Papers by Keyword: Herojunction Bipolar Transistor (HBT)

Abstract: An analytical expression for collector resistance of a novel vertical SiGe partially-depleted accumulation-subcollector HBT on thin SOI is obtained. Supported by simulation result, the resistance decreases quickly with the increase of substrate-collector bias and improves the transit frequency dramatically. The model is found to be significant in the design and simulation of 0.13 μm millimeter wave SiGe SOI BiCMOS technology.

Abstract: The standard Early voltage of the SPICE Gummel-Poon model (SGP) is generalized for SiGe npn heterojunction bipolar transistors (HBTs). An accurate model for Early effects compatible with the SGP model is obtained considering graded germanium induced bandgap narrowing effect in the base in modern SiGe HBTs and simplified to a compact model which is consistent with ISE TCAD simulation results. The presentation of the Early effect model is significant for the design and simulation of the high performance SiGe BiCMOS technology.

Abstract: GaN/SiC Heterojunction Bipolar Transistors (HBTs) with ultra-thin AlN insertion layers at the n-GaN/p-SiC emitter junction are proposed to improve carrier injection efficiency. The current-voltage characteristics of n-GaN/AlN/p-SiC heterojunctions have exhibited very small reverse leakage and good rectification. The capacitance-voltage measurement have revealed that the conduction band offset between n-GaN and p-SiC has been reduced from -0.74 eV to -0.54 eV by insertion of AlN, indicating that the GaN/AlN/SiC heterojunction may show better electron-injection efficiency. A significantly improved common-base current gain (α~0.2) is obtained for GaN/AlN/SiC HBTs with initial N* pre-irradiation, while it was very low (α~0.001) for GaN/SiC HBTs without AlN layers.

Abstract: Several device concepts have been further evaluated after the successful implementation of epitaxial Si, SiGe and/or Si:C layers. Most of the next device generations will put limitations on the thermal budget of the deposition processes without making concessions on the epitaxial layer quality. In this work we address the impact of ex-situ wet chemical cleans and in-situ pre-epi bake steps, which are required to obtain oxide free Si surfaces for epitaxial growth. The combination of defect measurements, Secondary Ion Mass Spectroscopy, photoluminescence, lifetime measurements, and electrical diode characterization gives a very complete overview of the performance of low-temperature pre-epi cleaning methods. Contamination at the epi/substrate interface cannot be avoided if the pre-epi bake temperature is too low. This interface contamination is traceable by the photoluminescence and lifetime measurements. It may affect device characteristics by enhanced leakage currents and eventually by yield issues due to SiGe layer relaxation or other defect generation. A comparison of state of the art 200 mm and 300 mm process equipment indicates that for the same thermal budgets the lowest contamination levels are obtained for the 300 mm equipments.

Abstract: The electrical properties of n+-GaN/p+-SiC heterojunction diodes have been investigated by varying the acceptor concentration of p+-SiC epilayers (Na) and polytype of SiC (4H- and 6H-SiC). The current-voltage (I-V) characteristics of diodes with Na ~ 1x1019 cm-3 were dominated by tunneling-assisted current. The diodes with Na ~ 1x1018 cm-3 exhibit excellent characteristics and 6H-SiC may be a better choice from a view point of electron injection into p-SiC base. Compared to previous investigations (Na<1016cm-3), we could obtain good rectification with p-SiC doped to two-order-of-magnitude higher acceptor concentration.

Abstract: A reliable fabrication method for providing close spacing between the emitter mesa and the base contact metal of InP-based heterojunction bipolar transistor is disclosed. The silicon nitride sidewall was formed on the emitter electrode and mesa periphery. It was used as a mask for emitter mesa etching and also as an overhang to self-align the base contact with respect to the emitter mesa. The self-aligned device fabricated by this technique exhibited better high-frequency performances with fT of 138 GHz and fmax of 143 GHz, respectively, superior to the re-aligned one on the same epitaxy wafer.

Abstract: Characterization of n+-GaN/p−-SiC and n+-GaN/p+-SiC heterojunctions as well as fabrication of GaN/SiC heterojunction bipolar transistors (HBTs) using these heterojunctions is presented. The electroluminescence spectrum from n+-GaN/p+-SiC heterojunction diodes under forward bias clearly indicates electron injection from n+-GaN into p+-SiC. HBTs consisting of n+-GaN emitter /p+-SiC base/n−-SiC collector/n+-SiC substrate have been fabricated. Although clear common-base properties were obtained, the current gain was very low (10-4). SiC homojunction bipolar junction transistors (BJT) using the same base-collector junction exhibited a current gain value of 0.5, suggesting the low current gain of GaN/SiC HBTs originates from low emitter efficiency.

Abstract: Pd/Ge/Ti/Pt and Pd/Si/Ti/Pt ohmic contacts to n-type InGaAs were investigated for applications to AlGaAs/GaAs HBT emitter ohmic contacts. In both ohmic contacts, low-resistance and non-spiking planar interfaces were obtained by rapid thermal annealing. RF performance of the AlGaAs/GaAs HBT was also examined by employing these contact systems.