Analyses of interface adhesion between porous SiO2 low-k film and SiC/SiN layers by nanoindentation and nanoscratch tests

In this study, the interface adhesion between porous SiO₂ low-dielectric-constant film and SiN capping layer as well as SiC etch stop layer has been investigated. The SiN capping layer was found mostly composed of Si to N bonds, and the porous SiO₂ film composed of Si to O bonds. Elements of Si, O, and N constructed an interlayer mixing region of about 20 nm at the interface between the porous SiO₂ film and SiN capping layer. Under nanoindentation and nanoscratch tests, interface delamination between the porous SiO₂ film and both SiN capping layer and SiC etch stop layer occurred around the indented regions, and the interface adhesion strengths were accordingly obtained. The interface adhesion energy between the porous SiO₂ film and SiN capping layer was measured as about 3.7 and 0.9 J/m² by nanoindentation and nanoscratch tests, respectively, and that between the porous SiO₂ film and SiC etch stop layer was about 8.3 and 1.2 J/m².     

湿法氧化Al0.85Ga0.15As时SiO2层的保护作用

本文研究了有无氧化硅保护层时Al0.85Ga0.15As层的高温湿法氧化。实验结果表明：氧化硅层对Al0.85Ga0.15As层的高温侧向湿法氧化速率基本无影响;被氧化区域SEM图像的衬度和有氧化硅保护层样品As拉曼峰的缺乏归因于被氧化区域中不存在氧化反应产物As,这有利于提高氧化层的热稳定性;有SiO2保护层样品的发光强度比无SiO2保护层样品的发光强度强的多,且具有SiO2保护层样品的发光峰位和半高全宽与氧化前的样品基本一致,而无SiO2保护层样品的发光峰位红移,半高宽展宽,这是由于氧化硅层阻止了GaAs盖层的氧化。     

Super-flat interfaces in In0.53Ga0.47As/In0.52Al0.48As quantum wells grown on (411)A InP substrates by molecular beam epitaxy

Effectively atomically flat interfaces over a macroscopic area (“(411)A super-flat interfaces”) were successfully achieved in In_0.53Ga_0.47As/In_0.52Al_0.48As quantum wells (QWs) grown on (411)A InP substrates by molecular beam epitaxy (MBE) at a substrate temperature of 570°C and V/III=6. Surface morphology of the In_0.53Ga_0.47As/In_0.52Al_0.48As QWs was smooth and featureless, while a rough surface of those simultaneously grown on a (100) InP substrate was observed. Photoluminescence (PL) linewidths at 4.2 K from the (411)A QWs with well width of 0.6–12 nm were 20–30 % narrower than those grown on a (100) InP substrate and also they are almost as narrow as each of split PL peaks for those of growth-interrupted QWs on a (100) InP substrate. In the case of the (411)A QWs, only one PL peak with very narrow linewidth was observed from each QW over a large distance (7 mm) on a wafer.     

氢离子注入法提高InAsP/InP应变多量子阱发光特性

采用气态源分子束外延系统生长了InAsP/InP应变多量子阱,研究了H 注入对量子阱光致发光谱的影响以及高温快速退火对离子注入后的量子阱发光谱的影响.发现采用较低H 注入能量(剂量)时,量子阱发光强度得到增强;随着H 注入能量(剂量)的增大,量子阱发光强度随之减小.H 注入过程中,部分隧穿H 会湮灭掉量子阱结构界面缺陷,同时H 也会对量子阱结构带来损伤,两者的竞争影响量子阱发光强度的变化.高温快速退火处理后,离子注入后的量子阱样品发光峰位在低温10K相对于未注入样品发生蓝移,蓝移量随着H 注入能量或剂量的增大而增加.退火过程中缺陷扩散以及缺陷扩散导致的阱层和垒层之间不同元素互混是量子阱发光峰位蓝移的原因.     

Temperature dependence of the photoluminescence properties and band gap energy of InxGa1−xAs/GaAs quantum wells

The effective band gap energy of In_xGa_1−xAs/GaAs strained quantum wells (QWs) is investigated by photoluminescence spectroscopy (PL) in the range 12–295 K. The temperature dependence of the band gap energy of strained QWs correlates well with that of bulk In_xGa_1−xAs of similar composition. Deviations from the band gap variation of bulk material at low temperatures (12–90 K) are interpreted in terms of exciton localization. The differences ΔE(12 K) between the measured PL peak energies and the expected transition energies at 12 K (obtained by simulating the measured temperature dependence of the PL peak positions by the well-known Varshni relation) are suggested to be closely related to the Stokes shifts that often exist between PL and PL excitation spectra of QWs. A linear relation is found between the PL full-width at half-maximum measured at 12 K and ΔE for a range of QWs prepared under different growth conditions. Excitonic recombination is inferred to be dominant in the PL transitions at the highest temperatures investigated—even at room temperature.     

Formation of photoluminescence centers during annealing of SiO2 layers implanted with Ge ions

Photoluminescence (PL), Raman scattering, and the Rutherford backscattering of α-particles were used to study the formation of the centers of radiative-recombination emission in the visible region of the spectrum on annealing of the SiO₂ layers implanted with Ge ions. It was found that the Ge-containing centers were formed in the as-implanted layers, whereas the stages of increase and decrease in the intensities of PL bands were observed following an increase in the annealing temperature to 800°C. The diffusion-related redistribution of Ge atoms was observed only when the annealing temperatures were as high as 1000°C and was accompanied by formation of Ge nanocrystals. However, this did not give rise to intense PL as distinct from the case of Si-enriched SiO₂ layers subjected to the same treatment. It is assumed that, prior to the onset of Ge diffusion, the formation of PL centers occurs via completion of direct bonds between the neighboring excess atoms, which gives rise to the dominant violet PL band (similar to the PL of O vacancies in SiO₂) and a low-intensity long-wavelength emission from various Ge-containing complexes. The subsequent formation of centers of PL with λ_m～570 nm as a result of anneals at temperatures below 800°C is explained by agglomeration of bonded Ge atoms with formation of compact nanocrystalline precipitates. The absence of intense PL following the high-temperature anneals is believed to be caused by irregularities in the interfaces between the formed Ge nanoc-rystals and the SiO₂ matrix.     

MBE growth and photoluminescent properties of InAsSb/AlSbAs quantum wells

Heterostructures with a single InAs_1−x Sb_x/AlSb_1−y As_y quantum well (QW) on (001) GaSb substrates have been grown by MBE and studied using X-ray diffraction, transmission electron microscopy, and photoluminescence (PL) spectroscopy. High-intensity PL was observed at a temperature of 80 K, with a peak half-width of 30–50 meV and a peak wavelength in the range from 2 to 4.5 μm, depending on the QW width, which varied between 4 and 20 nm, respectively. The fundamental absorption edge of such QWs was calculated for a wide range of alloy compositions, x and y. Good correlation between the experimental and calculated dependences of the band gap on the InAsSb/AlSbAs QW thickness was obtained. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 12, 2002, pp. 1470–1474. Original Russian Text Copyright ? 2002 by Solov’ev, Terent’ev, Toropov, Meltser, Semenov, Sitnikova, Ivanov, Meyer, Kop’ev.     

Effect of plasma treatments on interface chemistry and adhesion strength between porous SiO2 low-k film and SiC/SiN layers

In this study, the interface chemistry and adhesion strengths between porous SiO₂ low-dielectric-constant film and SiN capping layer as well as SiC etch stop layer have been investigated under different plasma treatments. Elements of Si, O, and N constructed an interlayer region with mixing Si-N and Si-O bonds at the interface between the porous SiO₂ film and SiN capping layer. After plasma treatments especially O₂ plasma, the oxygen content at the interface increased, and the binding energy obviously shifted to a higher level. Under nanoindentation and nanoscratch tests, interface delamination occurred, and the interface adhesion strength was accordingly measured. After plasma treatments especially the O₂ plasma, more Si-O bonds of high binding energy existed at the interface, and thus the interface adhesion strength was effectively improved. The adhesion energy of SiO₂/SiN and SiC/SiO₂ interfaces was enhanced to 4.7 and 10.5 J/m² measured by nanoindentation test, and to 1.3 and 2.0 J/m² by nanoscratch test, respectively.     

Photoluminescence study of AlGaAs/GaAs/AlGaAs double quantum wells separated by a thin AlAs layer

Photoluminescence (PL) spectra of Al_0.21Ga_0.79As/GaAs/Al_0.21Ga_0.79As double quantum wells (DQWs) separated by a thin AlAs barrier have been studied in the temperature range 77–300 K. The well width was varied from 65 to 175 Å, and the thickness of the AlAs barrier was 5, 10, or 20 Å. In the case of a sufficiently thin (5, 10 Å) AlAs barrier, the energy spectrum of QW states is considerably modified by coupling between the QWs. This effect shifts the main spectral peak of PL, and specific features associated with the splitting of the ground state into symmetric and asymmetric states are observed in the spectra at higher temperatures. The DQW structure with a 20-Å-thick AlAs barrier is a system of two uncoupled asymmetric Al_0.21Ga_0.79As/GaAs/AlAs QWs. The energy levels in double coupled QWs were calculated as functions of the well width and AlAs barrier thickness, and good correlation with the experimentally observed energies of optical transitions was obtained.     

Effects of growth interruption on the optical properties of AIGaAs/GaAs and GaAs/InGaAs quantum wells grown by atmospheric pressure organometallic chemical vapor deposition

In this study, the effects of growth interruptions on Al_0.17Ga_0.83As/GaAs and GaAs/ In_xGa_1-xAs quantum wells (QWs) grown by organometallic chemical vapor deposition (OMCVD) were assessed using low-temperature photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. Growth interruption times were varied between 60, 10, and 0 sec. For both material systems, as the interruption time was reduced, the ground-state QW transition energies increased, while the linewidths of the peaks decreased. For the Al_0.17Ga_0.83As/GaAs structures, 5 K PL data suggests that the incorporation of impurities is enhanced by longer growth interruption times. In addition, as the interruption time was reduced, the energy separation between the 5 K PL and PLE peaks (Stokes shift) decreased, and was as low as 2.6 meV for no interruption. For GaAs/In_0.11Ga_0.89As samples, 2 K PL data indicated that the incorporation of donor species was not a function of the growth interruption time.     

Investigation of Optical and Structural Stability of Localized Surface Plasmon Mediated Light‐Emitting Diodes by Ag and Ag/SiO2 Nanoparticles

Localized surface plasmon (LSP) effects due to Ag and Ag/SiO₂ nanoparticles (NPs) deposited on GaN/InGaN multiquantum well (MQW) light‐emitting diode (LED) structures are studied. The colloidal NPs are synthesized by a sol‐gel method and drop‐cased on the LED structures. The surface density of NPs its controlled by the concentration of the NP solution. Theoretical modeling is performed for the emission spectrum and the electric field distribution of LSP resonance for Ag/SiO₂ NPs. Enhanced photoluminescence (PL) efficiency is observed in the LED structures and the amount of PL enhancement increases with increasing the surface density of Ag and Ag/SiO₂ NPs. These effects are attributed to resonance coupling between the MQW and LSP in the NPs. It is also shown that the PL enhancement attainable with Ag NPs and Ag/SiO₂ NPs is comparable, but the latter displays a much higher stability with respect to long‐term storage and annealing due to a barrier for NP agglomeration, Ag oxidation, and impurity diffusion provided by the SiO₂ shell.     

InGaAsP/InP Double Quantum Well Intermixing Induced by Phosphorus Ion Implantation

A quantum well intermixing(QWI) investigation on double quantum well(DQW) structure with two different emitting wavelength caused by phosphorus ion implantation and following rapid thermal annealing (RTA) was carried out by means of photoluminescence(PL). The ion implantation was performed at the energy of 120 kev with the dose ranging from 1 × 1011 cm-2 to 1× 1014 cm-2. The RTA was performed at the temperature of 700 ℃ for 30 s under pure nitrogen protection. The PL measurement implied that the band gap blue-shift from the upper well increases with the ion dose faster than that from lower well and the PL peaks from both QWs remained well separated under the lower dose implantation(～1×1011 cm-2 ) indicating that the implant vacancy distribution affects the QWI. When the ion dose is over ～ 1 × 1012 cm-2 , the band gap blue-shift from both wells increases with the ion dose and finally the two peaks merge together as one peak indicating the ion implantation caused a total intermixing of both quantum wells.     

Gas-Source molecular beam epitaxy and characterization of inGaAs/lnGaAsP quantum well structures on InP

In this paper, we report the effect of using a group-V residual source evacuation (RSE) time on the interfaces of InGaAs/lnGaAsP quantum wells (QWs) grown by gas-source molecular beam epitaxy. High-resolution x-ray rocking curve and low-temperature photoluminescence (PL) were used to characterize the material quality. By optimizing the RSE time, a PL line width at 15K as narrow as 6.6 meV is observed from a 2 nm wide single QW, which is as good as or better than what has been reported for this material system. Very sharp and distinct satellite peaks as well as Pendellosung fringes are observed in the x-ray rocking curves of In_xGa_1−xAs/InxGa_1−xAS_yP_1−y multiple QWs, indicating good crystalline quality, lateral uniformity, and vertical periodicity. Theoretical considerations of the PL linewidths of In_xGa_1−xAs/InxGa_1−xAS_yP_1−y single QWs show that for QW structures grown with the optimized RSE time, the PL linewidth is mainly due to alloy scattering, whereas the contribution from interface roughness is small, indicating a good interface control.     

Quantum Confinement and Carrier Localization Effects in ZnO/Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O Wells Synthesized by Pulsed Laser Deposition

The optical properties of ZnO/Mg _x Zn_1−x O (x = 0.17) quantum wells (QWs) grown on c-plane sapphire substrates by pulsed laser deposition are presented. A blueshift in the low-temperature photoluminescence (PL) of the QWs illustrates quantum confinement effects as a function of ZnO well widths in the range from 3 nm to 10 nm. Enhanced luminescence properties are observed with increasing quantum confinement. PL data indicate weak polarization effects associated with the heterojunctions. Temperature-dependent PL measurements indicate carrier/exciton localization with activation energy of approximately 4−5 meV, which are attributed to potential fluctuations at the well-barrier interface.     

Preparation‐Condition Dependence of Hybrid SiO2‐Coated CdTe Nanocrystals with Intense and Tunable Photoluminescence

When aqueously prepared CdTe nanocrystals (NCs) are coated with a SiO₂ shell containing Cd ions and a sulfur source, they show a drastic increase in photoluminescence (PL) efficiency with a significant red shift and spectral narrowing after reflux. This is ascribed to the creation of a hybrid structure characterized by the formation of CdS‐like clusters in the vicinity of the NCs in the SiO₂ shell. Since these clusters are close to the NCs, their effective size increases to reduce the quantum size effect. The dependences of the PL properties on the preparation conditions are systematically investigated. The PL efficiency increases from 28% to 80% in the best case with a red shift of 80 nm. The PL behaviors differ from those of normal CdTe NCs and include less temperature quenching and longer PL lifetime. The SiO₂ coating enables bioconjugation with IgG without deterioration of PL efficiency, making hybrid NCs amenable for bioapplication.     

The effects of InP grown by He-plasma assisted epitaxy onquantum-well intermixing

He-plasma assisted InP (He*-InP) layers grown by gas source molecular beam epitaxy (GSMBE) have been employed to enhance quantum well (QW) intermixing induced by rapid thermal annealing in a 1.5 μm InGaAsP QW laser structure. Inserting a 40 nm He*-InP layer just above the active region enhances the blue-shift for anneal temperatures larger than 680°C, and a 42 nm additional blue-shift is obtained at 750°C for samples with the He*InP layer, compared to samples with normal InP replacing the He*-InP. This is accompanied by a reduction in the photoluminescence (PL) intensity for anneal temperatures greater than 600°C and is attributed to the migration of nonradiative defects from the He*-InP layer into the QWs. Insertion of a thin InGaAs layer between the He*-InP layer and the QW blocks the diffusion of these nonradiative defects into the QW. The results indicate that the He*-InP material could prove useful in QW intermixing to achieve integrated optoelectronic devices, in particular for high-frequency devices which require short carrier lifetimes     

Structural transformations and silicon nanocrystallite formation in SiOx films

The results of a comprehensive study by the methods of IR absorption, Raman scattering, photoluminescence (PL), and electron spin resonance (ESR) of SiO_x films prepared by thermal evaporation of SiO in a vacuum are presented. The nature of structural transformations occurring on annealing the films is determined. Annealing in the temperature range 300–600°C gives rise to a PL band at 650 nm, presumably related to structural defects in SiO_x film. Raising the annealing temperature further leads to healing of such defects and quenching of the PL band. Silicon precipitates pass from the amorphous to the crystalline state on being annealed at T _ann=1100°C, which gives rise to a new PL band at 730 nm. ESR spectra of P _b centers were recorded at the interface between randomly oriented silicon nanocrystallites and SiO₂.     

Investigation of the physical properties of semiconductor nanostructures using samples with laterally nonuniform layers: 1. Photoluminescence

A new technique for the experimental investigation of semiconductor structures is suggested and implemented. The technique is based on an analysis of correlations in the spectra of samples with laterally nonuniform layers. A molecular-beam-epitaxy-grown sample containing Al_xGa_1?xAs-GaAs and GaAs-In_yGa_1?yAs quantum wells (QWs) and a modulation doped Al_xGa_1?xAs-GaAs heterojunction was studied by photoluminescence (PL) spectroscopy at 77 K. The dependences of the PL spectra on the parameters describing sample nonuniformity were analyzed, which made it possible to characterize the processes of the charge-carrier redistribution in the structure and to reveal a number of specific features in the PL of narrow GaAs QWs. In the entire range of the nonuniformity-related variation in the semiconductor structure parameters, the values of the optical transition energies determined experimentally agree with those calculated theoretically and may serve as a basis for estimating these parameters. It is shown in this study that the suggested approach is highly informative, which stems from the capacity for precision control over the technologically adjustable parameters of the structure within the same sample.     

Effects of Substrate Materials on Self-Formation of Ti-Rich Interface Layers in Cu(Ti) Alloy Films

In our previous studies, thin Ti-rich layers were found to uniformly cover SiO₂/Si substrate surfaces at the interface with Cu(Ti) alloy films after annealing at elevated temperature. These Ti-rich layers were also found to prevent intermixing between the Cu(Ti) alloy films and the substrate, resulting in a simple barrier formation technique, called “self-formation of the diffusion barrier,” which is attractive for fabrication of ultra-large scale integrated (ULSI) interconnect structures. In the present study, to understand the mechanism of self-formation of the Ti-rich barrier layers on the substrate surface, the effects of SiO₂/Si, SiN/SiO₂/Si and NaCl substrate materials on the interfacial microstructure were investigated. The microstructures were analyzed by transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS), and correlated with the electrical properties of the Cu(Ti) interconnects. It was concluded that the chemical reaction of Ti with the substrate materials was essential for the self-formation of the Ti-rich layers.     

Optical properties of InAs<Subscript>1−x</Subscript>N<Subscript>x</Subscript>/In<Subscript>0.53</Subscript>Ga<Subscript>0.47</Subscript>As single quantum wells grown by gas source molecular beam epitaxy

Optical properties of InAs_1−xN_x/In_0.53Ga_0.47As (hereafter, abbreviated as InAsN/InGaAs) single quantum wells (SQWs) grown on InP substrates by gas source molecular-beam epitaxy are studied using photoluminescence (PL) measurements. By comparing the low-temperature PL spectra of InAs/InGaAs and InAsN/InGaAs SQWs, InAs and InAsN phases are found to coexist in the InAsN layer. Such serious alloy inhomogeneities result in obvious exciton localization by potential irregularities. The blue shift of the PL peak after rapid thermal annealing (RTA) is found to originate mainly from As-N interdiffusion inside the well layer. According to the temperature-dependent PL results, uniformity of the InAsN layer can be effectively improved by RTA, and the exciton localization is, thus, relieved. Comparison of luminescence quenching and excitation-power-dependent PL behavior between the QWs with and without nitrogen content suggests that the quality of the QW is degraded by the introduction of nitrogen, and the degradation can only be partially recovered by post-growth RTA.