Striped-channel low-noise AlGaAs/InGaAs pseudomorphic HEMTs with various stripe pitches have been developed. The DC and microwave characteristics have been investigated and compared to those of non-striped AlGaAs/InGaAs pseudomorphic HEMTs. It was found that both striped and non-striped HEMTs showed nearly constant noise figure for VDS1.0-3.0 V, in contrast to the case of AlGaAs/GaAs HEMTs. This suggests that in the case of AlGaAs/InGaAs pseudomorphic HEMTs, that short-channel effect is almost suppressed even in the non-striped structure. A relatively low noise figure of 0.53 dB with a high associated gain of 13.5 dB has been obtained at 18 GHz from the 0.4 µm-pitch striped-channel pseudomorphic HEMT.

0.25-µm gate low-noise high electron mobility transistors (HEMTs) have been developed, using epitaxial wafers grown by metal-organic-chemical vapour deposition (MOCVD) technique. Minimum noise figures of 0.75 dB and 1.2 dB with associated gains of 11.1 dB and 7.9 dB are obtained at 12 GHz and 18 GHz, respectively, at room temperature. These are the lowest noise figures yet reported for low-noise HEMTs fabricated on MOCVD epitaxial wafers.

Gamma(γ)-ray irradiation effects have been investigated on three types of low-noise HEMTs, AlGaAs/GaAs conventional HEMT (conv. HEMT), AlGaAs/InGaAs pseudomorphic HEMT (P-HEMT) and InAlAs/InGaAs/InP HEMT (InP-based HEMT). The dose of irradiated γ-rays ranges from 1105 to 1108 rad. DC and RF characteristics of each type of HEMT are measured before and after irradiation and the parameter changes are investigated. For conv. HEMT and P-HEMT, no degradation of DC parameter is observed up to 108 rad, while noise figure (NF) at 12 GHz remains constant up to 107 rad and degrades by 0.1 dB at 108 rad. The InP-based HEMT shows IDSS and gm increase by about 10% at a dose of 108 rad and its NF at 18 GHz lowers gradually with the radiation dose. It has been found that the radiation hardness is greater than 107 rad for all types of HEMTs and over a hundred years of life can be expected against γ-ray irradiation in the space environment.