Performance of Surface and Gate-Engineered AlGaAs ∕ InGaAs Pseudomorphic High-Electron Mobility Transistors

Abstract

The epilayers in pseudomorphic high-electron mobility transistor (pHEMT) structures are grown by metallorganic chemical vapor deposition on GaAs substrates. A treatment with ammonium polysulfide to passivate the surface of AlGaAs barrier layer is performed. Then, the surface morphology of the sulfur-treated AlGaAs layers was investigated by atomic force microscopy. The chemical compositions of AlGaAs surfaces before and after S treatment are studied using X-ray photoelectron spectroscopy. Two metals (Au and ) are used as Schottky contacts on the gate. The passivated gate pHEMT outperforms the other three pHEMTs investigated in this work in both dc and high-frequency characteristics. The Schottky barrier height varies from for Au on the unpassivated device to for on the passivated device. Sulfur treatment and metallization yield the highest turn-on voltage and reverse breakdown voltage. An outstanding feature of this gate high-electron mobility transistor with passivation is its high . Furthermore, at , the passivated gate pHEMT has an exceptionally high -ratio of 3.95. Following full characterization of these transistors at dc and radio frequencies, these devices undergo high-temperature tests. Experimental data reveal remarkably favorable characteristics of the sulfur-treated pHEMT with a gate. Surface and gate engineering are applied to pseudomorphic heterostructures in the device, to achieve an unprecedented combination of high dc and high-frequency characteristics.