Relaxation of photoinduced metastable states in a-Si:H films deposited at high temperatures

The results of an experimental study of dark-conductivity kinetics in a-Si:H after short-term and long-term illumination, are presented. The films were deposited at temperatures in the range T _s=300–390 °C. Data on relaxation of the photoinduced metastable states were found to correlate with the Fermi-level position. Fiz. Tekh. Poluprovodn. 32, 1269–1271 (October 1998)     

Photoinduced annealing of metastable defects in boron-doped a-Si:H films

Semiconductors - The effect of illumination on the isothermal relaxation of slow photoinduced metastable defects (metastable electrically active impurity atoms) in boron-doped a-Si:H films has been...     

Defects in a-Si:H films induced by Si ion implantation

Undoped a-Si:H films implanted with silicon ions (dose 10¹²–10¹⁴ cm⁻², mean energy ɛ=60 keV) at room temperature have been studied. The following results of the interaction of such films with ion beams have been established: formation of defects (dangling Si-Si bonds) in the neutral state (D ⁰), change in the charge state D ⁰→D ⁻, the a-Si:H→a-Si transition, and growth of inhomogeneity of the structure. It is shown that these effects depend on the initial structures and electronic characteristics of the films. Fiz. Tekh. Poluprovodn. 33, 464–468 (April 1999)     

Effect of temperature and illumination intensity on the formation of metastable states in a-Si:H

Nonmonotonic variation in the concentration of slow photoinduced metastable states and in the half-width of the distribution function for these states concerning their annealing times is observed in a-Si:H as temperature is increased in the range from 400 to 480 K. These nonmonotonic variations in the parameters of ensembles are determined by the temperature-dependent ratio between the rates of formation and annealing of the metastable states under study. It is also established that, as the film’s illumination intensity is decreased, a decrease in the concentration of metastable states and in the half-width of their annealing-time distribution sets in at higher temperatures. This behavior can be accounted for, in particular, by a substantial decrease in the rate of annealing of slow metastable states in comparison with a decrease in the rate of photoinduced formation of these states; according to the three-level model, this formation also involves a thermal process.     

a-Si:H热处理过程中形成的纳米硅粒及其光致发光

报道了氢化非晶硅薄膜在600～620℃温度下快速退火10 s可以形成纳米晶硅,其拉曼散射表明,所形成的纳米晶硅在薄膜中的分布是随机的,其直径在1.6～15 nm内.根据晶体生长理论和计算机模拟,讨论了升温快慢与所形成纳米硅颗粒大小之间的关系,并且在强光照射下观察了纳米晶硅在薄膜中的结晶和生长情况.经退火形成的nc-Si可见光辐射较弱,不能检测到它们的光致发光,但用氢氟酸腐蚀钝化后则可检测到较强的红PL,并且钝化后的nc-Si在空气中暴露一定时间后,其辐射光波长产生了蓝移.就表面钝化和量子限制对可见光辐射的重要性作了讨论.     

a-SiH 热处理过程中纳米硅粒尺寸的控制(英文)

报道了控制热处理过程中含氢非晶硅中纳米硅颗粒大小的一种新方法。用喇曼散射、X射线衍射和计算机模拟,发现在非晶硅中所形成的纳米硅颗粒的大小,随着热退火过程中升温速率的变化而变化。在退火过程中,若非晶硅薄膜升温速率较高(～100℃/s),则所形成纳米硅粒的大小在1.6～15nm;若非晶硅薄膜升温速率较低(～1℃/s),则纳米硅粒大小在23～46nm。根据晶体生长理论,讨论了升温速率的高低与所形成的纳米硅颗粒大小的关系。     

Anodic oxidation of a-Si:H films

It is shown that thick native oxide layers (up to 2500 ?) can be grown on a-Si:H films at room temperature by anodic oxidation. Ellipsometric measurements indicate uniformity of the oxide layer with a refractive index of 1.46. The voltage growth rate is found to be 5.3 ?/V.     

Long-term structural relaxation and photoinduced degradation in a-Si: H

The effect of heating-illumination cycling on the electrical properties of a-Si: H fabricated in a glow discharge was investigated. Comparison of experimental and theoretical results shows that photostimulated degradation of a-Si: H (the Staebler-Wronski effect) may occur due to long-term degradation of structural defects generated by preliminary heating. Fiz. Tekh. Poluprovodn. 32, 1272–1276 (October 1998)     

Relaxation of light-induced metastable state of boron-doped p-type a-Si:H

Relaxation of the dark conductivity of boron-doped a-Si: H films after illumination in the temperature range 360–470 K has been studied. It is shown that the measuring conductivity relaxation after illumination under different conditions (illumination time and temperature) makes it possible to separately investigate relaxation of the concentration of light-induced metastable defects of the “dangling-bonds” type and relaxation of the concentration of metastable states associated with impurity atoms. In both cases the relaxation obeys a stretched-exponential law. The main parameters of both relaxations and their temperature dependence have been measured. The experimental results can be explained within the framework of a model of the annealing activation energy distribution for light-induced metastable states. Fiz. Tekh. Poluprovodn. 32, 117–120 (January 1998)     

Structure and properties of a-Si:H films grown by cyclic deposition

Amorphous hydrogenated silicon films obtained by cyclic deposition with intermediate annealing in hydrogen plasma were studied. a-Si:H films deposited under optimal conditions are photosensitive (photoconductivity to dark conductivity ratio σ_ph/σ_d is as high as 10⁷ under 20 mW cm^?2 illumination in the visible region of the spectrum) and have an optical gap (E _g ) and activation energy of conductivity (E _a ) of 1.85 and 0.91 eV, respectively. Electron microscopy studies revealed a clearly pronounced layered structure of a-Si:H films and the presence of nanocrystalline inclusions in the amorphous matrix.     

Photoinduced relaxation of metastable states in (<Emphasis Type="Italic">a</Emphasis>-Si:H):B

The kinetics of thermal relaxation of an ensemble of photoinduced metastable electrically active B atoms in (a-Si:H):B films is studied after partial relaxation of the ensemble in the dark and under illumination of various intensities and duration. The parameters of a stretched exponential function that describes the ensemble kinetics are determined. It is found that photoinduced relaxation of metastable states manifests itself under conditions in which its rate exceeds the rate of the states’ photoinduced generation. It is shown that the variations in the relaxation-time distribution function of metastable states caused by thermal and photoinduced relaxation are similar.     

Silicon network in a-Si:H films containing ordered inclusions

a-Si:H films with inclusions of (SiH₂)_n clusters or Si nanocrystals have been grown by magnetron-assisted SiH₄ decomposition (dc-MASD). The films were characterized by the microstructural parameter R=0.7–1.0. Ultrasoft X-ray emission spectroscopy was applied to establish the effect of these inclusions on the increasing ordering of Si network. It is shown that, irrespective of the nature of the inclusions, their effect is strongest for films of intrinsic material deposited at high temperatures (up to 400°C).     

On the photoinduced effect in undoped a-Si:H films

The temperature dependences of the dark conductivity and photoconductivity of annealed and preliminarily illuminated undoped a-Si:H films are studied in different modes of temperature variation. Also, the variation kinetics of the photoconductivity and dark conductivity of the films during and after their exposure to light at different temperatures are analyzed. It is shown that the anomalous nature of the dependences obtained may be due to the formation of two kinds of photoinduced defects that have different energies of formation and thermal annealing and energy levels situated in different parts of the band gap of the films under study.     

Light-induced processes in a-Si:H films at elevated temperatures

At temperatures T>120 °C the kinetics of the dark conductivity (σ _d) of undoped and borondoped a-Si:H films during and after the cessation of illumination is observed to be nonmonotonic, with fast and slow processes of variation of σ _d of opposite sign. A fast or slow σ _d relaxation process described by a stretched exponential function can be isolated by varying the duration and intensity of illumination or the film temperature. The nonmonotonic relaxation of σ _d is described by a sum of two stretched exponentials, whose parameters τ and β depend on the film characteristics and on the temperature, exposure time, and intensity of illumination. The nature of the nonmonotonic relaxation is discussed. Fiz. Tekh. Poluprovodn. 31, 1455–1459 (December 1997)     

Nanostructured a-Si:H films obtained by silane decomposition in a magnetron chamber

Nanostructured a-Si:H films grown by the MASD method at various deposition temperatures (T _s =300–390°C) were studied. Among these films, those “on the verge of crystallinity” are of particular interest, because they tend to crystallize. In addition, although their electron-transport parameters are slightly inferior to those of conventional device-grade a-Si:H, they are preferable because of the higher stability of their photoconductivity under exposure to light.     

Study of light-induced annealing effects in a-Si:H thin films

Light-induced metastability was examined in hydrogenated amorphous silicon thin films using a 500 W xenon lamp and a 10 mW HeCd laser. Positron beam annihilation spectroscopy (PAS) and fourier transform infrared spectroscopy (FTIR) were examined to investigate the effects of light on the structural properties of the films. The experimental results exhibited significant decrease in the S-parameter of the PAS, indicating marked reduction in the defect density of the films. The FTIR spectroscopy showed significant reduction in the transmission coefficient of IR radiation at frequencies corresponding to Si–H and Si–H₃ phonon modes, indicating that the observed annealing effects were due to light-induced formation of Si–H and Si–H₃ bonds. A second thermal annealing process conducted after the light exposure experiment resulted in a further substantial decrease in defect density for the sample exposed to HeCd laser. The experimental results are explained by a competing, light induced, dangling bond creation/annealing process, in which the incoming photons caused the annealing of dangling bonds, particularly those at around the voids. However, in the bulk region, the photons caused both the breaking of weak Si–Si bonds as well as the annealing of dangling bonds.     

Effect of doping with nitrogen on electrical properties and erbium electroluminescence of a-Si:H(Er) films

The effect of nitrogen doping on the electrical and electroluminescence properties of amorphous hydrogenated silicon films doped with erbium has been studied. The parameters of the material, the characteristics of structures on its base, and the efficiency of Er electroluminescence (λ=1.54 μm) are determined by the excess of the nitrogen doping level over the background value depending on the Er concentration. It is shown that effectively luminescing structures can be obtained by reducing the background concentration, with nitrogen doping remaining at the level of ∼10²¹ cm⁻³. A possible mechanism is proposed, accounting for this effect in terms of two possible forms of nitrogen incorporation into an Er-doped a-Si:H structure: with either an Er-N complex or a Na ₄ ⁺ -Si ₃ ⁻ charged defect pair formed. In this case, the electroluminescence efficiency is determined by the number of these pairs. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 10, 2001, pp. 1250–1255. Original Russian Text Copyright ? 2001 by Kon’kov, Terukov, Granitsyna.     

利用热退火法从非晶硅薄膜中生长纳米硅粒

报道了一种从氢化非晶硅薄膜中生长纳米硅粒的方法.氢化非晶硅薄膜经过不同条件的热退火处理后,用拉曼散射和X射线衍射技术对样品进行了分析.实验结果表明:在快速升温条件下所形成的nc-Si在薄膜中的分布是随机均匀的,直径在1.6～15 nm范围内,硅粒大小随退火过程中升温快慢而变化.     

Bias sensitive a-Si(C): H multispectral detectors

New types of a-Si(C):H thin-film multispectral detectors were designed and successfully fabricated. It was found that the controlling of drift length in the active regions provides a simple and useful criterion for the design, by the aid of which novel multispectral detectors with ni'pi'δ(n)in or pini'δ(p)ip structure were developed. The device with a ni'pi'(δn)in structure show's spectral response peaks located at 450, 550, and 600 nm under bias voltages of 4.5, -1.5, and -7.0 V, respectively. This response is very similar to that of the human eye. In the corresponding pi'ni'δ(p)ip structure the maximum response can be shifted to 510 nm at a bias of -6.0 V, 560 nm at 1.0 V, and 610 nm at 5.5 V. Moreover, the prototypes exhibit excellent linearity within an illumination range from 10¹¹ to 10¹⁵ photons cm^-2 s^-1 and a high dynamic range of more than 56 dB under illumination of 1000 Ix