The magnetophonon effect

This article is a review of the magnetophonon effect, covering its origins, uses and the information which derives from it. The magnetophonon effect arises due to resonant phonon emission or absorption by free charge carriers in a solid in a high magnetic field. The most usual example of this is when longitudinal optic (L.O.) phonons are absorbed by electrons or holes in a semiconductor, causing resonant transitions between Landau levels at magnetic fields given by the resonance condition B = (1/N)m¹ω_L.O./e, where ω_L.O. is the optic phonon frequency, and m¹ is the effective mass of the carriers in question. These resonant transitions cause resonances in a wide variety of different transport parameters, such as resistivity, Hall and Seebeck coefficients. The article reviews the observation of normal magnetophonon resonances in a wide variety of semiconducting and semi-metallic materials, including alloys, p-type materials and semiconductor heterostructures. A section is devoted to the hot-electron magnetophonon effect, which results from resonant electron cooling, and gives information on the electron energy loss mechanisms. This review was completed in December 1984.     

Hg1—xCdxTe表面电子的子能带结构

讨论了Hg_(1-x)Cd_xTe MIS结构N型反型层电子子能带结构的理论和实验研究结果。描述了采用电容-电压谱,回旋共振谱和磁导振荡谱定量地研究电子子能带结构的模型和方法。推导得到的子能带色散关系,朗道能级和有效g~*因子,与测得的子能带电子的回旋共振和自旋共振结果符合得很好,从而可以定量地研究由于表面电子的自旋轨道相互作用引起的零场分裂效应,朗道能级的移动、交叉,波函数的混合效应以及电致自旋分裂的色散关系。     

Phonon-induced magnetoresistance oscillations in a high-mobility quantum well

We examine the temperature dependence of acoustic-phonon-induced magnetoresistance oscillations in a high-mobility GaAs-based quantum well with conventional transverse and longitudinal phonon modes, using a model in which the temperature increase of the Landau level broadening or the single-particle scattering rate 1/τs is attributed to the enhancement of electron-phonon scattering with rising temperature. The non-monotonic temperature behavior, showing an optimal temperature at which a given order of oscillation amplitude exhibits a maximum and the shift of the main resistance peak to higher magnetic field with rising temperature, is produced, in agreement with recent experimental findings.     

Multimode nature and magnetophonon resonance of quaternary solid solutions of zinc, cadmium, and mercury tellurides

The magnetophonon resonance in a multimode crystal of the solid solution Zn_xCd_yHg_1−x−y Te (x=0.08, y=0.11) was investigated in the temperature interval from 77 to 200 K. To interpret the obtained structure of the magnetophonon resonance spectrum, the phonon modes of three compositions of this solid solution were studied by the Raman scattering method. The results presented confirm the three-mode behavior (excluding cluster modes) of the phonon spectrum of the solid solutions of this class. The complicated structure of the magnetophonon resonance bands is interpreted on the basis of the values obtained for the phonon frequencies. The characteristic features of electron transport in such a lattice are shown. Fiz. Tekh. Poluprovodn. 32, 1006–1015 (August 1998)     

Magnetophonon oscillations in the transverse and longitudinal magnetoresistance of Hg1−xCdxTe

The transverse and longitudinal magnetoresistance (MR) as well as the longitudinal magneto-thermoelectric coefficient of n-type Hg_1-xCd_xTe (MCT) (0.20 < x < 0.33) have been measured at various temperatures (40 ≤ T≤ 140K) as a function of magnetic field (0 ≤ B≤18 kG). Both the transverse and the longitudinal MR clearly exhibit oscillations which are described in terms of magnetophonon (MP) transitions involving the HgTe-like and the CdTe-like longitudinal optical (LO) phonons of MC.T. The field positions of the transverse MR maxima agree with the calculated MP resonances taking into account nonparabolic bands (k • p model for narrow-gap zinc-blende-type semiconductors) and the polaron effect. Those of the longitudinal MR minima are found to coincide with the oscillation minima in the longitudinal magneto-thermoelectric coefficient. However, these minima are shifted by π/2 to lower fields with respect to the positions of the MP resonances. This phase shift was predicted by Barker1314 for the case of strong Landau level damping but has not been previously observed. In contrast, the MP oscillation minima of the longitudinal MR and the oscillation maxima of the transverse MR of n-type InSb (investigated here for comparison) occur exactly at the fields of the MP resonances. Only the oscillation minima of the longitudinal magneto-thermoelectric coefficient are slightly shifted to the side below the MP resonance fields. With regard to the band parameters and the dominant polar optical mode scattering of charge carriers InSb very much resembles MC.T. InSb, however, is a binary compound whereas MC.T is a solid solution. Thus, the phase shift by π/2 to lower fields observed for the oscillation minima in the longitudinal MR and magneto-thermoelectric coefficient of MC.T may be due to alloy scattering. The temperature coefficients of the MP resonance fields of MC.T are found to be substantially smaller than those reported by Takita et al.¹¹ and McClure et al.¹⁰ The larger temperature coefficents are presumably due to unresolved two-phonon structures of the MP oscillations.     

GaAs-Al_xGa_(1-x)As异质结的热电子磁声子共振测量

在4.2K,我们测量了GaAs-Al_xGa_(1-x)As异质结的二维热电子的磁声子共振。高电场下,SdH振荡消失以后,在二维系统中,除清楚地观察到LO声子振荡外,还观察到X点双TA声子振荡。     

Temperature distribution in Si-MOSFETs studied by micro-Ramanspectroscopy

The local rise of lattice temperature in n-MOSFETs is analyzed by the energy shift of the silicon optical phonon using Raman spectroscopy with submicrometer spatial resolution. When operating the devices in saturation, a source-drain temperature asymmetry is observed corresponding to the heat dissipation profile that peaks in the pinch-off region. In the substrate surrounding the transistor an anisotropic temperature distribution is found which is related to the geometric shape of the heat source. A reduction of channel length under standard conditions leads to a local temperature increase due to the higher power density. The authors found temperature increases of less than 20 K for an operating voltage of 5 V for a channel length down to 0.3 μm. The time constant of transient heating under pulse operation is determined by analyzing the inhomogeneous broadening of the Raman line. Thermal time constants of about 200 ns are obtained     

极性晶体中磁极化子声子色散效应

利用线性组合算符和幺正变换相结合的方法,研究了声子色散对极性晶体中磁极化子性质的影响．计及纵光学（LO）声子色散,在抛物近似下导出了极性晶体中磁极化子基态能量、自陷能和基态Landau能随声子色散系数、回旋共振频率和电子-纵光学声子耦合强度的变化关系．数值计算结果表明基态能量随声子色散系数、电子-纵光学声子耦合强度的增大而减小．自陷能随声子色散系数和电子-纵光学声子耦合强度的增大而增大．基态Landau能随电子-纵光学声子耦合强度的增大先增大到最大值后又减小,随声子色散系数的增大而增大．     

Intraband relaxation time in quantum-well lasers

Intraband relaxation time, which causes spectral broadening of optical gain and spontaneous emission spectra, is estimated theoretically for quantum-well lasers. Carrier-carrier and carrier-longitudinal-optical (LO) phonon scattering mechanisms are considered, and it is shown that hole-hole, electron-hole, and hole-LO phonon scattering are dominant in spectral broadening. Intraband relaxation time determined by all of these mechanisms increases slightly with the decrease of well width. The dependence of intraband relaxation time on temperature, carrier density, and energy of electron and hole is also shown. Spectral line shape is discussed as an extension of the above calculation, and an approximated formula is given     

Applications of Huang–Rhys theory in semiconductor optical spectroscopy

A brief review of Huang–Rhys theory and Albrechtos theory is provided,and their connection and applications are discussed.The former is a first order perturbative theory on optical transitions intended for applications such as absorption and emission involving localized defect or impurity centers,emphasizing lattice relaxation or mixing of vibrational states due to electron–phonon coupling.The coupling strength is described by the Huang–Rhys factor.The latter theory is a second order perturbative theory on optical transitions intended for Raman scattering,and can in-principle include electron–phonon coupling in both electronic states and vibrational states.These two theories can potentially be connected through the common effect of lattice relaxation – non-orthonormal vibrational states associated with different electronic states.Because of this perceived connection,the latter theory is often used to explain resonant Raman scattering of LO phonons in bulk semiconductors and further used to describe the size dependence of electron–phonon coupling or Huang–Rhys factor in semiconductor nanostructures.Specifically,the A term in Albrechtos theory is often invoked to describe the multi-LO-phonon resonant Raman peaks in both bulk and nanostructured semiconductors in the literature,due to the misconception that a free-exciton could have a strong lattice relaxation.Without lattice relaxation,the A term will give rise to Rayleigh or elastic scattering.Lattice relaxation is only significant for highly localized defect or impurity states,and should be practically zero for either single particle states or free exciton states in a bulk semiconductor or for confined states in a semiconductor nanostructure that is not extremely small.     

Electron recombination between Landau-levels in n-InSb

Experimental and theoretical investigations of electron recombination between Landau levels and associated impurity levels have been performed for n-InSb. The electronic lifetime in the first Landau level is found to be determined by electron-electron scattering what is experimentally confirmed by an inversely linear dependence on the electron concentration n₁ in the 1st Landau level. Values of 10⁻¹⁰ sec are obtained for n₁ 10¹³ cm⁻³. For n₁ ≤ 10¹⁰ cm⁻¹ acoustic phonon scattering determines the lifetime in the first Land level. For the recombination of electrons between the lowest Landau level and the impurity ground state times between 200 nsec and 50 nsec dependent on the magnetic field but independent of electron concentration are found indicating a phonon capture process. These times are also responsible for the observation that relaxation times from the (110) impurity level to the (000) ground state are the bottle neck in a three step process.     

强耦合作用下自旋与碳纳米管谐振器之间的动力学研究

理论分析了单电子自旋与碳纳米管机械谐振器之间的耦合对系统动力学行为的影响。用一个主方程,通过半经典的方法具体研究了系统在有量子位-谐振器耦合和没有耦合时平均声子占有数随频率失谐的变化情况、在不同耦合强度时对比了系统在旋波近似和非旋波近似下平均声子占有数随频率失谐的变化情况。在有耦合的情况下,平均声子占有数在共振时,产生了一个分裂,而且在分裂峰值的附近出现了双稳态。通过对碳纳米管谐振器平均声子占有数的分析发现,旋波近似和非旋波近似在耦合强度较弱的情况下能够很好的吻合。当系统进入超强耦合时,旋波近似不再有效,此时非旋波项变得不可忽略。     

Two-dimensional quantum-mechanical confinement of electrons in LED by strong magnetic fields

Two-dimensional quantum-mechanical confinement of electrons in a GaAlAs light emitting diode (LED) is realized by applying strong magnetic fields, in which electrons can move freely only in the direction of magnetic fields, and the dimensionality of the free carrier motion is reduced from three to one. With this confinement of electrons, considerable suppression of half-value width of the spectrum broadening from 80 to 60 Å at 80 K in the LED is observed. The systematic shift of the emission peak toward shorter wavelength is also observed in accordance with the theory, which takes into account the Landau level broadening due to finite electron mobility.     

Energy relaxation in GaInAs/AlInAs heterojunctions and GaAs/AlGaAs multiple quantum wells

We have studied electron energy relaxation in GaInAs/AlInAs heterojunctions and GaAs/AlGaAs multiple quantum wells using mobility measurements as a function of electric field and temperature, in the range 3K to 300K. The results in the range 3 to 20K show a power loss rate which is dependent on (T_e − T_l), suggesting that the energy relaxation occurs through acoustic phonon scattering. At electron temperatures greater than 20K, the experimental results are modelled using a standard expression for polar optical phonons. This modelling yields 30meV and 31meV for the polar optical phonon energy in GaAs and InGaAs respectively.     

HgCdTe反型层电子子能带物理

<正> 本文在4.2K下测定了p-HgCdTe MIS结构样品的量子电容谱,表面磁阻振荡,表面回旋共振以及表面电子自旋共振,确定了HgCdTe反型层电子子能带结构,包括能级位置、费米能级、有效质量、反型层耗尽层厚度等,并推导了由于自旋轨道相互作用而引起的电致自旋分裂子能带的色散关系和朗道能级扇形图,还研究了朗道能级以及自旋能级间的光跃迁问题。     

Impact of a Nonideal Metal Gate on Surface Optical Phonon-Limited Mobility in High- κ Gated MOSFETs

The effects of surface phonon scattering in an nMOSFET with a high-k gate insulator and a nonideal metal gate are examined. The nonideal metal gate model depends on three parameters: (1) the density of electrons in the gate; (2) the electron effective mass; and (3) the high-frequency dielectric constant associated with the choice of gate metal. The impact of these parameters on surface optical (SO) mobility is demonstrated using TiN as an example. For the selected choice of parameters and Landau damping limits, the results indicate that SO phonon scattering does not seem to play a significant role in the mobility degradation of TiN/HfO₂ MOSFETs for the entire range of sheet concentration.     

掺杂超晶格的等离子激元与纵光学声子的耦合模

在T＝77K,测量出掺杂（Si)GaAs/AlGaAs超晶格的拉曼散射谱,观察到拉曼位移分别为223cm^-1和422cm^-1的两个光散射峰。理论分析认为,这两个散射峰是掺杂超晶格的等离子激元与纵光学声子耦合模引起的。这事模引起的光散射峰位置的理论计算值与拉曼测量结果相当一致。     

Polaron effect-dependent third-order optical susceptibility in a ZnS/CdSe quantum dot quantum well

The effect of the electron-phonon interaction on the third-harmonic is investigated theoretically for electrons confined in a core-shell quantum dot. The interactions of electrons with different phonon modes in the core-shell system, including the confined longitudinal optical (LO) and the interface optical (IO) phonon modes, are investigated. We carried a detailed calculation of third-harmonic generation (THG) process on a ZnS/CdSe core-shell quantum dot as a function of pump photon energy with different incident photon energy and under different sizes. The results reveal that the polaron effects are quite important especially around the peak value of the third-order susceptibility. By increasing the size of the quantum dots, the peaks of χ_THG⁽³⁾ will shift to lower energy, and the intensities of the peaks will increase.     

The effect of the periodic bias on the electron transport in a magnetic quantum structure

With the help of the transfer matrix method, the transmission probability, the electron conductance and the spin-polarization of the ballistic electron are in detail studied in a nanostructure with the periodic bias. It is shown that these observable quantities strongly depend on the number of the periodic bias. With the number of the periods increasing, the resonance splitting increases, so the number of the resonance peaks is increasing and the peaks become sharper as well as the spin-polarization being enhanced, although the average magnetic field of the structure is zero.     

Special features of the photoluminescence of self-assembled Ge(Si)/Si(001) islands grown on a strained Si1−x Gex layer

The effect of the predeposition of strained Si_{1 ? x} Ge_x layers (x ≤ 20%) on photoluminescence (PL) of self-assembled Ge(Si)/Si(001) islands is studied. A shift of the PL peak related to dome-shaped islands (domes) to lower energies, with respect to the PL peak related to pyramidal islands is observed; this shift is related to a much larger height of the domes compared to that of pyramids. It is found that, as the Ge content in the Si_{1 ? x} Ge_x layer (x) becomes higher than 0.1, two separate peaks appear in the broad PL band related to the islands; these peaks are attributed to the zero-phonon and phonon-assisted optical transitions in the islands. The appearance of these transitions is caused by a change of the TO-phonon type involved in radiative recombination: a TO_Ge-Ge phonon is replaced by a TO_Si-Ge phonon with a shorter wavelength.