Investigation and Fabrication of AlGaN/GaN and GaN/InGaN HFETs by Metalorganic Vapor Phase Epitaxy system

• Main Authors: Chuan-I Huang, 黃全一
• Other Authors: Shoou-Jinn Chang
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/82795760655079615795

碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 92 === In this thesis, we first compare two different type ohmic contact metals on AlGaN/GaN heterostructure field effect transistors (HFETs) structure grown by metalorganic vapor phase epitaxy (MOVPE) system, and then discuss the device electrical characteristics .With Cr/Al for ohmic contact metals, the best specific contact resistivity we measured is 3.7*10-4Ω-cm2 annealed at 700℃ in N2 ambiance. In DC section, the maximal transconductance (GM) of device is 82.4mS/mm and the maximal drain current (Idmax) is 471mA/mm. For using Ti/Al/Ti/Au as ohmic contact metals, the best specific contact resistivity is 2*10-5Ω-cm2 annealed at 800℃in N2 ambiance. For DC measurement, the maximal transconductance and the maximal drain current (Idmax) are 100.9mS/mm and 481mA/mm. So, we know lower specific contact resistivity indeed has improvement on the device electrical characteristics. Beside, from measuring the HFETs structure with Ti/Al/Ti/Au as ohmic contact metals, we obtain the cut-off frequency fT=1.32GHz and maximum oscillation frequency fmax= 1.99 GHz by HP8150 network analyzer. We also get high 2DEG layers quality by using Ammonia-MBE system grown on MOVPE GaN template; the 2DEG sheet carrier density and hall nobility are 1.77E+13cm-2 and 1010cm2/V-sec at room temperature. We also compare devices electrical characteristics with devices grown totally on MOVPE system. In the second section, we study and fabrication of GaN/InGaN heterostructure field effect transistors caused by bend bending and piezoelectric effect. We find that grow a thin GaN buffer layer on GaN:Mg isolation layer and reduce InGaN layer thickness to 1000 Å can improve the GaN/InGaN 2DEG quality. The best evidences are 0.23nm surface roughness obtained from AFM technique and 376cm2/V-sec、1.2E+13cm-2 of hall mobility and sheet carrier density. Moreover, we also find that GaN:Mg isolation layer can lower leakage current from drain to source, but it provides more traps and defects in the structure and causes pronounced electrons and mobility fluctuation at channel layer, so higher noise power spectral density than structure without GaN:Mg isolation layer can be measured by Flicker noise measurement system.