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1.
The junction characteristics of the organic compound methyl-red film (2-[4-(dimethylamino)phenylazo]benzoic acid) on a p-type Si substrate have been studied. The current-voltage characteristics of the device have rectifying behavior with a potential barrier formed at the interface. The barrier height and ideality factor values of 0.73 eV and 3.22 for the structure have been obtained from the forward bias current-voltage (I-V) characteristics. The interface state energy distribution and their relaxation time have ranged from 1.68 × 1012 cm−2 eV−1 and 1.68 × 10−3 s in (0.73-Ev) eV to 1.80 × 1012 cm−2 eV−1 and 5.29 × 10−5 s in (0.43-Ev) eV, respectively, from the forward bias capacitance-frequency and conductance-frequency characteristics. Furthermore, the relaxation time of the interface states shows an exponential rise with bias from (0.43-Ev) eV towards (0.73-Ev) eV.  相似文献   

2.
Zinc diffusion in InAsP/InGaAs heterostructures   总被引:1,自引:0,他引:1  
A systematic study of the sealed ampoule diffusion of zinc into epitaxially grown InP, In0.53Ga0.47As, In0.70Ga0.30As, In0.82Ga0.18As, and through the InAsP/InGaAs interface is presented. Diffusion depths were measured using cleave-and-stain techniques, electrochemical profiling, and secondary ion mass spectroscopy. The diffusion coefficients, , were derived. For InP, D0=4.82 × 10−2cm2/sec and Ea=1.63 eV and for In0.53Ga0.47As, D0=2.02 × 104cm2/sec and Ea=2.63 eV. Diffusion into the heteroepitaxial structures used in the fabrication of planar PIN photodiodes is dominated by the effects of the InP/InGaAs interface.  相似文献   

3.
Argon ions were implanted into n-type 6H-SiC epitaxial layers at 600°C. Postimplantation annealing was carried out at 1,600°C for 5 min in an Ar ambient. Four implantation-induced defect levels were observed at EC-0.28 eV, EC-0.34 eV, EC-0.46 eV, and EC-0.62 eV by deep level transient spectroscopy. The defect center at EC-0.28 eV is correlated with ED1/ED2 and with ID5. The defect at EC-0.46 eV with a capture cross section of 7.8 × 10−16 cm2 is correlated with E1/E2, while the defect at EC-0.62 eV with a capture cross section of 2.6 × 10−14 cm2 is correlated with Z1/Z2. Photo deep level transient spectroscopy was also used to study these defects. Upon illumination, the amplitudes of the deep level transient spectroscopy (DLTS) peaks increased considerably. Two emission components of Z1/Z2 were revealed: one fast and the other slow. The fast component could only be observed with a narrow rate window. In addition, a new defect was observed on the low-temperature side of the defect at EC-0.28 eV when the sample was illuminated. [rl](Received ...; accepted ...)  相似文献   

4.
The electronic structure of silicon nanocrystals (∼2-6 nm in size) embedded in cubic Gd2O3 epi-layers grown on (1 1 1) Si was analyzed using spectroscopic ellipsometry and photocharging methods. With decreasing nanocrystal size down to the 2 nm range, the optical absorption exhibits a spectacular shift in spectral threshold to 2.9 ± 0.1 eV, as compared to the 1.12 eV absorption edge of the bulk Si crystal. This shift suggests a significant influence of quantum confinement on the Si nanocrystal/oxide interface band diagram, which effect is shown to be predominantly caused by an upshift of the nanocrystal conduction band.  相似文献   

5.
Optical properties of two Cu-induced deep acceptorlike levels in GaP with binding energies EA = 0.50 ± 0.01 eV and EB 0.7 eV have been investigated. Data are reported here from purely optical techniques, based on detection of photoluminescence. A detailed spectral analysis of the broad Cu-related 1.65 eV-emission reveals a moderate Frank-Condon shift ΔFC 105 ± 15 meV for the A-center. Accurate spectral data for optical cross section σpA0() and σnA0() were measured for the 0.50 eV A-center. Optical cross sections σpB0() and σnB0() could also be measured via luminescence, in spite of the fact that the B-center appears to have a completely nonradiative recombination.  相似文献   

6.
Near IR properties of the mixed TlInS2xSe2(1?x) have been studied previously by the present authors. In this work the temperature and frequency dependence's of the conductivity and the current-voltage characteristics (in relatively weak electric field), have been investigated for monoclinic TlInS2xSe2(1?x) crystals, which are perspective materials for IR applications. From the temperature dependence's of conductivity in the direction perpendicular to c- axis the band gap Eg = 2.22 eV was determined for β--TlInS2 crystals. The impurity centres were determined located at 0.43, 0.73 eV and 0.35, 0.48, 1.12 eV for the direction of current i//c and i ⊥ c, respectively. The concentration of the centres located at 0.48 and 1.12 eV were calculated to be NA ? ND = 4.8 · 109 cm?3 and 1.9 · 1011 cm?3, respectively. It was found that in the solid solutions TlInS2xSe2(1?x) for 0.3 ≤ x ≤ 1, the conductivity follows the dependence σ (v) = σ0·υs in the temperature range between 100 to 600 K. In the temperature range of 80-400 K charge bounce plays an important role in the conductivity mechanism. Occurrence of the deep and low-levels impurity centres and a “tail” of the density of energy states in TlInS2xSe2(1?x) crystals make them perspective for practical applications: switching and memory effects, N-type current-voltage characteristics, induced conductivity etc.  相似文献   

7.
The complex dielectric function of PbS thin films is studied by spectroscopic ellipsometry in the spectral range from 0.74 to 6.45 eV at a temperature of 293 K. The critical energies are determined to be E 1 = 3.53 eV and E 2 = 4.57 eV. For both energy regions, the best fit is attained at the critical point 2D (m = 0). In addition, the Raman spectra and the optical-absorption spectra of PbS thin films are studied. From the dependence of the quantity (αhν)2 on the photon energy hν, the band gap is established at E g = 0.37 eV.  相似文献   

8.
The paper presents the results of capacitance-voltage, conductance-frequency and current-voltage characterization in the wide temperature range (140-300 K) as well as results of low temperature (5-20 K) thermally stimulated currents (TSC) measurements of metal-oxide-semiconductor (MOS) structures with a high-κ LaSiOx dielectric deposited on p- and n-type Si(1 0 0) substrate. Interface states (Dit) distribution determined by several techniques show consistent result and demonstrates the adequacy of techniques used. Typical maxima of interface states density were found as 4.6 × 1011 eV−1cm−2 at 0.2 eV and 7.9 × 1011 eV−1cm−2 at 0.77 eV from the silicon valence band. The result of admittance spectroscopy showed the presence of local states in bandgap with activation energy Ea = 0.38 eV from silicon conductance band, which is in accord with interface states profile acquired by conductance method. Low-temperature TSC spectra show the presence of shallow traps at the interface with activation energies ranging from 15 to 32 meV. The charge carrier transport through the dielectric film was found to occur via Poole-Frenkel mechanism at forward bias.  相似文献   

9.
Across-wafer variation of deep traps in AlGaN/GaN heterostructure field- effect transistors (HFETs) has been studied using current-mode deep-level transient spectroscopy (I-DLTS). It is found that applying a bias to the gate corresponding to open-channel or nearly pinched-off operation while cooling from 550 K has significant effects on the threshold voltage of the device and spectral features of I-DLTS at T <~400 K. To compare I-DLTS spectra acquired under different measurement conditions (e.g., different filling pulse heights or widths), attention should be paid to the gate bias applied while cooling. We find that the spectral features observed across the wafer can be divided into three categories: (i) a dominant trap A 1 at ~360 K; (ii) a prominent hole-like trap H 1 at ~480 K; and (iii) for T < 340 K, several traps varying in magnitude, including A, B, and C 1, and a hole-like trap H 0. Based on I-DLTS, measured as a function of filling pulse height and filling pulse width, we suggest that: (i) trap A 1, with E T = 1.1 eV to 1.2 eV and σ = 4 × 10−13 cm2 to 2 × 10−12 cm2, is associated with extended defects, such as threading dislocations; (ii) traps A, B, and C 1, located mainly in the two-dimensional electron gas (2DEG) channel region, could be related to point defects; and (iii) the hole-like trap H 1, with E T = 1.2 eV to 1.3 eV and σ = 8 × 10−17 cm2 to 5 × 10−15 cm2, may be related to surface states. Note that traps A (~0.67 eV), B (0.58 eV to 0.61 eV), and C 1 (0.44 eV to 0.49 eV) are commonly observed in GaN layers grown by various techniques. For all of the HFETs near the center of the wafer, trap A 1 dominates the DLTS spectra, whereas trap B becomes prominent for some of the HFETs near the edge of the wafer.  相似文献   

10.
Crystal sizes of AgInS2 grown by a directional freezing depend on sulphur pressures at the preparation. The conductivity is only n-type and nominally undoped AgInS2 has the resistivity of 25 Ω-cm and the Hall mobility of 64 cm2/V sec. Sulphur vacancies of AgInS2 become electron-trapping levels in the forbidden band. It is obtained from the measurements of thermally stimulated current that the levels lie at ET1 = 0·19±0·01 eV and ET2 = 0·40±0·01 eV, and the concentrations depend on sulphur pressures at the crystal preparations. AuAgInS2 contacts operate as a Schottky barrier diode and the barrier height is 0·97 eV. AgInS2 has a dichroism because of its uniaxial lattice structure. The transition is direct for E⊥c and indirect for E∥c, and the values for the energy gap are Eg = 1·88±0·01 eV and Eg = 1·77±0·01 eV, respectively.  相似文献   

11.
Because gold doping can be used to suppress ionization-induced photocurrents in Si devices exposed to radiation environments, it is of interest to know whether or not radiation-induced mobile defects interact with Au to form deep level defect complexes. Trapping level studies have been undertaken using the technique of deep level transient spectroscopy (DLTS) prior to and following Co-60 gamma irradiation and thermal annealing of p+/n Si junctions doped with 3-6 × 1014 Au/cm3 and 1-3 × 1013 Au/cm3 , and of non-Au doped p+ /n and n+ /p junctions. Prior to irradiation, the Au acceptor level at Ec - 0.57 eV is observed in the gold doped junctions. During irradiation, five additional levels at Ec - 0.18 eV, Ec - 0.20 eV, Ec - 0.46 eV, Ev +0.17 eV, and Ev + 0.39 eV grow in linearly with gamma dose. None of these levels are associated with Au because they are observed at equal concentrations in the non-Au doped and Audoped junctions, and because the Au concentration as monitored by the Ec - 0.57 eV level does not change even when defect concentrations are of the same order. Isochronal annealing studies also indicate that the Au acceptors are inert to defect re-ordering effects which occur during annealing. This work was supported by the United States Department of Energy (DOE) under contract number DE-AC04-76-DP00789. A United States Department of Energy Facility.  相似文献   

12.
Two new small molecules, 5,5-bis(2-triphenylamino-3-decylthiophen-2-yl)-2,2-bithiazole (M1) and 2,5-bis(2-triphenylamino-3-decylthiophen-2-yl)thiazolo[5,4-d]thiazole (M2) based on an electron-donor triphenylamine unit and electron-acceptor thiophene-thiazolothiazole or thiophene-bithiazole units were synthesized by a palladium(0)-catalyzed Suzuki coupling reaction and examined as donor materials for application in organic solar cells. The small molecules had an absorption band in the range of 300-560 nm, with an optical band gap of 2.22 and 2.25 for M1 and M2, respectively. As determined by cyclic voltammetry, the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of M1 were −5.27 eV and −3.05 eV, respectively, which were 0.05 eV and 0.02 eV greater than that of M2. Photovoltaic properties of the small molecules were investigated by constructing bulk-heterojunction organic solar cell (OSC) devices using M1 and M2 as donors and fullerene derivatives, 6,6-phenyl-C61-butyric acid methyl ester (PC61BM) and 6,6-phenyl-C71-butyric acid methyl ester (PC71BM) as acceptors with the device architecture ITO/PEDOT:PSS/M1 or M2:PCBM/LiF/Al. The effect of the small molecule/fullerene weight ratio, active layer thickness, and processing solvent were carefully investigated to improve the performance of the OSCs. Under AM 1.5 G 100 mW/cm2 illumination, the optimized OSC device with M1 and PC71BM at a weight ratio of 1:3 delivered a power conversion efficiency (PCE) of 1.30%, with a short circuit current of 4.63 mA/cm2, an open circuit voltage of 0.97 V, and a fill factor of 0.29. In contrast, M2 produced a better performance under identical device conditions. A PCE as high as 2.39% was recorded, with a short circuit current of 6.49 mA/cm2, an open circuit voltage of 0.94 V, and a fill factor of 0.39.  相似文献   

13.
We present a novel approach based on conductive atomic force microscope (c-AFM) for nano-scale mapping in laterally inhomogeneous metal-semiconductors Schottky contacts. For ultra-thin (1-5 nm) metal films with resistivity exceeding by about two orders of magnitude the bulk value, the current localization under the tip (10-20 nm diameter) occurs. By spectroscopic analysis of the current-voltage characteristics for different tip positions, the 2D Schottky barrier height (SBH) distribution is obtained with ∼0.1 eV energy resolution. The method was applied to explain the experimentally observed SBH lowering in macroscopic Au/4H-SiC diodes, in the presence of a not uniform SiO2 layer at the SiC/Au interface. Nano-scale mapping on the oxide free Au/4H-SiC contact demonstrates a SBH distribution peaked at 1.8 eV and with tails from 1.6 eV to 2.1 eV. When ∼2 nm not uniform SiO2 layer is intentionally grown on SiC before contact formation, the Au/SiO2/4H-SiC SBH distribution exhibits a 0.3 eV lowering in the peak and a broadening (tails from 1.1 eV to 2.1 eV), thus explaining the macroscopically observed average effect.  相似文献   

14.
Deep levels have been investigated in Si-implanted and rapid-thermal-annealed semiinsulating GaAs:Cr, which was grown by a horizontal Bridgman method. Samples were implanted with a Si-dose of (1 - 5) x 1012 ions cm-2 with 100 keV energy, and treated by a two-step rapid thermal annealing process at 900 and 800&#x00B0; C. After these processes, three electron deep levels at 0.81, 0.53 and 0.62 eV below the conduction band and three hole deep levels at 0.89, 0.64 and 0.42 eV above the valence band were observed. The new deep levels Ec - 0.53 eV, Ec - 0.62 eV, andEv + 0.64 eV in fact, dominate the implantation and/or the thermally damaged region, but are not found in the bulk. These results indicate that high-density deep levels may be induced near or within the implanted region by rapid heating and cooling, and that these defects may effect carrier activation.  相似文献   

15.
The thermal emission rates and capture cross sections of majority carriers on the vandium associated centers in the depletion region of reverse biased silicon p-n junctions have been measured by the dark capacitance transient method. The three vanduim associated levels observed, two donor levels and a deep acceptor level, belong to the same vandium center. Least square fits of the emission data give the following emission rates; enlt = 1.047 × 106T2 exp [?0.179±0.004 eV/kT], en0t = 3.55 × 107T2 exp [?0.426±0.004 eV/kT] and ep-2t = 1.514 × 106T2 exp [?0.450±0.003 eV/kT]. The activation energy of the hole emission rate at the lower donor level is about 0.1 eV larger than the equilibrium thermal activation energy. The capture cross sections are σn0 = 3 × 10?17cm2 and σp0 = 8 × 10?16cm2 for the electron capture process at the deep acceptor level and the hole capture process at the upper donor level, respectively. The hole capture cross section on the lower donor level (σp-1) depends significantly on temperature. The large temperature dependence of the hole capture cross section can be expected due to the nonradiative multiphonon emission process.  相似文献   

16.
The structural and electrical properties of SrTa2O6(SrTaO)/n-In0.53GaAs0.47(InGaAs)/InP structures where the SrTaO was grown by atomic vapor deposition, were investigated. Transmission electron microscopy revealed a uniform, amorphous SrTaO film having an atomically flat interface with the InGaAs substrate with a SrTaO film thickness of 11.2 nm. The amorphous SrTaO films (11.2 nm) exhibit a dielectric constant of ∼20, and a breakdown field of >8 MV/cm. A capacitance equivalent thickness of ∼1 nm is obtained for a SrTaO thickness of 3.4 nm, demonstrating the scaling potential of the SrTaO/InGaAs MOS system. Thinner SrTaO films (3.4 nm) exhibited increased non-uniformity in thickness. From the capacitance-voltage response of the SrTaO (3.4 nm)/n-InGaAs/InP structure, prior to any post deposition annealing, a peak interface state density of ∼2.3 × 1013 cm−2 eV−1 is obtained located at ∼0.28 eV (±0.05 eV) above the valence band energy (Ev) and the integrated interface state density in range Ev + 0.2 to Ev + 0.7 eV is 6.8 × 1012 cm−2. The peak energy position (0.28 ± 0.05 eV) and the energy distribution of the interface states are similar to other high-k layers on InGaAs, such as Al2O3 and LaAlO3, providing further evidence that the interface defects in the high-k/InGaAs system are intrinsic defects related to the InGaAs surface.  相似文献   

17.
The spectral complex of optical functions of the calomel Hg2Cl2 single crystal is determined in the range 0–20 eV at 300 K in unpolarized light. The spectra of the imaginary part of the permittivity ε 2(E), the bulk–Imε–1 and the surface–Im(1 + ε)–1 electron energy losses are decomposed into elementary bands. Their main parameters, including energies and oscillator strengths of the transition bands are determined. Calculations are performed on the basis of the experimental reflectance spectrum of the crystal cleavage. Computer programs based on Kramers–Kronig relations, analytical formulas, and the advanced parameterfree method of combined Argand diagrams are used. The main features of the spectral set of optical functions and the parameters of expansion band components ε2(E),–Imε–1, and–Im(1 + ε)–1 are determined.  相似文献   

18.
We demonstrate a new flexible metal-insulator-metal capacitor using 9.5-nm-thick ZrO2 film on a plastic polyimide substrate based on a simple and low-cost sol-gel precursor spin-coating process. The surface morphology of the ZrO2 film was investigated using scan electron microscope and atomic force microscope. The as-deposited ZrO2 film under suitable treatment of oxygen (O2) plasma and then subsequent annealing at 250 °C exhibits superior low leakage current density of 9.0 × 10−9 A/cm2 at applied voltage of 5 V and maximum capacitance density of 13.3 fF/μm2 at 1 MHz. The as-deposited sol-gel film was completely oxidized when we employed O2 plasma at relatively low temperature and power (30 W), hence enhancing the electrical performance of the capacitor. The shift (Zr 3d from 184.1 eV to 184.64 eV) in X-ray photoelectron spectroscopy of the binding energy of the electrons towards higher binding energy; clearly indicates that the O2 plasma reaction was most effective process for the complete oxidation of the sol-gel precursor at relatively low processing temperature.  相似文献   

19.
We report the performance of 1‐eV GaNAsSb‐based photovoltaic samples grown on a Si substrate using molecular beam epitaxy at different As/Ga beam equivalent pressure (BEP) ratios. The light current–voltage curve and spectral response of the samples were measured. The sample grown at an As/Ga BEP ratio of 10 showed the highest energy conversion efficiency with an open circuit voltage (VOC) of 0.529 V and a short circuit current density of 17.0 mA/cm2. This measured VOC is the highest ever reported value in GaNAsSb 1‐eV photovoltaic cell, resulting in the lowest ever reported Eg/q‐VOC of 0.50 eV. The increase in the As/Ga BEP ratio also resulted in an increase in the bandgap‐voltage offset value (Eg/q‐VOC) and a decrease in quantum efficiency up to As/Ga BEP ratio of 18. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

20.
The energy distribution profile of the interface states (Nss) and their relaxation time (τ) and capture cross section (σp) of metal-insulator-semiconductor (Al/SiO2/p-Si) Schottky diodes have been investigated by using the high-low frequency capacitance and conductance methods. The capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of these devices were investigated by considering series resistance (Rs) effects in a wide frequency range (5 kHz-1 MHz.). It is shown that the capacitance of the Al/SiO2/p-Si Schottky diode decreases with increasing frequency. The increase in capacitance especially at low frequencies results form the presence of interface states at Si/SiO2 interface. The energy distributions of the interface states and their relaxation time have been determined in the energy range of (0.362-Ev)-(0.512-Ev) eV by taking into account the surface potential as a function of applied bias obtained from the measurable C-V curve (500 Hz) at the lowest frequency. The values of the interface state density (Nss) ranges from 2.34 × 1012 to 2.91 ×  1012 eV−1/cm2, and the relaxation time (τ) ranges from 1.05 × 10−6 to 1.58 × 10−4 s, showing an exponential rise with bias from the top of the valance band towards the mid-gap.  相似文献   

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