InGaP/GaAs HBT with novel ledge coupled capacitor (LCC) structure has been proposed and demonstrated for the first time. The LCC employs an extrinsic InGaP ledge layer as a capacitor parallel to the base resistor. This configuration enables feeding RF signals directly into the base without passing them through the base resistor. With the fabricated HBT, no increase of leakage current between emitter and base electrode was observed. The maximum oscillation frequency (fmax) of the HBT was improved by 10 GHz as compared with an HBT without the LCC.

We present ultra low noise- and wide dynamic range performances of an AlGaN/GaN heterostructure FET (HFET). An HFET fabricated on a high quality epitaxial layers grown on a semi-insulating SiC substrate exhibited impressively low minimum noise figure (NF min ) of 0.4 dB with 16 dB associated gain at 2 GHz. The low NF (near NF min ) operation was possible in a wide drain bias voltage range, i.e. from 3 V to 15 V. At the same time, the device showed low distortion character as indicated by the high third order input intercept point (IIP3), +13 dBm. The excellent characteristics are attributed to three major factors: (1) high quality epitaxial layers that realized a high transconductance and very low buffer leakage current; (2) excellent device isolation made by selective thermal oxidation; (3) ultra low gate leakage current realized by Pd based gate. The results demonstrate that the AlGaN/GaN HFET is a strong candidate for front-end LNAs in various mobile communication systems where both the low noise and the wide dynamic range are required.