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Presents a study that examined the photocapacitance-voltage and current-voltage characteristics of p[sup+]-gallium arsenide/i-alimunum arsenide/n-gallium arsenide heterojunction enhancement mode capacitors. Analysis of the constant illumination of the capacitor; Determination of the constant reverse sweep rate; Evaluation of the frequency dependence of the capacitor.

The capacitance-voltage (C-V) and the current-voltage characteristics of metal/ZnSe/p-GaAs capacitors have been investigated; both epitaxial layers were grown by molecular beam epitaxy. In the capacitor structures highly resistive, stoichiometric ZnSe functioned as the pseudoinsulator on the doped GaAs layers. The capacitance-voltage measurements demonstrated that the capacitors could be biased from accumulation through depletion, and into deep depletion, with current in the range of 10-8 A cm-2. Very little frequency dispersion was observed in the C-V data when measured from 1 kHz to 1 MHz. From the high-frequency C-V curve, the surface state density as a function of position in the GaAs band gap was determined. Surface state densities were comparable to densities reported for (Al,Ga)As/GaAs heterojunctions. [ABSTRACT FROM AUTHOR]

A buried five-period 94 Å Al0.3Ga0.7As/ 56 Å GaAs superlattice is employed to improve the dynamic retention of electrons at an AlGaAs/GaAs heterojunction. The improvement is attributed to the impurity trapping and gettering properties of this superlattice and the amount of time our molecular beam epitaxy system had been closed. Electron retention time constants of 29 s were obtained at a temperature of 77 K. This is more than 200 times longer than previously reported time constants and more than adequate for dynamic logic or memory applications compatible with AlGaAs/GaAs heterojunction field-effect transistors. [ABSTRACT FROM AUTHOR]

We report photosensitive capacitance-voltage characteristics of n+-GaAs/Al0.3Ga0.7As/p-GaAs heterostructures grown by molecular beam epitaxy. Inversion layers are observed due to minority charge retention in the triangular potential well at the AlGaAs/p-GaAs interface. Details of the device structure and experimental evaluation utilizing capacitance-voltage and current-voltage techniques are presented. [ABSTRACT FROM AUTHOR]

We report photocollection efficiency measurements of p+in GaAs/AlAs/GaAs diodes fabricated on films grown by molecular beam epitaxy. Both the zero-bias and bias-dependent photocollection characteristics can be explained by assuming that the band discontinuity between AlAs and GaAs is mostly accommodated in the valence band. [ABSTRACT FROM AUTHOR]

We have studied the capacitance-voltage (CV) and current-voltage (IV) characteristics of molecular beam epitaxially (MBE) grown p+-GaAs/AlAs/n-GaAs heterostructures as a function of illumination level and temperature. Under illumination we find clear evidence of a hole inversion layer at the AlAs/n-GaAs interface at 77 K, with a maximum inversion layer carrier concentration of about 4.1×1011 cm-2. The samples are essentially free of trapping in the AlAs, as indicated by the almost complete lack of hysteresis in the CV curves. At room temperature under steady-state illumination we see both a voltage shift and a peak in the CV curves. The shift is attributed to the formation of an inversion layer, while the peak is believed due to the ac response of space charge flowing through the AlAs. In contrast to recent reports on similar samples grown by metalorganic chemical vapor deposition, the MBE grown samples appear to be suitable for fabricating field-effect devices. [ABSTRACT FROM AUTHOR]

The pathophysiology of endemic goitre caused by excessive iodine intake is not well defined. By interacting with the immune system, iodine excess may trigger the development of autoimmune thyroid disease such as lymphocytic Hashimoto's thyroiditis (LT). In an attempt to examine this further, we compared the presence of thyroid autoantibodies in 29 goitrous children, from an iodine excess area, and in 26 healthy children, from an iodine sufficient area, of north central China. Serum was tested for antimicrosomal (MAb), anti-thyroglobulin (TgAb), second colloid antigen antibodies (CA2-Ab) and TSH binding inhibitory immunoglobulins (TBII). Affinity chromatographically purified IgG was tested for thyroid growth-stimulating activity (TGI) by two different methods: a sensitive cytochemical bioassay (CBA) using guinea-pig thyroid explants and a mitotic arrest assay (MAA) employing a continuous rat thyroid cell line (FRTL-5). We found no increased prevalence of LT in patients with endemic iodine goitre. The levels of MAb, TgAb and CA2-Ab did not differ significantly between the two groups of children. Further, TBII were not present in either group. Thyroid growth-stimulating immunoglobulins (TGI) were the major autoantibodies found in children with goitres caused by iodine excess. In the CBA, 12 of 20 (60%) goitrous children and 0 of 12 (0% P less than 0.05) healthy children were positive for TGI. Similar results were found in the MAA, and a good correlation between results of the CBA and MAA was found (P = 0.003). Maximal TGI activity in dose-response CBA showed a good relation with clinical goitre size (r = 0.63; P less than 0.05) indicating a possible pathophysiological role for these antibodies. We conclude that endemic iodine goitre is not associated with Hashimoto's lymphocytic thyroiditis. Nevertheless, autoimmune growth factors such as TGI may play a primary role in the pathogenesis of thyroid growth in this condition.

Thyroid status was examined in children from two villages in central China where the iodine concentrations in drinking water were 462.5 and 54 micrograms/l. Goitres were present in 65% (n = 120) and 15.4% (n = 51), respectively. All children in both groups were clinically euthyroid and neurologically normal. Growth measurements and intellectual performance were similar in the two groups. Children from the high-iodine village had a lower mean serum triiodothyronine and higher serum free thyroxine and serum thyroid-stimulating hormone concentrations than the children from the control village. 2 cases of overt hypothyroidism were detected in the high-iodine village.