Temperature dependence of photoluminescence in amorphous Si1-xCx:H films

We have investigated the temperature dependence of photoluminescence in hydrogenated amorphous silicon-carbon alloys a-Si_1-xC_x:H prepared by glow discharge in the low-power regime. The radiative recombination process, due to photocarriers trapped on band-edge states, is in competition with the thermal escape of the photocarriers into the mobility bands. The model gives a quantitative fit with experiment, without any adjustable parameter, provided the width of the band-edge distribution of states is taken as the width of the conduction band only (measured by “photo-induced infra-red spectroscopy”) and not as the Urbach energy, as it is usually assumed.     

Origin of photoluminescence in nanocrystalline Si:H films

We have studied the origin of photoluminescence (PL) from hydrogenated nanocrystalline silicon (nc-Si:H) films produced by a plasma-enhanced chemical vapor deposition technique using SiF₄/SiH₄/H₂ gas mixtures. The nc-Si:H films were characterized using X-ray diffraction, infrared, Raman spectroscopy, optical absorption and stress, and were examined for PL by varying the deposition temperature (T_d) under two different hydrogen flow rate ([H₂]) conditions. The PL exhibited two peaks at around 1.7-1.75 and 2.2-2.3 eV. The peak energy, E_PL, of the 1.7-1.75-eV PL band was found to shift as T_d or [H₂] changes. It was found that the decrease in T_d acts to decrease the average grain size, 〈δ〉, and to increase both the optical band gap, , and the E_PL values. By contrast, the increase in [H₂] decreased the 〈δ〉 value, while increased the values of and E_PL. Thus, as either T_d decreases or [H₂] increases, it is found that a decrease in 〈δ〉 corresponds well with increases in and E_PL. As a consequence, it was suggested that an increase in E_PL of the 1.7-1.75-eV PL band can be connected with an increase in , through a decrease in 〈δ〉. However, the PL process cannot be connected with the transition between both the bands, related to formation of nanocrystals. Based on these results, it was proposed that the use of both low T_d and high [H₂] conditions would allow to grow nc-Si:H films with small grains.     

Complex photoluminescence decay characteristics of the in-related isoelectronic bound exciton in Si

We present detailed photoluminescence decay measurements on the long-lived P, Q, R lines seen in In-doped Si, which reveal that the transient behaviour of this system is far more interesting than had been previously thought. At temperatures below 10K a double exponential behaviour is observed in the decay curves of all P, Q, R related lines, the long-lived part having a decay constant of up to 3.4 ms at 1.2K. These measurements provide the first evidence that the In-related isoelectronic bound exciton has two distinct configurations, as does the closely related Tl centre.     

The hopping kinetics of geminate recombination in organic crystals

The time dependences of the survival probability, recombination rate, and polarization current of geminate pairs were obtained by the Monte Carlo method for various lattice parameter values. Quantitative criteria of the applicability of the diffusion-drift approximation were found.     

A time-resolved photoluminescence study of amorphous phosphorus

Radiative recombination in amorphous phosphorus is studied by the technique of time-resolved photoluminescence. In the first 200 ns following excitation the luminescence band moves from 1.36 to 1.18 eV. The position of the band is also shown to depend on the energy of exciting photons. These observations are discussed in terms of Coulomb interaction and thermalisation, and their implication for a detailed modelling of excitation and radiation assessed.     

氮化硅薄膜中纳米非晶硅颗粒的键合结构及光致发光

采用螺旋波等离子体化学气相沉积技术以N₂/SiH₄/H₂为反应气体制备了镶嵌有纳米非晶硅颗粒的氢化氮化硅薄膜,通过改变N₂流量实现了薄膜从红到蓝绿的可调谐光致发光.傅里叶红外透射和紫外-可见光吸收特性分析表明,所生长薄膜具有较高的氢含量,N₂流量增加使氢的键合结构发生变化,非晶硅颗粒尺寸减小,所对应的薄膜的光学带隙逐渐增加和微观结构有序度减小.可调光致发光(PL)主要来源于纳米硅颗粒的量子限制效应发光,随N₂流量增加,PL的谱线展宽并逐渐增强. 关键词： 傅里叶红外透射谱 光吸收谱 纳米硅粒子镶嵌薄膜 光致发光     

Photoconductivity decay model in a-Si: H at low temperatures

Photoconductivity decay from steady-state level can be explained in terms of tunnel recombination through randomly distributed localized states in mobility gap. The calculations shows a good agreement between experiment and theory in the range of several orders of magnitude.     

Electroreflectance and Raman scattering investigation of glow-discharge amorphous Si:F:H

The electroreflectance and Raman scattering spectra of several samples of glow-discharge amorphous Si:F:H films have been investigated. We have observed for the first time modulated optical spectroscopy structure above the absorption edge for a disordered semiconductor. The energy positions of these structures, at 3.4 and 4.5 eV, correspond to peaks seen in crystalline silicon. In particular, the latter feature can be related to the degree of disorder in the material. Also we have seen for the first time in disordered silicon (except for ion-damaged, laser annealed samples) peaks in the Raman spectra intermediate between amorphous (465 cm^-1) and crystalline materials (522 cm^-1). These experimental results provide strong evidence that a-Si:F:H possesses “microcrystalline” or some other intermediate range order (i.e., an improved connectivity between the elements of the random network.)     

Non-geminate recombination in amorphous silicon

The excitation power dependence of the light-induced EPR signal in intrinsic a-Si: H is found to be sub-linear over the entire accessible range of excitation power. This result is shown to require a distant-pair model of the recombination of the carriers giving the LESR. If, as is thought, the same carriers give LESR and the 1.4 eV photoluminescence band, we show that the luminescence is also distant-pair.     

Electrical conductivity in amorphous Si(O or H)-Au films

SiO films obtained by sputtering in an ArO mixture with an oxygen partial pressure less than 3% are similar to a-Si films: the resistivity is proportional to exp (T₀/T)^{$\text{1}\text{4}$} and T₀ increases with oxygen content and decreases with increasing Au concentration (? 3.7 at.%). On the other hand, above an oxygen partial pressure of 5% one obtains insulating amorphous SiO₂ films. Conductivity appears in such films for Au? 13 at.% (? the percolation threshold) and then the resistivity is proportional to exp (T₀/T)^{$\text{1}\text{2}$}. The same behavior is observed when oxygen is replaced by hydrogen.     

Thermalization and recombination in amorphous semiconductors

The fate of carriers excited in an amorphous semiconductor by a pulse of light is described. Two processes are discussed: thermalization of carriers within a distribution of localized states, and carrier recombination.     

The metal-semiconductor transition in amorphous Si1-x Crx films: phenomenological model for the metallic region

A detailed phenomenological re-analysis of previously published conductivity data, (T, x), is presented. It was shown in [1] that the cusp-like low-temperature contribution can be described by wherep=0.19±0.03. Starting from this result, two furtherT dependent contributions are separated: The high-temperature region is dominated by a positive contribution _ht (T, x), which is approximately independent ofx, nearly linear inT above 100 K and nearly quadratic inT below 30 K. ForT 4 K, there is a small deviation, increasing withT, from the superposition of the above mechanisms. The relation between , being negative, and theT independent part, , exhibits a singularity, where and=0.68±0.05 –(p–0.19). This singularity should be related to the metal-semiconductor transition, taking place atT _c 0.14. The quantity should be interpreted as minimum metallic conductivity. The limitingT dependences asxx _c +0 agrees quantitatively with that one obtained previously for the activated region,xx _c –0. Extrapolation of the phenomenological model obtained leads to the hypothesis that the interplay of and _ht could be the main origin of the temperature coefficient changing its sign in the Mooijregion, at _tc=0. The model enables several trend predictions concerning the value of _tc=0.     

Radiative recombination in hydrogenated amorphous silicon

Hydrogenated amorphous silicon exhibits efficient optical transitions across a gap larger than that of crystalline Si. Hydrogen passivates the dangling bonds and endows the material with a reduced number of non-radiative recombination centers. A gap widening has been observed in other hydrogenated semiconductors.Research reported herein was supported by the Department of Energy, Division of Solar Technology, under Contract No. EY-76-C-03-1286 and by RCA Laboratories, Princeton, NJ 08540.     

A markovian approach to massless particle decay and recombination

Massless particle decay and recombination is treated from the viewpoint of pure probability theory, using as a guide the empirical success of the exponential decay law for massive systems. The result is a linked set of linear integro-differential equations. Lorentz invariance is shown to be easily accomodated. As derived, the equations contain two arbitrary functions, one governing decays and the other recombinations. These equations are analyzed in certain special cases. Forms for the decay and recombination functions are proposed on the basis of Lorentz invariance and simplicity. Using phase space considerations, an argument is given that verifies these forms of the decay and recombination functions, and in addition specifies their relative strengths. When this input is applied to photon instability it is found that, first, there is no infrared divergence and secondly a photon emitted at time t=0 will have a probability of $\text{24}\text{25}$ to be observed in its original state as t→∞.