ABSTRACT
In this study, single- and multiple-finger HBTs were fabricated from epilayers grown in-house by low-pressure metal organic vapor phase epitaxy (LP-MOVPE). Disilane and DEZn were used for Si and Zn sources for n- and p-type doping. The gas switching sequences were optimized for optimal layers and layer interfaces. The HBTs were fabricated with a double self-aligned wet-etch process designed for reduced device parasitics. Base contacts were Pt/Ti/Pt/Au, which gave a contact resistivity as low as 1.3 x 10-6 Ω-cm2. High-frequency performance for 1 x 10-μm2 emitter HBTs was 93 GHz and 67 GHz for fT and fmax , respectively. DC current densities were as high as 1.4 x 105 A/cm2. Power and load-pull measurements were carried out at 10 GHz to determine device performance at optimal matching conditions. The maximum power density achieved was 1.37 mW/μm2 for an HBT with a 4-finger (2 x 10 μm each) emitter. The maximum output power obtained was 22.58 dBm for a larger device (4 fingers of 5 x 10 μm each). These characteristics demonstrate good power driving capability for unthinned single HBTs which employ a simple InGaAs collector design.
