Electrical and optical properties of ZnTe-GaSb heterojunctions

Heterojunctions between ZnTe and GaSb is produced by the interface-alloy technique with the use of movable quartz tube loaded in a furnace instead of a strip-heater. X-ray measurement shows that the recrystallized GaSb is monocrystalline and oriented parallel to the ZnTe substrate with (111) as the growth direction. Photoresponse for p-p ZnTe-GaSb heterojunctions decreases exponentially with decreasing incident photon energy for hν < 2·18 eV at room temperature. This behavior is explained by a model of linearly-graded bandgap region of the order of 500 Å long, which was first proposed for GaAs-InSb heterojunction by Hinkley and Rediker. The photocurrent is produced by hot holes generated by absorbed photons in the graded-gap region which traverse this region with a mean free path of about 40 Å. Space-charge-limited current observed in I–V characteristics of p-p ZnTe-GaSb heterojunctions is explained by Lampert theory. The thickness of semi-insulating region is estimated at about 1 to 3 μm from the capacitance measurements without d.c. bias. This thickness is much larger than the graded bandgap region. Capacitance depends strongly on both forward d.c. bias voltage and a.c. frequency, but is almost independent of reverse bias voltage. The results of capacitance measurements for forward bias are qualitatively interpreted in terms of a change in the trapped charge density in the semi-insulating region. A significant discrepancy between the theory and experimental results exists in the region of trap-free limit.     

Electrical and optical properties of self-assembled quantum dots

One of the main directions of contemporary semiconductor physics is the production and study of structures with a dimension less than two, i.e. quantum wires (QWi) and quantum dots (QDs), in order to realise novel devices that make use of low-dimensional confinement effects.One of the promising fabrication methods is to use self-organised three-dimensional (3D) structures, such as 3D coherent islands, which are often formed during the initial stage of heteroepitaxial growth in lattice-mismatched systems. Quantum dots, for example, are believed to provide a promising way for a new generation of optical light sources such as injection lasers. While quantum well structures are already widely used in optoelectronic devices, QWi and QDs appear to be much more difficult to fabricate for this purpose. Some of the electrical and optical properties of self-assembled QDs will be reported in this paper.     

Electrical and optical properties of pristine and polymerized fullerenes

The band structure, optical, photoelectric and transport properties of solids composed of fullerene molecules linked by van der Waals bonds or forming polymers are considered. Particular attention is concentrated on different polymerization mechanisms.     

Electrical and optical properties of the three-terminaldouble-heterostructure optoelectronic switch

A theory is developed for the three-terminal version of the double-heterojunction optoelectronic switch (DOES), in which the third terminal, the injector, makes ohmic contact to the active layer of the device. The injector permits the biasing of the active-layer-substrate junction, the effect of which is to reduce the threshold voltage at which switching from the electrical and optical OFF-state to the ON-state occurs. Reverse baising the junction initiates switching from the ON- to the OFF-state. The current and optical output as a function of voltage with the injector current as a parametric variable are plotted in terms of the physical and geometrical properties of the device     

Electrical and optical properties of the four-terminaldouble-heterostructure opto-electronic switch

The authors extend the theory of the three-terminal double-heterostructure opto-electronic switch (DOES) device, in which the third terminal (the injector) makes contact to the bulk section of the active region, to the four-terminal DOES, in which the fourth terminal (the source) accesses the inversion channel at the n-n heterojunction. The source is shown to be capable of initiating switching at lower current densities than the injector. The effects of incident light on the device are also examined, yielding results similar to the injection of carriers at the source and injector. Incomplete ionization of the charge sheet and two-dimensional quantum effects in the channel, which have been neglected in previous DOES models, have been included. These effects are shown to affect significantly the characteristics of the device and to reduce the discrepancy between simulated and experimental results     

Electrical and optical properties of very thin gold films †

The electrical and optical properties of discontinuous and semi-continuous gold films evaporated on to dielectric substrates in a high vacuum have been measured. The electrical properties of the films were characterized by DC conductivity and by the temperature coefficient of resistance: the reflectance and transmittance at near-infrared wavelengths were the optical properties considered. Special attention was given to the films in the vicinity of the percolation threshold.     

Electrical and optical properties of Gen?SnO2 photodetectors

A solid-state photodetector is proposed using an SnO2 transparent layer as a constitutive element in conjunction with a Gen substrate. Special attention is paid to the photo-conductive mode (reverse-biased diode). The electrical characteristics and optical spectral responsivity are reported, noise measurements show a typical contact effect and allow n.e.p. determination. From measured specifications, it appears that, in comparison with commercially available photodiodes, such a structure could be of interest.     

Electrical and optical properties of AgInS2

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 E_T1 = 0·19±0·01 eV and E_T2 = 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 $\text{E}\text{⊥c}$ and indirect for $\text{E}\text{∥c}$, and the values for the energy gap are E_g^⊥ = 1·88±0·01 eV and E_g^∥ = 1·77±0·01 eV, respectively.     

Transverse mode control of vertical-cavity top-surface-emittinglasers

Transverse mode characteristics and control for vertical-cavity top-surface-emitting lasers (VCSELs) are discussed. A spatial filtering concept for the control of VCSEL transverse modes that allows over 1.5-mW single TEM₀₀ transverse mode emission to be routinely achieved from continuous-wave electrically excited VCSELs is introduced. Without spatial filtering, L-I and V-I kinks are observed     

Electrical and optical properties of InN with periodic metallic in insertions

We report on a growth by molecular beam epitaxy of InN:In semiconductor/metal composite structures containing periodically inserted arrays of In clusters formed by intentional deposition of In metal films in a thickness range of 2–48 monolayers. It was found that indium insertions do not change markedly carrier mobility in the composites, that remains in the 1300–1600 cm²/(V s) range, while carrier concentration increases with rising In amount. Spectra of thermally detected optical absorption do not exhibit a noticeable Burstein-Moss shift of a principal absorption edge with increasing the carrier concentration, but rather complicated modification of their shapes. The article is published in the original.     

利用同步测量研究二氧化钒薄膜的电学与光学相变特性

利用射频磁控溅射方法在蓝宝石衬底上制备了氧化钒薄膜,X射线衍射的测量结果表明薄膜的主要成分是多晶二氧化钒.实现了二氧化钒薄膜半导体-金属相变过程的电阻和五个不同波长下薄膜反射率的同步测量.实验结果表明,电学和光学测量都在相变过程中出现回滞曲线,但是二者的表现形式有明显差别.当用光学方法探测时,同一次相变过程中不同区域的反射率曲线几乎完全重合,证明了薄膜样品的均匀性.     

Electrical and optical properties of Ni-assisted grown single crystalline and transparent indium-tin-oxide nanowires

Transparent and single crystalline indium-tin-oxide (ITO) nanowires (NWs) were grown by sputtering method. A thin Ni film of 5 nm was deposited before ITO sputtering. Thermal treatment forms Ni nanoparticles, which act as templates to diffuse Ni into the sputtered ITO layer to grow single crystalline ITO NWs. This Ni diffusion through an ITO NW was investigated by transmission electron microscope to observe the Ni-tip sitting on a single crystalline ITO NW. Meanwhile, a single crystalline ITO structure was found at bottom and body part of a single ITO NW without remaining of Ni atoms. This indicates the Ni atoms diffuse through the oxygen vacancies of ITO structure.Rapid thermal process (RTP) applied to generate an initial stage of a formation of Ni nanoparticles with variation in time periods to demonstrate the existence of an optimum condition to initiate ITO NW growth. Modulation in ITO sputtering condition was applied to verify the ITO NW growth or the ITO film growth. The Ni-assisted grown ITO layer has an improved electrical conductivity while maintaining a similar transmittance value to that of a single ITO layer. Electrically conductive and optically transparent ITO nanowire-coated surface morphology would provide a great opportunity for various photoelectric devices.     

Electrical and optical properties of ITO and ITO:Zr transparent conducting films

ITO and ITO:Zr films were deposited on glass substrates by magnetron sputtering. Electrical and optical properties of the films at different experiment parameters such as substrate temperature, oxygen flow rate and annealing temperature were contrastively studied. The increase in substrate temperature remarkably improves the electrical and optical properties of the films. ITO:Zr films show better quality at low substrate temperature. The excessive oxygen can worsen the optical properties of the films. Better optical–electrical properties of the films can be achieved after the proper annealing treatment. Obvious Burstin–Moss effect can be revealed by transmittance spectra with different parameters, and the direct transition models show the change of optical band gap. ITO:Zr films prepared by co-sputtering show better optical–electrical properties than ITO films.     

Electrical and optical properties of copper indium ditelluride crystals grown from near-stoichiometric compositions

CuInTe₂ crystals grown by zone-leveling of nominally stoichiometric material are highly p-type. The net acceptor density is reduced by in-diffusion of zinc which acts as a donor impurity. Zinc-annealed crystals transmit in the infrared and exhibit an absorption edge at 0.92 eV.     

Electrical and optical properties of Mn-doped Hg3In2Te6 crystals

The effect of Mn impurities on the properties of Hg₃In₂Te₆ crystals is studied by electrical and optical measurements. It is shown that, despite the high dopant concentration (1 × 10¹⁹ cm^?3), the electron concentration remains the same as that in an undoped crystal (～10¹³ cm^?3 at 300 K). At the same time, narrowing of the band gap from 0.74 to 0.7 eV is observed. From an analysis of the absorption spectra, it is found that the absorption edge is formed by optical transitions involving density-of-states (DoS) tails and that two acceptor- and donor-type impurity bands are formed in the band gap. The two bands are described by a Gaussian distribution of the DoS, with an energy gap between the peaks of E ₀ = E _d ⁰ ? E _a ⁰ = 0.4 eV. The total donor and acceptor concentration N _d + N _a and the degree of compensation K = N _a /N _d → 1 are determined. Such compensation is responsible for pinning of the Fermi level near the middle of the band gap and for quasi-intrinsic conductivity at temperatures T ≥ 300 K.     

Electrical and optical properties of sputter-deposited cadmium sulfide thin films optimized by annealing temperature

Cadmium sulfide (CdS) is one of the most widely used materials as a window layer in heterojunction thin film solar cells. Sputtering method for the preparation of CdS thin film was employed for the mass-production of large-area deposited CdS thin films. The electrical and optical properties of sputter-deposited CdS thin films varied with the annealing temperature, which were caused by changes in phase composition, grain size, and stoichiometry of CdS thin films. The improved optical transmittance of 72.25% (at average thickness of 843.93 nm) and the optical band gap energy of 2.43 eV were obtained at the optimum annealing temperature of 400 °C. The resistivity below 10³-order Ω cm and carrier concentration above 10¹⁶ carriers/cm³ are suitable for the requirements of window layers at this optimum annealing temperature.     

Electrical and optical properties of N-type Alx Ga1-x as grown by MO-VPE

Growth conditions and properties of Al_xGa_1-xAs (0.1 ≤ × ≤O.3) using metalorganic vapour phase epitaxy (MO-VPE) are investigated. N-type is achieved either by silicon or by selenium doping. Properties of the layers are evaluated by Hall effect, cathodoluminescence and photoluminescence. It is shown that selenium doping leads to luminescent material : when x = O.1, the efficiency is only a factor of 2 smaller than for GaAs. Deposition temperature is a critical parameter : increasing the growth temperature yields more luminescent Al_x Ga_1-x As. This work has been partly supported by the Délégation à la Recherche Scientifique et Technique (D.G.R.S.T.)     

Electrical,optical and photoelectrochemical properties of natural enargite,Cu3AsS4

The semiconducting properties of natural samples of enargite, a copper and arsenic suphide (Cu₃AsS₄), have been studied. They have been found to be p-type semiconductors with a resistivity of about 7 Ω cm, a doping level of about 10¹⁷ cm^?3 and a mobility of 9 cm²V^?1 s^?1. The variation of the resistivity as a function of temperature allows to determine an activation energy of 0.11 eV. Two optical transitions have been determined, an indirect one at 1.19 eV and a direct one at 1.44 eV. The samples, mounted as working electrodes in a photoelectrochemical set-up, are photosensitive and behave as p-type photocathodes. The two transitions are found again from the analysis of photocurrent spectra. The direct band gap value is close to the ideal value required for photovoltaic applications. However the quantum efficiencies obtained here are still low.     

InGaN／AlGaN双异质结构蓝光LED的电学和光学性质

研究了ＩｎＧａＮ／ＡｌＧａＮ双异质结构（ＤＨ）蓝光发光二极管（ＬＥＤ）的电学和光学性质，实验表明，器件正向偏压下的Ｉ－Ｖ特性偏离了ｐｎ结二极管的肖克莱模型的结果，并且载流子的主要输运机制与载流子隧穿有关。通过对电致发光（ＥＬ）谱的测量，得到位于２．８ｅＶ的发射峰和位于３．２ｅＶ弱发射峰，随着电流增大而均出现蓝移。对大脉冲电流下ＬＥＤ的特性的退化作了研究。