Minority carrier diffusion length in LPE InxGa1−xP: N layers (x < 0.01)

Minority carrier diffusion length In_xGa_1?xP LPE layers has been measured using the electron beam method. It has been found that this parameter significantly changes with the composition of the alloy. The measured relationship proves that minority carrier mobility in In_xGa_1?xP alloys with low indium content strongly depends on the alloy composition. It is suggested that alloy scattering may be responsible for this behaviour. The effect of doping the In_xGa_1?xP LPE layers with nitrogen has also been investigated. Results indicate that carrier mobility drops when the nitrogen concentration exceeds certain limits and this most probably can be ascribed to carrier scattering on the nitrogen centers.     

Alloy splitting of Te-DX in AlxGa1−xAs analysis using the deep level transient spectroscopy technique

The paper reports on a deep level transient spectroscopy analysis of Te-related DX centers in Al_xGa_1−xAs with aluminum composition x=0.40. As was shown from experimental results, the state energy of this trap shows a microscopic structure due to an alloy effect. A theoretical analysis based on a multi-step scheme has been made to explain the electron emission from a multiconfigurate center. Using this model, we derived the binding energies of the splitted Te-DX states in the alloy material studied.     

Grown junction GaAs solar cells with a thin graded band-gap AlxGa1−xAs surface layer

Liquid phase epitaxial growth techniques were used to fabricate (n)GaAs:Sn-(p)GaAs:Ge-(p)Al_xGa_1?xAs:Ge heterostructure solar cells. Graded band-gap Al_xGa_1?xAs layers with thicknesses between 1500 and 2500 Å were prepared by isothermal growth from an undersaturated solution. Spectral response measurements show that the resulting built-in electric field at the surface of the solar cell reduces the surface recombination velocity and improves the collection efficiency.     

Luminescent properties of BexCd1−xSe thin films

We report photoluminescence (PL) study of Be_xCd_1−xSe epitaxial layers (x<0.21) grown by molecular beam epitaxy on InP substrates. Continuous wave PL spectra are taken within a 4.2-300 K temperature range. We observe an anomalous ‘s-shaped’ temperature dependence of emission energy and a severe decrease of emission intensity with the increase of temperature. We explain an ‘s-shaped’ temperature dependence of emission energy by exciton localization in the potential minima at low temperatures followed by thermal activation at higher temperatures. We attribute low emission intensity at high temperatures to exciton dissociation and electron/hole migration to non-radiative recombination centers.     

High-k TixSi1−xO2 thin films prepared by co-sputtering method

We report on high-k Ti_xSi_1−xO₂ thin films prepared by RF magnetron co-sputtering using TiO₂ and SiO₂ targets at room temperature. The Ti_xSi_1−xO₂ thin films exhibited an amorphous structure with nanocrystalline grains of 3-30 nm having no interfacial layers. The XPS analyses indicate that stoichiometric TiO₂ phases in the Ti_xSi_1−xO₂ films increased due to stronger Ti-O bond with increasing TiO₂ RF powers. In addition, the electrical properties of the Ti_xSi_1−xO₂ films became better with increasing TiO₂ RF powers, from which the maximum value of the dielectric constant was estimated to be ∼30 for the samples with TiO₂ RF powers of 200 and 250 W. The transmittance of the Ti_xSi_1−xO₂ films was above 95% with optical bandgap energies of 4.1-4.2 eV. These results demonstrate a potential that the Ti_xSi_1−xO₂ thin films were applied to a high-k gate dielectric in transparent thin film transistors as well as metal-oxide-semiconductor field-effect transistors.     

InxGa1-xAs高性能全固态数字化微光器件

作为全固态微光器件,InxGa1-xAs器件通过调节材料组分x值,其响应波段覆盖夜天光辐射的主要波段,对夜天光的能量利用率高。加之材料量子效率高,器件性能好,可望显著提高夜视系统作战距离;另外,采用半导体常规工艺制作,可完成大面阵、长线列器件制备,无需封装在（超）高真空系统,制备简单;采用CMOS读出电路进行信号数据的读取、传输与放大,有利于进行数据的处理和优化改善。由于具备的以上技术优势,InxGa1-xAs器件成为一种新型的高性能全固态数字化微光器件。InxGa1-xAs器件与传统的微光器件在光电转换原理以及器件制备方面存在不同,决定了两者在性能上存在的差异。文中对此进行了对比分析,分析结果体现了InxGa1-xAs全固态数字化微光器件的技术优势和特点,以及InxGa1-xAs全固态数字化微光器件存在的重要应用和发展需求。     

Anomalous light sensitivity of organometallic VPE AlxGa1−xAs

The capacitance of Al_0.3Ga_0.7As p-n junctions grown by organometallic vapor phase epitaxy at 690°C with V/III flux ratio of ～20 is found to be extremely light-sensitive. The light sensitivity is shown to be caused by the presence of two dominant hole traps having energy levels at 0.87 and 0.74 eV above the valence band. The traps were studied by three different schemes of DLTS measurements. The traps could be annealed out by post-growth annealing at 650°C for 1 hr in a hydrogen atmosphere.     

Impact of strain relaxation of AlmGa1−mN layer on 2-DEG sheet charge density and current voltage characteristics of lattice mismatched AlmGa1−mN/GaN HEMTs

An accurate charge control model to investigate the effect of aluminum composition, strain relaxation, thickness and doping of the Al_mGa_1−mN barrier layer on the piezoelectric and spontaneous polarization induced 2-DEG sheet charge density, threshold voltage and output characteristics of partially relaxed Al_mGa_1−mN/GaN HEMTs is proposed. The strain relaxation of the barrier imposes an upper limit on the maximum 2-DEG density achievable in high Al content structures and is critical in determining the performance of lattice mismatched Al_mGa_1−mN/GaN HEMTs. The model incorporates the effects of field dependent mobility, parasitic source/drain resistance and velocity saturation to evaluate the output characteristics of Al_mGa_1−mN/GaN HEMTs. Close proximity with published results confirms the validity of the proposed model.     

Cathodoluminescence assessment of GaAs1−x Px for light emitting diodes

The room temperature cathodoluminescence (CL) properties of selenium doped epitaxial layers of GaAs_1−xP_x, in the composition range 0·35 < x < 0.45, have been examined as a function of the Hall electron concentration. Material selected for this investigation had less than 2 per cent of the total CL emission in the i.r. For a fixed alloy composition the CL intensity is shown to increase with increasing electron concentration, while for a fixed electron concentration the intensity decreases with increasing GaP content. These results have been correlated with the electroluminescent efficiencies of zinc diffused diodes fabricated from the same material. It is shown that CL provides a rapid and reliable means of assessing the composition and emitting efficiency of epitaxial layers for use in the fabrication of light emitting diodes.     

Changes in effective work function of HfxRu1−x alloy gate electrode

Effective work function (?_m,eff) values of Hf_x Ru_1−x alloy gate electrodes on SiO₂ metal-oxide-semiconductor (MOS) capacitors were carefully examined to assess whether the ?_m,eff was determined by the crystalline structure or the composition of the Hf_xRu_1−x alloy. X-ray diffraction results indicated that the crystalline structures of Hf_xRu_1−x alloy were divided into hexagonal-Ru, cubic-HfRu or hexagonal-Hf with the increase of Hf content. The ?_m,eff values could be controlled continuously from 4.6 to 4.0 eV by changing the Hf content. The experimental ?_m,eff value showed a good agreement with theoretical results considering the compositional ratio of pure Hf and Ru. These results suggest that the ?_m,eff of Hf_xRu_1−x alloy gates on SiO₂ MOS capacitors is dominantly determined by the Hf_xRu_1−x composition rather than the crystalline structure.     

Characterization of CMOS sub-65 nm metallic contact by laser scattering: Thermal stability of Ni(Si1−xGex)

Very efficient in particles detection, light scattering also offers fast non-invasive full-mapping wafer surface state. This sensitivity was used in the case of germano-silicide process development. As a matter of fact, we report on haze measurement performances, compared to the usual methods used to investigate thermal stability of Ni(Si_1−xGe_x), such as sheet resistance (SR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). We observed defectivity related to thermal agglomeration and Ge-segregation of Ni(Si_1−xGe_x) on strain Si_1−xGe_x (x ? 30%) by haze measurement (like SEM observations) earlier than SR measurement. Moreover, we noticed that a high Ge content affects at lower temperature the stability of Ni(Si_1−xGe_x) with a segregation phenomena.     

Leakage currents and dielectric breakdown of Si1−x−yGexCy thermal oxides

A detailed study of the leakage currents and dielectric wear-out of thermal oxides grown on Si_1−xGe_x, Si_1−yC_y and Si_1−x−yGe_xC_y epilayers to determine their quality and reliability for Si_1−x−yGe_xC_y MOS technology is presented. After applying electrical stress to the samples, we have determined the conduction mechanisms and the dependence of leakage currents upon epilayer composition (Ge and C content). Conduction takes place mainly via Fowler-Nordheim tunneling injection. Ge and C introduce traps in the oxide which assist injection and thus lower the effective height of the tunneling barrier. We have also monitored the oxide reliability, focusing on time-dependent dielectric breakdown (TDDB). The nature of trapped charge in the oxide depends on the initial epilayer composition. We have found that the formation of defects induced by the presence of C leads to extrinsic oxide failure. While the presence of Ge in the oxide does not seem to introduce significant differences with respect to Si breakdown statistics, C in the oxide truly modifies the statistical profile.     

Comparative studies on electronic transport due to the reduced dimensionality at the heterojunctions of GaAs/A1xGa(1−x)As and GaxIn(1−x)As/InP systems at low temperatures

Comparative studies on ac/dc mobility due to the reduced dimensionality of spatially confined low dimensional systems, at the heterojunctions of GaAs/A1_xGa_(1−x)As and Ga_xIn_(1−x)As/InP forming quasi-two dimensional (Q2D) and quasi-one dimensional (Q1D) systems have been made. The effect of various low temperature nonphonon scattering mechanisms such as ionized impurity, alloy disorder scattering and surface roughness scattering mechanisms; and phonon scattering mechanisms such as acoustic phonon via deformation potential and piezoelectric scattering mechanisms on the systems has been studied. It is found that the surface roughness scattering mechanism dominates in Q2D system whereas acoustic phonon scattering mechanism dominates in Q1D system due to which the nature and magnitude of the temperature dependent dc/ac mobility curves shows significant variation. Whereas, it is observed that the confinement does not change the nature of the frequency dependent real and imaginary parts of ac mobility curves. However, the mobility is found to be enhanced with effective mass and also due to the confinement, i.e. the mobility for Q1D system is higher than that for Q2D system.     

X-ray metrology for high-k atomic layer deposited HfxZr1−xO2 films

Hafnium-based dielectrics are the most promising material for SiO₂ replacement in future nodes of CMOS technology. While devices that utilize HfO₂ gate dielectrics suffer from lower carrier mobility and degraded reliability, our group has recently reported improved device characteristics with a modified Hf_xZr_1−xO₂ [R.I. Hegde, D.H. Triyoso, P.J. Tobin, S. Kalpat, M.E. Ramon, H.-H. Tseng, J.K. Schaeffer, E. Luckowski, W.J. Taylor, C.C. Capasso, D.C. Gilmer, M. Moosa, A. Haggag, M. Raymond, D. Roan, J. Nguyen, L.B. La, E. Hebert, R. Cotton, X.-D. Wang, S. Zollner, R. Gregory, D. Werho, R.S. Rai, L. Fonseca, M. Stoker, C. Tracy, B.W. Chan, Y.H. Chiu, B.E. White, Jr., in: Technical Digest - International Electron Devices Meet, vol. 39, 2005, D.H. Triyoso, R.I. Hegde, J.K. Schaeffer, D. Roan, P.J. Tobin, S.B. Samavedam, B.E. White, Jr., R. Gregory, X.-D. Wang, Appl. Phys. Lett. 88 (2006) 222901]. These results have lead to evaluation of X-ray reflectivity (XRR) for monitoring high-k film thickness and control of Zr addition to HfO₂ using measured film density. In addition, a combination of XRR and spectroscopic ellipsometry (SE) is shown to be a fast and non-intrusive method to monitor thickness of interfacial layer between high-k and the Si substrate.     

Zinc diffusion in AlxGa1−xP

We report about Zn diffusion experiments at 700–850°C in (AlGa)P hetero-structures grown by liquid-phase epitaxy. The effective diffusion constant Al_0.35Ga_0.65P is found to be 10–50 times larger than in GaP and has a smaller activation energy. We discuss the implication of this for device work and give a tentative explanation.     

Novel In0.52Al0.48As/In0.53Ga0.47As metamorphic high electron mobility transistors on GaAs substrate with InxGa1−xP graded buffer layers

Compositionally graded In_xGa_1−xP (x=0.48→x=1) metamorphic layers have been grown on GaAs substrate by solid source molecular beam epitaxy using a valved phosphorus cracker cell. Three series of samples were grown to optimize the growth temperature, V/III ratio and grading rate of the buffer layer. X-ray diffraction (XRD) and photoluminescence (PL) were used to characterize the samples. The following results have been obtained: (1) XRD measurement shows that all the samples are nearly fully strain relaxed and the strain relaxation ratio is about 96%; (2) the full-width at half-maximum (FWHM) of the XRD peak shows that the sample grown at 480°C offers better material quality; (3) the grading rate does not influence the FWHM of XRD and PL results; (4) adjustment of the V/III ratio from 10 to 20 improves the FWHM of XRD peak, and the linewidth of PL peak is close to the data obtained for the lattice-matched sample on InP substrate. The optimization of growth conditions will benefit the metamorphic HEMTs grown on GaAs using graded InGaP as buffer layers.     

Determination of the minimum island size for full exciton localization due to thickness fluctuations in Zn1−xCdxSe quantum wells

Fluctuations of the thickness of quantum wells (QWs) of few monolayers are one of the causes of exciton localization. Here, we present the results of the determination of the minimum lateral dimensions of islands produced by thickness fluctuations in Zn_1−xCd_xSe QWs, which cause full exciton localization. We have calculated the localization energy of excitons in the frame of the factorized-envelope approximation. We found that the excitons are well localized in the islands of the QW when their lateral dimensions are larger than ∼15 times the exciton Bohr radius.     

Model generation of the silicon-germanium (Si1−xGex) bipolar inversion channel field effect transistor utilizing a two-dimensional device simulator

The development of an accurate model for an inversion base transistor in the bipolar inversion channel field effect transistor (BICFET) configuration is investigated in this report. Simulations were accomplished through the use of the Medici software, acquired from Avant! Corporation of Sunnyvale, California. This software, which is capable of modeling semiconductor devices comprised of conventional and/or user-defined materials, impurities, structures and operating conditions, was used to develop a model based on experimental device results from Stanford University.     

A high-performance δ-dopedGaAs/InxGa1-xAs pseudomorphic high electronmobility transistor utilizing a graded InxGa1-xAschannel

A δ-doped GaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (HEMT) utilizing a graded In composition InGaAs channel grown by low-pressure metalorganic chemical vapor deposition was demonstrated. This structure had an extrinsic transconductance as high as 175 (245) mS/mm and a saturation current density a high as 500 (690) mA/mm at 300 (77) K for a gate length of 2 μm. The maximum transconductance versus gate bias extended over a broad and flat region of more than 2 V at 300 K. A low gate leakage current (<10 μA at -7 V) at 300 K was obtained     

Electronic properties of Pb1−xHgxSSi heterojunctions

Two types of heterojunctions have been prepared by electroless deposition of Pb_1?xHg_xS (x = 0–0.33) films with α′ and β′ structures on n-type silicon single crystal substrates. Functional behaviour of the forward characteristics is explained on the basis of band to band tunnelling coupled with the recombination processes. The energy band diagram is given for both types of Pb_1?xHg_xS/Si heterojunctions in agreement with the experimental results.