Electrical and memory properties of silicon nitride structures with embedded Si nanocrystals

In this work, the electrical and memory behaviour of metal-silicon nitride-silicon structures with an embedded nanocrystalline silicon layer, which either consists of separated silicon nanocrystals, or is a continuous nanocrystalline layer, are presented. The structures were prepared by low-pressure chemical vapour deposition (LPCVD). The effect of the duration of deposition and the structure of the nanocrystalline layer were studied. The writing/erasing behaviour was similar for all the structures, but the retention properties were much worse in the structure with a continuous nanocrystalline layer, than in the structures with separated Si nanocrystals. This indicates that Si nanocrystals play role in charge storage in the studied structures.     

基于纳米硅结构的氮化硅基发光器件电致发光特性研究

利用等离子体增强化学气相沉积法制备了镶嵌于氮化硅的高密度纳米硅薄膜,并以此作为发光有源层构建基于p-Si/氮化硅基发光层/AZO结构发光二极管,在室温下观察到了电致可见发光.在此基础上,在器件p-Si空穴注入层与氮化硅基发光层之间加入纳米硅薄层作为空穴阻挡层,研究器件电致发光性质,实验结果表明器件的发光强度显著增强,并且发光效率较无纳米硅阻挡层的发光器件提高了80%以上.     

氮化硅薄膜中硅纳米颗粒的形成机制研究

采用等离子体增强化学气相沉积技术,以SiH₄作为硅源, NH₃和N₂共同作为氮源,在单晶硅衬底上制备了不同的氮化硅薄膜. X射线衍射分析薄膜晶体结构,通过计算晶格尺寸大小证明了纳米硅颗粒的存在. 傅里叶变换红外光谱分析了薄膜中的键合作用的变化并结合化学反应过程对氮化硅薄膜中纳米硅颗粒的形成机制进行了研究,发现Si—Si键作为硅纳米颗粒的初始位置, 当反应朝着生成Si—Si的方向进行时,可以促进氮化硅薄膜中硅纳米颗粒的形成. X射线衍射分析和光致发光实验结果表明Si—Si键浓度增大时, 所形成的纳米硅颗粒的尺寸和浓度都随之增大.     

Quantum confinement in amorphous silicon quantum dots embedded in silicon nitride

Amorphous silicon quantum dots (a-Si QDs) were grown in a silicon nitride film by plasma enhanced chemical vapor deposition. Transmission electron micrographs clearly demonstrated that a-Si QDs were formed in the silicon nitride. Photoluminescence and optical absorption energy measurement of a-Si QDs with various sizes revealed that tuning of the photoluminescence emission from 2.0 to 2.76 eV is possible by controlling the size of the a-Si QD. Analysis also showed that the photoluminescence peak energy E was related to the size of the a-Si QD, a (nm) by E(eV) = 1.56+2.40/a(2), which is a clear evidence for the quantum confinement effect in a-Si QDs.     

Excitonic photoluminescence characteristics of amorphous silicon nanoparticles embedded in silicon nitride film

We have investigated the photoluminescence (PL) properties of amorphous silicon nanoparticles (a-Si NPs) embedded in silicon nitride film (Si-in-SiN_x) grown by helicon wave plasma-enhanced chemical vapor deposition (HWP-CVD) technique. The PL spectrum of the film exhibits a broad band constituted of two Gaussian components. From photoluminescence excitation (PLE) measurements, it is elucidated that the two PL bands are associated with the a-Si NPs and the silicon nitride matrix surrounding a-Si NPs, respectively. The existence of Stokes shift between PL and absorption edge indicates that radiative recombination of carriers occurs in the states at the surface of the Si NPs, whereas their generation takes place in the a-Si NPs cores and the silicon nitride matrix, respectively. The visible PL of the film originates from the radiative recombination of excitons trapped in the surface states. At decreasing excitation energy (E_ex), the PL peak energy was found to be redshifted, accompanied by a narrowing of the bandwidth. These results are explained by surface exciton recombination model taking into account there existing a size distribution of a-Si NPs in the silicon nitride matrix.     

Visible photoluminescence from silicon nanoclusters embedded in silicon nitride films prepared by remote plasma-enhanced chemical vapor deposition

The photoluminescence (PL) of silicon nanoclusters embedded in silicon nitride films grown by remote plasma-enhanced chemical vapor deposition at 200 °C, using mixtures of SiCl₄/H₂/Ar/NH₃ is investigated. It was found that the color and the intensity of the PL of the as-grown samples depend on the H₂ flow rate, and there is an optimum flow for which a maximum luminescence is obtained. A strong improvement of the PL intensity and change in color was obtained with annealing treatments in the range of 500–1000 °C. The changes in the composition, structure and optical properties of the films, as a function of H₂ flow rate and thermal treatments, were studied by means of Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, ellipsometry and ultraviolet–visible transmission measurements. We conclude that the PL can be attributed to quantum confinement effect in silicon nanoclusters embedded in silicon nitride matrix, which is improved when a better passivation of the nanoclusters surface is obtained.     

Infrared electroluminescence from erbium-doped spark-processed silicon

The infrared (IR) electroluminescence (EL) of erbium-doped spark-processed silicon (sp-Si) was investigated. For this, a device was constructed which consisted of a silicon wafer on which an erbium layer was vapor deposited, followed by spark-processing and rapid thermal annealing for 15 min at 900 °C in air. The metallization consisted of a 200 nm Ag layer (above the spark-processed area) and a 50 nm thick Al film (on the “back side”), containing a window through which the light could escape. Maximal light emission occurred near 1.55 μm, that is, at a wavelength where commonly used fiber optical materials have their minimum in energy loss. The processing parameters for most efficient light emission were an Er thickness of 200-300 nm, a spark-processing time of about 30 s, an n-type Si wafer having a low (3-5 Ω cm) resistivity, an operating temperature near room temperature, and an operating voltage between 25 and 40 V under reverse bias. The results are interpreted by postulating an energy transfer from sp-Si to the Er³⁺ ions involving the first excited state ⁴I_13/2 to ground state ⁴I_15/2. Further, impact excitation and hot electrons that are accelerated into the erbium doped sp-Si by the applied field (100 kV/cm) are considered.     

Photoluminescence and electroluminescence from porous silicon

The properties and origins of the red, blue and infrared photoluminescence bands of porous silicon are reviewed and discussed in the light of the models that have been proposed to explain the experimental and theoretical results. The red band is due to quantum confinement possibly supplemented by surface states; the blue band is linked to the presence of silicon dioxide; the infrared band is correlated with dangling bonds and bandgap luminescence in large crystallites. The fabrication and characterization of light-emitting devices made of porous silicon are reported and discussed with respect to critical issues such as the device stability, efficiency, modulation speed, emission wavelength, and compatibility with microelectronic processing.     

Room-temperature electroluminescence from hydrogenated amorphous carbon nitride film

Electroluminescence devices in the structure of anode/poly(methylphenylsilane)/hydrogenated amorphous carbon nitride/cathode have been fabricated. A strong visible emission is observed at room temperature and the emission intensity increases with the increase of the current density. In this device, poly(methylphenylsilane) acts as a hole transporting and electron blocking layer. It is evidenced that the emission region is near the interface between the poly(methylphenylsilane) and hydrogenated amorphous carbon nitride layers. The electroluminescence properties are discussed and compared with the photoluminescence of the hydrogenated amorphous carbon nitride film.     

Effect of excimer laser annealing on the silicon nanocrystals embedded in silicon-rich silicon nitride film

The investigations of silicon-rich silicon nitride film grown by plasma-enhanced chemical vapor deposition and then annealed by excimer laser have been carried out systematically. The surface roughness and the crystallization of the films have significantly been improved after the excimer laser annealing. The samples demonstrate visible photoluminescence emission under optical excitation at room temperature. It is found that the emission peak energy as well as emission intensity changes with laser annealing conditions, and the relevant mechanism is discussed in detail. Our investigation exhibits the size controllability of silicon nanocrystals embedded in the silicon nitride film, which implies promising applications in optoelectronic devices such as light-emitting diodes and solar cells.     

Photoluminescence and optical absorption properties of silicon quantum dots embedded in Si-rich silicon nitride matrices

Silicon nitride (SiN_x) films were prepared with a gas mixture of SiH₄ and NH₃ on Si wafers using the plasma-enhanced chemical vapor deposition (PECVD) method. High-resolution transmission electron microscopy and infrared absorption have been used to reveal the existence of the Si quantum dots (Si QDs) and to determine the chemical composition of the silicon nitride layers. The optical properties of these structures were studied by photoluminescence (PL) spectroscopy and indicate that emission mechanisms are dominated by confined excitons within Si QDs. The peak position of PL could be controlled in the wavelength range from 1.5 to 2.2 eV by adjusting the flow rates of ammonia and silane gases. Absorbance spectra obtained in the transmission mode reveal optical absorption from Si QDs, which is in good correlation with PL properties. These results have implications for future nanomaterial deposition controlling and device applications.     

Room-temperature electroluminescence from erbium-doped amorphous hydrogenated silicon

We have studied electroluminescence (EL) in the amorphous silicon-based erbium-doped structures under reverse bias in the temperature range 77–300 K. The intensity of electroluminescence at the wavelength of 1.54 μm exhibits a maximum near the room temperature. The excitation of erbium ions occurs by an Auger process which involves the capture of conduction electrons by neutral dangling bonds (D⁰-centers) located close to erbium ions. The stationary current through the structure is kept by a reverse process of thermally activated tunnel emission of electrons from negatively charged dangling-bond defects (D⁻-centers) to the conduction band of the amorphous matrix. A theoretical model proposed explains consistently all of our experimental data.     

Enhanced electroluminescence from nanocrystallite Si based MOSLED by interfacial Si nanopyramids

The interfacial Si nano-pyramid-enhanced electroluminescence (EL) of an ITO/SiOx/p-Si/Al metal-oxidesemiconductor (MOS) diode with turn-on voltage of 50 V, threshold current of 1.23 mA/cm2, output power of 16 nW, and lifetime of 10 h is reported.     

Study on electroluminescence from porous silicon light-emitting diode

Porous silicon (PS) light-emitting diode (LED) with an ITO/PS/p-Si/Al structure was fabricated by anodic oxidation method. Photoluminescence (PL) of the PS LED was measured with a peak at 593 nm, and electroluminescence (EL) was measured with a peak at 556 nm under the conditions of 7.5-V forward bias and 210-mA current intensity. The spectral width of EL was measured to be about 160 nm.     

Chemical shifts in auger electron spectra from silicon in silicon nitride

The chemisorption of nitric oxide on (110) nickel has been investigated by Auger electron spectroscopy, LEED and thermal desorption. The NO adsorbed irreversibly at 300 K and a faint (2 × 3) structure was observed. At 500 K this pattern intensified, the nitrogen Auger signal increased and the oxygen signal decreased. This is interpreted as the dissociation of NO which had been bound via nitrogen to the surface. By measuring the rate of the decomposition as a function of temperature the dissociation energy is calculated at 125 kJ mol^?1. At ～860 K nitrogen desorbs. The rate of this desorption has been measured by AES and by quantitative thermal desorption. It is shown that the desorption of N₂ is first order and that the binding energy is 213 kJ mol^?1. The small increase in desorption temperature with increasing coverage is interpreted as due to an attractive interaction between adsorbed molecules of ～14 kJ mol^?1 for a monolayer. The (2 × 3) LEED pattern which persists from 500–800 K is shown to be associated with nitrogen only. The same pattern is obtained on a carbon contaminated crystal from which oxygen has desorbed as CO and CO₂. The (2 × 3) pattern has spots split along the (0.1) direction as $\text{(m,}\text{n}\text{3}\text{)}$ and $\text{(}\text{m}\text{2, n}\text{)}$. This is interpreted as domains of (2 × 3) structures separated by boundaries which give phase differences of $\text{2π}\text{3}$ and π. The split spots coalesce as the nitrogen starts to desorb. A (2 × 1) pattern due to adsorbed oxygen was then observed to 1100 K when the oxygen dissolved in the crystal leaving the nickel (110) pattern.     

Si nanocrystals in silicon nitride: An ellipsometric study using parametric semiconductor models

Low-pressure chemical vapour deposited Si₃N₄/nc-Si/Si₃N₄ layers prepared on Si substrates were characterized by spectroscopic ellipsometry. Model Dielectric Function (MDF) was applied to obtain the thickness and the dielectric spectra of the middle nc-Si layer. Sensitive effect of the deposition time was obtained on the MDF parameters. A comparison is presented between the studied samples and reference materials.     

Rectification and electroluminescence of nanostructured GaN/Si heterojunction based on silicon nanoporous pillar array

A GaN/Si nanoheterojunction is prepared through growing Ga N nanocrystallites(nc-GaN) on a silicon nanoporous pillar array(Si-NPA) by a chemical vapor deposition(CVD) technique at a relatively low temperature. The average size of nc-Ga N is determined to be ~10 nm. The spectral measurements disclose that the photoluminescence(PL) from GaN/SiNPA is composed of an ultraviolet(UV) band and a broad band spanned from UV to red region, with the feature that the latter band is similar to that of electroluminescence(EL). The electron transition from the energy levels of conduction band and, or, shallow donors to that of deep acceptors of Ga N is indicated to be responsible for both the broad-band PL and the EL luminescence. A study of the I–V characteristic shows that at a low forward bias, the current across the heterojunction is contact-limited while at a high forward bias it is bulk-limited, which follows the thermionic emission model and space-charge-limited current(SCLC) model, respectively. The bandgap offset analysis indicates that the carrier transport is dominated by electron injection from n-GaN into the p-Si-NPA, and the EL starts to appear only when holes begin to be injected from Si-NPA into GaN with biases higher than a threshold voltage.     

Formation and properties of high density Si nanodots

Laser induced crystallization of ultrathin hydrogenated amorphous Si films or amorphous Si-based multilayered structures were used to get high density Si nanodots. The present technique can get size controllable Si nanodots embedded in various dielectric materials with uniform distribution which was revealed by cross-section transmission electron microscopy. Room temperature photoluminescence and electroluminescence were achieved with the emission wavelength in a visible light region both from a-SiN/Si nanodots/a-SiN sandwiched and Si nanodots/SiO₂ multilayered structures. The luminescence was associated with the radiative recombination of generated electron-hole pairs in Si nanodots or the luminescent surface states. The electroluminescence intensity is increased with increasing the injection current implying the bipolar carrier injection plays an important role in enhancing the luminescence efficiency. The formed Si nanodots by the present approach can be applied for many kinds of devices such as high efficient light emitting diodes and solar cells.