p型掺杂1.3μm InAs/GaAs量子点激光器的最大模式增益特性的研究

对p型掺杂13 μm InAs/GaAs量子点激光器的最大模式增益进行了实验和理论分析.实验上,测量了不同腔长激光器阈值电流密度与总损耗的对应关系,拟合出的最大模式增益为175 cm^-1,与相同结构非掺杂量子点激光器的最大模式增益一致.同时理论分析表明,p型掺杂对InAs/GaAs量子点激光器的最大模式增益并无影响,并且最大模式增益的计算结果与实验值相符.具有较小高度或高宽比的量子点能达到更高的最大模式增益,而较高的最大模式增益对p型掺杂13 μm InAs/GaAs自组织量子点激光器在光通信系统中的应用具有重要意义. 关键词： 最大模式增益 p型掺杂 InAs/GaAs量子点激光器     

Scanning laser infrared microscopy of doping inhomogeneities in InAs single crystals

A scanned laser infrared microscope operating at 3.39 μm has produced optical transmission images of n-type InAs with free carrier concentrations ranging from 4.6 × 10¹⁷/cm³ to 2.4 × 10¹⁸/cm³. Variations in these infrared images are explained in terms of the Burstein effect. Images of normally opaque lightly-doped InAs have been produced by temperature-shifting the fundamental absorption edge wavelength. The optical perfection of both lightly- and heavily-doped n-type InAs were thus uniquely determined over large sample volumes.     

Novel mid-IR laser based on hybrid AlGaAsSb/InAs/CdMgSe heterostructure

We report on the development of a novel design of a mid-IR laser combining III–V and II–VI compounds in a “hybrid” double heterostructure. It possesses large (1.5 eV) potential barriers both for injected electrons and holes, suppressing their leakage from the active region, and provides strong optical confinement. An AlGaAsSb/InAs/CdMgSe laser diode with a III–V/II–VI heterovalent interface at the 0.6 μm-InAs active region has been grown by molecular beam epitaxy on an InAs substrate. Despite a far from optimal defect density at the CdMgSe/InAs interface and high losses inherent for bulk active region of the laser, the structure demonstrates lasing at 2.8 μm (up to 100 K) in the pulsed regime with a threshold current density of 3–4 kA/cm². Type II InSb monolayer insertions into an InAs layer show bright photoluminescence at 3.8 μm (77 K), confirming the great potential of the InAs-based nanostructure active region for longer wavelength applications.     

Numerical model of a proposed double heterostructure light-emitting diode for mid-infrared applications

A numerical model of a proposed InAs/InAs_0.88Sb_0.12 double heterostructure lightemitting diode (DH-LED) has been developed for its d.c. and transient characterization in the 3 to 5 m wavelength region. The dependence of the optical power and bandwidth on interfacial recombination and self-absorption have been studied. The active layer width has been optimized against interfacial recombination and self-absorption for maximum optical power, bandwidth and power-bandwidth products. The dependence of the power-bandwidth product of the DH-LED on the drive current for different active layer doping concentrations has also been studied. The electrical confinement in the proposed heterostructure has been estimated and its variation with the active layer thickness has been studied. The rise time of the proposed LED has been calculated by using the results of the transient analysis. On the basis of the proposed model, the device is expected to find useful applications as an optical source in future generations of fibre-optic communication systems in the 3 to 5 m wavelength region.The author is presently with the Department of Electronics Engineering, Institute of Technology, Banaras Hindu University, Varanasi-221005, India.     

Lateral Current Injection (LCI) Multiple Quantum-Well 1.55 μm Laser with Improved Gain Uniformity Across the Active Region

A simulation study of lateral current injection 1.55 m laser with strain-compensated multiple quantum-well (MQW) active region (InGaAsP well, InGaAlAs barrier) is presented using self-consistent 2D numerical simulations. The effects of different mesa width and p-doping in the QWs on the carrier and gain uniformity across the active region are explored. A high p-doping in the quantum wells is found to increases the carrier and gain non-uniformity across the active region. The QW region close to the n-contact side does not provide much gain at high optical powers. An asymmetric optical waveguide design is proposed to help reduce the gain non-uniformity across the active region. By shifting the optical modal peak toward the p-side, the modal overlap between the gain region and the optical mode is improved and a more even carrier and gain distribution is obtained. However, due to reduced bandgap of the quaternary InGaAsP p-cladding, an enhanced electron leakage out of the QWs into the p-cladding degrades the laser efficiency and increases the threshold current. Transient time–domain simulations are also performed to determine the small-signal modulation response of the laser promising a simulated high modulation bandwidth suitable for direct-modulation applications.     

Raman study of InAs/GaAs quantum dot solar cells

We report polarized and resonant Raman study of InAs/GaAs quantum dot solar cell (QDSC) structures. Raman spectra obtained from the top surfaces of the samples suggested that the formation of InAs QDs induced tensile strain in the overgrown GaAs layers. Furthermore, a longitudinal optical phonon-plasmon (LPP) coupled modes were observed in the p-type GaAs layers. The tensile strain was increased with an increase in the QD size. The hole concentrations estimated by fitting the individual LPP coupled modes were in the range of 2.4–3.5 × 10¹⁸ cm^?3. Resonant Raman spectra obtained from the cleaved sides, where the QDs were located, showed a 225 cm^?1 mode in parallel polarization configurations. Based on accurate analysis, this mode was identified as the LA(X) phonon of GaAs.     

Carrier hopping in InAs/AlyGa1−yAs quantum dot heterostructures: effects on optical and laser properties

The optical properties of InAs/Al_yGa_1−yAs self-assembled quantum dots are studied as a function of temperature from 10 K to room temperature. The temperature dependence of carrier hopping between dots is discussed in terms of the depth of the dot confinement potential and the dispersion in dot size and composition. We show that carrier hopping between dots influences both the electrical and optical properties of laser devices having dots as active medium.     

Growth and characterization of new transparent conductive oxides single crystals β-Ga2O3: Sn

Tin oxide doped β-Ga₂O₃ single crystals are recognized as transparent conductive oxides (TCOs) materials. They have a larger band gap (4.8 eV) than any other TCOs, thus can be transparent in UV region. This property shows that they have the potential to make the optoelectronic device used in even shorter wavelength than usual TCOs. β-Ga₂O₃ single crystals doped with different Sn⁴⁺ concentrations were grown by the floating zone technique. Their optical properties and electrical conductivities were systematically studied. It has been found that their conductivities and optical properties were influenced by the Sn⁴⁺ concentrations and annealing.     

High speed all-silicon optical modulator

Electrorefractive effect is experimentally demonstrated in an all-silicon optical structure. A highly doped Si P⁺ layer is embedded in the intrinsic region of a PIN diode integrated in a SOI waveguide. Holes are confined at equilibrium around the P⁺ layer. By applying a reverse bias to the diode, electrical field sweeps the carriers out of the active region. Free carrier concentration variations are responsible for local refractive index variations leading to an effective index variation of the waveguide optical mode and to an optical absorption variation. As a figure of merit, the product V_πL_π, determined from the measured effective index variation, is equal to 3.1 V cm. Furthermore, the device performances have theoretically been investigated. Estimations show that V_πL_π as small as 1 V cm are feasible using optimized structures. Response times lower than 2 ps are predicted, which gives the possibility to achieve very high-speed modulation. Furthermore, a temperature increases from 300 to 400 K does not change the index variation amplitude, and despite the carrier mobility reduction, response times are still lower than 2 ps.     

Quantum theory of free carrier absorption in polar semiconductors

A quantum mechanica treatment of the free carrier absorption by electrons in polar semiconductors has been constructed in terms of the Kane model. It takes into account overlap wavefunction factors, intermediate states in other bands, the finite optical phonon energy, and the effects of arbitrary spin orbit splitting on the electron energy and wavefunction. The scattering mechanisms considered include polar optical mode scattering, ionic scattering, piezoelectric and deformation coupled acoustic mode scattering, and electron-electron scattering.The theory, in the appropriate limits, applies to a wide range of photon energies, electron concentrations, and lattice temperatures. It relates the dominant scattering mechanism involved in the various limits to the characteristic behavior of the absorption coefficient as a function of the photon energy. In particular, the dominant scattering mechanism for small carrier concentrations is found to be polar optical mode scattering, which exhibits a λ³ dependence of the absorption coefficient times the index of refraction, (except at the lowest frequencies, where the expected λ² dependence is obtained).Ionic, or impurity, scattering becomes important as the carrier concentration is increased, and the characteristic wavelength dependence of the electron cross section times the index of refraction varies from λ⁴ to λ³, and the absorption coefficient times the index of refraction from λ⁴ to λ², depending on the ratio of the photon energy to the initial electron energies.Comparisons are made with the available data over a wide range of photon energies, temperatures, and electron concentrations, for the III–V compounds InSb, InAs, InP, and GaAs.     

Electrical and optical characteristics of the InAs/InAs0.7Sb0.1P0.2 single heterojunction photodiodes for the spectral range 1.6-3.5 μm

The electrical end optical characteristics of InAs/InAs_0.7Sb_0.1P_0.2 heterojunctions were studied. The dark current mechanisms in the heterostructures were investigated at several temperatures. The experimental results shows that, the low temperature region the tunneling mechanism of the current flow dominates in both, forward and reverse biases. At high temperatures region and in the range of voltage from 0.1 V to 1 V, the reverse current was defined by diffusion mechanism.     

Hydrogen gas-sensing properties of Pt/WO<Subscript>3</Subscript> thin film in various measurement conditions

A well-known gasochromic material is Pt particle-dispersed tungsten trioxide (Pt/WO₃). Its optical properties could make it effective as a hydrogen gas sensor. In this study, Pt nanoparticle-dispersed WO₃ thin films were prepared using the sol–gel process, and their optical and electrical properties dependent on the working environment (i.e., temperature, hydrogen gas concentration, oxygen partial pressure, etc.) were investigated. The Pt/WO₃ thin films prepared at 400 °C showed the largest change in optical transmittance and electrical conductivity when exposed to hydrogen gas compared with the films prepared at other temperatures. The optical absorbance and electrical conductivity were found to be dependent on the hydrogen and oxygen gas concentration in the atmosphere because generation and disappearance of W⁵⁺ in the thin films depend on the equilibrium reaction between injection and rejection of H⁺ into and from the thin films. In addition, the equilibrium reaction depends on the hydrogen and oxygen gas concentrations.     

InAs/AlAs quantum dots with InGaAs insertion layer: dependence of the indium composition and the thickness

We have systematically studied the effect of an In_xGa_1−xAs insertion layer (IL) on the optical and structural properties of InAs quantum dot (QD) structures. A high density of 9.6×10¹⁰ cm⁻² of InAs QDs with an In_0.3Ga_0.7As IL has been achieved on a GaAs (1 0 0) substrate by metal organic chemical vapor deposition. A photoluminescence line width of 25 meV from these QDs has been obtained. We attribute the high density and high uniformity of these QDs to the use of the IL. Our results show that the InGaAs IL is useful for obtaining high-quality InAs QD structures for devices with a 1.3 μm operation.     

Structure distortion, optical and electrical properties of ZnO thin films co-doped with Al and Sb by so--gel spin coating

ZnO thin films co-doped with Al and Sb with different concentrations and a fixed molar ratio of AlCl₃ to SbCl₃ at 1:2, are prepared by a sol--gel spin-coating method on glass annealed at 550 ℃ for 2 h in air. The x-ray diffraction results confirm that the ZnO thin films co-doped with Al and Sb are of wurtzite hexagonal ZnO with a very small distortion, and the biaxial stresses are 1.03×10⁸, 3.26×10⁸, 5.23×10⁸, and 6.97×10⁸ Pa, corresponding to those of the ZnO thin films co-doped with Al and Sb in concentrations of 1.5, 3.0, 4.5, 6.0 at% respectively. The optical properties reveal that the ZnO thin films co-doped with Al and Sb have obviously enhanced transmittance in the visible region. The electrical properties show that ZnO thin film co-doped with Al and Sb in a concentration of 1.5 at% has a lowest resistivity of 2.5Ω·cm.     

Optical and electrical properties of In-doped CdO thin films fabricated by pulse laser deposition

Transparent indium-doped cadmium oxide (In-CdO) thin films were deposited on quartz glass substrates by pulse laser deposition (PLD) from ablating Cd-In metallic target at a fixed pressure 10 Pa and a fixed substrate temperature 300 °C. The influences of indium concentrations in target on the microstructure, optical and electrical performances were studied. When the indium concentration reaches to 3.9 wt%, the as-deposited In-CdO film shows high optical transmission in visible light region, obviously enhanced direct band gap energy (2.97 eV), higher carrier concentration and lower electric resistivity compared with the undoped CdO film, while a further increase of indium concentration to 5.6 wt% induces the formation of In₂O₃, which reverse the variation of these parameters and performance.     

Optical and electrical characteristics of Al-doped ZnO thin films prepared by aqueous phase deposition

Transparent conducting Al-doped ZnO (AZO) thin films have been deposited by sol-gel route. Starting from an aqueous solution of zinc acetate by adding aluminum chloride as dopant, a c-axis oriented polycrystalline ZnO thin film 100 nm in thickness could be spin-coated on glass substrates via a two-step annealing process under reducing atmosphere. The effects of thermal annealing and dopant concentration on the structural, electrical and optical properties of AZO thin films were investigated. The post-treated AZO films exhibited a homogenous dense microstructure with grain sizes less than 10 nm as characterized by SEM photographs. The annealing atmosphere has prominent impact on the crystallinity of the films which will in turn influence the electrical conductivity. By varying the doping concentrations, the optical and electrical properties could be further adjusted. An optimal doping concentration of Al/Zn = 2.25 at.% was obtained with minimum resistivity of 9.90 × 10⁻³ Ω-cm whereas the carrier concentration and mobility was 1.25 × 10²⁰ cm⁻³ and 5.04 cm² V⁻¹ s⁻¹, respectively. In this case, the optical transmittance in the visible region is over 90%.     

The 6.1 Å family (InAs, GaSb, AlSb) and its heterostructures: a selective review

The three semiconductors InAs, GaSb, and AlSb form an approximately lattice-matched set around 6.1 Å, covering a wide range of energy gaps and other properties. Of particular interest are heterostructures combining InAs with one or both of the antimonides, and they are emphasized in this review. In addition to their use in conventional device types (FETs, RTDs, etc.), several heterostructure configurations with unique properties have been explored, especially InAs/AlSb quantum wells and InAs/GaSb superlattices.InAs/AlSb quantum wells are an ideal medium to study the low-temperature transport properties in InAs itself. With gate-induced electron sheet concentrations on the order 10¹² cm⁻², they exhibit a pronounced conductivity quantization. The very deep wells (1.35 eV) provide excellent electron confinement, and also permit modulation doping up to at least 10¹³ electrons cm⁻². Because of the very low effective mass in InAs, heavily doped wells are essentially metals, with Fermi energies around 200 meV, and Fermi velocities exceeding 10⁸ cm s⁻¹. Contacted with superconducting electrodes, such structures can act as superconductive weak links.InAs/GaSb-related superlattices with their broken-gap lineup behave like semimetals at large lattice periods, but if the lattice period is shortened, increasing quantization effects cause a transition to a narrow-gap semiconductor, making such structures of interest for infrared detectors, often combined with the deliberate addition of strain.     

Optical and Conductivity Studies of Cr3+ Doped Polyvinyl Pyrrolidone Polymer Electrolytes

Abstract

Polymer electrolyte films of polyvinyl pyrrolidone (PVP) embedded with various concentrations of Cr³⁺ ions were prepared by a solution casting technique. The complexation between the Cr³⁺ ions and the polymer was confirmed by Fourier transform infrared (FTIR) spectroscopy and UV–vis spectroscopy. The electrical conductivity of the films was measured using an impedence analyzer in the frequency range of 42?Hz to 5?MHz at ambient temperature. It was observed that the conductivity increased with the increase in the Cr³⁺ ion concentration. UV–visible absorption spectra in the wavelength range of 200–800?nm were used to determine the direct and indirect optical energy band gaps and optical absorption edge. Both of the optical band gaps decreased with the increase in Cr³⁺ ion concentration. FTIR studies on pure and Cr³⁺ doped PVP polymer films revealed the vibrational changes that occurred due to the effect of the dopant Cr³⁺ ions in the polymer. Our results suggested that Cr³⁺, as a dopant, is a good choice to improve the electrical properties of PVP polymer electrolytes.     

Optical and electrical properties of GaN: Si-based microstructures with a wide range of doping levels

The optical and electrical properties of silicon-doped epitaxial gallium nitride layers grown on sapphire have been studied. The studies have been performed over a wide range of silicon concentrations on each side of the Mott transition. The critical concentrations of Si atoms corresponding to the formation of an impurity band in gallium nitride (～2.5 × 10¹⁸ cm^?3) and to the overlap of the impurity band with the conduction band (～2 × 10¹⁹ cm^?3) have been refined. The maximum of the photoluminescence spectrum shifts nonmonotonically with increasing doping level. This shift is determined by two factors: (1) an increase in the exchange interaction leading to a decrease in the energy gap width and (2) a change in the radiation mechanism as the donor concentration increases. The temperature dependence of the exciton luminescence with participating optical phonons has been studied. The energies of phonon-plasmon modes in GaN: Si layers with different silicon concentrations have been measured using Raman spectroscopy.     

The emission wavelength tuning of InAs/InP quantum dots with thin GaAs, InGaAs, InP capping layers by MOCVD

InAs quantum dots (QDs) were grown on InP substrates by metalorganic chemical vapor deposition. The width and height of the dots were 50 and 5.8 nm, respectively on the average and an areal density of 3.0×10¹⁰ cm⁻² was observed by atomic force microscopy before the capping process. The influences of GaAs, In_0.53Ga_0.47As, and InP capping layers (5–10 ML thickness) on the InAs/InP QDs were studied. Insertion of a thin GaAs capping layer on the QDs led to a blue shift of up to 146 meV of the photoluminescence (PL) peak and an InGaAs capping layer on the QDs led to a red shift of 64 meV relative to the case when a conventional InP capping layer was used. We were able to tune the emission wavelength of the InAs QDs from 1.43 to 1.89 μm by using the GaAs and InGaAs capping layers. In addition, the full-width at half-maximum of the PL peak decreased from 79 to 26 meV by inserting a 7.5 ML GaAs layer. It is believed that this technique is useful in tailoring the optical properties of the InAs QDs at mid-infrared regime.