Polarised hot electron luminescence in p-GaAs: Electric field effects

Electrons photo-excited to high-energy conduction band states of GaAs exhibit complex energy and momentum distributions determined by the anisotropic valence band structure and the optical matrix elements. In p-type GaAs a fraction of these hot electrons combine with localised acceptor states, producing a hot electron luminescence (HEL) spectrum with a cascade of peaks corresponding to discrete energy losses resulting from LO-phonon emission. The highest peak involves unscattered electrons, and their energy distribution is due to warping of the initial heavy-hole (HH) bands. We report measurements of the line shape of this 0-HH peak, and its polarisation profile which identifies emission from electrons along particular directions. An applied electric field of 1 kV cm⁻¹ distorts the hot electron momentum distribution, and this is reflected in the polarisation profile. These line shapes and profiles, with and without field, are calculated using a computer model incorporating a band structure and optical matrix elements, the effect of electric field being included using a k-broadening model. The data and model are in good quantitative agreement assuming an electron lifetime of 100 fs, and confirm the expected differences in the profiles for different excitation polarisation states and applied field directions.     

静压下GaAs_(1-x)P_x:N(x≤0.88)中N等电子陷阱的束缚激子发光

通过研究77 K温度下不同组份的GxAs_(1-x)P_x:N(x≤0.88)的静压光致发光,在x=0.88的样品中首次观察到NH_3 的发光,压力使N_x谱带窄化及其LO声子伴线的黄昆因子变小等现象。结果表明,压力使得混晶无序效应减弱,加强了激子从N_x?NN_i的能量转移过程。     

The Tersoff potential for phonons in GaAs

We report on the use of the Tersoff empirical potential applied to GaAs. Cohesive and elastic properties, as well as phonon frequencies and Grüneisen parameters at the Γ and X points, are calculated and compared to experimental data. The limitations of the potential and its existing parametrisations are discussed.     

Controlling anisotropy of GaSb(As)/GaAs quantum dots by self-assembled molecular beam epitaxy

A systematic study was performed to control the geometrical anisotropy of GaSb(As)/GaAs quantum dot structures formed by the Stranski–Krastanov growth mode of molecular beam epitaxy. In particular, effects of both the Sb₄ beam flux and the As₄ background pressure on the geometrical anisotropy were clarified and elongated QDs with lateral aspect ratio greater than 3 were successfully formed. Under a low As₄ background pressure, As₄ is found to act as surfactant to influence the adatom diffusion and change the density of QDs. By contrast, under high As₄ background pressure, the intermixing of As and Sb takes place and reduces strains induced by the lattice mismatch.     

Noise Factor of Optically Controlled GaAs Field-Effect Transistors

The influence of IR radiation on the noise factor of GaAs field-effect transistors has been analyzed. It is shown that the noise factor of the indicated transistors decreases under IR irradiation. It has been established that a decrease in the noise factor of the field-effect transistors under IR irradiation is mainly due to an increase in the low-field mobility of electrons in them.     

GaAs／Ga1—xAlxAs 量子阱结构能带的不连续性

用改进的方势阱模型、半导体统计方法,研究了决定GaAs/Ga_(1-x)Al_xAS量子阱结构中能带不连续的参数Qe与热平衡费米能级的关系,Qe作为一个统计参数,不仅与组分x、阱宽L有关,还与温度有关,计算表明,对不同的x、L值,Qe的数值可在一个相当大的范围内变化,在同样组分下,阱宽越大,Qe越小;在同样阱宽下,组分越高,Qe越小,计算结果与一些实验结果符合得很好。     

p-n型GaInP_2/GaAs叠层太阳电池研究

报道了对p n型GaInP2 GaAs叠层太阳电池的研究结果 .采用低压金属有机物化学气相沉积工艺制备电池样品 .通过对GaInP2 顶电池中场助收集效应的计算机模拟 ,提出用p p- n- n 结构取代常用的p n结构 ,显著改善了GaInP2 顶电池和GaInP2 GaAs叠层太阳电池的光伏性能 ,使其光电转换效率 (Eff)分别达到 14 2 6 %和 2 3 82 %(AM0 ,2 5℃ ,2× 2cm2 )     

Franz–Keldysh oscillations at the miniband edge in a GaAs/AlxGa1 −xAs superlattice

We have systematically measured the electroreflectance spectra of a GaAs (7.0 nm)/Al_0.1Ga_0.9As (3.5 nm) superlattice at various electric fields to investigate Franz–Keldysh (FK) oscillations. In the low-field regime, we clearly observe the FK oscillations toward the low-energy side of theM₁critical point (mini-Brillouin-zone edge). As the electric field is increased, the direction of the FK oscillations is reversed, then the oscillations disappear. The change of the oscillation direction correlates with the transformation of the electronic structures from the miniband to the Stark-ladder states in the Wannier-Stark localization. We discuss these experimental results on the basis of a theory of the FK oscillations and envelope-function forms calculated by a transfer matrix method with Airy functions.     

Charging effects of ErAs islands embedded in AlGaAs heterostructures

Self-assembled ErAs islands were grown on GaAs between a two-dimensional electron gas (2DEG) and a backgate electrode by molecular-beam epitaxy. The islands have overlapping Schottky barriers that form an insulating potential barrier. A TiAu topgate was added by shadow mask evaporation. Thermal activation and charging experiments were employed to gain insight into the electronic properties of the ErAs island systems. In addition the 2DEG was characterized as a function of topgate and backgate voltage.     

Self-assembled GaAs/AlGaAs quantum dots by molecular beam epitaxy and in situ AsBr3 etching

We report on a new method to produce self-assembled, unstrained, GaAs/AlGaAs quantum dots (QDs) with large confinement energy. First we create nanoholes on a GaAs surface by growing InAs islands on GaAs(0 0 1), overgrowing them with GaAs and etching the surface in situ with AsBr₃ gas. Then we transfer the holes to an AlGaAs surface, fill them with GaAs and overgrow them with AlGaAs. In this way we obtain GaAs inclusions in an AlGaAs matrix. We investigate the optical properties of such QDs by photoluminescence spectroscopy and their morphology by atomic force microscopy. We show that the QD size can be tuned and emission with inhomogeneous broadening down to 8.9 meV can be achieved.