The (InAs)1(GaAs)n short period superlattice (SPS) channel 2DEGFET's with 0.2 µm T-Shaped gates have been successfully fabricated on a GaAs substrate for the first time, and DC and RF performances of the superlattice channel devices have been investigated. Compared to conventional InGaAs alloy channel devices, excellent results in both DC and RF characteristics have been obtained for the SPS channel devices. The dependence of the layer index n for (InAs)1(GaAs)n on device performances has been also investigated. The (InAs)1(GaAs)4 channel samples have shown higher cut-off frequencies as well as superior noise performances compared to those for the (InAs)1(GaAs)5 channel samples. The best noise figure of 0.55 dB with an associated gain of 11.26 dB has been obtained at 12 GHz. The superior performances obtained are due to the improved electron transport properties of (InAs)1(GaAs)n SPS compared to those of InGaAs alloy. These results indicate a great potential of SPS channel structures for high frequency low noise device applications.

This paper describes the recent advances in semiconductor photodiodes for use in ultra-high-speed optical systems. We developed two types of waveguide photodiodes (WG-PD) -- an evanescently coupled waveguide photodiode (EC-WG-PD) and a separated-absorption-and-multiplication waveguide avalanche photodiode (WG-APD). The EC-WG-PD is very robust under high optical input operation because of its distribution of photo current density along the light propagation. The EC-WG-PD simultaneously exhibited a high external quantum efficiency of 70% for both 1310 and 1550 nm, and a wide bandwidth of more than 40 GHz. The WG-APD, on the other hand, has a wide bandwidth of 36.5 GHz and a gain-bandwidth product of 170 GHz as a result of its small waveguide mesa structure and a thin multiplication layer. Record high receiver sensitivity of -19.6 dBm at 40 Gbps was achieved. Additionally, a monolithically integrated dual EC-WG-PD for differential phase shift-keying (DPSK) systems was developed. Each PD has equivalent characteristics with 3-dB-down bandwidth of more than 40 GHz and external quantum efficiency of 70% at 1550 nm.