第一性原理研究Mg,Si和Mn共掺GaN

采用基于密度泛函理论(DFT)的第一性原理平面波赝势法(PWP)计算Mg,Si和Mn共掺GaN电子结构和光学性质,分析比较计算结果.计算表明:掺杂后体系均在能隙深处产生自旋极化杂质带,具有半金属性,能产生自旋注入.与Mn掺杂GaN比较,Mg共掺后能使居里温度(TC)升高,并在1.0eV出现源于Mn4+离子基态4T1(F)到4T2(F)态跃迁的较强的光吸收,而Mn掺杂GaN时位于1.3eV处的吸收峰消失;Si共掺后没能使TC升高,且在低能区无光吸收现象.

Optical and Electrical Properties of GaN.Mg Grown by MOCVD

Mg-doped GaN layers prepared by metalorganic chemical vapor deposition were annealed at temperatures between 550 and 950℃. Room temperature （RT） Hall and photoluminescence （PL） spectroscopy measurements were performed on the as-grown and annealed samples. After annealing at 850℃, a high hole concentration of 8 × 10~(17) cm~(-3) and a resistivity of 0. 8lΩ·cm are obtained. Two dominant defect-related PL emission bands in GaN.. Mg are investigated; the blue band is centered at 2. 8eV （BL） and the ultraviolet emission band is around 3.27eV （UVL）. The relative intensity of BL to UVL increases after annealing at 550℃, but decreases when theannealing temperature is raised from 650 to 850℃, and finally increases sharply when the annealing temperature is raised to 950C. The hole concentration increases with increased Mg doping, and decreases for higher Mg doping concentrations. These results indicate that the difficulties in achieving high hole concentration of 10~(18)cm~(-3) appear to be related not only to hydrogen passivation, but also to self-compensation.

MOCVD生长Mg掺杂GaN的退火研究

用MOCVD技术在50mm蓝宝石衬底(0001)面上生长了GaN∶Mg外延膜,对样品进行热退火处理并作了Hall、双晶X射线衍射(DCXRD)和室温光致发光谱(PL)测试.Hall测试结果表明,950℃退火后空穴浓度达到5×1017cm-3以上,电阻率降到2.5Ω·cm;(0002)面DCXRD测试发现样品退火前、后的半峰宽均约为4′;室温PL谱中发光峰位于2.85eV处,退火后峰的强度比退火前增强了8倍以上,表明样品中大量被H钝化的受主Mg原子在退火后被激活.

Catalytic Activation of Mg-Doped GaN by Hydrogen Desorption Using Different Metal Thin Layers

The annealing of Mg-doped GaN with Pt and Mo layers has been found to effectively improve the hole concentration of such material by more than 2 times as high as those in the same material without metal. Compared with the Ni and Mo catalysts, Pt showed good activation effect for hydrogen desorption and ohmic contact to the Ni/Au electrode. Despite the weak hydrogen desorption, Mo did not diffuse into the GaNepilayer in the annealing process, thus suppressing the carrier compensation phenomenon with respect to Ni and Pt depositions, which resulted in the high activation of Mg acceptors. For the GaN activated with the Ni, Pt, and Mo layers, the blue emission became dominant, followed by a clear peak redshift and the degradation of photoluminescence signal when compared with that of GaN without metal.

~(133)Sm和~(149)Yb的β缓发质子衰变

利用40Ca+96Ru融合蒸发反应产生了近质子滴线核133Sm,配合氦喷嘴带传输系统采用“质子-γ”符合方法观测了它们的β缓发质子衰变,其中包括半衰期、质子能谱、第二代子核低位态之间的γ跃迁,并估计出衰变到第二代子核不同低位态的分支比．通过统计理论拟合上述实验数据,指认了133Sm的自旋宇称的可能范围．并用Woods-Saxon Strutinsky方法计算了限制组态的133Sm的核势能面,通过对比发现133Sm的自旋宇称可能有两种成分:5／2+和1／2-．这一结果与2001年发表的133Sm(EC+β+)衰变的简单衰变纲图是相容的．此外用同一方法分析了2001年Eur．Phys．J．A12: 1-4中发表的有关149Yb的β缓发质子衰变实验数据,由此指认了149Yb的基态自旋宇称为1／2-．

MG转轮收集探测系统的检验实验

利用SFC提供的束流对新建的转轮系统进行了检验实验,得到了相关的实验结果.实验证明了该装置的可靠性,为进一步开展超重核的研究完成了预实验.

~(22)Na(p,γ)~(23)Mg反应的实验研究

讨论了目前有关2 2 Na(p ,γ) 2 3Mg反应的实验研究工作 ,结合兰州放射性束流线上的放射性束流2 3Al的β+延发质子衰变实验的测量结果 ,给出了2 3Al延发衰变的质子能谱 ,并比较了近期实验给出的相关能级的自旋、宇称值 ,正是由于这种自旋、宇称和能级部分宽度的不确定性 ,导致了反应率计算的不确定性 .计算了同位旋相似态的共振强度 .对于测量到的新的延发衰变能级Ed =8.91 6MeV ,由于没有相应的能级宽度值 ,实验仅给出其相对共振强度值

Investigation of excited states in Mg-22 via resonant elastic scattering of Na-21+p and its astrophysical implications

The excited states in 22Mg have been investigated by the resonant elastic scattering of 21Na + p. A 4.0 MeV/nucleon 21Na beam was separated by the Center for Nuclear Study (CNS) radioactive ion beam separator (CRIB) and then used to bombard a thick (CH2)n target. The energy spectra of recoiled protons were measured at scattering angles of θc.m. ≈ 172◦ , 146◦, and 134◦, respectively. A wide energy-range of excitation function in 22Mg (up to Ex ∼ 8.9 MeV) was obtained simultaneously with a thick-target method, and a state at 7.06 MeV was newly observed. The resonant parameters were deduced from an R-matrix analysis of the center-of-mass (c.m.) differential cross-section data with a SAMMY-M6-BETA code. The astrophysical resonant reaction rate for the 18Ne(α,p)21Na reactionwas recalculated based on the present parameters. Generally speaking, the present rates are much smaller than the previous ones.