sp3sTight-binding parameters for transport simulations in compound semiconductors

A genetic algorithm approach is used to fit orbital interaction energies of sp3s* tight-binding models for the nine binary compound semiconductors consistent of Ga, Al, In and As, P, Sb at room temperature. The new parameters are optimized to reproduce the bandstructure relevant to carrier transport in the lowest conduction band and the highest three valence bands. The accuracy of the other bands is sacrificed for the better reproduction of the effective masses in the bands of interest. Relevant band edges are reproduced to within a few meV and the effective masses deviate from the experimental values typically by less than 10%.     

Transport properties of the two-dimensional electron gas in AlP quantum wells at finite temperature including magnetic field and exchange–correlation effects

We investigate the transport scattering time, the single-particle relaxation time and the magnetoresistance of a quasi-two-dimensional electron gas in a GaP/AlP/GaP quantum well at zero and finite temperatures. We consider the interface-roughness and impurity scattering, and study the dependence of the mobility, scattering time and magnetoresistance on the carrier density, temperature and local-field correction. In the case of zero temperature and Hubbard local-field correction our results reduce to those of Gold and Marty (Physica E 40 (2008) 2028; Phys. Rev. B 76 (2007) 165309). We also discuss the possibility of a metal–insulator transition which might happen at low density.     

(XY)12(X=B,Al;Y=P)团簇的结构与稳定性

采用B3LYP／6031G*方法,对(XY)12(X=B,Al;Y=P)笼状团簇的同分异构体进行优化,筛选出能量最低的构型．讨论它们的几何构型、HOMO-LUMO能隙、生成焓、核独立化学位移(NICS)和自由能．得到(BP)12和(AlP)12团簇的最稳定构型均为具有Th对称性的四、六元环组成的笼,亚稳态结构中含有五元环。     

Correlation between electronic states and optical properties in indirect GaAsP/GaP quantum wells with insertion of an ultrathin AlP layer

The optical properties of indirect semiconductor quantum wells (QWs), were studied in relation to their electronic states controlled by an ultrathin AlP layer. The insertion of 1 ML of AlP at the center of a 60 Å GaAsP/GaP QW drastically increased the photoluminescence (PL) intensity and the efficiency of the no-phonon (NP) transition. The NP intensity relative to its TO phonon replica was found to greatly depend on the structural parameters and decreased by decreasing the width of the AlP layer or by increasing the arsenic composition of the GaAsP QW. The comparison with numerical calculation clarified that the efficiency of the NP transition is improved when the X_z electrons rather than X_xy electrons are involved in the radiative recombination. This can be qualitatively understood that the X_z electrons are more strongly localized to the AlP layer, leading to the efficient relaxation of the selection rule. The Arrhenius behavior of the PL intensity was also studied and the quenching of the PL intensity was interpreted as being due to the thermally activated escape of carriers from the well region into the GaP barrier.     

Transport properties of the two-dimensional electron gas in wide AlP quantum wells including temperature and correlation effects

We investigate the mobility, magnetoresistance and scattering time of a quasi-two-dimensional electron gas in a GaP/AlP/GaP quantum well of width L>L_c=45.7 Å at zero and finite temperatures. We consider the interface-roughness and impurity scattering, and study the dependence of the mobility, the resistance and scattering time ratio on the carrier density and quantum well width for different values of the impurity position and temperature using different approximations for the local-field correction. In the case of zero temperature and Hubbard local-field correction our results reduce to those of Gold and Marty (Phys. Rev. B. 76 (2007) 165309) [3]. We also study the correlation and multiple scattering effects on the total mobility and the critical density for a metal–insulator transition.     

Spectra and excitation properties of (AlP)8: Effect of external electric fields

On the basis of density functional theory (DFT), the geometry and infrared spectrum of the (AlP)₈ cluster have been calculated under external electric fields (EEFs). In addition, on the basis of time-dependent DFT, the ultraviolet–visible absorption spectra, oscillator strengths, wavelengths, and hole–electron orbits of the first 20 excited states have been calculated. Under EEFs, the energy of (AlP)₈ gradually decreases, the dipole moment increases, and the molecular configuration significantly changes. In the infrared spectrum, the vibration frequency corresponding to the stretching vibration of the Al–P bond decreases, and a red shift occurs. With increasing EEF, the infrared spectrum splits and shows an obvious Stark effect; the ultraviolet absorption intensity is enhanced, and the molecular excitation energy decreases. Additionally, the excitation wavelength increases with increasing EEF. It is conclusively shown that the (AlP)₈ cluster is easily excited under an EEF. Separation of the holes and electrons of the (AlP)₈ cluster is obvious. Theoretical investigation of the spectra and excitation properties of (AlP)₈ is an important step toward a comprehensive understanding of the effects of EEFs on the molecular structure, stability, and dynamics.     

Atomic layer epitaxy of AlP and (AlP)n(GaP)n superlattice using ethyldimethylamine alane as a new aluminum source

Atomic layer epitaxy (ALE) of AlP was realized using ethyldimethylamine alane (EDMAAl) as a new Al source. Self-limiting growth of AlP took place at one and two monolayers per ALE cycle. Secondary ion mass spectroscopy revealed that the amounts of incorporated impurities (carbon, hydrogen and oxygen) in ALE-grown AlP layers was greatly suppressed by using the new Al source, to nearly the same levels as in high-quality MOVPE-grown layers. We also achieved the successful ALE growth of (AlP)_n(GaP)_n short-period superlattices (SLs), taking advantage of the overlapping temperature windows of ALE-GaP and ALE-AlP. X-ray diffraction measurements showed reasonably good interface abruptness of SLs as low as 3. The PL emission peak from SLs involving Al-containing layers was observed in ALE growth for the first time.     

AlP/SiO2纳米复合材料的光致发光研究

本文对用溶胶-凝胶方法制备的xAlP/100SiO₂凝胶玻璃的光致发光进行了研究,表明585nm附近的发光是凝胶玻璃中的AlP纳米晶粒表面态和缺陷复合发光.发光峰位与AlP的参杂量无关,但发光峰的强度随x的增加而减弱;另外与H₂的反应时间越长,发光强度减弱.     

AlPO4-5分子筛与NaF反应机理的研究

本文用XRD和³¹P NMR研究以Et₃N为模板剂合成的AlPO₄-5分子筛与NaF的反应机理。研究结果表明P、Al在AlPO₄-5分子筛中是严格有序交替排列的,且这种排列与合成中所用模板剂无关,并提出了上述反应的机理。     

(XY)12 (X═B, Al; Y═P)团簇的结构与稳定性

采用B3LYP/6-31G*方法, 对(XY)₁₂ (X═B, Al; Y═P)笼状团簇的同分异构体进行优化, 筛选出能量最低的构型. 讨论它们的几何构型、HOMO-LUMO能隙、生成焓、核独立化学位移(NICS)和自由能. 得到(BP)₁₂和(AlP)₁₂团簇的最稳定构型均为具有T_h对称性的四、六元环组成的笼, 亚稳态结构中含有五元环.