| dc.description.abstract | In recent years, microwave power devices play an important role in wireless communication systems. An electronic device with high linearity, high output power, and high-speed performance is essential for power application. Extensive studies have been focused on the AlGaAs/InGaAs and GaInP/InGaAs HFET devices, which demonstrated superior millimeter-wave performances. However, the conduction band offset (∆Ec) of AlGaAs/GaAs heterojunction is limited by the aluminum composition, which must be kept below 23%, to prevent the presence of donor complex (DX) center and ineffective donor activation. (AlxGa1-x)0.5In0.5P quaternary compounds, lattice matched to GaAs, are expected to substitute AlGaAs or GaInP materials as a Schottky layer, due to its wider bandgap and larger Schottky barrier height. Because of a larger conduction band discontinuity versus InGaAs channel, it provides a better carrier confinement for electrons and also a higher current density. In addition to these advantages, due to the nature of doped-channel design where a high linearity and a high current density can be achieved, this (AlxGa1-x)0.5In0.5P quaternary heterostructure devices are very promising for microwave power application.
In this thesis, a systematic approach for studying the etching characteristics of the quaternary (AlxGa1-x)0.5In0.5P compounds, using chlorine and fluorine mixing plasma, was applied. By adjusting the dry etching parameters, a high GaAs / AlGaInP etching selectivity ratio of 45 and 52 can be achieved for BCl3+CHF3 and BCl3+CF4 plasma systems, respectively. Based on the I-V, TLM, PL and AFM damage evaluations, BCl3+CHF3 gas system has been evidenced that it has a lower damage compared with the case using BCl3+CF4 system, and is suitable for the fabrication of heterojunction field electron transistor (HFETs) where the critical gate recess is involved. .
In chapter 3, the (AlxGa1-x)0.5In0.5P / In0.15Ga0.85As doped-channel FETs (DCFETs) were successfully fabricated and characterized, where the optimized RIE-recessed process was applied. Based on the experimental results, we conclude that for the aluminum content of (Al0.3Ga0.7)0.5In0.5P, i.e. x=0.3, is the best composition to realize DCFETs in terms of device characteristics. Its high Schottky barrier height (ΦB=1.0 eV) and large conduction-band discontinuity (△Ec= 0.27 eV versus GaAs) suppress the gate leakage current and enhance the current drive capability, and therefore increase the device operation dynamic range. From the reliability test, it could be more confirmed its superior quality of the Schottky performance in (Al0.3Ga0.7)0.5In0.5P layers. These remarkable properties indeed reveal that the studied device structure has a good potentiality for the high-power device applications.
In chapter 4, submicron Ga0.51In0.49P / In0.15Ga0.85As DCFETs with variable gate-lengths (0.2, 0.4, 0.6, and 1.0 μm) were developed by the e-beam lithography. Because the depletion region beneath the gate and the electric filed distribution along the channel are more uniform in the highly doped channel design, the short-channel effects in our 0.2 ?m gate-length devices can be eliminated. An excellent linearity of our 0.2 ?m gate-length devices also reveals that the GaInP / InGaAs doped-channel device developed in this work have a great potential candidate as a microwave power device in portable digital phone applications. Furthermore, in order to investigate the intrinsic transport characteristics of devices, a detailed delay time analysis was also performed on our 0.2 ?m gate-length devices. The 0.2 ?m GaInP / InGaAs DCFET demonstrates an electron transit time ?e.t of 1.88 psec, which is corresponding to an average saturated velocity ?s of 1.1 x 107 cm/sec. | en_US |