アモルファスSi中のErの発光に対するダングリングボンドの役割

Siダングリングボンドの果たすEr発光に対する役割を調べるために、Siダングリングボンドのある場所と発光に関わるErのある場所を空間的に分離することを考え、Erを光学ギャップの大きい薄膜材料に添加して、その上にダングリングボンド密度を制御してアモルファスSiを作製した。光学ギャップの大きな材料としてLiNbO_3結晶薄膜とアモルファスAl_2O_3薄膜を用いたが、界面が1層だけの場合は、Erの発光に対するa-Si:H堆積の発光強度の増大は観測されなかった。観測の感度を上げるために、Erを添加したアモルファスAl_2O_33薄膜のあいだに約20nmの厚さのa-Si:H層を挟んだAl_2O_3:Er/a-Si:H/Al_2O_3:Er/a-Si:H/Al_2O_3:Erの多層構造を作製し、300度Cでアニールした所、Erの発光が観測された。a-Si:Hを挟まないAl_2O_3:Erの3屑構造だけでは同じアニール条件でErの発光は観測されないことから、a-Si:Hが空間的には離れたErの励起に何らかの影響を及ぼすことを示している。しかし、これがSiダングリングボンドを介した励起エネルギー移行によるものかどうかは分からない。Er添加Al_2O_3とa-Si:Hの厚さを変えて詳細な発光特性を調べる必要がある。Erのまわりの結晶場の影響を配位子場理論に基づいて考察し、低温(19K)での実験で得られたスペクトルと比較することにより、Erの入り方を明らかにしてきた。素性のはっきりしないパラメータを用いるのではなく、波動関数に基づいてシュタルク準位を計算して、Erを囲む酸素の作る正8面体が歪んだ構造がErの発光スペクトルと矛盾しない結果を与えることを示した。また、発光スペクトルが低エネルギー側ほど広い幅を示すのは、アモルファス物質固有の構造乱れがその主な原因であることを示した。In order to see a role of Si dangling bonds in the photoluminescence(PL) mechanism of Er which is doped in a-Si : H, it is thought to be useful that the Er site is separated from the Si dangling bond site and the influence of changing the separation on the Er PL is observed. To realize the idea, Er ions are added in two kinds of wide gap materials to inhibit the optical absorption of the host materials. Crystalline LiNbO_3 or amorphous Al_2O_3 are tried as wide gap materials. On top of the Er-doped thin film of the wide gar material, a-Si : H was deposited. The Er PL was not enhanced, however, when there was only one interface between a-Si : H and the wide gap material. In order to have a better sensitivity, we prepared a multilayer structure of the formAl_2O_3 : Er/a-Si : H/Al_2O_3 : Er/a-Si : H/Al_2O_3 : Er with around 20 nm thick a-Si : H layers sandwiched between Er-doped Al_2O_3.After annealing at 300 C, the Er PL was observed, while the threefold-stacked layer without a-Si : H la yer did not exhibit the Er PL after the same procedure. The observed results indicate that the thin a-Si : H layer is useful to excite Er ions which locate apart from a-Si : H. We cannot conclude at present whether Si dangling bonds in a-Si : H really play a role in enhancing the Er PL or not. Further investigations by changing the thicknesses of a-Si : H and Er-doped Al_2O_3 are needed to clarify the mechanism.We also studied on the environment of an Er ion by calculating the Stark levels due to the ligand field and by comparing the results with the PL spectra observed at 19 K. A model fo the Er environment is one that an Er ion is surrounded six oxygens which are incorporated unintentionally into a-Si : H during preparation. It should be emphasized that we did not rely on fitting parameters whose physical meaning were not clear but started with the wavefunction of the Er ion. Thus the effect of changing the distance between the Er and 0 atoms on the Stark splitting can be deduced. We conlude that the environmental model is consistent with the observed Er PL spectra. The fluctuation of the structure due to the randomness of the amorphous network is most probably the origin of the linewidth of the Er PL spectra.研究課題/領域番号:16560005, 研究期間(年度):2004-2006出典：「アモルファスSi中のErの発光に対するダングリングボンドの役割」研究成果報告書　課題番号16560005 (KAKEN：科学研究費助成事業データベース（国立情報学研究所）)　　　本文データは著者版報告書より作

Fluorine-incorporation scheme in fluorinated amorphous silicon prepared by various methods.

Fluorinated amorphous silicon (a-Si:F) films are prepared by three different methods: glow-discharge decomposition of SiF2 gas, magnetron sputtering, and conventional diode sputtering. The incorporation scheme of F atoms is investigated by means of nuclear magnetic resonance (NMR) and infrared (ir) absorption measurements. 19F NMR signals observed at 4.2 K can be simulated by superposing signals from dispersed F atoms, clustered F atoms, SiF4 molecules, and SiF3 species. The content of SiF4 increases by annealing in agreement with an increase in the intensity of ir absorption at 1020 cm-1. 19F NMR signals at 77 K and at room temperature show the effect of motional narrowing because SiF4 molecules move easily in the amorphous network

アモルファスシリコンの光劣化に対するフローティングボンドの寄与

欠陥生成とランダムネスの関係を、共有結合半径の大きく異なるGeとCの原子からなる_Ge_C_x:H薄膜と共有結合半径の近いGeとSiの原子からなる_Ge_Si_x:H薄膜における欠陥生成の様子を比較することにより調べた。C添加の場合、共有結合半径の違いによるランダムネスの増加が大きいために、Ge原子1個当たりのGeダングリングボンド(DB)はxの増加と共に増加することを示した。さらに水素化アモルファスシリコンにおいて、Siダングリングボンド(DB)に対するスピン格子緩和時間T_1の光劣化に伴う変化を調べ、T_1はランダムネスに関係したアーバックエネルギーと良い相関があることを示した。光誘起ESR信号の幅の広い信号(BC)と幅の狭い信号(NC)に対するT_1は、DBに対するT_1とは異なり、光劣化と共に減少することを見出した。この知見はBCがフローティングボンド(FB)に起因するものかどうかを考える上でひとつの手がかりになるものと思われる。次にFBが介在したDBの生成モデルに基づいて、光照射や電子線照射による欠陥生成過程を総合的に説明することを試みた。FBとDBのペア生成とペア消滅、FBとDBの相互変換、およびFB間のペア消滅を考慮したレート方程式を用いて、先ず電子線照射の実験をシミュレートした。さらに照射エネルギーの相違を考慮して、FB-BDペア生成項を変えることによって、光劣化過程も統一的に説明できることを示した。熱平衡欠陥の生成過程およびアニール過程も同じレート方程式によって説明できる可能性が大きく、シミュレーションを続行中である。Relation between the randomeness of amorphous network and the creation of defects was first investigated in an amorphous system of a-Ge_ C_x : H films which contains constituent atoms with largely different covalent radii, and compared the results with those in a-Ge_Si_x, : H films which contains constituent atoms with close covalent radii. It. was found that the addition of C atoms makes the films stricture more random and increase the Ge dangling bonds per Ge atoms.Next we measured the spin-lattice relaxation time T_1 of Si dangling bonds and its dependence on the light-soaking time in a-Si : H.It was found that T_1 has a fairly good correlation with the randomness of the amorphous network estimated from the Urbach energy. It was also found that T_1\u27s for the broad and narrow component signals of the light-induced ESR decreases by light-soaking, in contrast to that for the dark component. This might be an important clue to judge whether the origin of the broad component of the light-induced ESR comes from the floating bonds.Finally we tried to explain the defect creation processes by the light-soaking and electron-beam irradiation, using rate equations based on a model in which the floating bonds contribute to create dangling bonds.研究課題/領域番号:09650010, 研究期間(年度):1997-1998出典：「アモルファスシリコンの光劣化に対するフローティングボンドの寄与」研究成果報告書　課題番号09650010 (KAKEN：科学研究費助成事業データベース（国立情報学研究所）)　　　本文データは著者版報告書より作

Investigation of the spatial distribution of dangling bonds in light-soaked hydrogenated amorphous silicon

金沢大学大学院自然科学研究科電子物性デバイス金沢大学工学部We report on a detailed investigation of the spatial distribution of dangling bonds (DB\u27s) in light-soaked hydrogenated amorphous silicon (a-Si:H) films. The results for light soaking at different light intensities (3 W/cm2 and 300 mW/cm2) show that the inverse power-law DB distribution, Nυ(x)=Cυx-α, holds regardless of the light soaking intensity. Here, Nυ(x) is the volume density of DB\u27s at depth x measured from the surface, and Cυ and α(≈0.6) are constants. The nonuniform spatial distribution of DB\u27s in light-soaked a-Si:H is thought to originate from a nonuniform distribution of photocarriers during light soaking rather than from an inhomogeneity of the material. The same annealing behavior of light-induced DB\u27s was observed regardless of the thickness of the sample and regardless of whether the sample was light soaked from one side or from both sides. This result, together with the observation of identical spin characteristics, indicates that the light-induced DB\u27s at various depths of a given a-Si:H sample are identical in nature. The surface DB density is found to be much less sensitive to light soaking than the bulk DB density and can be assumed unchanged if the light-soaking intensity is not much higher than 300 mW/cm2 and the light-soaking time is shorter than ∼10 h. We show that the conventional method of estimating the surface DB density is no longer appropriate for light-soaked a-Si:H, due to the highly nonuniform distribution of DB\u27s in the material. The nonuniform distribution of DB\u27s can lead to significant disagreements between different techniques in quantifying the Staebler-Wronski effect and should therefore be taken into account in studies of the SW effect

Improved leakage and ferroelectric properties of Mn and Ti codoped BiFeO3 thin films

金沢大学理工研究域　電子情報学系Polycrystalline BiFeO3 (BFO), Ti-doped BFO, Mn-doped BFO, and (Mn, Ti)-codoped BFO (BFMT) thin films were fabricated on Pt/ SrTiO3 (100) substrate by pulsed laser deposition. Observed leakage current behavior in those ion-doped BFO films indicated the dominance of space-charge-limited current in the high electric field region. The leakage current of the BFMT film was much reduced in relation to the other films due to the formation of deep traps. In the BFMT film, well saturated P-E hysteresis curves were observed. Remanent polarization and coercive field for maximum electric field of 2100 kV/cm were 75 μC/ cm2 and 310 kV/cm, respectively. © 2009 American Institute of Physics

Environment of Er doped in a-Si:H and its relation with photoluminescence spectra

金沢大学大学院自然科学研究科電子物性デバイス金沢大学工学部The crystal-field potential at the Er3+ ion surrounded by six oxygen ions is expanded in terms of polynomials. After converting it into equivalent angular momentum operators, the Stark-splitting of the 4I15/2 ground state of the Er3+ ion is calculated. Influence of the change in the environment of the Er3+ ion on the shift of the energy levels is investigated and compared with the observed Er photoluminescence spectrum in a-Si:H. The scattering of the calculated energy levels by the structural fluctuation around the Er 3+ ion is also compared with the linewidth of the component photoluminescence lines. © 2006 Materials Research Society

Doping effect of oxygen or nitorogen impurity in hydrogenated amoorphous silicon films

O, N, or C impurity was separately incorporated into a‐Si:H films by hot‐wall glow discharge decomposition. The effect of the impurity incorporation was investigated by electrical and electron spin resonance measurements. Both O and N impurities were found to increase the dark conductivity by decreasing its activation energy in a‐Si:H films. Furthermore, it was found that O and N impurities delay the photoresponse. C impurity, however, has no appreciable effect on them. These findings suggest that O and N impurities shift the Fermi level upward and form a trapping state for photoexcited electrons, supporting our O+3 and N+4 model

Thermal-equilibrium defects in undoped hydrogenated amorphous silicon, silicon-carbon, and silicon-nitrogen

Temperature dependence of the thermal-equilibrium defect density in undoped a-Si:H, a-Si1-xCx:H, and a-Si1-xNx:H is obtained both by in situ electron-spin-resonance (ESR) measurements at elevated temperatures and by ESR measurements of frozen-in defects at room temperature. The experimental results confirm that the defects in these alloy films, even for films with the defect density as high as 1017 cm-3, can reach thermal equilibrium above a certain temperature (200350°C). Thickness dependence of the defect density after various thermal treatments shows that only the bulk defect density increases with temperature, with the exception that thin a-Si:H films (<1 m) exhibit some extra increase. Results of ESR, light-induced ESR (LESR), and constant-photocurrent method (CPM) measurements indicate that the charged-defect density in these films does not appreciably increase with temperature. Relaxation of the frozen-in defect density follows a stretched exponential form and the relaxation time increases with the defect density in these alloys. © 1990 The American Physical Society

The influence of the hot wire temperature on the crystallization of μc-Si:H films prepared by hot wire-assisted-ECR-CVD

金沢大学大学院自然科学研究科電子物性デバイス金沢大学工学部We have constructed a hot-wire-assisted ECR-CVD system to prepare a-Si:H and μc-Si:H films. The effect of hot wire (HW) temperature on crystallization of a-Si:H films is studied in the films prepared by this system. At low HW temperature, about 20 at.% hydrogen is included in the film. With increasing the HW temperature, the contents of the total hydrogen, SiH2 and SiH decrease, and the microcrystalline phase appears. It is found from the area of the TO peak of the Raman scattering spectra that the volume fraction of the crystalline phase increases with increasing the HW temperature. The crystalline peak has a tendency to shift toward the higher wavenumber with increasing the HW temperature, suggesting that the grain size increases with increasing the HW temperature. © 2006 Materials Research Society