Abstraci-Position and speed sensorless drive of a brushless dc motor is presented which provide high-qiiality torque control. Rotor position and speed informations are obtained by using a current difference between a model and an actual motor. The current difference is decomposed into two components. One is used for estimation of position and another for estimation of speed. Therefore, independent estimation is possible. Exprrimental rrsults based on the proposed algorithm are presented which demonstrate desired control characteristics both in steady state and starting conditions.

The growth characteristics of thick (100) CdTe epitaxial layers of a thickness up to 200 µm on a (100) GaAs substrate in a metal-organic vapor-phase epitaxy (MOVPE) system and fabrication of CdTe/n ϩ -GaAs heterojunction diodes for their possible applications in low-energy x-ray imaging detectors are reported. The grown epilayers were of high structural quality as revealed from the x-ray double-crystal rocking curve (DCRC) analysis, where the full-width at half-maximum (FWHM) values of the (400) diffraction peaks was between 50 arcsec and 70 arcsec. The 4.2-K photoluminescence (PL) showed high-intensity bound-excitonic emission and very small defect-related peaks. The heterojunction diode fabricated had a good rectification property with a low value of reverse-bias current. The x-ray detection capability of the diode was examined by the time-of-flight (TOF) measurement, where good bias-dependent photoresponse was observed, but no carrier transport property could be deduced. It was found that the CdTe layer has a large number of trapping states as attributed to the cadmium-related vacancy and Ga-impurity, diffused from the substrate, related defect complexes.

Direct growth of high-quality, thick CdTe (211) epilayers, with thickness up to 100 mm, on Si (211) substrates in a vertical metalorganic vapor phase epitaxy system is reported. In order to obtain homo-orientation growth on Si substrates, pretreatment of the substrates was carried out in a separate chamber by annealing them together with pieces of GaAs at 800-900°C in a hydrogen environment. Grown epilayers had very good substrate adhesion. The full-width at half-maximum (FWHM) value of the x-ray double-crystal rocking curve from the CdTe (422) reflection decreased rapidly with increasing layer thickness and remained between 140-200 arcsec for layers .18 mm. Photoluminescence measurement at 4.2 K showed high-intensity, bound excitonic emission and very small defect-related deep emissions, indicating the high crystalline quality of the grown layers. Furthermore, a CdTe/n 1 -Si heterojunction diode was fabricated that exhibited clear rectifying behavior.

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Iodine is a useful n-type dopant for CdTe and HgCdTe layers grown by metal-organic vapor phase epitaxy (MOVPE) and molecular beam epitaxy because iodine is expected to have a lower diffusion coefficient compared to group III elements. 1-6 For MOVPE, ethyliodine (EI) is an especially important iodine source because EI has a higher vapor pressure than isopropyliodine and group III metal-organic dopant sources. This enables the achievement of excellent controllability of doping over a wide range without suffering the problem of memory effect. 5 We have studied the iodine doping of CdTe layers grown on GaAs substrates. However, the maximum electron density of as-grown layers has been limited to around 10 17 cm Ϫ3 . The doping condition to obtain higher electron density has not yet been clarified. The n-type CdTe layers with high electron density and low resistivity are considered to be useful for applications in not only infrared detectors but also x-ray and ␥-ray detectors and solar cells.In this paper, we report the doping characteristics of iodine in CdTe layers grown by MOVPE using dimethylcadmium (DMCd), diethyltelluride (DETe), and diisopropyltelluride (DiPTe) as precursors. Doping characteristics were studied using EI in a wide range of growth conditions. Higher electron densities were obtained for layers grown with DETe than those grown with DiPTe. A doping condition for layers with a high electron density of 2.8 ϫ 10 18 cm Ϫ3 was also obtained with DETe. Mechanisms for different doping characteristics between DETe and DiPTe were studied on the basis of observed growth characteristics for these precursors.Iodine doping of CdTe layers grown on (100) GaAs by metal-organic vapor phase epitaxy (MOVPE) was studied using diethyltelluride (DETe) and diisopropyltelluride (DiPTe) as tellurium precursors and ethyliodine (EI) as a dopant. Electron densities of doped layers increased gradually with decreasing the growth temperature from 425°C to 325°C. Doped layers grown with DETe had higher electron densities than those grown with DiPTe. When the hot-wall temperature was increased from 200°C to 250°C at the growth temperature of 325°C, doped layers grown with DETe showed an increase of the electron density from 3.7 ϫ 10 16 cm Ϫ3 to 2.6 ϫ 10 18 cm Ϫ3 . On the other hand, such an increase of the electron density was not observed for layers grown with DiPTe. The mechanisms for different doping properties for DETe and DiPTe were studied on the basis of the growth characteristics for these precursors. Higher thermal stability of DETe than that of DiPTe was considered to cause the difference of doping properties. With increasing the hot-wall temperature from 200°C to 250°C, the effective ratio of Cd to Te species on the growth surface became larger for layers grown with DETe than those grown with DiPTe. This was considered to decrease the compensation of doped iodine and to increase the electron density of layers grown with DETe. The effective ratio of Cd to Te species on the growth surface also increased with decreasing grow...