Fabrication of InGaP/GaAs Superlattice-Emitter Resonant-Tunneling Heterojunction Bipolar Transistors (SE-RTHBT’s)

• Main Authors: Shun-Ching Feng, 馮順清
• Other Authors: Wen-Chau Liu
• Format: Others
• Language: en_US
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/84281573984152204419

碩士 === 國立成功大學 === 電機工程學系 === 88 === In this thesis, superlattice-emitter resonant-tunneling heterojunction bipolar transistors (SE-RTBT’s) based on InGaP/GaAs material system were successfully fabricated and studied. We designed the emitter structure into two parts. One is a 5-period InGaP/GaAs superlattice-emitter structure, the other is a small bandgap GaAs emitter layer. The former one is employed as the resonant tunneling route for electrons. With altering the well width and doping density, different numbers of multiple negative-differential-resistance phenomena were observed. In addition, a designed 300A-thinckness emitter layer was served as the base surface passivation layer, and thus it can reduce the base surface recombination current. Furthermore, a wide-gap material InGaP was used in the collector region. This was expected to increase the breakdown voltage. Moreover, the design of a  -doped sheet sandwiched between two 30A spacer layer inserted at the base-collector junction can effectively suppress the potential spike at the base-collector junction. No knee-shaped phenomenon, which usually found in conventional heterostructure bipolar transistor, was observed in three-terminal current-voltage (I-V) characteristics. First, we use the multi-barrier-tunneling model to derive the wave function in each region of the superlattice via Airy’s function. At the same time, transfer-matrix approach is utilized to calculate the transmission coefficient and I-V characteristics both at thermal equilibrium and under various biases. In addition, the tunneling mechanisms of NDR phenomena are studied and discussed.From experimental results, the devices studied show good performances. In the common-emitter current-voltage characteristics, DC current gainβ and small-signal current gain are as high as 85 and 120, respectively. In addition, the offset voltage as low as 110 mV, low knee-voltage about 0.7V at collector current of 3.2mA, breakdown voltage BVCEO larger than 20 V, and Early voltage as large as 450V are obtained. It is verified that the studied devices have a wide and flat operation region. On the other hand, obvious multiple NDR phenomena are observed at high collector current regime both in two- and three-terminal characteristics. Hence, the devices studied are indeed suitable for the applications in high-speed and high-power systems. Moreover, the devices studied provide great potential for application in frequency multipliers, parity bit generators, and multi-valued logic circuit systems.