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We present two cases of biopsy‐proven hypertrophic cardiomyopathy (HCM). Both cases showed abnormal electrocardiographic (ECG) findings more than 8 years before diagnosis. A 16‐year‐old healthy male experienced a rescued cardiac arrest. Another male adolescent showed abnormal Q wave and thickened ventricular wall at 15 years old. Retrospective analyses of ECGs performed at 6 years old indicated abnormal ECG findings. However, the diagnosis was normal because no ventricular wall thickening was present in echocardiography. For early diagnosis of HCM to prevent sudden cardiac arrest or death, it is essential to establish ECG and echocardiographic criteria to screen HCM in the young.

We report the case of a 12-year-old girl who developed Guillain-Barré syndrome (GBS) and optic neuritis (ON) following Mycoplasma pneumoniae infection. Her symptoms, including bilateral vision impairment and tingling in her hands and right foot, were resolved after methylprednisolone pulse therapy. Serum anti-galactocerebroside (Gal-C) IgM antibodies were detected in our patient. This is the first report of a child with GBS and ON associated with M. pneumoniae infection.

Stenotrophomonas maltophilia causes pneumonia and CVC-CRBSI in HSCT. However, there are few reports of pyomyositis due to S. maltophilia. We report a patient with CRBSI and pyomyositis due to S. maltophilia after allogeneic HSCT who was successfully treated by removing the CVC and antibiotics without surgical drainage. Removing the CVC and the combined antibiotics without preventing the neutrophil engraftment could avoid surgical drainage in pyomyositis due to S. maltophilia when detected in an early stage.

The early-onset form of carnitine palmitoyltransferase (CPT) II deficiency has severe outcomes; patients typically die during the newborn period. We report a case of neonatal-onset CPT II deficiency with prolonged survival, exceeding 24 months. The patient was successfully treated by continuous hemodialysis (CHD), which enabled her to overcome repeated crises. We suggest that early intensive treatment, including CHD, is a key for prolonged survival in patients with neonatal-onset CPT II deficiency.

We aimed to validate the incidence of, risk factors for, and postoperative outcomes of acute kidney injury (AKI) according to the modified Kidney Disease Improving Global Outcomes (m-KDIGO) criteria and compare this criteria with both the paediatric Risk, Injury, Failure, Loss, End-stage disease (pRIFLE) and Acute Kidney Injury Network (AKIN) criteria in infants after cardiac surgery.We retrospectively enrolled 145 consecutive infants who underwent open-heart surgery at Kagoshima University Hospital.Acute kidney injury was present in 55 (37.9%), 111 (75.9%), and 95 (65.5%) patients according to the m-KDIGO, pRIFLE, and AKIN criteria, respectively. Among these, 71.9% of patients pRIFLE Risk patients and 60.5% of AKIN 1 patients were categorized in the 'no-AKI' group according to the m-KDIGO criteria. Low body weight (m-KDIGO odds ratio [OR], 0.73; P = 0.015; pRIFLE OR, 0.66; P = 0.001; AKIN OR 0.69, P = 0.002) and prolonged cross-clamp time (m-KDIGO OR, 1.02;P = 0.001; pRIFLE OR, 1.02; P = 0.003; AKIN OR, 1.02; P = 0.001) were independent risk factors for the development of AKI. Further, m-KDIGO-based AKI grade was more strongly associated with higher incidence of requiring renal replacement therapy and mortality than both the pRIFLE- and AKIN- based AKI grade.Application of the three criteria resulted in different AKI incidences, but each criterion could be useful for detecting risk factors for AKI. Notably, using m-KDIGO criteria provides more important subsequent postoperative outcomes. The m-KDIGO AKI criteria describe clinically relevant AKI in infants after cardiac surgery.

Background: Few data were available about the QT intervals during nighttime/daytime sleep and daytime activity, and circadian autonomic nerve activities in healthy and LQTS infants. Methods: Holter ECGs were recorded in infants with 12 LQTS infants (2 KCNQ1 , 5 KCNH2 , and 5 not mutation-identified; 12±7 weeks after birth; M/F=6/6) before treatment. Ten age-matched healthy infants (M/F=4/6) were evaluated at the same period (12±3 weeks) and at 40±6 weeks. Three consecutive QT/RR intervals were measured at maximum (max), minimum, and mean heart rates (HRs) at nighttime/daytime and daytime activity and QT intervals were corrected by Bazett’s formula. The power spectral density was computed hourly as low-frequency (LF) and high-frequency (HF) components and was log-transformed. Ln(HF) and the ratio of Ln(LF)/Ln(HF) were used as surrogate markers of para-sympathetic activity and sympathovagal balance, respectively. Results: LQTS infants showed a significantly longer QTc value (490±19 ms) at max HR at nighttime sleep than that (478±20 ms, P =0.008) at max HR in daytime sleep; On the other hand, healthy infants showed no difference in the QTc values between nighttime and daytime sleep in both early and late infantile periods (439 vs 435 in early and 433 vs 423 ms in late infantile periods, respectively). LQTS infants showed a significantly decreased (or premature) parasympathetic than controls during early infancy during nighttime (Figure). In healthy controls, nighttime parasympathetic activity significantly increased at late infancy. QTc values during nighttime sleep was inversely associated with parasympathetic activity ( P =0.002) and positively associated with sympathovagal imbalance ( P Conclusions: In early infantile periods, parasympathetic activity was not fully functioned, especially in LQTS infants. A long QTc values associated with impaired autonomic activity during nighttime sleep is one of risk factors of lethal arrhythmia in LQTS infants.

Cat scratch disease (CSD) is an infectious disease caused by Bartonella henselae. Atypical clinical presentations of CSD include prolonged fever and multiple hepatosplenic lesions. Furthermore, multiple renal lesions are extremely rare in CSD. An 11-year-old Japanese girl presented at our hospital with a prolonged fever of unknown cause after being scratched and bitten by a kitten. Abdominal computed tomography (CT) revealed multiple small, round hypodense lesions in both kidneys and the spleen. Based on her history and the CT results, her diagnosis was CSD. The diagnosis was confirmed by serological tests, which indicated antibodies against B. henselae. After treatment with azithromycin, her fever immediately improved. Careful history taking and imaging are essential for the diagnosis of atypical CSD. In CT images, not only hepatosplenic lesions but also renal lesions are important features indicative of a diagnosis of atypical CSD. Subsequently, a diagnosis of CSD can be confirmed by specific serological tests. This is the first reported Japanese case of multiple renal and splenic lesions in a patient with CSD. Although difficult to diagnose, an early diagnosis atypical CSD and appropriate treatment are important to prevent complications and the need for invasive examinations.

We study the basic mechanism for limiting the maximum operating temperature (Tm) of InP‐based multiple‐quantum‐well (MQW) lasers emitting at a wavelength of 1.3 μm. It is shown that laser operation is characterized in terms of the temperature dependence of threshold gain (gth) by introducing a critical temperature (Tc): gth exhibits a linear relationship with temperature below Tc, while it superlinearly increases with increasing temperature above Tc. This rapid increase in gth leads to a marked increase in threshold current and a significant reduction in differential quantum efficiency above Tc. We indicate that Tc exhibits a direct correlation with Tm: the higher Tc, the higher Tm. In the temperature range above Tc, laser operation moves into a loss‐multiplication regime, where a considerable portion of the injected carriers brings about a significant increase in internal loss rather than gain due to their pileup in the separate confinement heterostructure layers. We demonstrate that an anomalous increas...

By taking into account the temperature dependence of the intrasubband relaxation times for electrons and holes, we study the temperature sensitivity of the optical gain and of the gain saturation coefficient for 1.3‐μm InP‐based strained‐layer (SL) quantum‐well (QW) lasers. The band structures are obtained by the self‐consistent numerical solution of the Poisson equation, the scalar effective‐mass equation for the conduction band, and the multiband effective‐mass equation for the valence band. The intrasubband relaxation times are then calculated within the fully dynamic random phase approximation including carrier‐carrier and carrier‐phonon interactions on an equal basis. We demonstrate that the temperature dependence of the intrasubband relaxation times plays a key role in determining the temperature sensitivity of the optical gain and of the gain saturation coefficient of InP‐based SL‐QW lasers.

We study the electrostatic deformation in the conduction‐band and valence‐band profiles of 1.3‐μm InP‐based strained‐layer (SL) quantum‐well (QW) lasers in the temperature range of 273–373 K. Electrostatic deformation is analyzed by the self‐consistent numerical solution of the Poisson’s equation, the scalar effective‐mass equation for the conduction band, and the multiband effective‐mass equation for the valence band. It is shown that, in InP‐based QWs, electrostatic band‐profile deformation causes a significant change in effective barrier height for the conduction and valence bands, which has a pronounced influence on the electron and hole distribution throughout the whole QW structure in the temperature range studied. We demonstrate that it is necessary to take into account electrostatic deformation in both band profiles for an analysis of the high‐temperature characteristics of InP‐based SL‐QW lasers.

We analyze the strain effects (both compressive and tensile) on the intrasubband scattering rates for electrons and holes in InP‐based strained‐layer quantum‐well (SL‐QW) lasers. Carrier‐carrier and carrier‐LO‐phonon interactions are taken into account on an equal basis within the fully dynamic random phase approximation for multi‐subband structures at finite temperatures. The principal influences of the strain‐induced changes in the valence band structures on the scattering rates are discussed in terms of the changes in the valence‐band density of states and the phonon coupling with holes. We show that the hole‐hole interaction plays a dominant role in determining the hole scattering rates regardless of the carrier energy. On the other hand, for electron scattering rates, the dominant scattering mechanism switches from electron‐hole interaction to electron‐electron interaction as the initial energy of electron increases. We also demonstrate that it is essential to take into account the mutual interaction...

In the framework of envelope function approximation, the dependence on heterointerface boundary conditions of valence‐band dispersion relations in InP‐based quantum‐well structures is investigated. Under conventional boundary conditions, the root‐finding calculation for the eigenvalue problem of quantum well structures is carried out while taking into account a large difference in the effective‐mass parameters (the Luttinger parameters) among the constituting bulk materials. In spite of a decreasing interband mixing between heavy‐ and light‐hole states due to strain and the quantum size effect, hole subband structure of a compressive‐strained quantum well with a narrow well width is found to form an anomalous dispersion curve. It is clarified that the requirement for envelope continuity at interfaces is responsible for anomaly in the dispersion curves through off‐diagonal terms with an additional δ‐function‐like interface potential in the valence‐band effective‐mass Hamiltonian. We present the results of ...

Intrasubband scattering rates are calculated for electrons and holes at finite temperatures in highly excited semiconductor strained-layer quantum-well structures. Carrier-carrier and carrier-phonon interactions are taken into account on an equal basis within the fully dynamic random-phase approximation for multisubband structures. It will be shown that the strain-induced changes in the valence-band structure exert a significant influence on the scattering rates of the electrons as well as the holes. The screening of carrier-phonon interaction by the electron-hole plasma in the coupled electron-hole-phonon system is discussed and analyzed.

Basic design principles are formulated for increasing the differential gain of 1.55 μm InGaAsP/InP compressive‐strained multiple‐quantum‐well (MQW) lasers. An InGaAsP quaternary active layer can provide more freedom of design compared to an InGaAs ternary active layer since the amount of strain and the quantum‐well thickness can be independently determined in an InGaAsP material system for a given emission wavelength. Compressive strain ranging from 1% to 1.5% is large enough to reduce the density of states below one‐third of that of unstrained wells. No further reduction is expected even if more compressive strain is applied. When the well thickness is, in turn, determined, it is essential to incorporate a trade‐off between the conduction and valence subband energy spacings and the squared optical matrix elements. The extra enhancement of differential gain in MQW structures with a modulation p doping is also studied. By designing MQW structures according to these principles, differential gain can be incr...

A Monte Carlo analysis of the Auger-recombination effects in compressively strained quantum-well diode lasers covering a wide range of temperature has been carried out. Contrary to the conventional theory where Boltzmann statistics and parabolic band approximations were assumed, in this work, realistic valence-band structure of strained quantum wells and Fermi-Dirac statistics are employed. The results of calculations show that the temperature sensitivity of the Auger-recombination effect, as opposed to that predicted in the conventional theory, is an acute function of all variables considered: strain, carrier density, and temperature. In particular, it is found that under low carrier density levels or high temperature, the temperature sensitivity of the Auger-recombination coefficient in quantum wells is expected to be low regardless of the detailed structures of the valence subbands. Based on a sensitivity analysis of the Auger-recombination effects with respect to the spin-orbit splitting, it is also found that the temperature dependence of the Auger effects discussed in this report should remain valid within a reasonable range of uncertainty in the value of the spin-orbit splitting.

The current blocking mechanism in InP buried heterostructure (BH) lasers is analyzed with a self‐consistent, two‐dimensional numerical analysis method. It has been clarified that quasi‐Fermi potentials which are kept constant in the active region under lasing oscillation play a key role in determining the current blocking capability. Due to this potential pinning effect, the junction voltages at each constituent p‐n junction in the blocking regions are maintained lower than the electrical turn‐on voltage, which realizes an excellent current blocking in BH lasers.

We study the critical behavior of 1.3 μm InP-based strained-layer (SL) multiple-quantum-well (MQW) lasers at elevated temperatures. We show that, under the critical injection condition where the carrier density in the quantum wells reaches the maximum possible without causing any extra pile-up of carriers in the separate heterostructure confinement regions, an InP-based SL-MQW system exhibits an absorption-to-gain phase transition at some critical temperature (Tc). The characteristic feature of this phase transition shows excellent agreement with Landau theory of second-order phase transitions. It is demonstrated that Tc is a significant and meaningful quantity not only for laser design but also for characterizing the nature of an InP-based SL-MQW system in terms of condensed matter physics.

We study the dominant mechanism for the temperature sensitivity of the differential quantum efficiency and threshold current of 1.3 μm InP‐based strained‐layer multiple‐quantum‐well (MQW) lasers. We show that the temperature dependence of both properties is separated into two regions at critical temperature c). Below c, the temperature dependence of internal loss in the QWs plays a very important role in determining the temperature sensitivity of the differential quantum efficiency. On the other hand, above c, its temperature sensitivity is affected more by the internal loss in the separate confinement heterostructure (SCH) region. Excellent correlation is observed between the spillover of holes into the SCH region and c. It is also shown that the Auger recombination current plays a more significant role in determining the temperature dependence of threshold current below c. However, above c, electrostatic band‐profile deformation, which causes a significant increase in loss and radiative recombination current in the SCH region, plays the more dominant role than the Auger recombination current.

We derive a basic design rule for highly-efficient operation of 1.3-/spl mu/m InP-based strained-layer (SL) multiple-quantum-well (MQW) lasers at elevated temperatures on the basis of a self-consistent numerical approach including the Poisson equation and effective-mass equations. Following the derived design rule, high-efficiency (0.55 W/A at 363 K) and high-power (over 35 mW at 363 K) InP-based SL-MQW lasers have been fabricated. >

We study the temperature sensitivity of the Auger recombination rates in 1.55 μm InP‐based strained‐layer (SL) quantum‐well (QW) lasers on the basis of the band structures obtained by the self‐consistent numerical solution of the Poisson equation, the scalar effective‐mass equation for the conduction band, and the multiband effective mass equation for the valence band. The results of the theoretical analysis are then compared with the recent experimental results to clarify the basic physical mechanism which determines the Auger recombination rates in SL‐QW lasers. It is shown that the recent temperature sensitivity measurements of Auger recombination coefficients can be consistently explained in terms of the direct band‐to‐band Auger process in the quasi‐two‐dimensional system. We demonstrate that the Auger recombination process in 1.55 μm InP‐based SL‐QW lasers is mainly dominated by the direct band‐to‐band Auger process regardless of QW structures in the temperature range of 273–398 K.

High‐temperature operation of InAsP‐based laser diodes at 1.3 μm has been realized according to guidelines of a large conduction‐band‐offset material (ΔEc) with a large optical confinement factor (Γ). Using photoluminescence excitation spectroscopy measurements, it was found that the conduction‐band offset of InAs0.52P0.48P/InGaAsP is the half of the band‐gap energy difference (0.5 ΔEg), which is larger than that of conventional quaternary material systems. A strain‐compensation growth technique enabled the fabrication of a large number of wells for large Γ. For broad‐area laser diodes, the maximum operating temperature increased as the number of wells increased from 4 to 15. In buried heterostructure lasers with ten wells, with high‐reflectivity coating on both facets, continuous‐wave lasing operation at temperatures up to 150 °C was achieved with a characteristic temperature of 59 K (30

The primary mechanism that leads to the suppression of Auger recombination effects in compressively strained quantum wells is found due to the existence and the appropriate positioning of negative‐curvature zones in the first valence subbands (zones in k space where the radial curvature of the first valence subband is negative). By studying previous Monte Carlo calculation results, strong correlations between the negative‐curvature zones and its adverse effects on Auger recombinations are observed, thereby confirming this finding. Through this understanding, it is inferred that compressive strain is most effective for reduction of Auger recombination effects when the amount of strain is no more than 1.0%. Beyond 1.0%, the gain in device performance with respect to more compressive strain is expected to be greatly diminished.

Recent temperature sensitivity measurements of Auger recombination effects in compressively strained quantum‐well structures, which are seemingly inconsistent, are explained in terms of calculation results from a Monte Carlo analysis. In this analysis, realistic valence subband structures obtained using a 4×4 k⋅p method and Fermi–Dirac statistics are employed, where the conduction‐hole‐hole‐splitoff process is also assumed to be the dominant recombination process. It is found that at low carrier density levels and high temperature—often the conditions under which the Auger recombination coefficient is measured—the temperature sensitivity of the Auger recombination coefficient is expected to be low. A qualitative description of this behavior is also given.

The effects of both strain and quantum confinement on the differential gain of strained InGaAsP/InP quantum well lasers (QWLs) are studied on the basis of valence‐band structures calculated by k⋅p theory. Using an InGaAsP quaternary compound as an active layer makes it possible to separate the effect of strain (both tensile and compressive) from the quantum‐confinement effect. In tensile‐strained quantum wells, both strain and quantum‐confinement effects exert a significant influence not only on the valence‐band density of states (DOS) but also on the valence‐subband energy spacings. In compressive‐strained wells, on the other hand, the strain and quantum‐confinement effects play an independent role in determining the DOS and the subband energy spacings, respectively. On the basis of these characteristic features of the valence‐band structure of strained quantum wells, we discuss basic design principles for strained QWLs with larger differential gain.

The gain saturation coefficients of tensile‐strained, lattice‐matched, and compressive‐strained InGaAs/InGaAsP quantum‐well lasers (QWLs) are calculated from intrasubband relaxation times. The intrasubband relaxation times are in turn obtained within the random‐phase approximation including carrier–carrier and carrier–polar‐optical phonon interactions at room temperature. The effects of strain on the band structures are included by taking into account the strain‐dependent coupling among heavy‐hole, light‐hole, and spin‐orbit split‐off subbands on the basis of the multiband effective‐mass theory. It is demonstrated that the gain saturation coefficient in tensile‐strained QWLs is less sensitive to the amount of strain than in compressive‐strained QWLs where it markedly increases with strain.

The possibilities of extreme reduction in the linewidth enhancement factor α and of chirpless operation are theoretically investigated in InGaAs/InGaAsP quantum‐well lasers. First, the condition for lasing operation at the peak of the differential gain spectrum is derived. Lasing characteristics are then calculated taking into account the effects of strain on the valence subband structure. It is shown that by appropriate application of detuning and p‐type modulation doping to a compressive‐strained quantum well, it is possible to reduce the α factor to virtually zero while keeping the laser operating in the region of positive gain.

InP-based strained-layer quantum-well (SL-QW) lasers have become promising devices for various optical communication systems, such as high-speed, long-haul transmission systems and fiber-in-the-loop (FITL) systems [1]. This paper describes a fundamental analysis method for designing high-performance InP-based SL-QW lasers. We formulate basic design principles for minimizing the threshold current density by taking full advantage of the characteristic features of strain-induced changes in the valence-band structures. We also demonstrate that a more advanced numerical approach is crucial for an analysis of the high-temperature characteristics. Finally, we discuss some design rules for integrated SL-QW lasers applied in FITL systems.

InP-based strained-layer quantum-well (SL-QW) lasers have attracted much interest since they are among the most promising light sources for high-speed, long-haul optical transmission system. When designing high-speed lasers, one of the important criteria is to increase the differential gain large enough to overcome the gain saturation because the higher gain saturation is one of the major hurdles limiting the modulation bandwidth of QW lasers [1], [2]. Since the demonstration of the high potential for improving differential gain by the application of strain (both tensile and compressive) [3], extensive studies have been carried out to clarify the effects of strain on the resonance frequency of SL-QW lasers. However, the improvement of the actual modulation bandwidth is not guaranteed at all even if the resonance frequency is increased by the application of strain. This is mainly because the carrier transport, escape and capture processes [4], [5] also play a dominant role in determining the bandwidth as well. To properly evaluate the actual modulation bandwidth, it is necessary to take into account these carrier-transport-related effects as well as the strain effects. In this paper, we analyze the modulation bandwidth of InP-based SL-QW lasers on the basis of the unified formalism which includes both the strain effects and the carrier-transport-related effects. We demonstrate here that both effects compete with each other for determining the modulation bandwidth and that the tensile strain exerts a more pronounced impact on the modulation bandwidth of InP-based SL-QW lasers under the strain-limited situation.

I. Introduction Strained layer quantum well lasers (SL-QWLs) have attracted much interest since the application of band structure engineering [1], [2] can improve lasing properties such as lower threshold currents and larger differential gains. It has been expected that the larger differential gain due to strain can enhance modulation bandwidths of QWLs [3], However, the highest bandwidths found so far are much smaller than expected. One reason for this is that gain saturation also influences the modulation bandwidths of QWLs as well as the differential gain [4], [5]. We have alreiidy shown that the gain saturation coefficient increases with compressive strain in GaAs-based SL-QWLs due to an increase of the intra-subband relaxation times [6]. Recent experimental work has also shown that the gain saturation coefficient increases with compressive strain in InGaAs/InGaAsP SL-QWLs [7]. It is, therefore, necessary to take into account the effects of strain not only on differential gains but also on gain saturation coefficients to properly evaluate the enhancement of modulation bandwidths in SL-QWLs. Strained layer quantum well lasers (SL-QWLs) have attracted much interest since the application of band structure engineering [1], [2] can improve lasing properties such as lower threshold currents and larger differential gains. It has been expected that the larger differential gain due to strain can enhance modulation bandwidths of QWLs [3], However, the highest bandwidths found so far are much smaller than expected. One reason for this is that gain saturation also influences the modulation bandwidths of QWLs as well as the differential gain [4], [5]. We have alreiidy shown that the gain saturation coefficient increases with compressive strain in GaAs-based SL-QWLs due to an increase of the intra-subband relaxation times [6]. Recent experimental work has also shown that the gain saturation coefficient increases with compressive strain in InGaAs/InGaAsP SL-QWLs [7]. It is, therefore, necessary to take into account the effects of strain not only on differential gains but also on gain saturation coefficients to properly evaluate the enhancement of modulation bandwidths in SL-QWLs. The purpose of this paper is to clarify the relationship between gain saturation coefficients and the amount of strain in InP-based SL-QWLs. The gain saturation coefficients of a tensile-strained, a lattice-matched and a compressive-strained InGaAs/InGaAsP quantum well laser are analyzed on the basis of spectral hole burning theory. The intra-subband relaxation times are calculated by taking into account the strain effects within the common framework of carrier-carrier and carrier-phonon interactions. We demonstrate here that the gain saturation coefficient in tensile-strained QWLs remains constant independent of the amount of strain, while it increases with strain in compressive-strained QWLs.

The boost on gain, differential gain and reduction of the linewidth enhancement factor in InGaAs on InP system due to compressive strain have recently been demonstrated theoretically[1-3]. The linewidth enhancement factor a (hereafter termed as the a parameter) is a key parameter in determining wavelength chirping and laser linewidth. Up to now, theoretical studies on strained quantum well(QW) lasers have been limited to lasing characteristics at gain peak, which implies the assumption of Fabri-Perot cavity. On the other hand, distributed feedback(DFB) lasers, which is an indispensable light source in optical transmission system, have the feature where the lasing wavelength can be tuned independent of the gain peak. The application of this feature is called detuning. In this paper, we discuss ways of designing lasers with extremely small a parameter(chirpless lasers) by detuning strained modulation doped(MD) QW lasers.

InGaAsP/InP buried-heterostructure (BH) laser diodes play a significant role in long-haul optical transmission systems. Recent requirements for InGaAsP/InP lasers with light output of more than tens of milliwatts have led to the need for BH structures that have an ultimately low leakage current under high-current operation. Although the current leakage mechanism in conventional BH structures of which buried region consists of p-n-p-n structure has been extensively studied,1 the basic design principles for lowering leakage current under high-current operation have not been clarified yet.

The quantitative relationship between field-effect mobility ( mu /sub FE/) and grain-boundary trap-state density (N/sub t/) in hydrogenated polycrystalline-silicon (poly-Si) MOSFETs is investigated. The focus is on the field-effect mobility in MOSFETs with N/sub t/ 1*10/sup 2/ cm/sup -2/. It is found that reducing N/sub t/ to as low as 5*10/sup 11/ cm/sup -2/ has a great impact on mu /sub FE/. MOSFETs with the N/sub t/ of 4.2*10/sup 11/ cm/sup -2/ show an electron mobility of 185 cm/sup 2//V-s, despite a mean grain size of 0.5 mu m. The three principal factors that determine mu /sub FE/, namely, the low-field mobility, the mobility degradation factor, and the trap-state density N/sub t/ are clarified. >

Magnetron‐sputtered Ta2O5 films on Si are analyzed for their applications to semiconductor devices. It is clarified that the transition region formed at the Ta2O5/Si interface plays a significant role in determining electrical characteristics. This transition region formed during the initial stage of deposition consists of a mixture of Ta, Si, and O, and its thickness is in the range of 4 to 6 nm. The composition profile of this transition region and its thickness depend on two dominant factors: (1) oxygen partial pressure in the sputtering gas and (2) the surface oxide thickness on Si prior to deposition. Furthermore, it is initially indicated that 2.5‐nm‐thick surface oxide formed on Si prior to deposition produces a significant deterioration in leakage current. By reducing the surface oxide thickness to as low as 1.8 nm and adjusting the oxygen partial pressure, an optimum transition region is formed, which makes it possible to obtain high‐quality Ta2O5 films with high dielectric breakdown strength exc...

UV‐stimulated photocurrent spectroscopy and photocurrent transient methods have been used to determine the effects of deposition parameters on the electron trapping level density and its energy distribution in rf‐sputtered Ta2O5 films. Results of this investigation indicate that the electron trapping level density can be greatly reduced by depositing the film at a pressure of 2×10−3 Torr with an rf‐magnetron sputtering system. Experimental results also indicate the presence of the distribution for traps peaked at 2.7 eV below the conduction band in Ta2O5 films sputtered at a pressure of 2×10−3 Torr. A first‐order kinetic model was used to compute trapping parameters (trap density and photoionization cross section). The results of this analysis indicate that the density of the 2.7 eV level is on the order of 4×1015 cm−3, which is three orders of magnitude lower than that for anodic Ta2O5 films, and that the photoionization cross section (at 2.7 eV) is on the order of 10−20 cm2.

The relationship between crystallization processes in the formation of polycrystalline-silicon (poly-Si) films and trap state densities at grain boundaries is described. Three different crystallization techniques were used to obtain poly-Si films: 1) LPCVD, 2) solid-phase crystallization, and 3) laser recrystallization. Trap state densities in laser-recrystallized poly-Si are 9.2-9.6 × 1011cm-2, regardless of grain size. These values are half of those in LPCVD and solid-phase crystallized poly-Si. It is indicated quantitatively that laser-induced melting and the subsequent solidification process exert a significant influence on the electrical activity of silicon grain boundaries.

Leakage current characteristics of offset-gate-structure polycrystalline-silicon (poly-Si) MOSFET's are studied as a function of dopant concentration N off in offset-gate regions. Leakage current markedly decreases from 1 × 10-9to 2 × 10-11A at V D = 10 V as N off is varied from 1 × 1018to 1 × 1017cm-3. A maximum ON/OFF current ratio of 108is obtained at 1 × 1017cm-3. Calculations based on a quasi-two-dimensional model indicate that the reduction of leakage current is attributable to a decrease of the maximum lateral electric field strength in the drain depletion region. An analysis of the leakage current characteristics in terms of carrier emission from grain-boundary traps implies that thermonic emission accompanied by thermally assisted tunneling could be the dominant mechanism in determining leakage current.

La constante dielectrique de Ta 2 O 5 depose sur Si oriente est plus importante que celle de Ta 2 O 5 depose sur Si oriente et . Elle est independante de la resistivite du substrat. La variation est due a la couche de transition a l'interface. L'orientation cristallographique a une influence sur la formation de cette couche

Two-dimensional device simulator of laser diodes has been introduced and its capability for a quantitative device design of 1.3-µm InGaAsP ridge-waveguide lasers has been shown. It has been quantitatively clarified that the current spreading in the cladding layer plays a key role in determining the threshold current. In addition, it is found that the nonradiative recombination exerts a significant influence not only on the threshold current but also on the carrier distribution in the active layer, that is, the lateral gain profile.

Metal-gate thin-film transistors (TFT's) have been fabricated in layers of laser-recrystallized polycrystalline silicon on fused quartz substrates at processing temperatures below 625°C. Tantalum pentoxide (Ta 2 O 5 ) was used as a gate insulator instead of a conventional thermally grown silicon dioxide (SiO 2 ). Ta 2 O 5 gate insulator was deposited onto the recrystallized silicon layer at room temperature, using an RF-magnetron sputtering system. The reactive ion etching method, using CF 4 as a reactive gas, was employed in patterning deposited Ta 2 O 5 . These TFT's have exhibited p-channel depletion-mode characteristics with a threshold voltage of 2.5 V and a transconductance of 70 µS at V g = - 2 V. An on-off current ratio exceeding 105has been obtained.

Etching experiments were performed using a parallel plate, RF reactive ion etching (RIE) system (ANELVA DEM-451M) with a 13.56 MHz RF power supply. The 250 mm diameter electrodes with cathode coupled configuration are separated by 89 mm. The wafers are mounted on the water-cooled cathode during etching. The following fluorocarbon gases were used as etch gases: CF/sub 4/, CF/sub 4//H/sub 2/ (partial pressure ratio of CF/sub 4//H/sub 2/ = 80/20) and CF/sub 4//O/sub 2/ (partial pressure ratio of CF/sub 4//O/sub 2/ = 95/5). The system pressure during etching was controlled to between 10 mTorr and 100 mTorr. Ta/sub 2/O/sub 5/ films were fabricated using an RF magnetron sputtering system. The Ta/sub 2/O/sub 5/ target, which was 10 cm in diameter and 5 mm thick, was used in the sputtering experiments. The sputtering gas consisted of mixtures of argon and oxygen (partial pressure ratio of Ar/O/sub 2/ = 80/20). The wafers were patterned using Shipley AZ 1350 positive photoresist. Thickness measurements were performed with a Taylor-Hobson surface profilimeter. Etch rates for Ta/sub 2/O/sub 5/, SiO/sub 2/, single-crystalline silicon ( oriented, p-type and 1.2 to 1.8 ohm-cm) and Shipley AZ 1350 positive photoresist, and individual etch rate ratios were studied.