Investigation of GaAs- and InP-Based Heterojunction Bipolar Transistors and Schottky Diode Hydrogen Sensors

• Main Authors: Hsi-Jen Pan, 潘繫仁
• Other Authors: Wen-Chau Liu
• Format: Others
• Language: en_US
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/20517581385455318918

博士 === 國立成功大學 === 電機工程學系 === 89 === Heterojunction bipolar transistors (HBT’s) based on III-V compound semiconductor material systems have many prospects in digital and microwave applications due to the excellent high-speed performances combined with high current driving capability. In this dissertation, we present the HBT’s based on the GaAs- and InP-based material systems grown by low pressure-metal organic chemical vapor deposition (LP-MOCVD). We focus on the improved designs of conventional device structures, including the applications of InP/InGaAlAs material system used for the single HBT’s as well as the -doping related structure and the step graded layers used for the B-C junctions in the respective InGaP/GaAs and InP/InGaAs double HBT’s. The effects of different emitter, base and collector together with the emitter-base (E-B) and base-collector (B-C) junction structures on relevant DC characteristics are investigated on the basis of the theoretical calculations. On the other hand, the III-V compound semiconductor materials incorporated with palladium have been realized for the sensors with high sensitivity to hydrogen. In this dissertation, we also propose the hydrogen response, sensing mechanisms, and interface adsorption properties of the GaAs- and InP-based Schottky diode hydrogen sensors. The hydrogen adsorption behaviors are modeled by a theoretical simulation. The quaternary In0.53GaxAlyAs alloy lattice-matched to InP has an outstanding material property of variable band lineup and a wide tunable bandgap ranging depending on the alloy composition. For the aluminum composition of 0.22, the nearly continuous conduction band can be achieved between the InP emitter and the InGaAlAs base. This band lineup can effectively eliminate the undesired effects arising from the large potential spike at the E-B heterojunction such as the large offset voltage. Furthermore, to avoid poor quality related to high aluminum content, the InGaAlAs alloy with a bandgap of 0.93eV corresponding to the aluminum composition of 0.13 is chosen. The DC characteristics in contrast to the InP/InGaAs HBT’s including the higher breakdown voltage, lower output conductance, and better temperature stability are obtained particularly for the high-temperature operation. The superlattices structures incorporated into the InGaP/GaAs double HBT’s are the significant attempts to obtain the functional device characteristics and investigate the carrier transport mechanisms. The uniform and modulated widths of barriers are respectively utilized in the specific superlattice structures. The distinct electron transport of resonant tunneling through the miniband in superlattice structures can therefore be significantly dominated by the electric field behaviors across the barriers. Due to the insertion of the delta-doping related structure at the B-C heterojunction, the excellent transistor characteristics such as the low saturation voltage, low offset voltage, high breakdown voltage are obtained at low current regimes. Furthermore, at higher current regimes, the barrier width designs result in the double- and quaternary-negative difference resistance (NDR) phenomena in agreement with the theoretical prediction at 300K. By taking advantage of the effective mass filtering, the good hole confinement can be achieved by utilizing the tunneling barrier instead of the wide-gap emitter in the HBT’s. Furthermore, both the composite collector structures with the InGaAsP step-graded layers and an delta-doped InGaAs spacer can improve the current blocking effect. Due to less carrier multiplication, the step-graded junction DHBT has better breakdown characteristics and severe self-heating effect as compared to the employment of delta-doped InGaAs spacer. The high-frequency characteristics of the HBT’s with the techniques of self-aligned and no-self-aligned base contact are comparatively studied. The simulation and analysis of the delay times are performed based on the parasitic resistance and capacitance to find the influence on microwave characteristics. For the GaAs- and InP-based Pd metal-oxide-semiconductor (MOS) Schottky diodes, two main effects, i.e., the removal of Fermi-level pinning effect caused by the amphoteric native defects or the donor level in the oxide and the reduction of Pd metal work function dominate the hydrogen sensing mechanism. The reaction kinetics incorporating the water formation upon hydrogen adsorption is investigated to estimate the initial heat of adsorption. The interface coverage dependent heat of adsorption plays an important role in hydrogen response under steady-state conditions. From the experimental results and the theoretical prediction, both devices have a very high detection sensitivity and a wide sensing range under atmospheric conditions.