Jinshu Zhang

Emitter-ballasting-resistor-free SiGe microwave power heterojunction bipolar transistor

The emitter ballasting resistor is used to equalize the current distribution between the emitter stripes in power transistor, but it will degrade the output power, power gain, and power added efficiency. Experimental results indicate that the current gain of uniform-base SiGe heterojunction bipolar transistors (HBTs) decreases with the increase of the temperature above 160 K, so the current distribution is equalized by itself to some extent. Therefore, the microwave power SiGe HBTs without emitter ballasting resistor were fabricated for the first time, and the continuous output power of 5 W and power added efficiency of 63% were obtained under Class C operation at a frequency of 900 MHz. Hence, the emitter current density of the SiGe HBTs with emitter width of 6 /spl mu/m is 0.79 A/cm.

High-quality n-Si/i-p+-i SiGe/n-Si structure grown by ultra high vacuum chemical molecular epitaxy

The n-Si/i-p+-i SiGe/n-Si structure was grown by ultra high vacuum chemical molecular epitaxy, and analysed by high resolution X-ray diffraction, cross-sectional transmission electron microscopy, and secondary ion mass spectroscopy. A high-quality SiGe base layer with an abrupt interface to the Si was obtained. No defects were observed in the n-Si/i-p+-i SiGe/n-Si structure. Both the Ge and boron atoms are uniformly distributed in the p+-SiGe layer, and the changes of profile of both boron and Ge atoms are abrupt from the n-Si to the SiGe layer. A high-performance microwave power SiGe heterojunction bipolar transistor (HBT) was made from the n-Si/i-p+-i SiGe/n-Si structure. Therefore, device-quality n-Si/i-p+-i SiGe/n-Si structures can be grown by ultra high vacuum chemical molecular epitaxy.

n-Si/i-p-i SiGe/n-Si structure for SiGe microwave power heterojunction bipolar transistor grown by ultra-high-vacuum chemical molecular epitaxy

The n-Si/i-p-i SiGe/n-Si structure, grown by ultra-high-vacuum chemical molecular epitaxy, was analyzed by cross-sectional transmission electron microscopy and secondary ion mass spectroscopy. It is shown that no defects are observed in the n-Si/i-p-i SiGe/n-Si structure, the interfaces between the SiGe layer and the n-Si layers are clear and planar, both the Ge and boron atoms are uniformly distributed in the p-SiGe, and the profiles of boron and Ge are abrupt from the n-Si to the SiGe layer. A high-performance microwave power SiGe heterojunction bipolar transistor was fabricated using the n-Si/i-p-i SiGe/n-Si structure. Therefore, ultra-high-vacuum chemical molecular epitaxy is one of the most promising methods for the growth of the Si/SiGe strained epilayers.

Cross-Sectional Transmission Electron Microscopy Study of Si/SiGe Heterojunction Bipolar Transistor Structure Grown by Ultra-High Vacuum Chemical Vapor Deposition

Si/SiGe heterojunction bipolar transistor (HBT) structure, grown by ultra-high vacuum chemical vapor deposition (UHVCVD), was investigated with cross-sectional transmission electron microscopy (XTEM). It was determined that a very thin layer exists in the strained SiGe layer grown on Si, which is in parallel to the interface of SiGe and Si, and the position of thin layer changes with the intrinsic SiGe spacer width but not with the Ge content in the strained SiGe base layer. The base collector junction turn-on voltage of the HBT decreases from ~0.6 V to ~0.2 V when the spacer width decreases from 100 A to 75 A, and increases from ~0.2 V to ~0.4 V when the Ge content in the strained SiGe base layer decreases from 16% to 10%. A possible explanation for this phenomenon is that the Ge atom accumulates to form a very thin Ge-rich layer.

Characterization of SiGe base layer in Si/SiGe heterojunction bipolar transistor layer structure

Abstract Si/SiGe heterojunction bipolar transistor (HBT) layer structures, grown by ultra high vacuum chemical vapor deposition (UHVCVD), were investigated by high resolution X-ray diffraction (HRXRD) and cross-sectional transmission electron microscopy (XTEM). The SiGe base layer thickness in the Si/SiGe HBT structure is determined by HRXRD and confirmed by XTEM. HRXRD indicates that the high quality SiGe base layer and abrupt interfaces between Si and SiGe were obtained. The Ge content in the SiGe base layer, determined by HRXRD, is 16% for sample #a and #b and 10% for sample #c. XTEM shows no defects in both the strained SiGe base layer and the HBT structure. Mesa-type Si/SiGe HBT was fabricated and ideal base current over several orders was obtained.

On the intrinsic spacer layer in Si/SiGe heterojunction bipolar transistor grown by ultra high vacuum chemical vapor deposition

In this paper, we report the study on the intrinsic SiGe spacer layer in Si/SiGe HBT and a novel phenomenon in Si/SiGe HBT layer structure grown by ultra high vacuum chemical vapor deposition (UHVCVD) using Si/sub 2/H/sub 6/ and GeH/sub 4/. When intrinsic SiGe spacer layer width decreases from 100 A to 75 A, the BC junction turn-on voltage decreases from /spl sim/0.6 V to /spl sim/0.2 V, while the BE junction turn-on voltage remains /spl sim/0.6 V. As a result, the offset voltage of the HBT operated at common emitter configuration increases from nearly zero to /spl sim/0.4 V. Therefore, 100 A is used as the intrinsic SiGe spacer layer width. Furthermore, the Si/SiGe HBT layer structures with different SiGe spacer layer widths grown by UHVCVD were investigated by cross-sectional transmission electron microscopy (XTEM). It is shown that a Ge-rich very thin layer exists in the strained SiGe layer grown on Si, which is in parallel with the interface of SiGe and Si. When the SiGe spacer layer width decreases from 100 A to 75 A, the Ge-rich thin layer moves closer to the interface of SiGe base and Si collector, and makes the BC junction turn-on voltage decrease, the offset voltage of HBT, therefore, increases.

900 MHz 7.4 W SiGe heterojunction bipolar transistor

The SiGe heterojunction bipolar transistor (HBT) suitable for microwave power applications was fabricated by a simple planar process compatible with Si process. The current gain of the SiGe HBT is 70, and the breakdown voltages of the collector junction and emitter junction are about 28 V and 5 V respectively. In common emitter configuration and class C operation, the SiGe HBT with continuous wave output power of 7.4 W and power added efficiency of 53% and power gain of 8.7 dB was obtained at the frequency of 900 MHz. Hence, the emitter current linear density of the SiGe HBT with emitter region width of 6 /spl mu/m is 1.7 A/cm.

Electrochemical etching used on UHV/CVD epitaxial thin films

Ultra High Vacuum Chemical Vapor Deposition (UHV/CVD) is carried out to deposit silicon. The deposition is carried out in the temperature range of 550 to 800/spl deg/C. Electrochemical etching is used to test the defects in epitaxial films. Two different ways of etching were performed to validate the thin film etching. The results is almost the same. The defects are visible by the microscope at about 600/spl times/. It is found that the film quality is good in two extreme temperature ranges, i.e. 500 to 700/spl deg/C and above 750/spl deg/C, which was also observed by other authors. The defect density is estimated to be in the order of 10/sup 6/ to 10/sup 8/ cm/sup -2/, including line defects, even micro-defects because of the poor environment cleanliness.