Elevated Temperature Characteristics of Carbon-Doped GaInP/GaAs Heterojunction Bipolar Transistor Grown by Solid Source
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Elevated Temperature Characteristics of Carbon-Doped GaInP/GaAs Heterojunction Bipolar Transistor Grown by Solid Source Molecular Beam Epitaxy Zhang Rong, Yoon Soon Fatt, Tan Kianhua, Sun Zhongzhe, and Huang Qingfeng School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798 ABSTRACT This paper reports the characteristics of GaInP/GaAs heterojunction bipolar transistor (HBT) with carbon-doped GaAs base layer grown by solid source molecular beam epitaxy (SSMBE) using carbon tetrabromide (CBr4) as p-type dopant precursor. Hydrofluoric acid (HF) was used to passivate the GaInP/GaAs HBTs. At base bias voltages below 0.8V in the Gummel plot, the base current of large-area devices after HF treatment was greatly reduced. This indicates that the extrinsic base surface recombination current was greatly reduced. After HF treatment, detailed DC characterization of the device performance from 300K to 380K was carried out and the carrier transport properties were investigated. The base current and collector current ideality factors at 300K were 1.12 and 1.01, respectively. This indicates that the space- charge region recombination current in the base is insignificant. From the temperature- dependent Gummel plot, the activation energies of collector current and base current were obtained. For the collector current, the activation energy is 1.4eV, which is close to the bandgap of the GaAs base. This indicates that the collector current is determined by the drift-diffusion process, in which an energy barrier of the same magnitude as the base bandgap is to be overcome by electrons before they reach the collector. For the base current, the activation energy is also 1.4eV, which is close to the bandgap of GaAs, indicating that band-to-band recombination plays a dominant role in the base current. No trap-related recombination was observed for the base and collector currents, which further indicates the high quality carbon-doped GaAs base material for the HBT structures. INTRODUCTION Carbon is an attractive p-type dopant to replace the commonly used beryllium or zinc in GaAs and InGaAs primarily because of its low diffusion coefficient and high electrical activation [1-3]. The usage of carbon in the base of GaAs-based heterojunction bipolar transistors (HBTs) increases the wafer yield and device reliability by eliminating dopant diffusion into the emitter during epitaxial growth [4], and reducing the current induced degradation of DC gain during operation [5]. Carbon tetrabromide (CBr4) has become a popular choice for carbon doping precursors because of its high doping efficiency and relative insensitivity to growth conditions. Solid-source molecular beam epitaxy (SSMBE) offers the advantage of a hydrogen-free environment for the growth of carbon-doped III-V semiconductor layers, eliminating the passivation of carbon acceptors by hydrogen that is commonly observed in carbon-doped GaAs layers grown by techniques which use hydrides as a source of group V elements [6]. In th
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