Growth mode and effect of carrier gas on In0.53Ga0.47As/InP surface morphology grown with trimethylarsine and arsine

Different growth mode have been observed for InGaAs/InP grown with trimethylarsine and arsine by Metalorganic Vapor Phase Epitaxy (MOVPE) when changing the carrier gas. The surface has been investigated by Atomic Force Microscope (AFM) for epilayers grown at 600°C under pure hydrogen or a mixture of hydrogen and nitrogen as carrier gas. The step/terrace surface morphology was observed for InP/InP and InGaAs/InP (001) using 0.2° off substrates. InP epilayers grown under nitrogen flow show step-bunched terraces as large as 170 nm. The effect of the group V source for InGaAs/InP has been studied. It is shown that the step edge characteristic of step flow growth appears for lattice-matched InGaAs/InP grown with arsine. When using TMAs and hydrogen as a carrier gas, the growth mode and surface roughness depends greatly on V/III ratio and growth temperature. Under nitrogen flow with the combination of TMI+TMG+TMAs, pit-like defects (5–8 nm deep) are visible at high surface concentration (10⁹–10¹⁰/cm²). When increasing V/III ratio, 3D growth occurs simultaneously with pit-like defects, recovering the whole surface of the sample. Various surface morphology characteristics of InGaAs epilayers assessed by AFM characterisation will be presented and discussed.     

TiCN/TiNbCN multilayer coatings with enhanced mechanical properties

Enhancement of mechanical properties by using a TiCN/TiNbCN multilayered system with different bilayer periods (Λ) and bilayer numbers (n) via magnetron sputtering technique was studied in this work. The coatings were characterized in terms of structural, chemical, morphological and mechanical properties by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nanoindentation. Results of the X-ray analysis showed reflections associated to FCC (1 1 1) crystal structure for TiCN/TiNbCN films. AFM analysis revealed a reduction of grain size and roughness when the bilayer number is increased and the bilayer period is decreased. Finally, enhancement of mechanical properties was determined via nanoindentation measurements. The best behavior was obtained when the bilayer period (Λ) was 15 nm (n = 200), yielding the highest hardness (42 GPa) and elastic modulus (408 GPa). The values for the hardness and elastic modulus are 1.6 and 1.3 times greater than the coating with n = 1, respectively. The enhancement effects in multilayer coatings could be attributed to different mechanisms for layer formation with nanometric thickness due to the Hall-Petch effect; because this effect, originally used to explain the increase in hardness with decreasing grain size in bulk polycrystalline metals, has also been used to explain hardness enhancements in multilayers taking into account the thickness reduction at individual single layers that make the multilayered system. The Hall-Petch model based on dislocation motion within layers and across layer interfaces, has been successfully applied to multilayers to explain this hardness enhancement.     

Strain relaxation at cleaved surfaces studied by atomic force microscopy

Atomic force microscopy (AFM) in air is used to study the (110) cleaved surface of strained (100) In_xGa_1-xAs/ InP heterostructures for different compositions and thicknesses of the ternary compound layers. We find that the elastic strain relaxation induces a surface undulation of a few ? amplitude, even for very small misfits, provided the layers are thick enough. Using finite-element calculations of the strain relaxation near the cleaved edge, we reproduce quantitatively the AFM observations for compressive- as well as for tensile-strained layers with an accuracy better than 0.1 nm. This demonstrates the ability of AFM to quantify strain distributions by making use of surface profile measurements. Received: 9 November 1998 / Accepted: 11 March 1999 / Published online: 7 July 1999     

Numerical study on gain and optical properties of AlGaInAs, InGaNAs, and InGaAsP material systems for 1.3-μm semiconductor lasers

In reference to real devices fabricated in laboratories, the optical properties of AlGaInAs, InGaNAs, and InGaAsP semiconductor material systems for 1.3-μm semiconductor lasers are systematically studied. Simulation results show that both the AlGaInAs/InP and InGaNAs/GaAs material systems have better gain performance and smaller transparency carrier density than the InGaAsP/InP material system. For the AlGaInAs/InP material system, the characteristic temperature is improved by using compensating tensile strain in barrier. Specifically, for a 250-μm-long short-cavity AlGaInAs/InP laser, when the barrier is with a compensating tensile strain of 0.39%, the characteristic temperatures in 290-330 K and 330-350 K can be enhanced to 121.7 K and 58.9 K, respectively. For the InGaNAs/GaAs material system, simulation results suggest that the laser performance can be significantly improved when the laser is with strain-compensated GaNAs barriers.     

InGaAsP/InP双异质结发光管频响特性的研究

本文研究了光纤通信用1.3μmInGaAsP/InP双异质结发光管的频响特性。结果表明:器件有源区掺杂浓度;有源层厚度;注入电流;光谱特性;P-n结特性等因素,对发光管的频响特性有重要影响。老化前有源区DSD的存在与否对频响无明显关系。     

Effect of laser fluence on the deposition and hardnessof boron carbide thin films

We deposited amorphous thin films of boron carbide by pulsed laser deposition using a B₄C target at room temperature. As the laser fluence increased from 1 to 3 J/cm², the number of 0.25–5 μm particulates embedded in the films decreased, and the B/C atomic ratio of the films increased from 1.8 to 3.2. The arrival of melt droplets, atoms, and small molecular species depending on laser fluence appeared to be involved in the film formation. In addition, with increasing fluence the nanoindentation hardness of the films increased from 14 to 32 GPa. We believe that the dominant factor in the observed increase in the films’ hardness is the arrival of highly energetic ions and atoms that results in the formation of denser films. Received: 23 March 2001 / Accepted: 1 July 2001 / Published online: 2 October 2001     

InGaAsP/InP边发光管特性的研究

用液相外延技术生长的外延片,制成了SiO2条形限制的InGaAsP/InP边发光管,100mA下光功率1mW,最高值1.3mW,发射波1.31μm,半宽860A。研究了外延材料特性(如p-n结位置,有源层厚度和浓度)对器件光功率,光谱特性,和Ⅰ-Ⅴ特性的影响。有源层厚度(d)对光功率和光谱半宽有重要影响,p-n结不偏位的器件,光谱特性为单一的长波长发射蜂,具有正常的Ⅰ-Ⅴ特性。p-n偏离有源层的器件,光谱特性除长波长发射峰外,尚有9700A的InP发射峰,其Ⅰ-Ⅴ特性具有异常特性,导通电压>0.9V。     

Effect of microstructure on the nanomechanical properties of Zn1−xCdxSe alloys

We present a study of the nanoindentation behavior of Zn_1−xCd_xSe epilayers grown using molecular beam epitaxy; the surface roughness, microstructure, and crystallinity were analyzed using atomic force microscopy, cross-sectional transmission electron microscopy, and X-ray diffraction; the hardness H and elastic modulus E were studied using nanoindentation techniques. We found that these highly crystalline materials possessed no stacking faults or twins in their microstructures. We observed a very marked increase in the value of H and a significant decrease in the value of E upon increasing the concentration of Cd, presumably because of an increase in the stiffness of the CdSe bond relative to that of the ZnSe bond. We observed a corresponding shrinkage of the contact-induced damage area for those films having a small grain size and a higher value of H. It appears that resistance against contact-induced damage requires a higher Cd concentration.     

Nanoindentation hardness measurements using real-shape indenters: application to extremely hard and elastic materials

We study the technique of nanoindentation hardness measurement applied to extremely hard and elastic thin films. We do the study with the aid of Hertz’s solutions for elastic contacts. The effect of different apical angles in ideally sharp conical diamond indenters is analyzed. In addition, the blunt tip shape of practical diamond indenters is discussed. The area function of the tip of real indenters is deduced from experimental nanoindentation measurements performed with these indenters on fused quartz. Triangular-base pyramidal indenters with Berkovich and cube corner geometries are considered. Theoretical hardness values applying Hertz’s and Oliver and Pharr’s methods of analysis are obtained and compared with the experimental data deduced from nanoindentation measurements performed on very hard and elastic ta-C films. The theoretical analysis shows a necessary dependence of the calculated hardness values with the apical angle of the indenter in totally elastic materials and to some extent in elastoplastic materials. Moreover, when the indenter tip is blunt or when there are inaccuracies in the measured area function of the indenter tip, hardness values decrease for very small penetration depths. Besides, in these films, because of their very small thickness, measured hardness values also decrease for measurements with penetration depths larger than a fraction of film thickness, due to the effects of the softer substrate. Received: 13 June 2000 / Accepted: 21 June 2000 / Published online: 5 October 2000     

外电场对InGaAsP/InP量子阱内激子结合能的影响

在有效质量近似下采用变分法计算了InGaAsP/InP量子阱内不同In组分下的激子结合能,分析了结合能随阱宽和In组分的变化情况,并且讨论了外加电场对激子结合能的影响. 结果表明：激子结合能是阱宽的一个非单调函数,随阱宽的变化呈现先增加后减小的趋势;随着In组分增大,激子结合能达到最大值的阱宽相应变小,这与材料的带隙改变有关;在一定范围内电场的存在对激子结合能的影响很小,但电场强度较大时会破坏激子效应. 关键词： 激子 InGaAsP/InP量子阱 结合能 电场     

InGaAsP/InP evanescent mode waveguide optical isolators and their application to InGaAsP/InP/Si hybrid evanescent optical isolators

We theoretically investigated InGaAsP/InP evanescent mode waveguide optical isolators and proposed their application to InGaAsP/InP/Si hybrid evanescent optical isolators. InGaAsP/InP evanescent optical isolators are composed of semiconductor optical amplifier (SOA) waveguides having InGaAsP multiple quantum well (MQW) active layer and upper InGaAsP waveguide layer with ferromagnetic layer. Optical isolation is obtained for evanescent optical mode in the InGaAsP waveguide layer. InGaAsP/InP/Si hybrid evanescent optical isolators are theoretically proposed based on the idea of InGaAsP/InP evanescent optical isolators. InGaAsP/InP/Si hybrid evanescent optical isolators are composed of ferromagnetic metal loaded silicon evanescent waveguides with wafer-bonded InGaAsP/InP optical gain material. The optical isolation and propagation loss are discussed with the structure of silicon evanescent waveguides, and optical isolation of 8.0 dB/mm was estimated. The concept of semiconductor evanescent mode optical isolators is feasible with InP based photonic integrated circuits and advanced silicon photonics.     

1.3μmInGaAsP/InP发光管退化的研究

研究了InGaAsP/InP双异质结发光管在老化,存储过程中的退化现象及其影响因素.有快慢二种退化模式,正向I-V特性变坏是产生突然退化的最主要因素,焊料的润湿不良是导致器件退化的原因之一;在70℃,85℃老化及存储过程中,个别器件有源区内有DSD产生并长大,这并不是引起突然退化的原因.     

Influences of As flux on the lattice constants, magnetic and transport properties of (Ga, Mn)As epilayers

A series of (Ga, Mn)As epilayers have been prepared on semi-insulating GaAs (001) substrates at 230  ^°C by molecular-beam epitaxy under fixed temperatures of Ga and Mn cells and varied temperatures of the As cell. By systematically studying the lattice constants, magnetic and magneto-transport properties in a self-consistent manner, we find that the concentration of As antisites monotonically increases with increasing As flux, while the concentration of interstitial Mn defects decreases with it. Such a trend sensitively affects the properties of (Ga, Mn)As epilayers.     

Observation of oxygen contamination at ZnSe/GaAs interfaces using SIMS

ZnSe epilayers were grown on GaAs (1 0 0) substrates using MBE. The native contamination (oxide and carbon) was removed in situ from the substrate surfaces by conventional thermal cleaning and by exposure to atomic hydrogen. A maximum substrate temperature of 600 °C was required for the thermal cleaning process, while a substrate temperature of 450 °C was sufficient to clean the substrate using hydrogen. ZnSe epilayers were also grown on As capped GaAs epilayers, which were decapped at a maximum temperature of 350 °C. SIMS profiles showed the existence of oxygen at the interface for all of the substrate preparation methods. The oxygen surface coverage at the interface was found to be 0.03% for the atomic hydrogen cleaned substrate and 0.7% for the thermally cleaned substrate.     

Effect of strain relaxation of oxidation-treated SiGe epitaxial thin films and its nanomechanical characteristics

In this study, we examined the effect of high-temperature oxidation treatment on the SiGe epitaxial thin films deposited on Si substrates. The X-ray diffraction (XRD), atomic force microscopy (AFM), and nanoindentation techniques were employed to investigate the crystallographic structure, surface roughness, and hardness (H) of the SiGe thin films, respectively. The high-temperature oxidation treatment led to Ge pileup at the surface of the SiGe thin films. In addition, strain relaxation occurred through the propagation of misfit dislocations and could be observed through the cross-hatch pattern (800-900 °C) and SiGe islands (1000 °C) at the surface of the SiGe thin films. Subsequent hardness (H) measurement on the SiGe thin films by continuous penetration depth method indicated that the phenomenon of Ge pileup caused a slightly reduced H (below 50 nm penetration depth), while relaxation-induced defects caused an enhanced H (above 50 nm penetration depth). This reveals the influence of composition and defects on the structure strength of high-temperature oxidation-treated SiGe thin films.     

Mechanical properties of carbon nanotubes

A variety of outstanding experimental results on the elucidation of the elastic properties of carbon nanotubes are fast appearing. These are based mainly on the techniques of high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM) to determine the Young’s moduli of single-wall nanotube bundles and multi-walled nanotubes, prepared by a number of methods. These results are confirming the theoretical predictions that carbon nanotubes have high strength plus extraordinary flexibility and resilience. As well as summarising the most notable achievements of theory and experiment in the last few years, this paper explains the properties of nanotubes in the wider context of materials science and highlights the contribution of our research group in this rapidly expanding field. A deeper understanding of the relationship between the structural order of the nanotubes and their mechanical properties will be necessary for the development of carbon-nanotube-based composites. Our research to date illustrates a qualitative relationship between the Young’s modulus of a nanotube and the amount of disorder in the atomic structure of the walls. Other exciting results indicate that composites will benefit from the exceptional mechanical properties of carbon nanotubes, but that the major outstanding problem of load transfer efficiency must be overcome before suitable engineering materials can be produced. Received: 17 May 1999 / Accepted: 18 May 1999 / Published online: 29 July 1999     

Nanoindentation and nanoscratch behaviors of Ag/Ni multilayers

The hardness, elastic modulus and scratch behaviors of Ag/Ni mulitlayers deposited by evaporation have been carried out by nanoindentation and nanoscratch. It has been found that the hardness (H) increases, while the modulus (E) decreases, that is to say an increase of H/E as the periodicity decreases. Many mechanisms are included in nanoscratch, including initial elastic contact, plowing and fracture stage, in each multilayer. Coefficient of friction during plowing decreases with the decrease of the periodicity, which can be ascribed to decreasing material pile-up due to the increase of H/E. Elastic recovery after scratching also increases as the periodicity decreases because of the increase of H/E, which leads to improved wear resistance. The fracture stage will be postponed with decreasing periodicity, which also leads to better wear behavior.     

Influence of buffer layer thickness and epilayer’s growth temperature on crystalline quality of InAs0.6P0.4/InP grown by LP-MOCVD

InAs_0.6P_0.4 epilayers grown on InP (100) substrates using two-step growth method by LP-MOCVD were investigated. A low temperature (450 °C) In_0.18Ga_0.82As buffer layer was introduced to relax the lattice mismatch between the InAs_0.6P_0.4 epilayer and the InP substrate. The influence of In_0.18Ga_0.82As buffer layer thickness and epilayer’s growth temperature on crystalline quality of InAs_0.6P_0.4 epilayer was characterized by Scanning electron microscopy, X-ray diffraction, Hall measurements, Transmission electron microscopy and Photoluminescence. The experimental results showed that the crystalline quality of InAs_0.6P_0.4 epilayers could be greatly improved by optimizing the In_0.82Ga_0.18As buffer layer thicknesses and the InAs_0.6P_0.4 epilayer’s growth temperatures. It was found that, when In_0.82Ga_0.18As buffer layer thickness was 100 nm and InAs_0.6P_0.4 epilayer’s growth temperature was 580 °C, the InAs_0.6P_0.4 epilayer exhibited the best crystalline quality and properties.     

Investigation of surface cleaning procedure of InP:S (1 0 0) substrates by high resolution XPS

The angle resolved X-ray photoelectron spectroscopy measurements were used to monitor a level of contamination of the InP:S (1 0 0) substrates during the cleaning processes with deionized water and isopropanol. Some contaminations with carbon and oxygen were found for a broken under ultrahigh vacuum InP:S substrate, indicating the contamination of the crystal during the growth process. The substrates after cleaning with deionized water and isopropanol were contaminated with carbon, oxygen, nitrogen and silicon. Concentration of carbon decreases inwards the substrates while concentration of oxygen is enhanced even in the deeper layers for both processes. The nitrogen concentration is higher for the samples rinsed with water. Roughness of the surfaces is higher for the samples rinsed with water what indicated the AFM measurements.