Investigations of New Dilute InGaAsN, InGaAsNSb and InGaAsSb Channel Heterostructure Field-Effect Transistors

Autor: Ke-hua Su, 蘇科化
Rok vydání: 2008
Druh dokumentu: 學位論文 ; thesis
Popis: 96
We have successfully fabricated and investigated GaAs-based heterostructure field-effect transistors (HFETs) with dilute InGaAsN/InGaAsNSb/InGaAsSb channel layers, respectively. Through proposed the dilute N and Sb channel engineering, the influences on device performances, such as drain current, breakdown, extrinsic transconductances, gate-voltage swing, thermal stability, and high-frequency characteristics, have been comprehensively investigated. First, we have investigated the device characteristics of the HFET structure with a dilute InGaAsN channel layer, grown by the molecular beam epitaxy (MBE) system. By integrating N atoms into the InGaAs channel can effectively decrease the effective energy bandgap as compared to conventional InGaAs channels. The present device exhibits improved DC characteristics and thermal stability due to the enhanced channel confinement capability by using a novel, low-gap and dilute InGaAsN channel. Although the energy bandgap can be reduced in the dilute InGaAsN channel, the InGaAsN material must be growth in low temperatures. Consequently, the resulted poor crystalline quality tends to degrade the carrier transport for the electronic device applications. Therefore, we’ve further presented an HFET design using a dilute antimony InGaAsN(Sb) channel grown by MBE system. The incorporation of surfactant-like Sb atoms can effectively improve the interfacial quality of InGaAsN/GaAs heterostructure, and thus improve the carrier transport characteristics, as compared to the low-temperature grown InGaAsN channel structure. Enhanced DC characteristics, improved high-temperature device performance, and superior thermal stability have been successfully achieved in the dilute InGaAsN(Sb) channel HFET design. Recently, some efforts have been devoted to using Sb atoms as surfactants in the GaAs/InGaAsNSb QW laser to improve the crystal quality. The advantages of incorporating Sb atoms into the optoelectronic devices can not only improve the threshold current densities but also reduce the energy bandgap and red-shift the light emission. Besides, based on our learning from the investigations of HFET designs with dilute InGaAsN and InGaAsNSb channel structures, respectively, we found that the incorporation of Sb atoms can not only serve as surfactants to smooth out the heterointerface and, but can also decrease the effective bandgap from the InGaAs channel. Both influences are beneficial to the improvement of the electron transport property, and thus facilitate the device operations in high-frequency applications. Therefore, we have further devised the HFET structure using a dilute antimony In0.2Ga0.8AsSb channel to improve the interfacial quality, carrier transport properties, and the channel confinement capability at the same time. Compared with conventional InGaAs-channel devices, the proposed InGaAsSb/GaAs HFET device has demonstrated significant improvement of about 25% in the maximum extrinsic transconductance, 12.3% in the drain current density, 21% in the unity-current-gain cut-off frequency, and 10.5% in the maximum oscillation frequency. Finally, in order to serve the needs for high-temperature with superior linearity millimeter-wave integrated circuit (MMIC) applications, we have further designed a dilute In0.2Ga0.8AsSb antimony-doped-channel HFET structure, grown by the MBE system, to improve the interfacial quality and the thermal stability at the same time. At 450 K, we’ve observed only 4.3% decrease for the drain current densities, 12% decrease for the extrinsic transconductance, and only 5.16% variation for the threshold voltage, as compared to its room-temperature characteristics. In summary, this dissertation has successfully investigated GaAs-based HFET and doped-channel HFET designs with dilute InGaAsN, InGaAsNSb, and InGaAsSb channels, respectively. Upon the step-by-step investigations on the dilute channel engineering, the present devices have exhibited superior device performance with improved thermal stability. Various electrical, optical, and material characterizations have also been performed to verify the device designs. The devised HFET devices in this dissertation can be promisingly applied to MMIC applications.
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