribute the degradation of the figure-of-merit (product of n(s) x mu) of 2DEG to the defects induced by neutron irradiation. Raman measurements show that neutron irradiation does not yield obvious change to the strain state of AlGaN/GaN heterostructures, which proves that degradation of sheet carrier density has no relation to strain relaxation in the present study. The increase of the product of n(s) x mu of 2DEG during rapid thermal annealing processes at relatively high temperature has been attributed to the activation of Ge-Ga transmuted from Ga and the recovery of displaced defects.

Raman Spectroscopy of Irradiation Effect in Three Carbon Allotropes Induced by Low Energy B Ions

Irradiation efect in three carbon allotropes C60, diamond and highly oriented pyrolytic graphite (HOPG) induced by 170 keV B ions, mainly including the process of the damage creation, is investigated by means of Raman spectroscopy technique. The diferences on irradiation sensitivity and structural stability for C60, HOPG and diamond are compared. The analysis results indicate that C60 is the most sensitive for B ions irradiation,diamond is the second one and the structure of HOPG is the most stable under B ion irradiation. The damage cross sections ? of C60, diamond and HOPG deduced from the Raman spectra are 7.78×10−15 , 6.38×10−15 and1.31 × 10−15cm2, respectively.

Molecular vibration spectroscopy study of irradiation effect in C-60 films induced by low energy ion

Irradiation effect in C-60 films induced by 170 keV B ion was investigated by means of Fourier transform infrared (FTIR) and Raman spectroscopies. The damage cross section sigma and the effective damage radius R are deduced from the experimental data of all four IR active modes and evident four Raman active modes of C-60 molecule. The differences on irradiation sensitivity and structural stability of the different active modes of C-60 molecule are compared. The results indicate that T-1u (4) of infrared active mode and A(g) (1) of Raman active mode are most sensitive for B ion irradiation. On the other hand T-1u (2) of infrared active mode and H-g (3) of Raman active mode are comparatively stable under B ion irradiation. (C) 2010 American Institute of Physics. [doi:10.1063/1.3512968]

蓝宝石中子辐照色心的研究

研究了中子辐照对蓝宝石(α-Al2O3)单晶体缺陷形成及光学性能的影响，对采用提拉法与温度梯度法生长的蓝宝石晶体进行中子辐照，通过对比辐照前后的吸收及荧光光谱变化，发现辐照使得蓝宝石晶体内形成F、F^+和F2^+色心缺陷，但不同方法生长的晶体样品中色心浓度差异明显。其中提拉法样品的F心浓度要高于温度梯度法样品，而温度梯度法样品中F^+色心浓度要高于提拉法样品。分析表明，这与两种方法生长的晶体中杂质含量差异有关。通过研究辐照后晶体的热致发光谱发现提拉法与温度梯度法生长的蓝宝石晶体分别在145℃与150℃有明

重离子在C60薄膜中引起的辐照效应研究

本项工作选择了不同种类、不同电荷态的从低能到高能的多种荷能重离子，对C60薄膜进行了辐照。并且通过多种分析测试手段（Raman、FTIR、XPS、AFM）分析了荷能重离子在C60薄膜中的辐照效应，并对机理进行了研究。同时也研究了低能B离子在碳的三种同素异构体：石墨、金刚石和C60中引起效应的差异。对于以弹性碰撞为主导的低能区，用170keV B离子辐照了碳的三种同素异构体，并从这些辐照样品的Raman谱数据演绎出了C60、金刚石和石墨的损伤截面σ。首次在完全相同的辐照条件下，研究了碳的三种同素异构体对辐照的敏感性和结构稳定性的差异，研究结果表明：C60对B离子辐照的敏感性最强，金刚石次之，相比之下石墨在B离子辐照下结构最为稳定，而且在辐照过程中，随辐照量的增加三种靶材料遭破坏的程度截然不同，表明它们的辐照敏感性差异随辐照量而变化。由XPS谱得知，在最高辐照量下石墨的sp2 C转变不多；而金刚石的sp3 C基本转变成了sp2 C。再次证明在B离子辐照下石墨的结构最为稳定。随着170keV B离子辐照量的增加，C60薄膜的FTIR和Raman谱中各激活模的强度都有不同程度的衰减，最终消失，即C60分子完全被破坏。在B离子的辐照下，C60分子的不同红外激活模和Raman激活模的辐照敏感性和结构稳定性也有差异：在C60分子的4个红外激活模中，T1u(4)对辐照最为敏感，而T1u(2)最为稳定。并率先确定了明显可见的5个Raman激活模对辐照的敏感性和结构稳定性的差异，其中Hg(4)对辐照最敏感，而Hg(3)最稳定。在以非弹性碰撞为主导的高能区，用2.15GeV的Kr离子辐照了多层堆叠的C60样品，辐照样品的分析结果表明：在相同能量或相同电子能损下，C60分子的辐照损伤随辐照量的增加趋于严重；而在相同辐照量下，C60的损伤程度随电子能损的增加而增强；但C60分子的损伤在某居中的电子能损值和辐照量下有一定的恢复。在电子能损相同或相近时，速度较低的Kr离子对C60分子的损伤更为严重，揭示了团簇材料的快重离子损伤建立过程中的离子速度效应。为了研究低速高电荷态离子在C60薄膜中引起的辐照效应，用不同电荷态的Xe离子辐照了C60薄膜。由AFM形貌图可知，不同电荷态Xe离子辐照C60薄膜，使其表面形貌发生了不同程度的改变。其粗糙度随着辐照Xe离子电荷态的不断增加而不断减小

Effect of annealing and gamma irradiation on undoped and Eu3+-doped Y2SiO5 single crystals

The absorption spectra of the undoped Y2SiO5 and Eu3+-doped Y2SiO5 crystals grown by the Czochralski technique were compared before and after annealing and, similarly, the unannealed and annealed crystals after gamma-ray irradiation. The absorption bands of Eu2+ ions with peaks at 300 and 390 nm were observed in the as-grown Y2SiO5:Eu3+ crystal. These peaks were more intense in H-2-annealed and irradiated Y2SiO5:Eu3+ crystals. The additional absorption peaks at 260 and 320-330 nm which were attributed to F color centers and O- hole centers were observed in irradiated undoped Y2SiO5 and Y2SiO5:Eu3+ crystals, respectively. (c) 2005 Elsevier B.V. All rights reserved.

Effect of gamma-irradiation on spectral properties of undoped Y2SiO5 crystals

The absorption spectra of undoped Y2SiO5 crystals were studied before and after gamma-irradiation. After gamma-irradiation, the additional absorption peaks at 260-270 and 320nm were observed in as-grown and H,annealed Y2SiO5 crystal, but it did not occur in air-annealed Y2SiO5 crystal. These absorption peaks were attributed to F color centers and O- hole centers, respectively. Owing to more oxygen vacancies and color centers in H-2-annealed Y2SiO5 crystal than that in as-grown Y2SiO5 crystal after gamma-irradiation, the additional absorption peaks were more intense in the former than that in the latter. With the irradiation dose increasing from 20 to 220kGy, the intensity of additional absorption peaks increased.

Effect of beta-irradiation on photoluminescence of MOCVD grown GaN

The effect of beta particles interaction on the optical properties of MOCVD grown GaN is reported. A significant change in luminescence properties of GaN is observed after exposing the material with 0.6 MeV beta particles with low dose of 10(12) cm(-2). The results obtained from photoluminescence measurements of irradiated GaN samples in low dose are found contradictory to those reported in literature for samples irradiated with heavy dose (> 10(15) cm(-2)) of electron. An increase in intensity of yellow luminescence has been observed with increasing dose of beta particles which is in disagreement to the already reported results in literature for heavily irradiated samples. A model has been proposed to sort out this inconsistency. The increase in YL intensity at low dose is attributed to the increase in concentration of VGaON complex whereas production of non-radiative VGaON clusters is assumed to justify the decrease in YL intensity at high dose.

Electron irradiation and thermal annealing effect on GaAs solar cells

This paper describes the effect of electron irradiation and thermal annealing on LPE AlGaAs/GaAs heterojunction solar cells with various p/n junction depths. The electron irradiation experiments were performed with energy of 3 MeV, fluences ranging from 1 x 10(14) to 5 x 10(15) e/cm(2). The results obtained demonstrate that the irradiation-induced degradation of performances of the cells is mainly in the short circuit current and could be mostly recovered by annealing at 260 degrees C for 30 min. Four electron traps, E-c - 0.24 eV, E-c - 0.41 eV, E-c - 0.51 eV, E-c - 0.59 eV, were found by DLTS analysis, only two shallow levels of which could be removed by the annealing. (C) 1998 Elsevier Science B.V. All rights reserved.

High efficiency AlxGa1-xAs/GaAs solar cells: Fabrication, irradiation and annealing effect

High efficiency AlxGa1-xAs/GaAs heteroface solar cells have been fabricated by an improved multi-wafer squeezing graphite boat liquid phase epitaxy (LPE) technique, which enables simultaneous growth of twenty 2.3 X 2.3cm(2) epilayers in one run. A total area conversion efficiency of 17.33% is exhibited (1sun, AM0, 2.0 x 2.0cm(2)). The shallow junction cell shows more resistance to 1 MeV electron radiation than the deep one. After isochronal or isothermal annealing the density and the number of deep level traps induced by irradiation are reduced effectively for the solar cells with deep junction and bombardment under high electron fluences.