The Study of Nitride-based Optoelectronics and Microwave Devices

• Main Authors: Chun-Kai Wang, 王俊凱
• Other Authors: Yan-Kuin Su
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/76288288074263802210

博士 === 國立成功大學 === 微電子工程研究所碩博士班 === 94 === 　The main goal of this dissertation is the fabrications and analyses of nitride-based optoelectronics and microwave devices. Hence, the dissertationis divided into two parts, one is the investigation of nitride-based UV photodetectors, and the other is that of nitride-based metal-oxidesemiconductor heterostructure field effect transistors (MOS-HFETs). 　For metal-semiconductor-metal (MSM) UV photodetectors, two kinds of transparent electrodes, titanium tungsten (TiW) and tungsten (W) were studied. The transmittance of TiW and W were 75.1% and 65.4% at a wavelength of 300 nm, respectively. Then, the 0.192 A/W for TiW and 0.15 A/W for W peak responsivity of our detectors corresponded to the maximum quantum efficiency of 66.4% and 51.8%, respectively, at 360 nm. It should be noted that transmittance of TiW and W films only decreased very slightly and improved the responsivity in the UV-B range compared with other transparent contact electrodes, such as ITO, TiN, RuO2, and IrO2. On the other hand, the noise behavior of MSM UV photodetectors was 1/f-type noise. The minimumnoise equivalent power (NEP) and maximum detectivity (D*) was calculated to be 1.987×10-10 W and 6.365×109 cmHz0.5W-1, respectively. 　In addition, the nitride-based p-i-n band-pass photodetectors with a p-Al0.1Ga0.9N blocking layer, which were designed to detect the UV-A range, were fabricated and characterized. The device with a 300 nm-thick p-Al0.1Ga0.9N layer showed the best characteristic for response. The peak responsivity was estimated to be around 0.13 A/W corresponding to a quantum efficiency of around 46%. On the other hand, the noise behavior of p-i-n band-pass photodetectors was thermal noise, and maximum D* was calculated to be 8.22×1013 cmHz0.5W-1. 　On the part of AlGaN/GaN MOS-HFETs by using photo-CVD SiO2 as gate oxide, the gate leakage current can be reduced by more than four orders of magnitude. Ids, max, gm, max, and gate voltage swing (GVS) were 633 mA/mm, 90 mS/mm, and 7.5V, respectively, at room temperature. Even at 300oC, the electrical characteristics of MOS-HFETs still remain relatively reasonably. Such a result indicated that the AlGaN/GaN MOS-HFETs with photo-CVD SiO2 films was highly potential for application in hash environment. Furthermore, the temperature-induced degradation of saturation velocity was predominantly responsible for the degradation mechanisms of Ids,max and gm,max. 　Low frequency noise of AlGaN/GaN MOS-HFETs with photo-chemical vapor deposition (photo-CVD) SiO2 gate oxide was fitted well by the 1/f law up to 1 kHz in the linear region. The Hooge’s coefficient α was estimated to be around 10-3. The normalized noise power density of the MOS-HFETs was proportional to Vgs-1 when -4V < Vgs < 0V, and was independent of the gatevoltage when 0V < Vgs < 4V, and the devices noise were contributed from the gated and un-gated region, respectively. On the other hand, the noise behavior in the saturation region was degenerated 1/f-type noise. The 1/fΓ noise characteristics and Γ value were affected by the interface state distribution in the energy band-gap as the gate bias varied in the saturation region. Furthermore, the electrical and noise characteristics were improved by using AlGaN/GaN/AlGaN double heterostructure, which showed Ids, max, GVS, and α were 755 mA/mm, 8V, and 2.95×10-4, respectively. 　We also reported low temperature photo-CVD SiNxOy layers and room temperature photo-CVD SiO2 onto GaN/sapphire templates. The refractive index for photo-CVD SiNxOy was 1.65~1.7. The 0.845 nm RMS roughness observed from the photo-CVD SiNxOy layer was much smoother than that observed from photo-CVD SiO2 layer grown at 300oC. The breakdown field of the capacitors with photo-CVD SiNxOy could reach 13 MV/cm. The interface state density at the SiNxOy/GaN interface was also found to be reasonably low, which was 1.04×1011 cm-2eV-1. Furthermore, the quality of Al/room temperature photo-CVD SiO2/GaN capacitors was also reasonably good for application. These properties suggested that the low temperature photo-CVD SiNxOy and room temperature photo-CVD SiO2 were potentially useful in nitride-based MIS-FETs and MIS-HFETs.