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Laser-assisted doping of intrinsic silicon carbide (SiC) films deposited on Si (100) substrates by pulsed laser deposition (PLD) method and its influence on simultaneous annealing of the thin film is studied. PLD grown intrinsic SiC films are transformed to p-type SiC and n-type SiC, using laser-assisted doping in aqueous aluminum chloride and phosphoric solutions, respectively. Simultaneous doping and annealing of the SiC film are observed during laser-assisted doping. By precisely positioning the selectively doped region, lateral p–n diodes are formed on the SiC films without using any mask. Electric characteristics confirmed the formation of a lateral p–n diode structure. Numerical analysis of temperature distribution along the depth of the SiC films explains the mechanism of simultaneous doping and annealing during the laser treatment.

Currently, low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs), which are characterized by high mobility of electrons, are fabricated by excimer laser annealing. High mobility in low-temperature polycrystalline silicon is achieved by controlling the grain size to approximately 300 nm. However, with future potential growth of active-matrix organic light-emitting diodes in terms of their increasing use as backlight in active matrix micro-LEDs, even higher mobility is required. One of the methods to improve mobility is to produce grains of sizes above 300 nm. However, as far as we know, there are no reports of investigating the dependence between the device characteristics and the grain size of above 300 nm. In this study, we examine the possibility of controlling the grain size above approximately 350 nm by laser annealing with an intensity distribution and investigate the grain size dependence of the TFT characteristics. We show that the grain size can be controlled approximately in the range of 1–2.5 $\mu \text{m}$ , and mobility of 248±28 cm2 V−1s−1 is achieved at a grain size of 2.5 $\mu \text{m}$ . Furthermore, we compare the device characteristics of the step-and-repeat and scan annealing and verify that the device characteristics do not deteriorate even during scan annealing. The study confirms that it is technically possible to produce LTPS with grain sizes controlled in the range of 1–2.5 $\mu \text{m}$ for customizing device characteristics.

We demonstrated that p- and n-type activation layers can be formed in Si films by laser doping with H3PO4 solution and Al2O3 sol coating. The phosphorus and aluminum concentrations at the laser doped region were found to be over 1019 cm-3 in Si films. In addition, generations of the activation carriers for n- and p-type layers were confirmed by Hall effects measurement. In this study, the characteristic of CMOS invertors fabricated by laser doping are presented.

A singlecrystalline diamond (100)(Ib) plate immersed in 2% boric acid was irradiated by 193-nm ArF excimer laser beams for the formation of conductive layers on the surface of an insulating diamond substrate. From current-voltage measurements of the irradiated areas, it was confirmed that semiconducting layers with high conductivities are formed on the diamond surface. It was possible to form ohmic contacts by directly touching tungsten probes with the layer surface. Since Raman spectra exhibited only peaks due to diamond and no peaks due to amorphous carbon, the drastically enhanced conductivity is not attributed to amorphous carbon formation but due to the incorporation of boron atoms into the diamond subsurface from the dopant acid. Secondary ion mass spectrometric depth profile showed the incorporation of boron atoms up to 40 nm depths from the surface. From cathodoluminescence measurements at low temperatures, it was difficult to detect clear peaks for the substitutional incorporation of boron atoms into diamond lattices, which could be attributed to the small thickness of the doped layer for detection. The proposed technique is a new potential method for shallow doping and formation of conductive layers on singlecrystalline diamond surfaces.

Cubic silicon carbide (3C-SiC) films were grown by pulsed laser deposition (PLD) on magnesium oxide [MgO (100)] substrates at a substrate temperature of 800°C. Besides, p-type SiC was prepared by laser assisted doping of Al in the PLD grown intrinsic SiC film. The SiC phases, in the grown thin films, were confirmed by x-ray diffraction (XRD), Si–C bond structure is identified by Fourier-transform infrared spectroscopy spectrum analysis. Measurements based on the XRD and Raman scattering techniques confirmed improvement in crystallization of 3C-SiC thin films with the laser assisted doping. The studies on I–V characteristics by two probe technique, elemental analysis by energy dispersion spectrum, binding energy by x-ray photoelectron spectroscopy and carrier concentration by Hall effect, ensured Al doping in SiC thin film. From the UV–visible NIR spectroscopic analysis, the optical bandgap of the PLD grown 3C-SiC was obtained. Numerical analysis of temperature and carrier concentration distribution is simulated to understand the mechanism of laser assisted doping.

SiO2 nanoporous films has been attracting attention as low-k dielectric constant insulating films. We have succeeded in SiO2 nanoparticles with a particle size of a few nm and depositing a nanoporous film by pulsed laser deposition with controlling the ambient gas pressure. However, the details of the formation process of SiO2 nanoparticles have not been clarified. In this study, we visualized the time-resolved nanoparticle distribution in the gas phase by laser imaging technique to clarify the nanoparticle formation process and to be helpful for optimizing the growth condition of the low-k nanoporous film.

We demonstrate a radiation hydrodynamic simulation of optical vortex pulse-ablated microcone structures on silicon (Si) substrates. Doughnut-shaped craters were formed by single pulse irradiation on the Si substrate, and a twisted cone structure with a height of 3.5 µm was created at the center of the irradiation spot by the circularly polarized optical vortex pulse. A two-dimensional (2-D) radiation hydrodynamic simulation reproduced the cone structure well with a height of 3 µm. The central part of the incident laser power was lowered from the initial profile due to plasma shielding over the laser pulse duration for an inverted double-well laser profile. The acute tip shape of the silicon surface can survive over the laser irradiation period.

One option in enhancing metal-oxide-semiconductor transistor devices is by replacing silicon with high-mobility material of germanium. However, fabrication of Ge np junction faces low dopant activation problem due to the interaction between dopant and defect that was originated from ion implantation, during thermal annealing process results in dopant deactivation. Eventually, series resistance of np junction between source and drain regions will increase and affect the device drive current. Therefore, minimizing junction resistance remains an important issue to be solved. In this work, ultrafast/high temperature excimer laser of KrF was adopted for post-implantation annealing process in order to achieve high activation level. Laser energy fluences and shot numbers were varied between 100–2000 mJ/cm2 and 1–1000 shots, respectively to investigate the influence of laser parameter to the np junction resistance value, surface morphology and recrystallization. It is found that resistance lower than 300 Ω can be obtained when annealing the substrate between 500–1000 mJ/cm2 with shot number up to two. Taking into consideration on the morphological and structural analyses leads to the conclusion that an optimum parameter for LTA in the sample implanted with phosphorus at higher energy/dose concentration of 40 keV/6.0×1014 cm−2 is 700 mJ/cm2, with shot number of two.

Selective laser annealing system was developed to realize fabrications of low-temperature poly-Si thin-film transistors (TFTs) even for large substrate, while the conventional excimer laser annealing system has the limitation in substrate size due to the difficulty in obtaining uniform beam line. In this paper, this new system was applied to fabricate poly-Si TFTs, using two laser exposure methods such as the static exposure and the scan exposure. Grain size increased as the laser energy density increased, and TFTs with the field-effect mobility larger than 100 cm2V−1s−1 with the ON– OFF ratio of drain current of approximately 106 could be obtained. Furthermore, for the scan exposure, periodic grain structure was observed resulting from the lateral solidification. In this condition, variations of electrical properties of TFT could be reduced compared to the case of the static exposure.

Impact of laser doping on the formation of ohmic contacts to 4H-SiC has been investigated. The laser doping was performed by irradiating pulse-width stretched KrF excimer laser to an Al film coated on the surface of 4H-SiC. Doping and contact formation on the carbon face of 4H-SiC were investigated. The doping was carried out while keeping the sample at room temperature. It is found that the laser doping is able to introduce Al up to a concentration as high as 5×1021 cm-3. As a result of heavy doping, the contact made of Ti/Al metallization provides the ohmic contact whose specific contact resistance as low as 4.0×10-6 Ωcm2 without additional heat treatment. The specific contact resistance is lower than that reported for ohmic contacts formed by using ion implantation.

We have succeeded in synthesizing zinc oxide (ZnO) microspherical crystals and Silicon microspheres by a simple laser ablation technique in air, and demonstrated whispering-gallery-mode (WGM) lasing from optically-pumped ZnO microsphere. ZnO/MgO alloy microspheres were also successfully fabricated, and blue-shift of WGM lasing wavelength was achieved. Recently, size-controlled and on-demand fabrication of semiconductor microspheres by introducing of an optical vortex beam.

Higher carrier mobility in germanium has made germanium as a favorable candidate to replace silicon as a device substrate for a high-performance device. Further optimization on fabrication process parameters in germanium involving ion-implantation and thermal annealing is important to form a highly activated np junction. Co-implantation technique has prompted interest due to its reported stress-induced activation; which may be due to the implementation of two atoms different in size. Combining with ultra-fast/high temperature of laser thermal annealing may promotes the improvement in activation and damage removal. This works focused on introducing stress to the germanium substrate through co-implantation of dopant ions, follows by laser thermal annealing to activate and remove the implanted damages. It is found that Raman shift of the annealed co-implanted sample can be observed with 0.2% increase in the strain value, when comparing to the single implanted sample. 12% improvement of sheet resistance can also be observed, which may be related due to the increase in stress.

In this paper, we report on super low temperature doping of phosphorus to poly-Si thin films using XeF excimer laser irradiation in a phosphoric acid solution. In this method, the implantation of P atoms and dopant activation can be performed simultaneously. We prepared poly-Si films with a thickness of 50 nm, and these films were crystallized using XeF excimer laser annealing. After laser doping, the concentration of P atoms in the poly-Si films was approximately 3.5 × 1018 cm−3, and the resistance of the poly-Si films decreased by approximately 0.003 times as compared with that before laser doping.

Germanium (Ge) is a potential candidates to replace silicon (Si) due to its higher carrier mobility, which is the key point for realizing device high-drive-current. However, fabricating highly activated np junction in Ge is challenging due to the severe damages introduced from ion-implantation interact with dopant during subsequent annealing process, and results in dopant deactivation. Further optimization of fabrication process parameters is needed to overcome this problem. Co-implantation technique has gained attention due to its stress-induced carrier activation by implanting two atoms with different size. Combining with laser thermal annealing promise further improvement in activation and recrystallization. In this work, co-implantation of phosphorus (P) and tin (Sn) were performed, followed by KrF laser thermal annealing, to form an np junction in Ge. Laser fluence was varied to achieve np junction with higher activation and recrystallization. It is found that high degree of recrystallization was obtained in higher-fluence annealed sample, with 40% decrease of sheet resistance compare to those of lower-fluence annealed sample. Raman peak shift (≈ 3.5 cm−1) was also observed in the higher-fluence annealed sample, suggesting increase of localized strain in the sample.

Silicon carbide (SiC) is a promising semiconductor for high-power devices due to its superior material properties; high breakdown field, high electron saturation velocity, and high thermal conductivity. To implement SiC power devices, pn junction must be formed in the SiC. However, ion implantation for impurity doping has several issues for the SiC. For example, while a high-temperature (~1700 °C) post-implantation annealing is required to electrically activate implanted species [, it induces generation of crystallographic defects in the SiC, such as segregation of carbon atoms at the surface from the SiC bulk [. Therefore, development of new technology for local doping of SiC is highly demanded.

We have proposed a novel method of low-temperature nitrogen doping into 4H-SiC(0001) induced by KrF excimer laser irradiation to a SiNx film. The SiNx film with a thickness of 100 nm was deposited on an n-type 4H-SiC(0001) substrate by chemical vapor deposition. Laser beam size on the sample surface was 300 μm×300 μm. Irradiation fluence was 1.0 J/cm2-4.0 J/cm2, and the number of shots was from 1 shot to 30 shots. Laser irradiation was performed in a vacuum chamber to avoid oxidation of the SiC surface. High concentration nitrogen doping (~1×1021 /cm3 at the surface) and very low contact resistance with ohmic I-V characteristics can be achieved by laser ablation of the SiNx film. In the case of laser irradiation at the fluence of 2.0 J/cm2, the SiNx film was almost ablated without laser ablation of the SiC substrate. Then, excellent ohmic contact characteristics was obtained at the irradiation number of 5 shots, and it was hardly deteriorated up to 30 shots. In the case of irradiation fluence above 3.0 J/cm2, ablation of the SiC substrates was induced and ohmic contact characteristics were deteriorated with increasing the number of shots. From these results, we conclude that excellent ohmic contact characteristics without irradiation damage to SiC substrates can be obtained in a stable.

Observation of graphene growing process on SiC(0001) step and terrace structure formed by direct laser patterning is proposed. We have proposed a novel method of direct growth of patterned graphene on SiC(0001) surfaces using KrF excimer-laser irradiation. KrF excimer-laser with a wavelength of 248 nm and a duration of 55 ns was used to graphene forming in this study. Laser irradiation was achieved with various laser fluenece. Grain size and number of layers of the graphene was varied by laser irradiation condition. Through conductive atomic force microscopy, it was observed that graphene grain expanded from (112 _ n) faced step area to (0001) faced terrace area in initial graphene growth process. From the result of the Raman spectroscopy, transmission electron microscopy and Conductive AFM, we summarized graphene growth process on SiC(0001) surfaces.

Preparation of lithium niobate thin-film on silicon is demonstrated. The process employed is composed of mechanical thinning of the lithium niobate and bonding by using laser irradiation to the face-to-face interface of the two materials. The process is performed in the ambient air while keeping the wafers at room temperature.

We examined the formation of pn-junction didoes on Ge(100), Ge(110), and Ge(111) substrates by P-doping with immersion laser irradiation in phosphoric acid solution at RT. We achieved high-concentration phosphorus doping in all orientation, and the maximum concentrations of electrically activated P of 2.4×1019, 5.1×1019, and 9.8×1019 cm−3 for the Ge(100), Ge(110), and Ge(111) substrates, respectively, are obtained with 1000-times laser shots. On the other hand, the diffusion depth is significantly different with the orientation, which concerned with the melt depth.

We proposed CO2 laser doping technique as a fabrication method of c-Si solar cell, and demonstrated its availabilities with the cell characteristics. P and B-doping with relatively high carrier density around 1020 cm−3 were realized by the CO2 laser irradiation. We found that the pulse frequency is one of the most important parameter to improve the cell performances.

The formation of perhydropolysilazane (PHPS)-based SiO2 films by CO2 laser annealing is proposed. Irradiation with a CO2 laser with optimum fluence transformed a prebaked PHPS film into a SiO2 film with uniform composition in the thickness direction. Polycrystalline silicon thin-film transistors (poly-Si TFTs) with a SiO2 film as the gate insulator were fabricated. When the SiO2 film was formed by CO2 laser annealing (CO2LA) at the optimum fluence of 20 mJ/cm2, the film had fewer OH groups which was one-twentieth that of the furnace annealed PHPS film and one-hundredth that of the SiO2 film deposited by plasma-enhanced chemical vapor deposition (PECVD) using tetraethyl orthosilicate (TEOS). The resulting TFTs using PHPS showed a clear transistor operation with a field-effect mobility of 37.9 ? 1.2 cm2 V?1 s?1, a threshold voltage of 9.8 ? 0.2 V, and a subthreshold swing of 0.76 ? 0.02 V/decade. The characteristics of such TFTs were as good as those of a poly-Si TFT with a SiO2 gate insulator prepared by PECVD using TEOS.

Thionamides have various side effects.The effectiveness of potassium iodide (KI) was evaluated in hyperthyroid patients who experienced side effects to thionamides.An observational study was conducted at an academic medical center.Among 1388 patients with Graves' hyperthyroidism treated with thionamides, 204 (14.7%) exhibited side effects, and 44 were treated with KI and followed for 17.6 (median; range, 8.6-28.4) years.The primary endpoint was the initial response to KI, and the secondary endpoint was the long-term prognosis.The conditions of 29 (65.9%) of the 44 patients were well controlled with KI alone (10-400 mg/d) (A group), and 17 (38.6%) patients went into remission after 7.4 (1.9-23.0) years. The conditions of 15 (34.1%) patients were not controlled with KI alone (B group), even at a high dose (100-750 mg/d), but seven patients (15.9%) were controlled with a combination of KI and low-dose thionamides, resulting in remission after 7.2 (2.8-10.8) years. The initial parameters did not predict the response to KI or long-term prognosis. However, remission occurred in 70.8% of the patients treated with less than 200 mg of KI, compared with 35.0% of the patients who required 200 mg or more of KI (P.05).Among hyperthyroid patients with thionamide-associated side effects, KI therapy was effective in two-thirds of cases, and about 40% of the patients experienced remission after KI therapy alone. The chance of remission was small among the patients refractory to KI.

We have demonstrated that fabrication of the ZnO nanowire/GaN hetero-junction light emitting diode (LED) by contacting the tip of the ZnO nanowires with the GaN film, and UV electroluminescence from the p-n junction. In this study, we fabricated the heterojunction by directly-growth of the ZnO nanowires on the GaN film using nanoparticleassisted pulsed laser deposition. Photoluminescence spectrum of the ZnO nanowires showed a weak near-band-edge ultraviolet (UV) emission and a visible broad emission, which was related to transition by ZnO defect state. We applied a selective laser irradiation to the p-n junction of the ZnO-based LED. The UV emission was strongly enhanced from the laser-irradiated p-n junction.

In this report, we extend our investigation to characterization of junctions produced by the excimer laser irradiation to 4H-SiC immersed in phosphoric acid.

In this paper, we introduce a bonding method in ambient air using laser irradiation to the face-to-face interface of dissimilar materials. This method is performed while keeping whole wafers of the materials at room temperature. We demonstrate the bonding of LiNbO3 to Si using pulsed nanosecond green laser irradiation. Laser use can minimize thermal stress owing to a large thermal expansion mismatch. The bonding characteristic obtained by an irradiation laser up to 2.5 J/cm2 in fluence is investigated. It is found that a LiNbO3 chip is strongly bonded to a Si chip by setting the laser fluence at the optimum range. A bond strength of over 2 MPa, which may be enough for the device applications, can be obtained.

We propose a low-temperature laser annealing method of a underwater laser annealing (WLA) for polycrystalline silicon (poly-Si) films. We performed crystallization to poly-Si films by laser irradiation in flowing deionized-water where KrF excimer laser was used for annealing. We demonstrated that the maximum value of maximum grain size of WLA samples was 1.5 μm, and that of the average grain size was 2.8 times larger than that of conventional laser annealing in air (LA) samples. Moreover, WLA forms poly-Si films which show lower conductivity and larger carrier life time attributed to fewer electrical defects as compared to LA poly-Si films.

Direct patterning of Si films is one of promising methods for TFT display fabrication to achieve low cost. We have proposed laser direct patterning of Si films by Ag-induced layer exchange. In this method, an Ag film was deposited for middle layer between an a-Si film and a substrate. Next, pulsed laser was locally irradiated to the Si/Ag film, and the Ag film was segregated to Si film surface. After that, the Ag film at irradiation area and the Ag film of middle layer at non-irradiation area were etched off by nitric acid treatment. In the result, direct patterning of Si thin films can be achieved at laser irradiation area. Moreover, in order to observe segregation behavior of Ag to Si surface, CW laser was coaxially inserted to surface with the pulsed laser, and reflective intensity of the CW laser was measured by Si-photo detector.

Recovery of thyroid function in patients with both thyroid and renal dysfunction was studied. Among 245 patients with primary hypothyroidism (serum TSH greater than 10 mU/l), 36 had mild to severe renal dysfunction (serum urea nitrogen greater than 7.1 mmol/l and creatinine greater than 106 mumol/l). Of these 36 patients, recovery of the thyroid function after iodine restriction was observed in 30 (83%), in whom an elevated serum non-hormonal iodine level (median 236, range 67-15,591 micrograms/l, N = 19) and a high thyroidal radioactive iodine uptake (51.5 +/- 29.3% at 24 h, N = 26) were observed. The perchlorate discharge test was positive in 7 of 13 patients examined, suggesting an iodide organification defect rather than an atrophic or destructive change in the thyroid. Antithyroid antibodies were negative in 22 patients (73%) and an almost normal thyroid gland or colloid goitre was confirmed histologically in 8 of them. After a 13.2 mg potassium iodide loading test, 24 h urinary excretion of iodine was about 60% in normal controls, but only 10% in a different group of six euthyroid patients with renal dysfunction. These findings suggest that impaired renal handling of iodine rather than autoimmune mechanism may have a significant role in the pathogenesis of reversible hypothyroidism found in patients with renal dysfunction, probably through a prolonged Wolff-Chaikoff effect.

We have investigated phosphorus (P) doping into Ge(001) surfaces by using ultraviolet laser irradiation in phosphoric acid solution at room temperature. We demonstrated that the diffusion depth of P in Ge and the concentration of electrically activated P can be controlled by the number of laser shots. Indeed, a high concentration of electrically activated P of 2.4 × 1019 cm−3 was realized by 1000-times laser shots at a laser energy of 1.0 J/cm2, which is comparable or better than the counterparts of conventional n-type doping using a high thermal budget over 600 °C. The generation current is dominant in the reverse bias condition for the laser-doped pn-junction diodes independent on the number of laser shots, thus indicating low-damage during the pn-junction formation. These results open up the possibility for applicable low thermal budget doping process for Ge-based devices fabricated on flexible substrates as well as Si electronics.

Catalyst-free growth of one-dimensional zinc oxide (ZnO) nanowires is reported. ZnO nanowires were synthesized on ZnO buffer layers deposited on various-oriented sapphire substrates. Syntheses of ZnO buffer layers and nanowires were performed by ultraviolet pulsed-laser deposition. ZnO nanowire's number density was the lowest in the case of using m-cut sapphire substrates. ZnO nanowires grown on a-cut sapphire substrates had vertical alignment with distances of tens to hundreds of nanometers. On the other hand, ZnO nanowires grown on c-cut sapphire substrates had the biggest nucleation rate. The dependence of crystalline orientation of ZnO buffer layers on the orientation of sapphire substrates were investigated by electron back scatter diffraction measurement. From their results, the growth models of ZnO buffer layers were suggested and the variations in morphological properties of ZnO nanowires were discussed.

To realize next-generation flexible thin-film devices, solid-phase crystallization (SPC) of amorphous germanium tin (GeSn) films on insulating substrates combined with seeds formed by laser annealing (LA) has been investigated. This technique enables the crystallization of GeSn at controlled positions at low temperature (∼180 °C) due to the determination of the starting points of crystallization by LA seeding and Sn-induced SPC enhancement. The GeSn crystals grown by SPC from LA seeds showed abnormal lateral profiles of substitutional Sn concentration. These lateral profiles are caused by the annealing time after crystallization being a function of distance from the LA seeds. This observation of a post-annealing effect also indicates that GeSn with a substitutional Sn concentration of up to ∼10% possesses high thermal stability. These results will facilitate the fabrication of next-generation thin-film devices on flexible plastic substrates with low softening temperatures (∼250 °C).

We report nitrogen (N) doping of 4H-SiC by KrF excimer laser irradiation in liquid N2. In comparison to phosphorus (P) doping performed using phosphoric acid solution, the laser N doping can introduce N atoms deeper (~1 µm depth) into the 4H-SiC, which results in reduction of doped layer resistance by approximately 3 orders of magnitude. Doping is shown to proceed by the thermal diffusion of species, while loss of the host material from the surface by ablation takes place at the same time. Chemical analysis shows that high density carbon (C) vacancies are generated in the N doped region, which suggests enhanced diffusion of N assisted by the presence of C vacancies. pn junction diodes are formed by using the N doping technique. Turn-on voltage is ~−3 V, which is reasonable for a pn junction diode of 4H-SiC.

We have found that aluminum doping into 4H-SiC is performed by irradiating excimer laser light to 4H-SiC immersed in aluminum chloride solution. Aluminum is introduced in SiC at the concentration of over 1 ? 1020 cm?3 near the surface while, chlorine hardly diffuses into 4H-SiC. After the laser irradiation in aluminum chloride solution, the resistance of the laser-irradiated region decreases with increasing laser fluence. Hall effect measurement shows that the laser irradiation produces a p-type layer and that its sheet carrier concentration is 2.14 ? 1011 cm?2. In addition, we produce a pn junction by doping the surface of n-type 4H-SiC and by aluminum doping. The pn junction shows rectifying characteristics whose on/off ratio is about 7 decades and ideality factor is 1.15. This technique is one of the strong candidate local doping techniques for SiC.

We investigate Sn incorporation effects on the growth characteristics of Ge-rich Ge1−xSnx (x

We developed a method to dope phosphorus into 4H-SiC by irradiating excimer laser light to 4H-SiC immersed in phosphoric acid solution. A KrF excimer laser was used. The surface is slightly ablated by the laser irradiation. However, no amorphous layer is generated near the surface. Phosphorous is introduced at a concentration of over 1020 cm-3 near the crystal surface. The laser irradiation in phosphoric acid solution significantly improves the ohmic contact characteristic between metal and 4H-SiC. Hall effect measurement shows that the irradiation produces an n-type layer at the surface whose sheet carrier concentration is 2.25×1012 cm-2. In addition, we produce a pn junction by irradiating p-type 4H-SiC. The pn junction shows a rectifying characteristic whose on/off ratio is over 8 decades and ideality factor is 1.06.

OBJECTIVE Spontaneous improvement occurs in about one-half of patients with primary hypothyroidism who reside in an iodine-sufficient area of Japan, but the pathogenetic factors related to reversible hypothyroidism are still not fully understood. We therefore investigated the clinical features and prognosis of patients with reversible hypothyroidism with or without iodine excess and antithyroid antibodies. DESIGN Amelioration of hypothyroidism was diagnosed when the elevated serum TSH concentrations (serum TSH concentration > or = 40 mU/l) decreased by 50% or more during an iodine restriction period of 2-15 weeks without replacement therapy. Reversible hypothyroidism occurred in a post-partum group (n = 20) and a non-post-partum group (n = 91). The latter was then further classified into chemical (n = 28), immunological (n = 20), and mixed (n = 43) groups, according to the presence of iodine excess (serum non-hormonal iodine level > 50 micrograms/l or a history of excess iodine ingestion), antithyroid autoantibody, or both, respectively. MEASUREMENTS Clinical characteristics and long-term prognosis were compared among the four groups. The rate at which hypothyroidism recovered was expressed as the number of days required for a 50% decrease in the serum TSH concentration. The level of thyroid echogenicity was measured by 10-MHz ultrasonography. RESULTS In the chemical group, the mean age, male:female ratio, and serum non-hormonal iodine concentrations were all higher than those in the immunological group. The estimated rate at which hypothyroidism recovered was rapid (6.1 +/- 3.1 (mean +/- SD) days), the levels of thyroid echogenicity were near normal, and a histological examination (n = 7) revealed either colloid goitre or a normal thyroid in the chemical group. In the immunological and post-partum groups, the recovery rate was slow (16.8 +/- 9.6 days and 16.2 +/- 5.8 days, respectively). The levels of thyroid echogenicity were markedly reduced but increased after the spontaneous recovery of the thyroid function in both groups. Aspiration cytology suggested lymphocytic infiltration in all patients examined in the immunological (n = 6) and post-partum groups (n = 4). Relapse to overt hypothyroidism was observed more frequently in the immunological (38%) and mixed groups (35%) than in the chemical group (5%). CONCLUSION Thyroid damage was more severe, recovery slower and the rate of relapse higher in the immunological than in the chemical type of reversible hypothyroidism.

Phosphorus doping of 4H SiC is performed by KrF excimer laser irradiation of 4H SiC immersed in phosphoric acid. Phosphorus is incorporated to a depth of a few tens of nanometers at a concentration of over 1020/cm3 without generating significant crystal defects. Formation of a pn junction diode with an ideality factor of 1.06 is demonstrated.

Okamura K, Sato K, Ikenoue H, Nakagawa M, Kuroda T, Yoshinari M, Fujishima M. Primary hypothyroidism manifested in childhood with special reference to various types of reversible hypothyroidism. Eur J Endocrinol 1994;131:131–7. ISSN 0804–4643 The clinical courses of 15 patients with overt primary hypothyroidism manifested in childhood were studied. Nine female patients with goitrous hypothyroidism due to chronic thyroiditis showed almost normal height and became euthyroid spontaneously during iodine restriction. The other 6 non-goitrous patients (3M and 3F) (atrophic thyroiditis in 2, lingual goiter in 2 and probable hypoplastic thyroid in 2) showed physical growth retardation and remained irreversibly hypothyroid requiring replacement therapy. In the reversible group, the characteristic findings were high thyroidal radio-active iodine uptake (58 ± 19%/24 h, N = 8) and positive perchlorate discharge test. Serum non-hormonal iodine levels were high in 4 of 6 patients measured. During the long-term follow-up period of 6 years in 6 patients, 2 patients remained euthyroid with normal growth and regular menstrual cycle and 4 patients became hypothyroid again (after eating seaweed in 1, despite iodine restriction in 2 and after the episode of painless thyroiditis in 1). Transient retardation of growth was observed during the second episode of hypothyroidism. In the irreversible group, one patient with blocking type TSH binding inhibitor immunoglobulin (TBII) became thyrotoxic 4 years later with the decrease in activity of blocking type TBII. These results suggested that reversible recovery of the thyroid function could be expected in patients with juvenile hypothyroidism due to chronic thyroiditis after (1) iodine restriction, (2) improvement of immunological perturbation, or (3) disappearance of blocking type TBII. However, careful follow-up is necessary, because hypothyroidism would recur again with transient retardation of growth in children. Ken Okamura, Second Department of Internal Medicine, Faculty of Medicine, Kyushu University, 3-1-1 Maidashi, Higashiku, Fukuoka 812, Japan

The effect of protease inhibitors, leupeptin and pepstatin A, on the metabolism of acetylated low density lipoprotein (acetyl-LDL) was investigated in cultured rat peritoneal macrophages and compared with that of chloroquine. While both leupeptin and pepstatin inhibited the proteolytic degradation of 125I-acetyl-LDL, a combination of both showed an additive effect. Similar to chloroquine, both protease inhibitors diminished [3H] oleate incorporation into cellular cholesteryl[3H] oleate and increased cholesterol content of macrophages. These results suggest that both thiol protease and cathepsin D participate in the physiological degradation of apolipoprotein in macrophages. The inhibition of apolipoprotein degradation seemed to have an effect on cholesterol metabolism in macrophages cultured with acetyl-LDL.

We observed local electrical properties of polycrystalline silicon films by conductive atomic force microscopy. Moreover, we investigated the effects of hydrogen termination on the polycrystalline silicon films. Before hydrogen termination, conductive regions in grain disappeared with the repeated scanning of the cantilever, while conductive regions in grain boundary almost unchanged. It is considered that hopping conduction is a major electrical conduction mechanism at grain boundaries. After 5 min hydrogen termination, locally nonterminated regions were observed near grain boundaries. This suggests that hydrogen termination of the polycrystalline silicon does not randomly progress, and there are regions that cannot be easily inactivated near grain boundaries.

The clinical significance of the thyroidal radioactive iodine uptake (RAIU) test was reevaluated in patients with various thyroid disorders. Compared with 262 normal subjects or 194 patients with euthyroid diffuse goiter with normal serum TSH levels, RAIU values were significantly higher in 100 patients with latent primary hypothyroidism (serum TSH, 5-40 mU/L). In 126 patients with overt primary hypothyroidism (serum TSH, greater than 40 mU/L), RAIU values were either extremely high (49 patients with reversible hypothyroidism and 10 patients with postpartum hypothyroidism) or low (67 patients with irreversible hypothyroidism). The increase in RAIU values in latent, or reversible overt hypothyroidism was TSH dependent, and there was a good correlation between RAIU values and serum TSH levels (r = 0.6203; P less than 0.001). In overt primary hypothyroidism, spontaneous recovery of thyroid function during iodide restriction alone occurred in 52 of 53 patients with RAIU values above 35%, in only 7 of 23 patients with RAIU values between 10-35%, and in none of 50 patients with RAIU below 10%. Thus, recovery was predicted by high RAIU values (P less than 0.001; prediction rate, 91.4%). Goiter was found in about 80% of the patients with reversible hypothyroidism, compared with only 34% of the patients with irreversible hypothyroidism. Recovery of thyroid function during iodide restriction also occurred in 71% of the patients with latent hypothyroidism. However, RAIU measurements did not predict the prognosis of patients with latent hypothyroidism. We conclude that iodine-induced reversible hypothyroidism is common in our patient population, and RAIU measurements may be helpful in determining the prognosis of patients with overt primary hypothyroidism.

Iodination of tyrosyl residues in thyroglobulin is one of the essential steps of biosynthesis of thyroid hormones. In 1944, Dempsy demonstrated a peroxidase in the thyroid histochemically (1). Since then, the study concerned with thyroid hormone production has progressed greatly. So far, evidence has been provided, indicating that thyroid peroxidase is the key enzyme for iodide organification in the thyroid. Subsequently, it was also demonstrated that the process of thyroid hormone synthesis involves hydrogen peroxide.