AlGaN/GaN Metal Oxide Semiconductor High-Electron Mobility Transistors with Annealed TiO2 as Passivation and Dielectric Layers.

This paper reports on improved AlGaN/GaN metal oxide semiconductor high-electron mobility transistors (MOS-HEMTs). TiO2 is used to form the dielectric and passivation layers. The TiO2 film is characterized using X-ray photoemission spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM). The quality of the gate oxide is improved by annealing at 300 °C in N2. Experimental results indicate that the annealed MOS structure effectively reduces the gate leakage current. The high performance of the annealed MOS-HEMTs and their stable operation at elevated temperatures up to 450 K is demonstrated. Furthermore, annealing improves their output power characteristics.

Large-Signal Linearity and High-Frequency Noise of Passivated AlGaN/GaN High-Electron Mobility Transistors.

This study proposes AlGaN/GaN/silicon high-electron mobility transistors (HEMTs) grown by a metallorganic chemical vapor deposition (MOCVD) system. The large-signal linearity and high-frequency noise of HEMTs without and with different passivation layers are compared. The experimental data show that the addition of a TiO2 passivation layer to undoped AlGaN/GaN HEMT's increases the value of the third-order intercept point (OIP3) by up to 70% at 2.4 GHz. Furthermore, the minimum noise figure (NF min) of the HEMT with TiO2 passivation is significantly reduced.

Optical characterization of a GaAs/In(0.5)(AlxGa(1-x))(0.5)P/GaAs heterostructure cavity by piezoreflectance spectroscopy.

Optical properties of a lattice matched GaAs/In(0.5)(AlxGa(1-x))(0.5)P/GaAs heterostructure cavity have been characterized using piezoreflectance (PzR) measurements in the temperature range between 20 and 300 K. The measurements were carried out in the energy range of 1.3-6 eV. The PzR spectra of In(0.5)(AlxGa(1-x))(0.5)P at 20 and 300K clearly show a lot of interband transition features present at energies above the band edge. There is also a feature of interference-fringes oscillations observed in each PzR spectrum below band gap E0 of In(0.5)(AlxGa(1-x))(0.5)P. The oscillation period in between the PzR interference fringes can be utilized to determine the index of refraction (n) for the In(0.5)(AlxGa(1-x))(0.5)P at different temperatures. The Al composition x of In(0.5)(AlxGa(1-x))(0.5)P can be estimated from the evaluation value of E(0) by PzR. The obtained Al composition of x=0.691 is in good agreements with the original design for growing the quaternary compound. Electronic band structure of In(0.5)(AlxGa(1-x))(0.5)P is determined by the interband transitions from PzR. The temperature variations of the transition energies and index of refraction n for the In(0.5)(AlxGa(1-x))(0.5)P are analyzed discussed. The PzR is proven to be very sensitive in determining the optical parameters in III-V GaAs/InAlGaP/GaAs Fabry-Perot system.

Practical photoluminescence and photoreflectance spectroscopic system for optical characterization of semiconductor devices.

We present a practical experimental design for performing photoluminescence (PL) and photoreflectance (PR) measurements of semiconductors with only one PL spectroscopic system. The measurement setup is more cost efficient than typical PL-plus-PR systems. The design of the experimental setup of the PL-PR system is described in detail. Measurements of two actual device structures, a high-electron-mobility transistor (HEMT) and a double heterojunction-bipolar transistor (DHBT), are carried out by using this design. The experimental PL and PR spectra of the HEMT device, as well as polarized-photoreflectance (PPR) spectra of the DHBT structure, are analyzed in detailed and discussed. The experimental analyses demonstrate the well-behaved performance of this PL-PR design.