N型掺杂应变Ge发光性质

应变锗材料具有准直接带特性,而且与标准硅工艺兼容,成为实现硅基发光器件重要的候选材料之一.本文基于vandeWalle形变势理论,计算了应变情况下半导体Ge材料的能带结构以及载流子在导带中的分布;通过分析载流子直接带和间接带间的辐射复合以及俄歇复合、位错等引起的非辐射复合的竞争,计算了N型掺杂张应变Ge材料直接带跃迁的内量子效率和光增益等发光性质.结果表明,张应变可有效增强Ge材料直接带隙跃迁发光.在1.5%张应变条件下,N型掺杂Ge的最大内量子效率可以达到74.6%,光增益可以与III-V族材料相比拟.     

Raman scattering and bond structure in chalcogenide glasses (SeGe system)

The Raman Scattering from amorphous SeGe is studied in the whole range of germanium content up to 80%. The result suggests an appearance of three-fold coordinated bond between Se and Ge above the germanium con- content of 40%.     

单晶锗表面键合光敏染料的研究

本文在烯丙醇单体上进行了两种一甲川菁的合成,并用一种新的化学键合法将两种一甲川菁染料键合在抛光的半导体单晶锗表面。将键合有光敏染料的锗片进行了激光Raman光谱及XPS谱测试,结果表明,与对照锗片相比,键合后的锗片表面,锗衬底的一级拉曼峰强度减少,并在600～3200cm~(-1)范围内出现了与键合颜料分子相应的拉曼频移;在XPS谱中,分别进行了C,N,O,S,卤素等原子的谱图分析,证实了键合颜料后半导体单晶锗表面增加了C—N,S—C,C—O等键,结果与键合的颜料分子结构相符,表明两种光敏染料通过锗氧键共价键合于锗表面。     

Applying an improved phonon confinement model to the analysis of Raman spectra of germanium nanocrystals

The improved phonon confinement model developed previously [11] is applied for definition of germanium nanocrystal sizes from the analysis of its Raman scattering spectra. The calculations based on the model allow determining the sizes of germanium nanocrystals more precisely from the analysis of their Raman spectra. In some cases, the comparative analysis of Raman data and electron microscopy data is carried out, and good agreement is observed.     

表面复合速度对于锗的光电导光谱分布的影响(一)

以不同波长的光分别照射半导体时,虽然各入射光的能量都相等,但所能产生的光电导却因波长而异。也就是说,以光电导对波长所作的图线——即光电导光谱分布——并不是一条与波长轴相平行的直线,而是一条有一定形状的曲线。事实上,半导体的光电导光谱分布一般都有一个峰值,位于该半导体的本征吸收带的长波限附近;光电导自峰值向长波方面迅速下降,向短波方面也有某种程度的下降。     

拉曼光谱研究n型4H-和6H-SiC晶体的载流子浓度

半导体材料的纵光学声子与等离子体激元耦合模(LOPC模)能够提供材料电学方面的相关信息。本文在室温下测得了n型4H-和6H-SiC的拉曼光谱,分析了掺入的杂质对于SiC晶体拉曼光谱的影响,通过拟合n型4H-和6H-SiC晶体的LOPC模的线型得到等离子体频率,并由此从理论上计算了载流子浓度。载流子浓度的理论计算值与霍尔测量的结果符合得很好。研究结果进一步证实了对于n型4H-和6H-SiC晶体,可以通过分析LOPC模的线形来较准确地给出相关材料的载流子浓度。     

Nonlinear absorption of CO2 laser radiation by nonequilibrium carriers in germanium

Nonlinear absorption of CO₂ laser pulses at the multi-MW level has been studied in n-type germanium at room temperature. This nonlinear absorption limits the level of CO₂ laser intensity that can be transmitted through an optical grade germanium crystal. The observed nonlinearity may be interpreted in terms of nonequilibrium electron-hole pairs generated by hot electrons created by the intense laser field. The number of nonequilibrium carriers generated is measured by photoconductivity experiments, and the results are correlated to the absorption measurements.     

Resonant Raman scattering by strained and relaxed germanium quantum dots

This paper reports on the results of resonant Raman scattering investigations of the fundamental vibrations in Ge/Si structures with strained and relaxed germanium quantum dots. Self-assembled strained Ge/Si quantum dots are grown by molecular-beam epitaxy on Si(001) substrates. An ultrathin SiO₂ layer is grown prior to the deposition of a germanium layer with the aim of forming relaxed germanium quantum dots. The use of resonant Raman scattering (selective with respect to quantum dot size) made it possible to assign unambiguously the line observed in the vicinity of 300 cm^?1 to optical phonons confined in relaxed germanium quantum dots. The influence of confinement effects and mechanical stresses on the vibrational spectra of the structures with germanium quantum dots is analyzed.     

Measurement of active carbon on ruthenium (110): Relevance to catalytic methanation

Hall measurements of charge carrier mobility and concentration in the channels appearing at germanium surfaces cleaved in liquid nitrogen, have been carried out to define the surface state charge Q_ss. The n-type germanium samples with various Sb atom concentrations and p-type germanium samples with various Sb and Au atom concentrations have been investigated. It has been established that surface states lie below the valence band top, and ¦Q_ss¦increases with the growth of the bulk doping level. The results obtained imply that the surface state density depends on the bulk impurity concentration. Possible explanation of the found bulk impurity influence on the surface state characteristics is proposed.     

Splitting of frequencies of optical phonons in tensile-strained germanium layers

Tensile-strained germanium films in Ge/GeSn/Si/GeSnSi multilayer heterostructures grown by molecularbeam epitaxy on Si(001) substrates are investigated by Raman spectroscopy. Biaxial tensile strains in the films reach 1.5%, which exceeds values previously obtained for this system. Splitting of frequencies of long-wavelength optical phonons is experimentally observed; i.e., the shift of the frequency of the singlet induced by biaxial tensile strains is larger than the shift of the frequency of the doublet in agreement with calculations. The strain-induced shift of Raman scattering peaks from two-phonon scattering in germanium is also detected.     

Phonon localization in Ge nanoislands and its manifestation in Raman spectra

Multilayer structures with germanium nanoislands that are formed on the silicon (111) surface upon submonolayer deposition by molecular-beam epitaxy have been investigated using Raman spectroscopy. To interpret the experimental Raman spectra, numerical calculations of the spectra have been performed for nanoislands containing from several to several hundred germanium atoms. The calculations demonstrate that the in-plane sizes of nanoislands (with sizes less than 2–3 nm) substantially affect the frequencies of phonons localized in these nanoislands. The experimental Raman spectra confirm the occurrence of the quantum size effect.     

Enhancement of Raman scattering by ultramarine using silver films on surface of germanium quantum dots on silicon

The germanium on silicon (Ge-on-Si) semiconductor nanostructures with a vacuum-deposited silver coating are tested as substrates for detecting microamounts of inorganic crystalline ultramarine pigment by enhanced Raman scattering (SERS). At least tenfold enhancement of Raman lines is obtained. The quantum-chemical calculations are performed and used to assign the bands in the Raman spectra. A significant electrooptic anharmonicity of vibrations of chromophore groups in the presence of an SERS-active compound is found.     

The electrical properties of dislocations in semiconductors

According to the theory of Read, closely spaced acceptor sites occur at dangling bonds along dislocations in semiconductors and lead to the formation of space-charge tubes which scatter electrons. In order to test Read's theory, parallel arrays of dislocations have been introduced by plastic bending and extensive electrical and galvanomagnetic measurements have been made on n-type germanium crystals. The experimental results are not in agreement with Read's theory; however, it is shown that Read's basic model is applicable but it must be modified by the assumption of non-specular electron scattering at the edges of the space-charge tubes—the electrical and galvanomagnetic consequences of the theory plus modification are worked out and good agreement with experiments obtained. The following quantities are derived: conductivity (σ), Hall constant (R), and magnetoresistance (MR) for current both parallel (‖) and perpendicular (⊥) to the long axis of the tubes with magnetic field (H) at right angles to the current. The quantities R, σ_‖ and σ_⊥ were measured versus temperature from 78°K to 300°K and MR was measured at 78°K as a function of the angle between H and the normal to the neutral plane (N). It was found that the variation of the electrical properties in the sample, particularly along the N direction, is so great that to obtain valid data one must use small samples cut from bent crystals; data are presented for whole samples, as well as small samples, in order to illustrate this effect. The dislocation acceptor level in n-type germanium is found to lie at ～0.50 ev below the conduction band edge. By using the above theory one can determine values of the dislocation density (N) from the result of electrical measurements on semiconductors; this was done in order to determine, on deformed n-type germanium, variations in N from region to region of bent samples as a function of temperature and time of deformation and annealing. In addition, other experiments were performed on plastically bent indium antimonide; it was found that the electrical effects of dislocations, although considerably different from those in germanium, can also be explained by the theory presented here.     

Photoluminescence of GeO<Subscript>2</Subscript> films containing germanium nanocrystals

Germanium nanocrystals were formed in a GeO₂ film during the process of germanium monoxide gas-phase deposition onto a sapphire substrate and studied by photoluminescence (PL) and Raman scattering spectroscopy. A PL peak in this heterosystem was observed in the visible region at room temperature. The sizes of Ge nanocrystals were estimated from the position of a Raman peak corresponding to scattering by localized optical phonons in germanium. The PL peak position calculated with allowance for the electron and hole size quantization in Ge nanocrystals coincides well with the experimentally observed position of this peak.     

Thermal conductivity of <Emphasis Type="Italic">n</Emphasis>-type Ge monocrystals

The pyroelectric method is used to demonstrate the dependence of the thermal conductivity and thermal diffusivity coefficients of n-type germanium monocrystals on the concentration of antimony impurities (6 × 10¹³, 1.3 × 10¹⁴, 1.7 × 10¹⁴, 3.7 × 10¹⁴, 6 × 10¹⁴ cm^?3). The investigated samples are cut from germanium crystals grown from a melt using the Czochralski method with crystallographic orientation [111].     

双能谷效应对N型掺杂Si基Ge材料载流子晶格散射的影响

性能优越的Si基高效发光材料与器件的制备一直是Si基光电集成电路中最具挑战性的课题之一.Si基Ge材料不仅与成熟的硅工艺相兼容,而且具有准直接带特性,被认为是实现Si基激光器最有希望的材料.对Si基Ge材料N型掺杂的研究有利于提示出其直接带发光增强机理.本文研究了N型掺杂Si基Ge材料导带电子的晶格散射过程.N型掺杂Si基Ge材料具有独特的双能谷(Γ能谷与L能谷)结构,它将通过以下两方面的竞争关系提高直接带导带底电子的占有率:一方面,处于Γ能谷的导带电子通过谷间光学声子的散射方式散射到L能谷;另一方面,处于L能谷的导带电子通过谷内光学声子散射以及二次谷间光学声子散射或者直接通过谷间光学声子散射的方式跃迁到Γ能谷.当掺杂浓度界于10~(17)cm~(-3)到10~(19)cm~(-3)时,适当提高N型掺杂浓度有利于提高直接带Γ能谷导带底电子占有率,进而提高Si基Ge材料直接带发光效率.     

Carrier concentrations and Fermi-levels in extrinsic semiconductors

We have investigated theoretically the carrier concentrations and Fermi-levels in extrinsic semiconductors (both n- and p-type), taking into account the existence of holes in valence band for n-type semiconductors and of electrons in conduction band for p-type systems. To indicate the quantitative implications of the theoretical analyses, we have performed some numerical calculations with respect to n-type germanium and explored the physical conditions under which we would be required to take account of the role of carriers excited over the band gap, in evaluating the statistics of carriers in extrinsic semiconductors.The author is grateful to Professors H. N.Bose, G.Bandopadhyaya and G. B.Mitra for their interest and encouragement.     

IR absorption and Raman spectra of single crystals of stable germanium isotopes

The Raman and IR absorption spectra of single crystals of germanium isotopes ⁷²Ge, ⁷³Ge, ⁷⁴Ge, and ⁷⁶Ge in the region of phonon absorption and interband electronic transitions are studied at room temperature. The dependence of the Raman peak position on the atomic mass has the form ν ~ M^–1/2. The shifts of the phonon absorption peaks of individual isotopes with respect to germanium of natural isotopic composition ^natGe are determined. With increasing average atomic mass of germanium, these peaks shift to longer wavelengths. In the region of interband electronic transitions, the intrinsic absorption edge of ⁷⁶Ge is observed to shift by 1 meV to higher energies with respect to Ge of natural isotopic composition. For isotopes with atomic masses close to that of natural germanium (⁷²Ge,⁷³Ge, ⁷⁴Ge), we found no significant difference in the band gap width at room temperature.     

Hexagonal germanium formed via a pressure‐induced phase transformation of amorphous germanium under controlled nanoindentation

We have studied the stable end phase formed in amorphous germanium (a‐Ge) films that have been subjected to a pressure‐induced phase transformation under indentation loading using a large (20 µm) spherical indenter. After indentation the samples have been annealed at room temperature to remove any residual unstable R8 and BC8 phases. Raman spectroscopy indicates a single broad peak centred around 292 cm^–1 and we have used first principles density functional perturbation theory calculations and simulated Raman spectra for nano‐crystalline diamond cubic germanium (DC‐Ge) to help identification of the final phase as hexagonal diamond germanium (HEX‐Ge). Transmission electron microscopy and selected area diffraction analysis confirmed the presence of a dominant HEX‐Ge end phase. These results help explain significant inconsistencies in the literature relating to indentation‐induced phase transitions in DC‐ and a‐Ge. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

磷离子注入纳米金刚石薄膜的n型导电性能与微结构研究

系统研究了磷离子注入并在不同温度退火后的纳米金刚石薄膜的微结构和电学性能.研究表明,当退火温度达到800 ℃以上时,薄膜呈良好的n型电导.Raman光谱和电子顺磁共振谱的结果表明,薄膜中金刚石相含量越高和完整性越好,薄膜电阻率越低. 这说明纳米金刚石晶粒为薄膜提供了电导.1000 ℃退火后,薄膜晶界中的非晶石墨相有序度提高,碳悬键数量降低,薄膜电阻率升高.薄膜导电机理为磷离子注入的纳米金刚石晶粒提供了n型电导,非晶碳晶界为其电导提供了传输路径. 关键词： 纳米金刚石薄膜 n型 磷离子注入