低补偿度n－Hg＿（1－x）Cd＿xTe的磁致金属－绝缘体相变和相变后的温度激活输运行为

报道了ｘ＝０．２１４组份、低补偿度（Ｋ《１）ｎ－Ｈｇ＿（１－ｘ）Ｃｄ＿ｘＴｅ晶体在０．３─３０Ｋ温度范围，０─７Ｔ强磁场下的横向磁阻、电子霍耳迁移率、霍耳系数测量结果，观测到了磁致金属－绝缘体相变和相变后的温度激活输运行为。分析实验数据，提出：低补偿度、组份：ｘ＝０．２附近的ｎ－Ｈｇ＿（１－ｘ）Ｃｄ＿ｘＴｅ，磁致金属－绝缘体相变（ＭＩＴ）发生的机理是载流子在浅施主杂质态上的磁冻结；发生磁冻结的前提是热冻出（ｔｈｅｒｍａｌｆｒｅｅｚｅ－ｏｕｔ），即首先必须在很低的温度下将导带电子冻出到施主态上。相变后的温度激活输运行为可以表示成Ｒ＿Ｈ（Ｔ）＝Ｒ＿（Ｈ０）ｅｘｐ［ａ／ｋＴ］，它实际上反映了磁冻结在施主上的电子，随温度的升高，逐步热激发到导带的过程，从磁致ＭＩＴ后的激活能初步推知，导带下存在两个浅施主能级。     

n型碲镉汞MIS器件动态存储时间研究

通过对动态存储时间的测量，分析了ｘ＝０．３１的ｎ型碲镉汞（Ｈ_1-xＣｄ_xＴｅ）ＭＩＳ器件的少子暗电流机理．理论计算和实验结果都表明，在其工作温度区域（～７７Ｋ），通过禁带中深能级中心辅助的间接隧道电流将限制器件的电学性能。 关键词：     

Gd1-xCaxBa2Cu3O7-y高温超导体压力效应的研究

研究了Ｇｄ_1-xＣａ_xＢａ₂Ｃｕ₃Ｏ_7-y（０．０≤Ｘ≤０．２０）高温超导体在常压和高压下的超导电性在１－３００Ｋ温度范围内，利用Ｂｒｉｄｇｍａｎ对顶砧获得压力达９．０ＧＰａ，测量了（Ｘ＝０．１０，０．１５，０．２０）样品的ｄＴ_c／ｄｐ分别为７．６８，７．８和４．４６Ｋ／ＧＰａ。发现Ｔ_c的压力导数随着ｃａ²⁺含量的增加而下降，分析了氧含量对Ｔ_c和ｄＴ_c／ｄＰ的影响．利用常压下晶格参数精修值和阳离子与氧离子间距随压力的改变，说明ＣｕＯ₂面在超导电性上的作用，用ＣｕＯ₂面之间耦合解释Ｔ_c（Ｐ）曲线的非线性关系。 关键词：     

Sm2(Fe,M)17C1.5(M=Ga,Si)化合物的形成和磁性

用电弧炉熔炼方法制备了Ｓｍ₂Ｆｅ_17-xＭ_xＣ_1.5（Ｍ＝Ｇａ，Ｓｉ）化合物，研究了它们的形成、结构与磁性。实验结果表明，用Ｇａ替代Ｆｅ，当２≤ｘ≤６时，可形成Ｔｈ₂Ｚｎ₁₇型单相化合物，而Ｓｉ的替代仅在ｘ＝２时为单相结构。居里温度随Ｇａ含量的增加从ｘ＝２时的６３３Ｋ下降到ｘ＝６时的３５１Ｋ，Ｓｍ₂Ｆｅ₁₅Ｓｉ₂关键词：     

LaxBi2-xTi4O11的合成及相变研究

合成了Ｌａ_xＢｉ_2-xＴｉ₄Ｏ₁₁系列样品，并完成了它们的喇曼光谱和ｘ射线衍射测量；结果表明，该体系在Ｘ＝１．２经历了一次相变，且相变与最低频声子模随Ｘ的变化有关。Ｌａ_0.2Ｂｉ_1.8·Ｔｉ₄Ｏ₁₁的相变温度为２００℃。初步获得Ｌａ₂Ｔｉ₄Ｏ₁₁的结构为正交结构。 关键词：     

典型颗粒超导体YBa2Cu3O7/V2O5中临界电流随温度变化的特性

通过制备（ＹＢａ₂Ｃｕ₃Ｏ₇）_1-x（Ｖ₂Ｏ₅）_x（０≤ｘ≤０．１５）复合材料，获得了一系列典型的弱连接的颗粒超导体，其中以ｄＲ／ｄＴ－Ｔ关系中呈现出双峰转变为主要特征。第一峰代表晶粒的超导转变，第二峰代表颗粒系统超导长程序的形成。对于具有双峰转变的样品，其临界电流密度一致地符合ｉ_c～（１－ｔ）^ｎ，ｎ＝１．６．这一行为与三维Ｊｏｓｅｐｈｓｏｎ结网络系统的渗流行为相一致；对于不具有双峰转变的系统，临界电流密度随温度的变化尽管也可以用ｊ_c～（１－ｔ）^ｎ描述，但是幂指数ｎ明显地大于１．６，且随样品的不同而离散地分布。本文还对产生这种离散的原因进行探索和分析。 关键词：     

BaSn1-xSbxO3-δ和Ba1-yLaySnO3-δ的导电机制

测量了ＢａＳｎ_1-xＳｂ_xＯ_3-δ和Ｂａ_1-yＬａ_yＳｎＯ_3-δ样品的低温电阻率和磁化率．实验结果表明，在较低温度区域，两类样品的导电机制均是传导电子的范围可变跳跃。而在较高温度区域，ＢａＳｎ_1-xＳｂ_xＯ_3-δ样品的电导主要是电子从定域态到扩展态的跃迁所贡献，Ｂａ_1-yＬａ_yＳｎＯ_3-δ样品的电导则可能来源于电子的最近邻跳跃。 关键词：     

NdFe10M2(M=Mo,Cr)渗C(N)化合物的结构和内禀磁性研究

本文采用气—固反应，将Ｃ、Ｎ原子渗入到ＮｄＦｅ₁₀Ｍ₂结构中的间隙位，不改变它们的ＴｈＭｎ₁₂型结构，进而研究了ＮｄＦｅ₁₀Ｍ_xZ_x（ｚ＝Ｃ，Ｎ）的内禀磁性，Ｃ，Ｎ原子对它们的磁性影响不尽相同，其中ＮｄＦｅ₁₀Ｍｏ₂Ｃ_0.8有单轴各向异性，磁晶各向异性场Ｈ_s＝１１６．０ｋＯｅ。最后对样品进行了穆斯堡尔谱测量，研究了它们的超精细场特性。 关键词：     

(Ba_(1-x)K_x)BiO_3电子结构与超导电性

用第一原理的ＬＤＦ-ＬＭＴＯ-ＡＳＡ超元胞法，模拟由Ｘ射线吸收谱精细结构测定的ＢａＢｉＯ_３中，Ｂｉ有两种价态Ｂｉ^３＋和Ｂｉ^5＋及与之相应的两种不同键长的Ｂｉ—Ｏ八面体，以及Ｋ掺杂对晶体结构的影响．计算了Ｂａ₄Ｂｉ₄Ｏ₁₂，（Ｂａ_３Ｋ）Ｂｉ₄Ｏ₁₂，（ＢａＫ）Ｂｉ₂Ｏ₆，（ＢａＫ_３）Ｂｉ₄Ｏ₁₂，Ｋ₂Ｂｉ₂Ｏ₆（简记为（４０４），（３１４），（１１２），（１３４），（０２２））五种“样本”的电子结构．结果表明，（４０４）和（３１４）分别为Ｅ_g＝１.６ｅＶ及Ｅ_g＝１.５ｅＶ的半导体，其它“样本”为金属．总能的分析表明（１３４）是不稳定的，故溶解极限为ｘ＝０.５．以“取样”方式按伯努利分布确定任意组分各“样本”的概率，进而计算了（Ｂａ_1-xＫ_x）ＢｉＯ_３电子结构随组分的变化．最后用逾渗模型说明了超导转变温度Ｔ_c在ｘ＝０．２５附近的突变 关键词：     

非晶态(Fe1-xCox)77.5Nd4B18.5合金的电阻率的压力系数和压力弛豫研究

在０．０００１－２．４ＧＰａ流体静压力范围详细研究了非晶(Fe_1-xCo_x)_77.5Nd₄B_18.5（０≤ｘ≤１．０）合金的电阻率与压力的关系，得到该非晶合金电阻率的压力系数随组分ｘ变化的规律。结果表明：用少量的钴（ｘ＝０．２）替代铁，不会影响其硬磁性和热稳定性，同时却可减小电阻率的压力系数，从而增强电磁性能在压力下的稳定性。此外还观测到在０．５１ＧＰａ保压３－２４h的结构弛豫，进一步求出该非晶台金电阻率的压力弛豫时间对组分ｘ的依赖关系。 关键词：     

n-Hg1-xCdxTe的Shubnikov-de Haas振荡

在T=2.3—24K的温度范围里,研究了不同组分的n-Hg_1-xCd_xTe样品的SdH效应。测量了纵向和横向的磁阻振荡峰,能清晰地分辨n>3的自旋分裂峰。由此计算了n-Hg_1-xCd_xTe的能带参数,讨论了导带的非抛物线性和费密能级随磁场的变化对实验结果的影响。 关键词：     

n-Hg0.80Mg0.20Te界面积累层中二维电子气的输运特性研究

通过变磁场霍耳测量研究了MBE生长的Hg_0.80Mg_0.20Te薄膜在15 —250K温度范围内的输运特性.采用迁移率谱(MS)和多载流子拟合过程(MCF)相结合的方法对 实验数据进行了分析,由该方法获得的结果和Shubnikov de Hass(SdH)振荡测量的结果都证 明材料中存在二维(2D)电子和三维(3D)电子.其中2D电子主要来自于Hg_1-xMgxTe-CdTe的界面积累层或Hg_1-x关键词： 变磁场霍耳测量 界面积累层 二维电子气 1-xMg_xTe')" href="#">Hg_1-xMg_xTe     

The fluctuation freeze-out of electrons in Cdx Hg1−x Te

The model was developed on the basis of experimental data, explaining pecularities of galvanomagnetic properties of Cd_x Hg_1?xTe by the “fluctuation freeze-out” of electrons - i.e. by their localization in fluctuation potential wells. In semimetallic samples this process is associated with a sharp increase in the fluctuation potential amplitude when the acceptor level goes out from the conduction band with the growth of magnetic field.     

Sb掺杂Hg1-xCdxTe的光致发光

对不同Sb掺杂浓度Hg_1-xCd_xTe（x≈0.38）样品在3.9—115K的温度范围内进行了光致发光实验测量，观察到与局域激子、带到带和施主受主对有关的辐射复合过程．并用光致发光手段发现Sb掺杂在x≈0.38的Hg_1-xCd_xTe中引入的约30meV的受主能级 关键词：     

Galvanomagnetic properties of n-type Hg0.8Cd0.2Te

Galvanomagnetic properties of low and high mobility n-Hg_0.8Cd_0.2Te are reported. The experiments were carried out in magnetic fields up to 60 kG and between 1.8 and 77 K. The Hall coefficient does not show thermal and magnetic freeze-out of carriers. At 77 K the transversal magnetoresistance shows a proportionality ?⊥ ∝ B as was predicted by Gurevich and Firsov for the case of polar optical scattering in non-degenerated semiconductors. At 4 K where the mobility is governed by impurity scattering ?⊥ ∝ B^2.4 was observed in the extreme quantum limit. A negative longitudinal magnetoresistance was found at 77 K. The experimental results of high and low mobility samples show significant differences.     

On the Einstein Relation in Ternary Semiconductors in the Presence of Crossed Electric and Magnetic Fields

We investigate theoretically the Einstein relation for the diffusivity-mobility ratio of the electrons in ternary semiconductors at low temperatures in the presence of crossed electric and quantizing magnetic fields on the basis of threeband Kane model. It is found, taking n-Hg_1-xCd_xTe as an example, that DMR shows an oscillatory magnetic field dependence. Besides, the DMR increase both with increasing electron concentration and decreasing alloy composition respectively.     

Temperature dependence of 1.98 eV photoluminescence band in Cd1-xMnxTe semiconductor alloys

The 1.98 eV photoluminescence (PL) band in Cd_1-xMn_xTe has been studied over the composition range 0.4 ≤ x ≤ 0.7. This emission is shown to be insensitive to magnetic phase transitions. Above ～ 70 K, the emission intensity displays two temperature activated regions which appear to be intrinsic to the manganese system. The band maximum undergoes a red shift on cooling down to 60 K, followed by a nearly equal blue shift down to 1.8 K: models explaining these behaviors are discussed.     

Transient response of hot electrons in narrow-gap semiconductors at low temperatures in the presence of a longitudinal quantizing magnetic field

Transient response of hot electrons in narrow-gap semiconductors to a step electric field in the presence of a longitudinal quantizing magnetic field has been studied at low temperatures using displaced Maxwellian distribution. The energy and momentum balance equations are used assuming acoustic phonon scattering via deformation potential responsible for the energy relaxation and elastic acoustic phonon scattering together with ionized impurity scattering for momentum relaxation. The calculations for the variation of drift velocity and electron temperature as functions of time are made for n-Hg_0.8Cd_0.2 Te in the extreme quantum limit at 1.5 K and 4.2 K. The momentum and energy relaxation times are found to be of the same order of magnitudes as with the experimental values. The magnetic field and lattice temperature dependences of the relaxation rates have been investigated.One of the authors, Suchandra Bhaumik, acknowledges the Council of Scientific and Industrial Research (New Delhi) for financial support.     

CdxHg1-xTe混晶声子谱的远红外光谱研究

在温度4.2—300K和波数15—5OOcm^-1的范围内研究了x=0.18到0.45的不同组分的Cd_xHg_1-xTe的远红外吸收光谱。除剩余射线吸收带两侧的双声子吸收结构外,实验首次观察到一个位于波数20—50cm^-1的低频吸收带。用面间力常数的密度函数法等估计了Cd_xHg_1-xTe混晶的声子谱,并将上述低频吸收带归之于混晶导致的无序和“掺杂”诱发TA声子带模吸收效应。 关键词：     

Quantum corrections to the electrical conduction in an AlGaN/GaN heterostructure

A new method for magneto-transport characterisation of semiconductor heterostructures is presented. The classical model of mixed conduction, modified by corrections resulting from quantum effects, has been used in the analysis of the conductivity-tensor components, magnetoresistance, and Hall coefficient in n-type Al_0.85Ga_0.15N/GaN in magnetic fields up to 12 T, in the temperature range from 2 to 295 K. The mixed conduction is due to high-mobility carriers in the conduction band in the interface and to low-mobility carriers in the conduction band in the GaN layer and in an impurity band. The corrections to the conduction of high-mobility carriers result from quantum effects: negative magnetoresistance, extraordinary Hall effect, and freeze-out of electrons. Negative magnetoresistance is due to localisation of electrons and to increasing tunnel coupling between electron states in different minima of a random potential, due to interface roughness. The extraordinary Hall effect has been explained by interaction of electrons with magnetic moments of dislocations in the interface. Decreasing concentration of electrons is probably due to Landau quantisation of the conduction band in the interface of the heterostructure. Received: 27 November 2000 / Accepted: 18 December 2000 / Published online: 3 April 2001