The reasons for a change in the lifetime of minority carriers in germanium under the action of an anisotropic pressure

The possible reasons for a reduction in the lifetime of minority carriers in the base of a diode under the action of an anisotropic pressure are investigated.     

Effect of anisotropic pressure on the parameters of silicon diodes

We analyze experimental data on the effect of external pressure on the following parameters of silicon alloyed diodes: charge capacitance of the p-n junction, lifetime of the minority charge carriers in the diode base, the rate of surface recombination on the base surface, and the reverse current.     

Hot́ hole anisotropic effect in silicon and germanium

Anisotropic effect of the hole drift velocity in silicon and germanium has been investigated with the time of flight technique by applying the electric field parallel to the <100 and <111 crystallographic axis. The measurements were performed for electric fields ranging from 10 to 3 × 10⁴V/cm and temperatures from 40 to 200°K. The results indicate that the anisotropic effect v_d<100/v_d<111 increases with decreasing temperature and increasing electric field, and reaches a saturation value at high electric fields (? 10⁴V/cm). The maximum anisotropic effect for Ge is 1.25 at 40°K and for Si is 1.2 at 45°K. A qualitative analysis of the experimental data indicates that the anisotropic effect is due to the warped heavy-valence-band shape.     

Temperature dependence of the lifetime of nonequilibrium charge carriers in GaP diodes under condition of recombination current domination

Temperature dependence of the lifetime of nonequilibrium charge carriers limited by recombination process in a p-n junction space-charge region has been obtained from current–voltage, capacitance–voltage and thermometric characteristics of GaP p⁺-n junctions in the temperature range 150–500 K. The results have been refined using the data of the junction relaxation characteristics. Parameters of the carriers' lifetime sensitivity to the temperature and current have been determined. It has been established that the charge carriers recombine predominantly through deep single-level amphoteric-type centres. The depth of the centres makes approx. (E_C-1.25 eV). We suppose that the nature of the centres formation is not connected with the junction fabrication technology. It has rather fundamental origin. The results of the present investigation could be used in the development of devices based on wide bandgap semiconductors and particularly high temperature diode sensors.     

Theory of the photon-drag effect inp-type germanium with a parabolic and anisotropic band-structure approximation

This paper shows that many features of the photon-drag voltage generated by illumination ofp-germanium with 10.6 μm radiation can be understood on the basis of a parabolic but anisotropic band-structure model. The group velocities of the heavy and light holes participating in the optical transitions are obtained by an analysis of the conservation laws. Since the nonequilibrium hole densities in both bands depend directly on the momentum relaxation times in the determinant equations of continuity, these times are the parameters with the strongest influence on the numerical results. The photon-drag voltage consists of components longitudinal and transverse with respect to the axis of illumination. For the longitudinal components, good agreement between our theoretical results and experimental data from the literature is achieved if the crystal is illuminated along a [100] or [111] direction. Though a transition probability independent of light polarisation has been assumed, the transverse effect (illumination along [111]) can be computed for special measuring conditions. The calculated effects of anisotropy are higher than known from experiments possibly due to the approximations used for the valence bands and the transition probability. An erratum to this article is available at .     

The influence of interface states and bulk carrier lifetime on the minority carrier behavior in an illuminated metal/insulator/GaN structure

An influence of electronic states at an insulator/GaN interface on the behavior of excess holes in an ultraviolet-illuminated metal/ SiO₂/n-GaN structure has been studied by numerical simulations for weak (gate bias of −0.1 V ) and strong (−1 V ) depletion, in a wide range of excitation light intensities (from 10¹⁰ to 10²⁰ photons cm⁻² s⁻¹) and for various bulk carrier lifetimes (from 1 to 100 ns). It has been found that the interface states with densities of 10¹² eV ⁻¹ cm⁻² dramatically reduce the total (integrated in the whole GaN layer) density of photogenerated holes and thus degrade the sensitivity of the metal/insulator/GaN-based photodetector.     

Measurements on the photoconductive lifetime of carriers in GaAs by optoelectronic gating technique

Picosecond gating techniques utilizing optically controlled switch have been carried out to resolve the photoconductive impulse response of carriers in GaAs.     

The hyperconjugation effect on the graphene counterparts based on silicon and germanium

Bending of the A = A (A of the group IVA) double bond neighboring is rationalized by the hyperconjugation phenomenon analysis. The bending is also observed for the high sized linear, cyclic or graphene-like compounds that imply the conjugated double bonds. The electronic delocalization takes place between occupied σ(π) and unoccupied π*(σ*) orbitals especially for compound implying Si and Ge atoms. Leading to rippled structure, this phenomenon affects the silicene and germane thickness sheets and probably would have some consequences on the properties of such compounds when they will be involved in the industries in the future. However we introduce a new parameter to assess the thickness of graphenic structures when the hyperconjugation takes place in the bonding framework. The study has been undertaken at high levels of theory like B3LYP/6-311 + G(3df,2p).     

Evaluation of the diffusion length of minority carriers in bulk GaAs

The diffusion length of minority charge carriers has been investigated in LEC GaAs, silicon-doped with doping density N_D - N_A ranging from 10¹⁶ to 10¹⁸ cm^-3, by surface photovoltage (SPV) and electron-beam-induced current (EBIC) of scanning electron microscopy (SEM) measurements. Au Schottky diodes have been evaporated along the diameter of wafers cut from different doping density ingots to determine the variation of minority carrier diffusion length with both the radial position on the slice and the carrier concentration. The diffusion length values obtained by optical and electron excitation enhance systematic differences, which can be explained by the different surface recombination weight in the carrier generation volume and by the injection level, too. In all the examined samples an M-shaped radial variation of the diffusion length has been observed; on the other hand, the mean value of L_p increases from 0.5 to 7 μm when the doping concentration increases. The authors correlate this distribution to the electrical inhomogeneity induced by native defects and associated recombination centres. The role of the dislocations, which induce two competitive effects, i.e. an enhanced recombination probability and a precipitate condensation, is here discussed.     

The anisotropic effect of hexagonal warping on the transport

In the presence of hexagonal warping (HW), the surface state of a topological insulator (TI) exhibits anisotropic Fermi surface. In this work, we study the transport properties of a TI junction, focusing on the influence of anisotropic effect of the HW on the scattering. We establish general expressions for calculating the scattering with an arbitrary angle between TI surface and the potential step, and find that the transmission probability and conductance have a strong dependence on the angle, making TI junction a promising platform for studying the geometry control of transport. Remarkably, we find that the HW can induce a triple refraction, which gives rise to an anomalous increase of the transmission probability when varying incident angle. The general expressions here for calculating the scattering can be extended to the systems with trigonally and tetragonally warped Fermi surface.     

新型AlGaInP系发光二极管饱和特性与寿命的研究

针对AlGaInP系发光二极管(LED)电极阻挡出光、衬底吸收、全反射角小导致器件出光效率低、热积累大、饱和特性差等问题,提出了一种具有复合电流输运增透窗口层、复合DBR反射镜和电流阻挡层结构的新型LED,并测试了其饱和特性和寿命.电流分布模拟显示:新型LED电极下仅存在极小的无效电流;实验结果表明新型LED出光效率高,饱和电流大,饱和电流时光强约为常规LED的3倍,光电性能明显提升.器件饱和特性和老化实验研究显示:新型LED寿命长达17.8×104h,器件内部发热量低,具有高饱和特性和高可靠性,适合在大电流大功率下工作.