零砷压下Ga液滴在AlGaAs表面扩散行为的研究

本文研究了Ga液滴在Al_(0.4)Ga_(0.6)As表面的扩散行为.在衬底温度为380℃时,在Al_(0.4)Ga_(0.6)As薄膜上沉积3 MLGa液滴;在零砷压下,通过改变退火时间(0 s, 150 s, 300 s, 450 s, 600 s)观察液滴形貌变化,利用剖面线、坑洞和液滴的比例变化分析发现液滴高度随时间延长越来越低,直至形成坑洞,Ga液滴内部的原子在Al_(0.4)Ga_(0.6)As表面上首先向外扩散,而后与表面As原子结合成环,约在退火时间到500 s时扩散模式逐步变化为向下溶蚀.利用公式计算出最初Ga覆盖率约为2.6 ML,并且在380℃下Ga液滴在Al_(0.4)Ga_(0.6)As表面的液滴消耗速率为0.0065 ML/s.     

Al_xGa_(1-x)As(100)表面性质的研究

用紫外光电子能谱研究了Al_(0.7)Ga_(0.3)As的表面态结构,观察到Al_(0.7)Ga_(0.3)As在价带中的两个表面态结构。在1500L原子氢吸附后消失。研究了这两个表面态结构在热退火消除表面损伤过程中的变化。结合LEED和XPS的实验结果,确定在450℃左右的热退火可以有效地消除损伤,获得一个完整的Al_(0.7)Ga_(0.3)As(100)表面。     

低温下InAs纳米结构在GaAs(001)表面形成机制的研究

改变生长工艺、控制并调整液滴中原子扩散机制是对复杂纳米结构制备的关键途径,并且对基于液滴外延方法研究半导体纳米结构十分重要.本文在不同衬底温度,不同As压下在GaAs(001)上沉积相同沉积量(5 monolayer)的In液滴并观察其表面形貌的变化.原子力显微镜图像显示,液滴晶化后所形成的扩散"盘"且呈现一定的对称性.随着衬底温度的增高,圆盘半径逐渐扩大,扩散圆盘中心出现了坑.而随着As压的增高,所形成的液滴密度增加,以液滴为中心所形成的扩散圆盘宽度逐渐减小.基于经典的成核扩散理论对实验数据拟合得到:GaAs(001))表面In原子在[110]和[110]晶向上的扩散激活能分别为(0.62 ± 0.01) eV和(1.37 ± 0.01) eV,且扩散系数D_0为1.2 × 10~(-2) cm~2/s.对比其他研究小组的结果证实了理论的正确性.实验中得到的In原子的扩散激活能以及In液滴在GaAs(001)上扩散机理,可以为InAs纳米结构特性的调制提供实验指导.     

Al_(0.17)Ga_(0.83)As/GaAs(001)薄膜退火过程的热力学分析

在As_4束流等效压强为1.2×10~(-3)Pa、退火60 min条件下改变退火温度,对Al_(0.17)Ga_(0.83)As/GaAs薄膜表面平坦化的条件进行了探讨.定量分析了薄膜表面坑、岛与平台的覆盖率和台阶-平台间薄膜粗糙度随退火温度变化的规律,得到最合适的退火温度为545℃(±1℃);根据退火模型发现退火温度的改变会影响参与熟化的原子的数量,熟化原子比θ正比于退火温度,即θ∝Τ.退火温度540℃条件下退火约60 min,薄膜表面达到基本平坦,推测此时0.20θ0.25;退火温度为545℃时,推测退火时间约为55-60 min.本实验得到的结论可以为生长平坦的Al_(0.17)Ga_(0.83)As/GaAs薄膜提供理论与实验指导.     

高In组分InGaNAs/GaAs量子阱的生长及发光特性

采用分子束外延技术(MBE)在Ga As衬底上外延生长高In组分(40%)In Ga NAs/Ga As量子阱材料,工作波长覆盖1.3~1.55μm光纤通信波段。利用室温光致发光(PL)光谱研究了N原子并入的生长机制和In Ga NAs/Ga As量子阱的生长特性。结果表明:N组分增加会引入大量非辐射复合中心;随着生长温度从480℃升高到580℃,N摩尔分数从2%迅速下降到0.2%;N并入组分几乎不受In组分和As压的影响,黏附系数接近1;生长温度在410℃、Ⅴ/Ⅲ束流比在25左右时,In_(0.4)Ga_(0.6)N_(0.01)As_(0.99)/Ga As量子阱PL发光强度最大,缺陷和位错最少;高生长速率可以获得较短的表面迁移长度和较好的晶体质量。     

Co/GaAs(100)界面形成以及Co超薄膜磁性质的研究

利用同步辐射光电发射和铁磁共振(FMR)研究了Co/GaAs(100)界面形成以及Co超薄膜的磁性质.结果表明,在低覆盖度(约为0.2nm)下,Co吸附原子与衬底发生强烈的界面反应,在覆盖度为0.9nm时,形成稳定的界面.从衬底扩散出的Ga原子与Co覆盖层合金化,而部分As原子与Co原子发生反应,形成稳定的键合,这些反应产物都停留在界面处很窄的区域(0.3—0.4nm)内.另一部分As原子偏析在Co覆盖层表面.结合理论模型,详细地讨论了界面结构及Ga，As原子的深度分布.FMR结果表明,生长的Co超薄膜具 关键词：     

用低能电子衍射研究GaAs(110)表面的弛豫

用低能电子衍射研究了GaAs(110)表面的弛豫。发现当理论与实验之间符合得最好时,得到的结构是,保持表面上As—Ga键长不变用一个27.32°±0.24°的旋转角(ω),使As原子向外移动0.10±0.02?,Ga原子向内移动0.55±0.02?,而从Ga到第二层时空间为d₂=1.45±0.01?,从第二层Ga到第三层的空间为d₃=2.01±0.01?。对此结构As的背键长l_As=2.43±0.01?(收缩0.56％),而Ga的背键长l_Ga=2.253±0.004?(收缩8.0％)。 关键词：     

GaAs/Al_(0.23)Ga_(0.77)As双量子阱的带边不连续性和阱间耦合

本文报道在300和77K对一组具有不同垒宽Lb的GaAs/Al_(0.23)Ga_(0.77)As双量子阱样品的光调制反射谱(PR)的研究结果。除观察到11H,11L和22H等容许跃迁外,同时还识别一个从Al_(0.23)Ga_(0.77)As价带顶至量子阱第一电子束缚能级的跃迁,另一个从量子阱第一轻空穴束缚能级至Al_(0.23)Ga_(0.77)As导带底的跃迁。利用这些跃迁确定导带边不连续性为0.63。对Lb≤40实验观察到11H和11L跃迁都明显地分裂成对称和反对称分量,对分裂大小的实验值与理论计算作了比较。在77K的11H的PR谱中在高能端明显地出现一个肩形峰,其形状不能用PR标准线形来拟合。如认为它对应于带间跃迁,并由此估计激子的束缚能约为8meV。     

Co/S钝化GaAs(100)界面形成的SRPES研究

利用同步辐射光电发射谱研究了Co与CH\-3CSNH\-2处理的S钝化GaAs(100)的界面形成.发现 其界面反应较弱,Co覆盖层达到0.8nm时,形成稳定的界面.GaAs表面上和S原子形成桥 键的Ga原子与Co发生交换反应并扩散到覆盖层中,形成Co—S键.Co覆盖层表面无偏析As的出现,与Co/GaAs(100)界面不同,这表明GaAs表面的S钝化可有效地阻止As原子向覆盖层的扩散. 关键词：     

形成半导体量子线结构的质子注入方法研究

用20keV的质子(H~+)注入到Al_(0.3)Ga_(0.7)As/GaAs/Al_(0.3)Ga_(0.7)As单量子阱,经快速退火,促使势垒上的Al向量子阱内扩散,尝试制备了线宽从0.5μm到0.1μm的量子线结构.由低温(14K)下阴极射线发光谱测量,观察到量子线中发光谱峰的蓝移,并通过与理论计算比较,讨论注入区内外Al的内扩散及掩膜区边缘横向离散的影响. 关键词：     

Effect of Ga and As vacancies on electronic properties of Ga0.9375Al0.0625As

Electronic properties of Ga_0.9375Al_0.0625As with Ga and As monovacancies are investigated with the density functional theory. A perfect GaAlAs, which specifically produces a radiation wavelength of ～825.6 nm, has been determined in terms of size and number of atoms of substances. We have introduced eight types of vacancies depending on the distance from the Al atom to the vacancy to obtain the changes in charges, band structures, density of states, and optical conductivity. We found that the Fermi level enters into the valence band due to the formations of the Ga or As vacancies so that the vacant materials may show the characteristics of the p-type semiconductor. Interestingly, Ga-vacancy systems make direct band gaps, which are still good for the use in a semiconductor laser. But, As-vacancy systems, where the indirect gaps appear, are not feasible for the same application. It has been found that the latter phenomenon is induced by a newly formed density of state, which comes from the overlapping of hybridised 4s and 4p orbitals of Ga atoms around As vacancy.     

Influence of Ga/(Ga + In) grading on deep‐defect states of Cu(In,Ga)Se2 solar cells

The benefits of gallium (Ga) grading on Cu(In,Ga)Se₂ (CIGS) solar cell performance are demonstrated by comparing with ungraded CIGS cells. Using drive‐level capacitance profiling (DLCP) and admittance spectroscopy (AS) analyses, we show the influence of Ga grading on the spatial variation of deep defects, free‐carrier densities in the CIGS absorber, and their impact on the cell's open‐circuit voltage V_oc. The parameter most constraining the cell's V_oc is found to be the deep‐defect density close to the space charge region (SCR). In ungraded devices, high deep‐defect concentrations (4.2 × 10¹⁶cm^–3) were observed near the SCR, offering a source for Shockley–Read–Hall recombination, reducing the cell's V_oc. In graded devices, the deep‐defect densities near the SCR decreased by one order of magnitude (2.5 × 10¹⁵ cm^–3) for back surface graded devices, and almost two orders of magnitude (8.6 × 10¹⁴ cm^–3) for double surface graded devices, enhancing the cell's V_oc. In compositionally graded devices, the free‐carrier density in the absorber's bulk decreased in tandem with the ratio of gallium to gallium plus indium ratio GGI = Ga/(Ga + In), increasing the activation energy, hindering the ionization of the defect states at room temperature and enhancing their role as recombination centers within the energy band. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

High-spin spectroscopy of 63 31Ga32 and 65 31Ga34

High-spin states in the nuclei ⁶³Ga and ⁶⁵Ga were studied following the reaction ³²S + ⁴⁰Ca at a reaction energy of 125 MeV and using the GASP γ-ray spectrometer in combination with the ISIS charged-particle detector system. In addition to low-lying negative-parity states with single-particle character, rotational-like cascades built on the 9/2⁺ and 19/2^- states have been observed in both nuclei. Sidebands with negative parity in ⁶³Ga and positive parity in ⁶⁵Ga could be established. The experimental results are compared with Total Routhian Surface calculations which describe the nuclei as moderately deformed (β₂≈ 0.25) and γ soft at low rotational frequencies. The highest experimentally observed positive-parity state in ⁶⁵Ga (41/2⁺) is in good agreement with the calculated crossing of the collective band with a non-collective one terminating at this spin. Received: 20 December 2000 / Accepted: 2 May 2001     

The hyperfine structure anomalies of67Ga,69Ga,71Ga,72Ga,113In,115In,and117mIn

The ratios of theg _i -factors of⁶⁹Ga and⁷¹Ga and of¹¹³In and¹¹⁵In have been measured by the NMR method. Using hyperfine interaction constants from literature, the hyperfine structure anomalies⁶⁷Δ⁶⁹,⁶⁹Δ⁷¹,⁷¹Δ⁷² of gallium and¹¹³Δ¹¹⁵,¹¹⁵Δ^117m of indium in the² P _1/2 and² P _3/2 atomic ground states have been calculated.     

Relaxation rates of 69Ga and 71Ga nuclei in aqueous solutions

Line widths in the ⁶Li, ⁷Li, ²³Na, ³⁹K, ⁸⁵Rb, ⁸⁷Rb and ¹³³Cs N.M.R. spectra of solutions of the alkali salts of biphenyl and fluorenone are reported as a function of solvent and temperature. From a numerical analysis of the room temperature data the contribution of the various relaxation mechanisms to the line widths are established. It is shown that the results are consistent with the observed solvent and temperature dependence of the line widths. Values of the electron spin correlation time are obtained and a value of 1·6 ± 0·4 Å is found for the ‘Van der Waals radius’ of the biphenyl anion. Line width expressions for the static and the dynamic ion pair model are presented. It is demonstrated that the static ion pair model applies to solutions of caesium biphenylide. Semi-empirical rules are presented concerning the importance of various relaxation mechanisms for the different alkali nuclei in the type of solution studied here.     

Ga梯度分布对Cu(In,Ga)Se_2薄膜及太阳电池的影响

传统制备Cu(In,Ga)Se2(CIGS)手段之一是共蒸发三步法,工艺中通过Cu,In,Ga,Se 4种元素相互扩散、作用形成抛物线形的Ga梯度分布.本文通过调整Ga源温度制备了Ga梯度分布不同的CIGS薄膜及电池.利用多种测试方法,研究了Ga梯度分布不同对CIGS薄膜表面及背面结构性质及电性质的影响,计算分析了表面导带失调值及背面电场对电池性能的影响,从而获得了合适的Ga梯度分布,提高了电池光谱相应,获得了较好的电池性能参数.     

Possible mixed valence behavior of CeIr2Ga and YbIr2Ga

We report possible mixed valence behavior in the new ternary compounds CeIr₂Ga and YbIr₂Ga. These materials crystallize in the hexagonal Na₃As structure of space group P6₃ cm. Magnetization, specific heat and transport measurements show reduced magnetic moments and the absence of magnetic order above 0.04 K. The quasi-2D structure of these compounds offers the possibility for investigating the role of spatial dimensionality on mixed valence phenomena.     

Effect of Ga alloying on thermoelectric properties of InSb

As a potential thermoelectric (TE) material, the high lattice thermal conductivity and relatively low weighted mobility severely limit TE property optimization of InSb binary compound. In this paper, we substituted In of InSb with Ga and systematically investigated the effect of Ga alloying on the Seebeck coefficient, electrical conductivity and lattice thermal conductivity of InSb between 300 K and 770 K. We found that Ga alloying simultaneously reduced the lattice thermal conductivity and optimized the weighted mobility of InSb. The lattice thermal conductivity has been analyzed using Abeles model to gain more insight on the roles of Ga in In_1-xGa_xSb(x = 0, 0.1, 0.15, 0.2) solid solution. The synergetic effect of Ga alloying on the electron and phonon transport leads to a marked enhancement in TE potential of InSb. The dimensionless figures of merit of InSb and In_0.8Ga_0.2Sb reach, respectively, 0.54 and 0.52 at 770 K.