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Based on the InAlAs/InGaAs heterostructure doping-channel field-effect transistors (DCFETs), three co-integrated devices are demonstrated. After removing some material layers, the enhancement/depletion-mode devices and inverter logic were formed. The InAlAs/InGaAs co-integrated structures consist of an enhancement-mode device with single channel and two depletion-mode devices with double and triple channels, respectively. The insertion of an undoped large energy-gap layer between the metal gate and active channels can improve the gate breakdown voltage and turn-on voltage. Besides, by the studied integrated DCFETs two transfer characteristics are implemented for direct-coupled FET logic (DCFL) circuit applications as compared to the previous reports with only single logic transfer characteristic. Consequently, the integrated AlInAs/GaInAs DCFETs provide a promise for signal amplification and multiple inverter logic applications.

Based on the employments of an InGaP/GaAs superlattice emitter and a thin InGaAs pseudomorphic base structure, the device with excellent transistor action and multiple S-shaped negative-differential-resistance (NDR) switching behavior are achieved. Under normal transistor operation mode, the tunneling electrons could easily transport from InGaP/GaAs superlattice over the n-GaAs emitter layer into the thin InGaAs pseudomorphic base region for reducing the base–emitter turn-on voltage and promoting the current gain. In particular, an interesting multiple S-shaped NDR behavior is observed under inverted operation mode due to the avalanche multiplication and confinement effect for electrons at the interface between superlattice and emitter layer, respectively. As an appropriate voltage source and a load resistor are applied, three stable operation points are obtained.

Excellent dc performance of an InP/InGaAs metamorphic δ-doped heterojunction bipolar transistor (HBT) using a linearly graded In x Ga 1 − x P metamorphic buffer layer grown on GaAs substrate is demonstrated. The employment of a δ-doped sheet between two undoped spacer layers could eliminate the potential spike at base–emitter junction and increase the effective barrier, which could prevent the hole injection from base into emitter. A maximum current gain of 255, a low offset voltage of 105 mV, and a small second (third) harmonic distortions of 0.545 (− 0.05) at V CE = 2.5 V are obtained. The current gain and offset voltage are the best values than that of the previous InP/InGaAs metamorphic HBT.