High electron mobility transistors with a pseudomorphically strained InAs channel (InAs‐PHEMTs) have superior electron‐transport properties and high electron density, which are due to a large conduction‐band discontinuity. In this work, we demonstrate that InAs‐PHEMTs have an additional property: they exhibit an ultra‐fast optical response with a time‐constant of 3.5 × 10–11 s. By irradiating the optical signal onto the InAs‐PHEMTs, hole‐electron pairs are created in the channel layer. Holes accumulated in the source region of the channel layer recombine immediately with 2DEG due to an Auger recombination mechanism. Holes generated in the region outside the gate also recombine immediately with the 2DEG due to the Auger recombination mechanism before they drift or diffuse toward the gate region. This is why the optical response time of an InAs‐PHEMT is extremely small and it is restricted by the time for holes to transit across the gate region. A circuit incorporating an InAs‐PHEMT as a transistor and an InAlAs/InAs/InGaAs MSM photodiode that has the same structure as an InAs‐PHEMT as an optical detector has the potential to be applied as an ultra‐fast receiver optoelectronic integrated circuit. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High electron mobility transistors (HEMTs) with a pseudomorphically strained InAs channel (InAs-PHEMTs) were fabricated, and their high frequency characteristics were estimated by measuring the S-parameters. For a VDS of 1.4 V and VGS of 0.3 V, InAs-PHEMTs showed an excellent intrinsic cut-off frequency (fT, int.) as high as 90 GHz regardless of their longer LG (0.7 μm). Since fT is known to be inversely proportional to LG to the first approximation, fT, int. of our InAs-PHEMTs may reach 630 GHz if their LG is reduced to 0.1 μm.Moreover, we calculated the InAs-PHEMTs' energy state and potential profile by self-consistently solving the Schrödinger and Poisson equations. In solving the Schrödinger equation, the energy-dependent effective mass was employed to take into account the strong non-parabolicity of InAs conduction-band based on the k·p perturbation theory by E. O. Kane. It was clarified that most electrons are confined to the InAs layer. On the contrary, if the non-parabolicity is not taken into account, electrons will spread over the InGaAs channel layer.