DC, RF, and microwave noise performance of AlGaN-GaN field effect transistors dependence of aluminum concentration

AlGaN-GaN heterostructures with different Al concentrations (20, 27, and 35%) were grown by metal-organic vapor phase epitaxy (MOVPE) on sapphire substrates. Ti-Al-Ti-Au ohmic contact optimization was investigated at different temperatures and annealing time. Heterojunction field effect transistors (HFET) with a gate length of 0.25 /spl mu/m were fabricated. Low contact resistances of 0.2, 0.26, and 0.33 /spl Omega//spl middot/mm were obtained for HFET device samples with Al concentrations of 20, 27, and 35%, respectively. For Al concentration of 20, 27, and 35%, the AlGaN-GaN devices exhibited extrinsic transconductances of 143, 152, and 210 mS/mm, I/sub dss/ of 398, 566, and 784 mA/mm, unity cutoff frequencies (f/sub T/) of 24.9, 34.6, and 50 GHz and maximum oscillation frequencies (f/sub MAX/) of 54.9, 61.8, and 100.9 GHz and minimum noise figures (F/sub min/) of 2.01, 1.47, and 1.02 dB at 12GHz, respectively. The calculated minimum noise figures have a good agreement with the measured values for all the devices with different Al mole fractions. The noise analysis shows that intrinsic noise of these AlGaN-GaN FETs plays a prominent part in the noise behavior because of improved device parasitics.