Effect of deposition and annealing conditions on the optical properties of amorphous silicon

The spectral characteristics of the refractive index and the extinction coefficient in the range 0.6–2.0 eV for amorphous silicon films prepared by electron-beam evaporation with variation of the substrate temperature, deposition rate, and annealing temperature in air are presented. The results obtained are discussed on the basis of the changes in the Penn gap energy as a function of the indicated preparation and treatment conditions. Fiz. Tekh. Poluprovodn. 32, 879–881 (July 1998)     

Formation of optically active centers in films of erbium-doped amorphous hydrated silicon

We have observed photoluminescence at 1.54 μm from a-Si:H films doped with erbium of various degrees of purity. It is shown that the additional introduction of oxygen activates the Er ions. The effect of silicides and defects in amorphous silicon a-Si:H films and in crystalline silicon c-Si is investigated. Fiz. Tekh. Poluprovodn. 33, 1260–1263 (October 1999)     

Effect of thermal annealing on optical and photoelectric properties of microcrystalline hydrogenated silicon films

The effect of thermal annealing in the temperature range T _a=300–600°C of films of microcrystal-line hydrogenated silicon (μc-Si:H) lightly doped with boron on the spectral dependences of the absorption coefficient (α) at photon energies hν=0.8–2.0 eV, dark conductivity (σ_d), and photoconductivity (Δσ_ph) was studied at room temperature. With increasing annealing temperature, a nonmonotonic variation of α (at hν<1.2 eV), σ_d, and Δσ_ph was observed. The data obtained are attributed to a change in the concentration of electrically active impurities and formation of defects, caused by hydrogen effusion and bond restructuring at high annealing temperatures.     

衬底和退火温度对多晶硅薄膜结构及光学性质影响

通过射频等离子体增强化学气相沉积(RF-PECVD)技术与退火处理制备多晶硅薄膜,研究了衬底和退火温度对所制薄膜的结构及光学性质的影响。本次试验最大的晶粒尺寸是在衬底温度为250℃获得,考虑薄膜表面的质量,最佳的退火温度为635℃,衬底温度为225℃,在玻璃衬底形成的晶粒大于50 nm,光学带隙为1.5 e V。结果表明:衬底温度影响着薄膜中氢含量以及相关的缺陷。随着退火温度的升高,晶化率的提高,光学带隙先减小后增大。     

Influence of the deposition and annealing conditions on the optical properties of amorphous silicon

The refractive index and extinction coefficient in the range 0.6–2.0 eV of amorphous silicon films deposited by electron-beam evaporation with variation of the substrate temperature, deposition rate, and anneal temperature in an air atmosphere are presented. The results are discussed in terms of variation of the Penn energy gap as a function of the deposition and treatment conditions. Fiz. Tekh. Poluprovodn. 32, 1390–1392 (November 1998)     

Effect of low-temperature annealing on photoluminescence of silicon nanocluster structures

Experimental data on the photoluminescence spectra of Si nanocluster structures obtained after high-temperature annealing (1150°C) of SiO _x films deposited onto Si and subsequent low-temperature annealing of the films at the temperature 450°C in different ambient are reported. It is shown that the photoluminescence intensity substantially increases after low-temperature annealing and the most-pronounced effect is observed after annealing in the oxygen-nitrogen mixture. In this case, the photoluminescence spectrum is shifted to longer wavelengths and shaped as a broad band with a peak around 800 nm. The processes responsible for the increase in the PL intensity on low-temperature annealing in the oxygen-nitrogen mixture are defined by reconstruction of the Si/SiO₂ interfaces and by energy levels formed at the interfaces and involved in recombination of nonequilibrium charge carriers. The quasichemical reactions that bring about the formation of such levels involve oxygen and nitrogen atoms, and the centers, at which the reactions are initiated, are unsaturated valence bonds at the interfaces between Si nanoclusters and the SiO₂ matrix.     

Growth of silicon nanoclusters in thermal silicon dioxide under annealing in an atmosphere of nitrogen

It is found for the first time that silicon nanoclusters are formed in the surface layer of thermal silicon dioxide under high-temperature annealing (T = 1150°C) in dried nitrogen. Analysis of the cathodoluminescence spectra shows that an imperfect surface layer appears upon such annealing of silicon dioxide, with silicon nanoclusters formed in this layer upon prolonged annealing. Transmission electron microscopy demonstrated that the silicon clusters are 3–5.5 nm in size and lie at a depth of about 10 nm from the surface. Silicon from the thermal film of silicon dioxide serves as the material from which the silicon nanoclusters are formed. This method of silicon-nanocluster formation is suggested for the first time.     

退火对纳米VO2薄膜结构及电性能的影响

采用直流反应磁控溅射法在K9玻璃和DBr衬底上制备了VO2薄膜.利用扫描电镜(SEM)、X射线衍射(XRD)、傅里叶红外光谱(FT-IR)对薄膜的形貌、晶相和分子结构等进行分析.结果表明,在氧气气氛下退火后,薄膜颗粒变得清晰可见,平均尺寸约25 nm,薄膜由非晶态结构转变为晶态的VO2,且在(011)方向出现明显择优取...     

Effects of annealing conditions on the properties of tantalum oxide films on silicon substrates

The formation of a SiO₂ layer at the Ta₂O₅/Si interface is observed by annealing in dry O₂ or N₂ and the thickness of this layer increases with an increase in annealing temperature. Leakage current of thin (less than 40 nm thick) Ta₂O₅ films decreases as the annealing temperature increases when annealed in dry O₂ or N₂. The dielectric constant vs annealing temperature curve shows a maximum peak at 750 or 800° C resulting from the crystallization of Ta₂O₅. The effect is larger in thicker Ta₂O₅ films. But the dielectric constant decreases when annealed at higher temperature due to the formation and growth of a SiO₂ layer at the interface. The flat band voltage and gate voltage instability as a function of annealing temperature can be explained in terms of the growth of interfacial SiO₂. The electrical properties of Ta₂O₅ as a function of annealing conditions do not depend on the fabrication method of Ta₂O₅ but strongly depend on the thickness of Ta₂O₅ layer.     

Effect of nanocrystalline inclusions on the photosensitivity of amorphous hydrogenated silicon films

Photosensitivity of amorphous hydrogenated silicon films containing inclusions of Si nanocrystals, along with spectral characteristics of photoconductivity, were studied. A correlation between photosensitivity and features of the Raman spectra was established. The highest photosensitivity is observed in films with medium-range order formed to the maximum extent.     

Si基薄膜太阳电池绒面ZGO透明导电膜的研究

采用孪生对靶直流磁控溅射的方法在室温下制备高质量的Ga掺杂ZnO(ZGO)透明导电薄膜,用HCl腐蚀的方法获得满足光散射特性的绒面ZGO薄膜。制备的ZGO样品为具有六角纤锌矿结构的多晶膜,具有(002)方向的择优取向。腐蚀后,绒面ZGO薄膜的晶粒度减小,电阻率基本不变。在可见光范围内,绒面ZGO的反射率比平面ZGO的反射率下降了10%左右。将绒面ZGO薄膜应用于p-i-n型非晶Si薄膜太阳电池中,有效提高了太阳电池性能,使得电池的短路电流提高到17.79 mA/cm2,电池的转换效率增加到7.23%。     

Influence of atomic-hydrogen treatment on the surface properties of n-n + GaAs structures

Tunneling scanning electron microscopy (TSEM) has been used to study the properties of n-GaAs (100) epilayers treated in a flow of atomic hydrogen (AH). The results obtained demonstrate the effects of atomic-hydrogen treatment on the surface, which consist in etching out of the surface oxide layer, micropolishing, stabilization in relation to the alkaline environment (solution of dimethylformamide and monoethanolamine in the ratio 1:3) and oxidation, as well as a change in the surface structure due to dimer formation. It is found that treatment with atomic hydrogen leads to the formation of a thin (less than 0.05 μm), poorly conducting surface layer, which probably greatly affects the static device parameters of Schottky-barrier diodes. Fiz. Tekh. Poluprovodn. 33, 1209–1216 (October 1999)     

退火对非晶态碲镉汞薄膜稳定态光电导的影响

利用射频磁控溅射方法,在宝石衬底上制备了非晶态碲镉汞(a-HgCdTe)薄膜。对原生a-HgCdTe薄膜进行了不同退火时间和不同退火温度的热退火,在80～300K温度范围内,分别测量了原生和退火处理后的a-HgCdTe薄膜样品的稳定态光电导,研究了退火时间和退火温度对非晶态HgCdTe薄膜的稳定态光电导和激活能的影响。结果表明,原生和退火a-HgCdTe薄膜的稳定态光电导具有热激活特性;随着退火时间增加或退火温度升高,a-HgCdTe薄膜的晶化程度提高,导致光电导增大,光电导激活能降低。利用非晶-多晶转变机制讨论了实验结果。     

Effect of the charge state of defects on the light-induced kinetics of the photoconductivity of amorphous hydrated silicon

The photoconductivity and defect density in films of nondoped a-Si:H soaked with light (W=114 mW/cm², λ<0.9 μm) for 5 h were investigated. It is shown that σ_ph ~ t ^-γ and N _D ~ t ^β, where γ>β or γ⋍β, depending on the position of the Fermi level prior to light soaking, i.e., depending on the charge state of the defects: D ⁻ and D ⁰ or D ⁺ and D ⁰. It is also shown that the light-induced kinetics of σ _ph is affected by a transition of the defects into the D ⁰ state because of a corresponding shift of the Fermi level during light soaking. Fiz. Tekh. Poluprovodn. 32, 345–348 (March 1998)     

Characteristic structural features of amorphous hydrated silicon films deposited by direct-currect decomposition of silane in a magnetic field

Data on the hydrogen content and different forms of hydrogen bonds with silicon in a-Si:H films deposited by direct-current decomposition of silane in a magnetic field (MASD) as a function of the deposition conditions are presented: temperature, pressure of the mixture 25%SiH₄+75%Ar, pumping rate, and insertion of a grid into the discharge chamber. The correlations between the photoconductivity and the structural features of the films are established. Fiz. Tekh. Poluprovodn. 31, 816–819 (July 1997)     

退火对用PLD法制备ZnO薄膜的发光影响

用脉冲激光沉积(PLD)方法在Si(111)和蓝宝石衬底上制备的氧化锌薄膜,在不同的退火温度和不同的退火氛围中进行了退火处理.退火温度及退火氛围对ZnO薄膜的结构和发光特性的影响用X射线衍射(XRD)谱和光致发光谱进行了表征.实验结果表明,随着退火温度的提高,ZnO薄膜的压应力减小,并向张应力转化.在不同的退火温度退火...     

Effect of the femtosecond laser treatment of hydrogenated amorphous silicon films on their structural, optical, and photoelectric properties

The effect of the femtosecond laser treatment of hydrogenated amorphous silicon (a-Si:H) films on their structural, optical, and photoelectric properties is studied. Under the experimental conditions applied in the study, laser treatment of the film with different radiation intensities induces structural changes that are nonuniform over the film surface. An increase in the radiation intensity yields an increase in the contribution of the nanocrystalline phase to the structure, averaged over the sample surface, as well as an increase in the conductance and photoconductance of the samples. At the same time, for all of the samples, the absorption spectrum obtained by the constant-photocurrent method has a shape typical for those of amorphous silicon. Obtained results indicate the possibility of a-Si:H films photoconductance increase by femtosecond pulse laser treatment.     

Study of the electronic properties of hydrogenated amorphous silicon films by femtosecond spectroscopy

Experimental results on the electron relaxation time and diffusion coefficient in hydrogenated amorphous silicon films that exhibit intrinsic and electronic conductivity at room temperature are reported. It is found that, for these two types of films, the relaxation times are 1 ns and 465 ps and the diffusion coefficients are 0.54 and 0.83 cm² s^?1. It is established that, as the pulse intensity is increased, the decay time of the induced-grating signal shortens.     

Effect of annealing on electrical properties of radio-frequency-sputtered ZnO films

We report on the electrical properties of ZnO films and devices grown on different substrates by radio-frequency magnetron sputtering. The films grown on c-plane sapphire were annealed in the range 800–1,000°C. The electron concentration increased with annealing temperature reaching 1.4×10¹⁹ cm^?3 for 1,000°C. Mobility also increased, however, reaching its maximum value 64.4 cm²/V · sec for 950°C anneal. High-performance Schottky diodes were fabricated on ZnO films grown on n-type 6H-SiC by depositing Au/Ni(300/300 Å). After annealing at 900°C, the leakage current (at ?5 V reverse bias) decreased from 2.2 × 10^?7 A to ～5.0 × 10^?8 A after annealing at 900°C, the forward current increased by a factor of 2, and the ideality factor decreased from 1.5 to 1.03. The ZnO films were also grown on p-type 6H-SiC, and n-ZnO/p-SiC heterostructure diodes were fabricated. The p-n diode performance increased dramatically after annealing at 950°C. The leakage current decreased from 2.0×10^?4 A to 3.0×10^?7 A at ?10 V reverse bias, and the forward current increased slightly from 2.7 mA to 3.9 mA at 7 V forward bias; the ideality factor of the annealed diode was estimated as 2.2, while that for the as-grown sample was considerably higher.     

Characteristic properties of macroporous silicon sintering in an argon atmosphere

The temperature and time dependences of the sintering of macroporous silicon in Ar or Ar + 3% H₂ are studied. The contribution of various mechanisms governing this process is determined. The specific features of the sintering of macroporous silicon are examined by means of isochronous and isothermal annealing of the samples with ordered and random macropores in the temperature range 1000–1225°C. It is found that the sintering of macroporous silicon under atmospheric pressure in an inert gas flow containing 2 × 10–4% O₂ is greatly affected by thermal etching. Thermal etching competes with the substance-transfer processes characteristic of sintering and hinders the formation of a defect-free surface crust. The reason for etching consists in that gaseous silicon monoxide is generated and then carried away by the gas flow. The etching effect is dominant in the low-temperature range and is independent of whether H₂ is added. The values obtained for the activation energy of the silicon diffusion coefficient, E _a = 2.57 eV, and for the exponent n = 3.31–3.74 in the time dependence of the pore radius, r ~ t ^1/n are indicative of a mixed substance-transfer mechanism via the surface and volume diffusion of silicon atoms.