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High efficiency, low offset voltage InGaP/GaAs power heterostructure-emitter bipolar transistors (HEBTs) have been demonstrated. The large signal performance of the HEBTs is characterized. Output power of 0.25 W with power added efficiency (PAE) of 63.5% at 1.9 GHz has been achieved from a 26-finger HEBT with total emitter area of 873.6 /spl mu/m/sup 2/. Output power of 1.0 W with PAE of 63% has been obtained from the composition of four above-mentioned power cells at the optimum conditions of impedance matching. The thermal performance of HEBT is presented and the results show better thermal management than conventional HBT. The experimental results demonstrate good power performance and capability of HEBTs.

The temperature dependence of the current gain is investigated for GaAs-based heterostructure-emitter bipolar transistors (HEBT's). With the separation of the p-n junction and the heterojunction, the mechanism of hole injection from the base to emitter in the HEBT is different from that of a conventional HBT. Theoretical results demonstrate that the thermionic emission current plays an important role for the hole current which results in a smaller negative or even positive temperature coefficient for the current gain. Experimental data show that the base current for HEBTs is indeed dominated by thermionic emission as predicted. This finding indicates that the HEBT structure is the suitable choice for high power and high speed applications.

The temperature effect on current gain is presented for GaInP/GaAs heterojunction and heterostructure-emitter bipolar transistors (HBTs and HEBTs). Experimental results showed that the current gain of the HEBT increases with the increase of temperature in the temperature range of 25-125/spl deg/C and decreases slightly at temperatures above 150/spl deg/C. The smaller the collector current, the larger is the positive differential temperature coefficient. At high current levels, the current gain dependence on temperature is significantly reduced. On the other hand, a large negative coefficient is observed in the HBT in all current range. This finding indicates that the HEBT is a better candidate than the HBT for power devices.

A C-doped GaInP/GaAs heterojunction bipolar transistor (HBT) with a selective buried sub-collector has been fabricated by two growth steps. The active HBT region was made on the selective buried sub-collector layer with minimum overlap of the extrinsic base and the sub-collector region resulting in substantial reduction of the base-collector capacitance. The experiment shows that the base-collector capacitance is reduced to about half of that of a conventional HBT while the base resistance remains unchanged resulting in a 40-50% increase in the maximum oscillation frequency. Both DC and RF characteristics are investigated and compared with a conventional HBT. A current gain of 40, cutoff frequency of 50 GHz and maximum oscillation frequency of 140 GHz were obtained for the GaInP/GaAs HBT. It is demonstrated that the selective buried sub-collector provides an effective means for enhancing RF performance of an HBT.

Carbon-doped GaInP/GaAs double heterostructure-emitter bipolar transistors (DHEBT's) grown by MOCVD were fabricated. DC current gain of 430 (differential gain of 500) and an offset voltage of 25 mV were obtained. A gain up to 9 was achieved at a low collector current density of 10/sup -3/ A/cm/sup 2/. By using a 600 /spl Aring/ set-back layer in the collector, the saturation (knee) voltage was found to be lower than 2 V at a collector current density of 1/spl times/10/sup 4/ A/cm/sup 2/. A cutoff frequency of 23 GHz and a maximum oscillation frequency of 17.8 GHz were obtained. >

Carbon-doped GaInP/GaAs heterojunction bipolar transistors (HBT's) and heterostructure-emitter bipolar transistors (HEBT's) grown by MOCVD were fabricated. Experimental comparison of HBT's and HEBT's has been made based on the dc and the RF performance. HBT's have higher current gains than those of HEBT's in the high current regime, while HEBT's offer a smaller offset voltage and better uniformity in dc characteristics across the wafer. The current gain and cutoff frequency of the DEBT with a 150 /spl Aring/ emitter set-back layer are comparable to those of HBT's. DC (differential) current gains of 600 (900) and 560 (900) were obtained at a collector current density of 2.5/spl times/10/sup 4/ A/cm/sup 2/ for the HBT and HEBT, respectively. The cutoff frequencies are 37 and 31 GHz for the HBT and HEBT, respectively. It is shown that there is negligible contribution of the diffusion capacitance to the emitter capacitance in HEBT's with a thin emitter set-back layer but not with a thick emitter set-back layer. The behavior of HEBT's both in dc and RF characteristics is similar to that of HBT's. >

The behavior of the surface recombination current was examined in InGaP/GaAs heterostructure-emitter bipolar transistors (HEBT's) with both exposed GaAs surface and InGaP passivated surface based on the emitter-size effect on current gain. The results indicate that the GaAs surface recombination current has a 1 kT-like dependence in the high current regime and a 2 kT-like dependence in the low current regime which is similar to published experimental results in AlGaAs/GaAs and InGaP/GaAs HBT's. The surface recombination current in devices with an InGaP passivation layer has an order of magnitude lower value in low current regime and more than two orders lower in high current regime than that in devices with exposed GaAs surface. >

The composition of as-grown BiSrCaCuO superconducting thin films has been investigated as a function of the RF magnetron sputtering variables, i.e. total sputtering pressure, substrate temperature, and oxygen partial pressure in an off-axis configuration. This study shows that use of off-axis geometry alone is insufficient to completely overcome the resputtering problem due to energetic particle bombardment on the substrate. The bismuth loss in the sputtered films at low sputtering pressure and copper loss at high pressure, both of which were aggravated at increasing temperatures, were observed. The mechanisms of thermally enhanced resputtering and gas scattering effects at high pressure are proposed to interpret the discrepancy between target and film composition. >

Investigations of the junctions made between Pb and polycrystalline Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ (BSCCO) are reported. The BSCCO surfaces were treated with a number of methods, including mechanical scraping, plasma sputtering, plasma oxidation, and Br etch, before junctions were fabricated. The current-voltage characteristics and dynamic resistance (dV/dI) vs. voltage were measured at both 77 K and 4.2 K. The authors observed a Pb gap structure similar to that seen in Pb/YBa/sub 2/Cu/sub 3/O/sub 7- delta / junctions, a magnetic-dependent supercurrent, an asymmetric I-V curve, and narrow resistance peaks. Properties of junctions prepared in different manners are compared. Both X-ray photoemission spectroscopy and electrical studies indicated that Br etch is not suitable for the BiSrCaCuO system in spite of its successful application in YBa/sub 2/Cu/sub 3/O/sub 7- delta /.

A C-doped GaInP/GaAs HBT using a selective buried sub-collector has been fabricated by two growth steps. The device was fabricated with minimum overlap of the extrinsic base and the sub-collector region to reduce base-collector capacitance. The experiment shows that the base collector capacitance is reduced to about half of that of an HBT without selective buried sub-collector while the base resistance remains unchanged. A current gain of 35, f/sub T/ of 50 GHz and f/sub max/ of 140 GHz are obtained with this technology.

Integration of carbon-doped GaInP/GaAs heterojunction bipolar transistors (HBTs) and high electron mobility transistors (HEMTs) is demonstrated by growing an HBT on the top of a HEMT. A current gain of 60, a cutoff frequency of 59 GHz and a maximum oscillation frequency of 68 GHz were obtained for a 5/spl times/15 /spl mu/m/sup 2/ self-aligned HBT. The HEMT, with a gate length of 1.5 /spl mu/m has a transconductance of 210 mS/mm, a cutoff frequency of 9 GHz and a maximum oscillation frequency of 22 GHz. It is shown that the GaInP/GaAs HBT on the HEMT is a simple Bi-FET technology suitable for microwave and mixed signal applications.

A brief overview is given of techniques for constructing descriptions of 3D solid objects based on active sensing, whereby scene illumination is manipulated by controlling the light source or the imaging geometry. The light source can be controlled to cast light of a certain spatial pattern to reveal the surface structure of imaged objects. The pattern can be a single point, a single line segment, a set of parallel line segments, or orthogonal grids: and this spatially encoded scene is observed from one or more camera positions. Two types of analysis are possible to relate the encoded images to the 3D configuration of objects. In the first type, the relative position of the light source and the camera is obtained through a calibration process. The correspondence of features of the projector and the image is then established. The 3D positions of the encoded surface points are recovered by means of triangulation. The second type relates the orientation of the projected stripes in the image plane to the surface orientation and structure without the correspondence of features being established. >

Superconducting thin films of Bi-Ca-Sr-Cu oxide, with T/sub c/ onset of approximately 90 K were prepared by RF magnetron sputtering on sapphire with and without a CaZrO/sub 3/ buffer layer, on ZrO-coated silicon