As压对LT-GaAs/AlGaAs多量子阱光学特性的影响

在衬底温度为 3 5 0°C的条件下 ,用分子束外延的方法 ,在不同的砷压条件下生长了 Ga As/Al0 .3Ga0 .7As多量子阱结构。 77K的荧光实验证明 ,砷压对样品的光学特性影响显著。认为砷压对低温多量子阱光学特性的影响是点缺陷随砷压的演化和能级间相互补偿的共同结果。通过优化砷压 ,样品的荧光峰的半峰宽减小到 3 me V,这是到目前为止所报道过的最窄的低温多量子阱的荧光峰。相应的垂直场光折变器件的电吸收为 60 0 0 cm     

MOCVD生长的CdZnTe／ZnTe多量子附的激子光学特性

用常压ＭＯＣＶＤ方法在ＧａＡｓ（１００）衬底上生长了ＣｄＺｎＴｅ／ＺｎＴｅ多量子阱。在室温下，观测到了ＣｄＺｎＴｅ／ＺｎＴｅ多量子阱的三个谱带发光。根据ＣｄＺｎＴｅ／ＺｎＴｅ多量子阱的吸收光谱和不同激发光强下的发光光谱，分别归结ＣｄＺｎＴｅ／ＺｎＴｅ多量子阱中观测到的三个发光谱带于覆盖层发光、ｎ＝１的重空穴激子发光及杂质发光。     

Optical properties of imperfect In<Subscript>2</Subscript>Se<Subscript>3</Subscript>

Spectra of complete sets of optical functions for α-and β-In₂Se₃ in the range of 0–20 eV were calculated using experimental reflection spectra and the Kramers-Kronig relation. Special features in the spectra of optical functions for both In₂Se₃ phases were analyzed. The spectra of both permittivity and characteristic electron energy losses were decomposed into elementary transverse and longitudinal components using the combined Argand diagrams. The main parameters of the electron transitions for these components were determined. The structure of the components was compared with the structure of the expected spectrum of interband transitions.     

Optical properties of In<Subscript>2</Subscript>Se<Subscript>3</Subscript> thin films

In₂Se₃ films are produced by ion-beam evaporation at substrate temperatures of 313 and 623 K. As the target, In₂Se₃ single crystals grown by the vertical Bridgman method are used. The composition and structure of the crystals and films are determined by the X-ray spectral analysis and X-ray diffraction techniques, respectively. It is established that the crystals and films crystallize with the formation of a hexagonal structure. The band gap and refractive index of the In₂Se₃ films are determined from the transmittance and reflectance spectra. It is found that, as the substrate temperature is increased, the band gap increases.     

Density-Functional Study of the Electronic Structure and Optical Properties of Transparent Conducting Oxides In<Subscript>4</Subscript>Sn<Subscript>3</Subscript>O<Subscript>12</Subscript> and In<Subscript>4</Subscript>Ge<Subscript>3</Subscript>O<Subscript>12</Subscript>

The electronic structure and optical properties of In₄Sn₃O₁₂ and In₄Ge₃O₁₂ are studied by the projector-augmented-wave method based on the density-functional theory within the generalized gradient approximation. The cation ordering of the two compounds is explored by means of first-principles calculations. It is found that the valence-band maximum of the materials is determined by the d states of metal elements and O-2p states; the conduction-band minimum is occupied by an admixture of the O-2p states, In-5s states, and Sn-5s or Ge-4s states, respectively. The two compounds are direct-bandgap semiconductors. The low intensity of the absorption coefficient, reflectivity, and loss function shows that they are good transparent conducting oxides.     

Influence of Mg Doping on the Morphological, Optical, and Structural Properties of InGaN/GaN Multiple Quantum Wells

In this report, the influence of magnesium doping on the characteristics of InGaN/GaN multiple quantum wells (MQWs) was investigated by means of atomic force microscopy (AFM), photoluminescence (PL), and X-ray diffraction (XRD). Five-period InGaN/GaN MQWs with different magnesium doping levels were grown by metalorganic chemical vapor deposition. The AFM measurements indicated that magnesium doping led to a smoother surface morphology. The V-defect density was observed to decrease with increasing magnesium doping concentration from ∼10⁹ cm⁻² (no doping) to ∼10⁶ cm⁻² (Cp₂Mg: 0.04 sccm) and further to 0 (Cp₂ Mg: 0.2 sccm). The PL measurements showed that magnesium doping resulted in stronger emission, which can be attributed to the screening of the polarization-induced band bending. XRD revealed that magnesium doping had no measurable effect on the indium composition and growth rate of the MQWs. These results suggest that magnesium doping in MQWs might improve the optical properties of GaN photonic devices.     

ZnMgSe/ZnCdSe多量子阱的光学性质

通过光致发光 (PL)和拉曼 (Raman)光谱研究了分子束外延 (MBE)生长的 Zn Mg Se/ Zn Cd Se多量子阱的光学性质。在 80 K到 3 0 0 K温度范围内 ,观测到了 PL光谱中来自量子阱的自由激子发光 ,通过发光强度与温度的变化关系 ,计算了激子束缚能。结果表明在 Zn Mg Se/ Zn Cd Se多量子阱 (MQWs)势垒层中 ,Mg的引进增强了量子阱的限制效应 ,导致激子具有较好的二维特性。在室温下的 Raman光谱中观测到了多级纵光学声子(LO)和横光学声子 (TO)的限制模 ,表明多层结构具有较高的质量     

Thermoelectric Properties of In<Subscript>0.3</Subscript>Ga<Subscript>0.7</Subscript>N Alloys

We report on the experimental investigation of the potential of InGaN alloys as thermoelectric (TE) materials. We have grown undoped and Si-doped In_0.3Ga_0.7N alloys by metalorganic chemical vapor deposition and measured the Seebeck coefficient and electrical conductivity of the grown films with the aim of maximizing the power factor (P). It was found that P decreases as electron concentration (n) increases. The maximum value for P was found to be 7.3 × 10⁻⁴ W/m K² at 750 K in an undoped sample with corresponding values of Seebeck coefficient and electrical conductivity of 280 μV/K and 93␣(Ω cm)⁻¹, respectively. Further enhancement in P is expected by improving the InGaN material quality and conductivity control by reducing background electron concentration.     

Electrical properties of In<Subscript>2</Subscript>Se<Subscript>3</Subscript> single crystals and photosensitivity of Al/In<Subscript>2</Subscript>Se<Subscript>3</Subscript> Schottky barriers

In₂Se₃ single crystals ∼40 mm long and 14 mm in diameter were grown by the Bridgman method. The composition of grown single crystals and their crystal structure were determined. The conductivity (σ) and Hall constant (R) of grown single crystals were measured and the first Schottky barriers Al/n-In₂Se₃ were fabricated. Rectification and photovoltaic effect were detected in the new structures. Based on the study of the photosensitivity spectra of Al/n-In₂Se₃ structures, the nature of the interband transitions and band gap of In₂Se₃ crystals were determined. It was concluded that the new structures can be applied to develop broadband photoconverters of optical radiation.     

InGaN/GaN多量子阱电池的垒层结构优化及其光学特性调控

InGaN基量子阱作为太阳电池器件的有源区时,垒层厚度设计以及实际生长对其光学特性的影响极为重要.采用金属有机化学气相沉积(MOVCD)技术,在蓝宝石衬底上外延生长了垒层厚度较厚的InGaN/GaN多量子阱,使用高分辨X射线衍射和变温光致发光谱研究了垒层厚度对InGaN多量子阱太阳电池结构的界面质量、量子限制效应及其光学特性的影响.较厚垒层的InGaN/GaN多量子阱的周期重复性和界面品质较好,这可能与垒层较薄时对量子阱的生长影响有关.同时,厚垒层InGaN/GaN多量子阱的光致发光光谱峰位随温度升高呈现更为明显的“S”形(红移-蓝移-红移)变化,表现出更强的局域化程度和更高的内量子效率.     

Influence of the Thermal Conditions of Fabrication and Treatment on the Optical Properties of In<Subscript>2</Subscript>O<Subscript>3</Subscript> Films

In₂O₃ films on Al₂O₃ (012) substrates are fabricated by dc magnetron sputtering at various temperatures (20–600°C). The effect of annealing and the substrate temperature on the film properties are studied by the ellipsometric method and the optical transmission method. Refractive-index profiles are constructed and band gaps for direct and indirect transitions are found. It is established that annealing leads to densification of the film material and unifies the refractive index. Annealing also decreases and unifies the energies of band-to-band transitions, which can be explained by lowering the influence of barriers in annealed films. However, the band gap for direct transitions varies greater than for indirect transitions. This fact can be associated with the mechanism of indirect transitions, notably, the participation of phonons facilitates interband transitions even if they are hindered by extra barriers caused by grain boundaries. The latter can be indirect evidence of the actuality of indirect transitions in indium oxide.     

Thermoelectric Properties of Spark Plasma-Sintered In<Subscript>4</Subscript>Se<Subscript>3</Subscript>-In<Subscript>4</Subscript>Te<Subscript>3</Subscript>

We report the thermoelectric properties of spark plasma-sintered In₄Se₃-In₄Te₃ materials. For comparison, pure In₄Se₃ and In₄Se₃ (80 wt.%)/In₄Te₃ (20 wt.%) mixture samples were prepared. In₄Se₃ and In₄Te₃ powders were synthesized by a conventional melting process in evacuated quartz ampoules, and a spark plasma method was used for the sintering of the pure In₄Se₃ and mixture samples. Thermoelectric and structural characterizations were carried out, and the mixing effect of In₄Se₃ and In₄Te₃ on the thermoelectric properties was investigated.     

In<Subscript>0.8</Subscript>Ga<Subscript>0.2</Subscript>As Quantum Dots for GaAs Solar Cells: Metal-Organic Vapor-Phase Epitaxy Growth Peculiarities and Properties

The growth peculiarities of In_0.8Ga_0.2As quantum dots and their arrays on GaAs surface by metalorganic vapor-phase epitaxy are investigated. The bimodal size distribution of In_0.8Ga_0.2As quantum dots is established from the photoluminescence spectra recorded at different temperatures. The growth parameters were determined at which the stacking of 20 In_0.8Ga_0.2As quantum-dot layers in the active area of a GaAs solar cell makes it possible to enhance the photogenerated current by 0.97 and 0.77 mA/cm² for space and terrestrial solar spectra, respectively, with the high quality of the p–n junction retained. The photogenerated current in a solar cell with quantum dots is higher than in the reference GaAs structure by ~1% with regard to nonradiative-recombination loss originating from stresses induced by the quantum-dot array.     

Photoelectric properties of In/In<Subscript>2</Subscript>Se<Subscript>3</Subscript> structures

The hexagonal modification of In₂Se₃ single crystal is grown by planar crystallization from nearly stoichiometric melt and by the vapor-phase method. For the first time, the Schottky barriers In/n-In₂Se₃, which are photosensitive in a wide incident-photon energy range of 1–3.8 eV at 300 K, are obtained. The nature of the interband photoactive absorption is studied. The energy-barrier height and interband optical-transition energy are estimated. It is concluded that the grown crystals can be used in broadband optical-radiation converters.     

Optical and Dielectric Properties and Microstructures of rf-Magnetron Sputtered ZnO-Doped Zr<Subscript>0.8</Subscript>Sn<Subscript>0.2</Subscript>TiO<Subscript>4</Subscript> Films on Indium Tin Oxide/Glass Substrates

Optical and dielectric properties and microstructures of ZnO-doped (Zr_0.8Sn_0.2)TiO₄ thin films prepared by radiofrequency (rf)-magnetron sputtering on indium tin oxide/glass substrates at different rf powers and substrate temperatures have been investigated. Selected-area diffraction patterns showed that the deposited films exhibited a polycrystalline microstructure. All films exhibited the ZnO-doped (Zr_0.8Sn_0.2)TiO₄ structure with the (111) orientation perpendicular to the substrate surface. The grain size as well as the deposition rate of the film increased with an increase in both rf power and substrate temperature. At an annealing temperature of 700°C, the ZnO-doped (Zr_0.8Sn_0.2)TiO₄ film possessed a dielectric constant of 47 at 10 MHz, a dissipation factor of 0.02 at 10 MHz, a leakage current density of 7.35 × 10⁻⁹  A/cm² at an electrical field of 1 kV/cm, average transmission in the visible range of over 70%, and an optical bandgap of 3.6 eV. This film will allow fabrication of fully transparent semiconductor devices such as a resistive random-access memory (RRAM) and thin-film transistors (TFTs) completely based on ZnO-doped (Zr_0.8Sn_0.2)TiO₄ thin films.     

Bimodality in Arrays of In<Subscript>0.4</Subscript>Ga<Subscript>0.6</Subscript>As Hybrid Quantum-Confined Heterostructures Grown on GaAs Substrates

Hybrid quantum-confined heterostructures grown by metal-organic vapor-phase epitaxy (MOVPE) via the deposition of In_0.4Ga_0.6As layers with various nominal thicknesses onto vicinal GaAs substrates are studied by photoluminescence spectroscopy and transmission electron microscopy. The photoluminescence spectra of these structures show the superposition of two spectral lines, which is indicative of the bimodal distribution of the size and/or shape of light-emitting objects in an array. The dominant spectral line is attributed to the luminescence of hybrid “quantum well–dot” nanostructures in the form of a dense array of relatively small quantum dots (QDs) with weak electron and hole localization. The second, lower intensity line is attributed to luminescence from a less dense array of comparatively larger QDs. Analysis of the behavior of the spectral line intensities at various temperatures showed that the density of larger QDs grows with increasing thickness of the InGaAs layer.     

Ultrafast Dynamics of Photoexcited Charge Carriers in In<Subscript>0.53</Subscript>Ga<Subscript>0.47</Subscript>As/In<Subscript>0.52</Subscript>Al<Subscript>0.48</Subscript>As Superlattices under Femtosecond Laser Excitation

The results of experimental studies of the time dynamics of photoexcited charge carriers in In_0.53Ga_0.47As/In_0.52Al_0.48As superlattices grown by molecular-beam epitaxy on a GaAs substrate with a metamorphic buffer are reported. On the basis of the results of the numerical simulation of band diagrams, the optimal thickness of the In_0.52Al_0.48As barrier layer (4 nm) is chosen. At this thickness, the electron wave functions in In_0.53Ga_0.47As substantially overlap the In_0.52Al_0.48As barriers. This makes it possible to attain a short lifetime of photoexcited charge carriers (τ ~ 3.4 ps) at the wavelength λ = 800 nm and the pumping power 50 mW without doping of the In_0.53Ga_0.47As layer with beryllium. It is shown that an increase in the wavelength to λ = 930 nm (at the same pumping power) yields a decrease in the lifetime of photoexcited charge carriers to τ ~ 2 ps. This effect is attributed to an increase in the capture cross section of trapping states for electrons with lower energies and to a decrease in the occupancy of traps at lower excitation densities.     

Thermal Stability of Barium and Indium Double-Filled Skutterudite Ba<Subscript>0.3</Subscript>In<Subscript>0.2</Subscript>Co<Subscript>3.95</Subscript>Ni<Subscript>0.05</Subscript>Sb<Subscript>12</Subscript> Coated by SiO<Subscript>2</Subscript> Nanoparticles

Filled skutterudite thermoelectric (TE) materials have been extensively studied to search for better TE materials in the past decade. However, there is no detailed investigation about the thermal stability of filled skutterudite TE materials. The evolution of microstructure and TE properties of nanostructured skutterudite materials fabricated with Ba_0.3In_0.2Co_3.95Ni_0.05Sb₁₂/SiO₂ core–shell composite particles with 3 nm thickness shell was investigated during periodic thermal cycling from room temperature to 723 K in this work. Scanning electronic microscopy and electron probe microscopy analysis were used to investigate the microstructure and chemical composition of the nanostructured skutterudite materials. TE properties of the nanostructured skutterudite materials were measured after every 200 cycles of quenching in the temperature range from 300 K to 800 K. The results show that the microstructure and composition of Ba_0.3In_0.2Co_3.95Ni_0.05Sb₁₂/SiO₂ nanostructured skutterudite materials were more stable than those of single-phase Ba_0.3In_0.2Co_3.95Ni_0.05Sb₁₂ bulk materials. The evolution of TE properties indicates that the electrical and thermal conductivity decrease along with an increase in the Seebeck coefficient with increasing quenching up to 2000 cycles. As a result, the dimensionless TE figure of merit (ZT) of the nanostructured skutterudite materials remains almost constant. It can be concluded that these nanostructured skutterudite materials have good thermal stability and are suitable for use in solar power generation systems.     

Measurement of the absorption coefficient for light laterally propagating in light-emitting diode structures with In<Subscript>0.2</Subscript>Ga<Subscript>0.8</Subscript>N/GaN quantum wells

A procedure for measuring the absorption coefficient for light propagating parallel to the surface of a GaN-based light emitting diode chip on a sapphire substrate is suggested. The procedure implies the study of emission from one end face of the chip as the opposite end face is illuminated with a light emitting diode. The absorption coefficient is calculated from the ratio between the intensities of emission emerging from the end faces of the sapphire substrate and the epitaxial layer. From the measurements for chips based on p-GaN/In_0.2Ga_0.8N/n-GaN structures, the lateral absorption coefficient is determined at a level of (23 ± 3)cm^?1 at a wavelength of 465 nm. Possible causes for the discrepancy between the absorption coefficients determined in the study and those reported previously are analyzed.     

Effect of Proton Irradiation on Interface State Density in Sc<Subscript>2</Subscript>O<Subscript>3</Subscript>/GaN and Sc<Subscript>2</Subscript>O<Subscript>3</Subscript>/MgO/GaN Diodes

Proton irradiation of Sc₂O₃/GaN and Sc₂O₃/MgO/GaN metal-oxide semiconductor diodes was performed at two energies, 10 MeV and 40 MeV, and total fluences of 5 × 10⁹ cm⁻², corresponding to 10 years in low-earth orbit. The proton damage causes a decrease in forward breakdown voltage and a flat-band voltage shift in the capacitance-voltage characteristics, indicating a change in fixed oxide charge and damage to the dielectric. The interface state densities after irradiation increased from 5.9 × 10¹¹ cm⁻² to 1.03 × 10¹² cm⁻² in Sc₂O₃/GaN diodes and from 2.33 × 10¹¹ to 5.3 × 10¹¹ cm⁻² in Sc₂O₃/MgO/GaN diodes. Postannealing at 400°C in forming gas recovered most of the original characteristics but did increase the interfacial roughness.